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Background: Ocular foreign bodies (OFBs) are a relatively common occurrence in ocular injuries, and a severe risk factor for vision disorders. They are notoriously challenging to identify and localize precisely to allow surgical removal, even with the most recent technological advancements. Purpose: To compare the efficiency of different imaging methods in detecting and localizing OFBs. Methods: We conducted a retrospective analysis of the medical records of patients with OFBs, detected by ultrasound biomicroscopy (UBM) and confirmed during surgery. Patients who presented to our medical center between January 2016 and January 2022 and also underwent computed tomography (CT), X ray, and/or ocular B‐scan ultrasonography (B‐scans) were selected. Results: This study included 134 patients with a history of ocular trauma and OFBs (mean age: 47.25 years, range: 8–78). The mean time interval from injury to UBM examination was 36.31 months (range: 0.2–120 months). Most OFBs were metallic (51.82%) or plant‐based (25.37%); 22.39% of them were located in the sclera, 26.87% in the anterior chamber, and 23.88% in the ciliary body and iris. OFBs ranged in size from 0.10 to 6.67 mm (mean: 1.15 ± 1.10 mm). B‐scans identified OFBs in 37 of the 119 patients examined (31.09%); CT in 52 of 84 patients (61.90%); and radiography in 29 of 50 patients (58.00%). Univariate and multivariate analyses determined that both CT and radiography showed low detection rates for plant‐based versus non‐plant‐based OFBs (CT: p < 0.001; radiography: p = 0.007), small particles (<1.00 mm vs. >1.00 mm; CT: p = 0.001, radiography: p = 0.024), and with eyeball wall locations (vs. intraocular; CT: p < 0.001, radiography: p = 0.021). Similarly, B‐scans were less efficient for plant‐based and eyeball wall‐located OFBs (both p = 0.001), whereas the difference based on dimensions was not significant (p = 0.118). Conclusions: CT, radiography, and B‐scans showed lower detection rates for plant‐based, small, and eyeball wall‐located OFBs. Our findings strongly suggest that UBM could be a more adequate imaging modality when such OFBs are suspected. [ABSTRACT FROM AUTHOR]

Background: EOSedge™* (EOS Imaging, Paris, France) is an X-ray imaging system using automatic exposure control (AEC) with tube current modulation, in order to optimize dose deposition in patients. Purpose: This study aims at characterizing EOSedge organ dose deposition in comparison to a digital radiography (DR) system and the previous EOS system (EOS-1st generation), in relation to their respective image quality levels. Method: Organ doses were measured in an anthropomorphic female adult phantom and a 5-year-old pediatric phantom using optically stimulated luminescence (OSL) dosimeters, which were carefully calibrated within the studied energy range. Organ doses were recorded on the EOSedge and the Fuji Visionary DRF (Fujifilm Medical Systems U.S.A., Inc, Lexington, MA). The resulting effective doses were compared to the EOS-1st-generation values present in the literature. Image quality assessment was carried out on end-user images. Quantitative image quality metrics were computed for all tested modalities on a quality assurance phantom. Qualitative assessment of EOSedge image quality was based on anthropomorphic phantom acquisitions against the EOS-1st-generation system, and on clinical images against the tested DR system. Results: For a full-spine exam, and on the female adult phantom (respectively, the pediatric phantom), an effective dose of 92 Sv (respectively, 32 Sv) was obtained on EOSedge, and 572 Sv (respectively, 179 Sv) on the DR system; these values were compared to effective dose values of 290 Sv (respectively, 200 Sv) from the literature on EOS-1st generation, leading to an effective dose reduction factor of 6 with respect to the DR system, and of 3-6 with respect to EOS-1st generation. EOSedge provides the best compromise between contrast-to-noise ratio (CNR) and dose, with more consistent CNR values than the other tested modalities, in a range of attenuation from 10 to 40 cm of poly(methyl methacrylate) (PMMA). Within this range, EOSedge is also comparable to DR for 10 and 20 cm of PMMA, and better than DR for 30 and 40 cm of PMMA, both in terms of spatial resolution and low-contrast detection. The anatomical landmarks of interest in the follow-up of spinal deformities can be detected in all tested modalities. Conclusion: Results showed that EOSedge provides significant dose reduction factors for full spine imaging in both adults and children compared to the other tested modalities, without compromising image quality. We believe that this work could help raise awareness on the capabilities of modern X-ray systems, when equipped with appropriate AEC strategies, to perform ultra-low-dose, long-axis images. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate the dose characteristic for patient examinations at the first clinical X‐ray dark‐field chest radiography system and to determine whether the effective patient dose is within a clinically acceptable dose range. Methods: A clinical setup for grating‐based dark‐field chest radiography was constructed and commissioned, operating at a tube voltage of 70 kVp. Thermoluminescent dosimeter (TLD) measurements were conducted using an anthropomorphic phantom modeling the reference person to obtain a conversion coefficient relating dose area product (DAP) to effective patient dose at the dark‐field system. For 92 patients, the DAP values for posterior–anterior measurements were collected at the dark‐field system. Using the previously determined conversion coefficient, the effective dose was calculated. Results: A reference person, modeled by an anthropomorphic phantom, receives an effective dose of 35 µSv. For the examined patients, a mean effective dose of 39 µSv was found. Conclusions: The effective dose at the clinical dark‐field radiography system, generating both attenuation and dark‐field images, is within the range of reported standard dose values for chest radiography. [ABSTRACT FROM AUTHOR]

Purpose: Inkjet printers can be used to fabricate anthropomorphic phantoms by the use of iodine‐doped ink. However, challenges persist in implementing this technique. The calibration from grayscale to ink density is complex and time‐consuming. The purpose of this work is to develop a printing methodology that requires a simpler calibration and is less dependent on printer characteristics to produce the desired range of x‐ray attenuation values. Methods: Conventional grayscale printing was substituted by single‐tone printing; that is, the superposition of pure black layers of iodinated ink. Printing was performed with a consumer‐grade inkjet printer using ink made of potassium‐iodide (KI) dissolved in water at 1 g/ml. A calibration for the attenuation of ink was measured using a commercial x‐ray system at 70 kVp. A neonate radiograph obtained at 70 kVp served as an anatomical model. The attenuation map of the neonate radiograph was processed into a series of single‐tone images. Single‐tone images were printed, stacked, and imaged at 70 kVp. The phantom was evaluated by comparing attenuation values between the printed phantom and the original radiograph; attenuation maps were compared using the structural similarity index measure (SSIM), while attenuation histograms were compared using the Kullback–Leibler (KL) divergence. A region of interest (ROI)‐based analysis was also performed, where the attenuation distribution within given ROIs was compared between phantom and patient. The phantom sharpness was evaluated in terms of modulation transfer function (MTF) estimates and signal spread profiles of high spatial resolution features in the image. Results: The printed phantom required 36 pages. The printing queue was automated and it took about 2 h to print the phantom. The radiograph of the printed phantom demonstrated a close resemblance to the original neonate radiograph. The SSIM of the phantom with respect to that of the patient was 0.53. Both patient and phantom attenuation histograms followed similar distributions, and the KL divergence between such histograms was 0.20. The ROI‐based analysis showed that the largest deviations from patient attenuation values were observed at the higher and lower ends of the attenuation range. The limiting resolution of the proposed methodology was about 1 mm. Conclusion: A methodology to generate a neonate phantom for 2D imaging applications, using single‐tone printing, was developed. This method only requires a single‐value calibration and required less than 2 h to print a complete phantom. [ABSTRACT FROM AUTHOR]

Purpose: This work seeks to investigate new methods to determine the absorbed dose to water from kilovoltage x rays. Current methods are based on measurements in air and rely on correction factors in order to account for differences between the photon spectrum in air and at depth in phantom, between the photon spectra of the calibration beam and the beam of interest, or in the radiation absorption properties of air and water. This work aims to determine the absorbed dose to water in the NIST‐matched x‐ray beams at the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL). This will facilitate the use of detectors in terms of dose to water, which will allow for a simpler determination of dose to water in clinical kilovoltage x‐ray beams. Materials and methods: A model of the moderately filtered x‐ray beams at the UWADCL was created using the BEAMnrc user code of the EGSnrc Monte Carlo code system. This model was validated against measurements and the dose to water per unit air kerma was calculated in a custom built water tank. Using this value and the highly precise measurement of the air kerma made by the UWADCL, the dose to water was determined in the water tank for the x‐ray beams of interest. The dose to water was also determined using the formalism defined in the report of AAPM Task Group 61 and using a method that makes use of a 60Co absorbed dose‐to‐water calibration coefficient and a beam quality correction factor to account for differences in beam quality between the 60Co calibration and kilovoltage x‐ray beam of interest. The dose to water values as determined by these different methods was then compared. Results: The BEAMnrc models used in this work produced simulations of transverse and depth dose profiles that agreed with measurements with a 2%/2 mm criteria gamma test. The dose to water as determined from the different methods used here agreed within 3.5% at the surface of the water tank and agreed within 1.8% at a depth of 2 cm in phantom. The dose‐to‐water values all agreed within the associated uncertainties of the methods used in this work. Both the Monte Carlo‐based method and the 60Co‐based method had a lower uncertainty than the TG‐61 methodology for all of the x‐ray beams used in this work. Conclusion: Two new dose determination methods were used to determine the dose to water in the NIST‐matched x‐ray beams at the UWADCL and they showed good agreement with previously established techniques. Due to the improved Monte Carlo calculation techniques used in this work, both of the methods have lower uncertainties compared to TG‐61. The methods presented in this work compare favorably with calorimetry‐based standards established at other institutions. [ABSTRACT FROM AUTHOR]

Purpose: X-ray dark-field imaging promises information on the small angle scattering properties even of large samples. However, the dark-field image is correlated with the object's attenuation and phase-shift if a polychromatic x-ray spectrum is used. A method to remove part of these correlations is proposed. Methods: The experimental setup for image acquisition was modeled in a wave-field simulation to quantify the dark-field signals originating solely from a material's attenuation and phase-shift. A calibration matrix was simulated for ICRU46 breast tissue. Using the simulated data, a dark-field image of a human mastectomy sample was corrected for the finger print of attenuation- and phase-image. Results: Comparing the simulated, attenuation-based dark-field values to a phantom measurement, a good agreement was found. Applying the proposed method to mammographic dark-field data, a reduction of the dark-field background and anatomical noise was achieved. The contrast between microcalcifications and their surrounding background was increased. Conclusions: The authors show that the influence of and dispersion can be quantified by simulation and, thus, measured image data can be corrected. The simulation allows to determine the corresponding dark-field artifacts for a wide range of setup parameters, like tube-voltage and filtration. The application of the proposed method to mammographic dark-field data shows an increase in contrast compared to the original image, which might simplify a further image-based diagnosis. [ABSTRACT FROM AUTHOR]

Purpose: In EGSnrc, atomic transitions to and from the M and N-shells are treated in an average way by default. This approach is justified in which the energy difference between explicit and average M and N-shell binding energies is less than 1 keV, and for most applications can be considered negligible. However, for simulations of low energy x-raysources on thin, high-Z targets, characteristicx-rays can make up a significant portion of the sourcespectra. As of release V4-2.4.0, EGSnrc has included an option to enable a more complete algorithm of all atomic transitions available in the EADL compilation. In this paper, the effect of M and N-shell averaging on the calculation of half-value layer (HVL) and relative depth dose (RDD) curve of a 50 kVp intraoperative x-ray tube with a thin gold target was investigated. Methods: A 50 kVp miniature x-raysource with a gold target (The INTRABEAM System, Carl Zeiss, Germany) was modeled with the EGSnrc user code cavity, both with and without M and N-shell averaging. From photon fluence spectra simulations, the source HVLs were determined analytically. The same source model was then used with egs_chamber to calculate RDD curves in water. Results: A 4% increase of HVL was reported when accounting for explicit M and N-shell transitions, and up to a 9% decrease in local relative dose for normalization at 3 mm depth in water. Conclusions: The EGSnrc default of using averaged M and N-shell binding energies has an observable effect on the HVL and RDD of a low energy x-raysource with high-Z target. For accurate modeling of this class of devices, explicit atomic transitions should be included. [ABSTRACT FROM AUTHOR]

Purpose: This work investigates the energy response and dose-response curve determinations for XR-QA2 radiochromic film dosimetry system used for synchrotron radiation work and for quality assurance in diagnostic radiology, in the range of effective energies 18-46.5 keV. Methods: Pieces of XR-QA2 films were irradiated, in a plane transverse to the beam axis, with a monochromatic beam of energy in the range 18-40 keV at the ELETTRA synchrotron radiation facility (Trieste, Italy) and with a polychromatic beam from a laboratory x-ray tube operated at 80, 100, and 120 kV. The film calibration curve was expressed as air kerma (measured free-in-air with an ionization chamber) versus the net optical reflectance change (net R) derived from the red channel of the RGB scanned film image. Four functional relationships (rational, linear exponential, power, and logarithm) were tested to evaluate the best curve for fitting the calibration data. The adequacy of the various fitting functions was tested by using the uncertainty analysis and by assessing the average of the absolute air kerma error calculated as the difference between calculated and delivered air kerma. The sensitivity of the film was evaluated as the ratio of the change in net reflectance to the corresponding air kerma. Results: The sensitivity of XR-QA2 films increased in the energy range 18-39 keV, with a maximum variation of about 170%, and decreased in the energy range 38-46.5 keV. The present results confirmed and extended previous findings by this and other groups, as regards the dose response of the radiochromic film XR-QA2 to monochromatic and polychromatic x-ray beams, respectively. Conclusions: The XR-QA2 radiochromic film response showed a strong dependence on beam energy for both monochromatic and polychromatic beams in the range of half value layer values from 0.55 to 6.1 mm Al and corresponding effective energies from 18 to 46.5 keV. In this range, the film response varied by 170%, from a minimum sensitivity of 0.0127 to a maximum sensitivity of 0.0219 at 10 mGy air kerma in air. The more suitable function for air kerma calibration of the XR-QA2 radiochromic film was the power function. A significant batch-to-batch variation, up to 55%, in film response at 120 kV (46.5 keV effective energy) was observed in comparison with published data. [ABSTRACT FROM AUTHOR]

The use of Monte Carlo simulations in diagnostic medical imaging research is widespread due to its flexibility and ability to estimate quantities that are challenging to measure empirically. However, any new Monte Carlo simulation code needs to be validated before it can be used reliably. The type and degree of validation required depends on the goals of the research project, but, typically, such validation involves either comparison of simulation results to physical measurements or to previously published results obtained with established Monte Carlo codes. The former is complicated due to nuances of experimental conditions and uncertainty, while the latter is challenging due to typical graphical presentation and lack of simulation details in previous publications. In addition, entering the field of Monte Carlo simulations in general involves a steep learning curve. It is not a simple task to learn how to program and interpret a Monte Carlo simulation, even when using one of the publicly available code packages. This Task Group report provides a common reference for benchmarking Monte Carlo simulations across a range of Monte Carlo codes and simulation scenarios. In the report, all simulation conditions are provided for six different Monte Carlo simulation cases that involve common x-ray based imaging research areas. The results obtained for the six cases using four publicly available Monte Carlo software packages are included in tabular form. In addition to a full description of all simulation conditions and results, a discussion and comparison of results among the Monte Carlo packages and the lessons learned during the compilation of these results are included. This abridged version of the report includes only an introductory description of the six cases and a brief example of the results of one of the cases. This work provides an investigator the necessary information to benchmark his/her Monte Carlo simulation software against the reference cases included here before performing his/her own novel research. In addition, an investigator entering the field of Monte Carlo simulations can use these descriptions and results as a self-teaching tool to ensure that he/she is able to perform a specific simulation correctly. Finally, educators can assign these cases as learning projects as part of course objectives or training programs. [ABSTRACT FROM AUTHOR]

Purpose: To fabricate organic photovoltaic (OPV) cells with nanometric active layers sensitive to ionizing radiation and measure their dosimetric characteristics in clinical x-ray beams in the diagnostic tube potential range of 60-150 kVp. Methods: Experiments were designed to optimize the detector's x-ray response and find the best parameter combination by changing the active layer thickness and the area of the electrode. The OPV cell consisted of poly (3-hexylthiophene-2,5-diyl): [6,6]-phenyl C61 butyric acid methyl ester photoactive donor and acceptor semiconducting organic materials sandwiched between an aluminum electrode as an anode and an indium tin oxide electrode as a cathode. The authors measured the radiation-induced electric current at zero bias voltage in all fabricated OPV cells. Results: The net OPV current as a function of beam potential (kVp) was proportional to kVp-0.5 when normalized to x-ray tube output, which varies with kVp. Of the tested configurations, the best combination of parameters was 270 nm active layer thicknesses with 0.7 cm² electrode area, which provided the highest signal per electrode area. For this cell, the measured current ranged from approximately 0.7 to 2.4 nA/cm² for 60-150 kVp, corresponding to about 0.09 nA-0.06 nA/mGy air kerma, respectively. When compared to commercial amorphous silicon thin film photovoltaic cells irradiated under the same conditions, this represents 2.5 times greater sensitivity. An additional 40% signal enhancement was observed when a 1 mm layer of plastic scintillator was attached to the cells' beam-facing side. Conclusions: Since both OPVs can be produced as flexible devices and they do not require external bias voltage, they open the possibility for use as thin film in vivo detectors for dose monitoring in diagnostic x-ray imaging. [ABSTRACT FROM AUTHOR]

Purpose: The authors note that the concept of the Talbot self-image distance in x-ray phase grating interferometry is indeed not well defined for polychromatic x-rays, because both the grating phase shift and the fractional Talbot distances are all x-ray wavelength-dependent. For x-ray interferometry optimization, there is a need for a quantitative theory that is able to predict if a good intensity modulation is attainable at a given grating-to-detector distance. In this work, the authors set out to meet this need. Methods: In order to apply Fourier analysis directly to the intensity fringe patterns of twodimensional and one-dimensional phase grating interferometers, the authors start their derivation from a general phase space theory of x-ray phase-contrast imaging. Unlike previous Fourier analyses, the authors evolved the Wigner distribution to obtain closed-form expressions of the Fourier coefficients of the intensity fringes for any grating-to-detector distance, even if it is not a fractional Talbot distance. Results: The developed theory determines the visibility of any diffraction order as a function of the grating-to-detector distance, the phase shift of the grating, and the x-ray spectrum. The authors demonstrate that the visibilities of diffraction orders can serve as the indicators of the underlying interference intensity modulation. Applying the theory to the conventional and inverse geometry configurations of single-grating interferometers, the authors demonstrated that the proposed theory provides a quantitative tool for the grating interferometer optimization with or without the Talbotdistance constraints. Conclusions: In this work, the authors developed a novel theory of the interference intensity fringes in phase grating x-ray interferometry. This theory provides a quantitative tool in design optimization of phase grating x-ray interferometers. [ABSTRACT FROM AUTHOR]

Purpose: To test the feasibility of a dual detector concept for comprehensive verification of external beam radiotherapy. Specifically, the authors test the hypothesis that a portal imaging device coupled to a 2D dosimeter provides a system capable of simultaneous imaging and dose verification, and that the presence of each device does not significantly detract from the performance of the other. Methods: The dual detector configuration comprised of a standard radiotherapy electronic portal imaging device (EPID) positioned directly on top of an ionization-chamber array (ICA) with 2 cm solid water buildup material (between EPID and ICA) and 5 cm solid backscatter material. The dose response characteristics of the ICA and the imaging performance of the EPID in the dual detector configuration were compared to the performance in their respective reference clinical configurations. The reference clinical configurations were 6 cm solid water buildup material, an ICA, and 5 cm solid water backscatter material as the reference dosimetry configuration, and an EPID with no additional buildup or solid backscatter material as the reference imaging configuration. The dose response of the Purpose: To investigate the impact of x-ray beam energy, exposure intensity, and flat-bed scanner uniformity and spatial resolution on the precision of computed tomography (CT) beam width measurements using Gafchromic XR-QA2 film and an off-the-shelf document scanner. Methods: Small strips of Gafchromic film were placed at isocenter in a CT scanner and exposed at various x-ray beam energies (80-140 kVp), exposure levels (50-400 mA s), and nominal beam widths (1.25, 5, and 10 mm). The films were scanned in reflection mode on a Ricoh MP3501 flat-bed document scanner using several spatial resolution settings (100 to 400 dpi) and at different locations on the scanner bed. Reflection measurements were captured in digital image files and radiation dose profiles generated by converting the image pixel values to air kerma through film calibration. Beam widths were characterized by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of dose profiles. Dependences of these parameters on the above factors were quantified in percentage change from the baselines. Results: The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within 4.5% and 7.6%, respectively. Increasing scanner spatial resolution significantly increased the uncertainty in both FWHM and FWTM, with FWTM affected by almost 8 times more than FWHM (48.7% vs 6.5%). When uncalibrated dose profiles were used, FWHM and FWTM were over-estimated by 11.6% and 7.6%, respectively. Narrower beam width appeared more sensitive to the film calibration than the wider ones (R² = 0.68 and 0.85 for FWHM and FWTM, respectively). The global and maximum local background variations of the document scanner were 1.2%. The intrinsic film nonuniformity for an unexposed film was 0.3%. Conclusions: Measurement of CT beam widths using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. With proper film calibration and scanner resolution setting, it can provide adequate precision for meeting ACR and manufacturer's tolerances for the measurement of CT dose profiles. [ABSTRACT FROM AUTHOR]

Purpose: In digital x-ray radiography, an antiscatter grid is inserted between the patient and the image receptor to reduce scattered radiation. If the antiscatter grid is used in a stationary way, gridline artifacts will appear in the final image. In most of the gridline removal image processing methods, the useful information with spatial frequencies close to that of the gridline is usually lost or degraded. In this study, a new stationary gridline suppression method is designed to preserve more of the useful information. Methods: The method is as follows. The input image is first recursively decomposed into several smaller subimages using a multiscale 2D discrete wavelet transform. The decomposition process stops when the gridline signal is found to be greater than a threshold in one or several of these subimages using a gridline detection module. An automatic Gaussian band-stop filter is then applied to the detected subimages to remove the gridline signal. Finally, the restored image is achieved using the corresponding 2D inverse discrete wavelet transform. Results: The processed images show that the proposed method can remove the gridline signal efficiently while maintaining the image details. The spectra of a 1D Fourier transform of the processed images demonstrate that, compared with some existing gridline removal methods, the proposed method has better information preservation after the removal of the gridline artifacts. Additionally, the performance speed is relatively high. Conclusions: The experimental results demonstrate the efficiency of the proposed method. Compared with some existing gridline removal methods, the proposed method can preserve more information within an acceptable execution time. [ABSTRACT FROM AUTHOR]

Purpose: To present the results of a patient dose evaluation program in pediatric cardiology and propose local diagnostic reference levels (DRLs) for different types of procedure and age range, in addition to suggesting approaches to correlate patient dose values with patient weight. This study was the first conducted in Latin America for pediatric interventional cardiology under the auspices of the International Atomic Energy Agency. Methods: Over three years, the following data regarding demographic and patient dose values were collected: age, gender, weight, height, number of cine series, total number of cine frames, fluoroscopy time (FT), and two dosimetric quantities, dose-area product (DAP) and cumulative dose (CD), at the patient entrance reference point. The third quartile values for FT, DAP, CD, number of cine series, and the DAP/body weight ratio were proposed as the set of quantities to use as local DRLs. Results: Five hundred and seventeen patients were divided into four age groups. Sample sizes by age group were 120 for <1 yr; 213 for 1 to <5 yr; 82 for 5 to <10 yr; and 102 for 10 to <16 yr. The third quartile values obtained for DAP by diagnostic and therapeutic procedures and age range were 1.17 and 1.11 Gy cm2 for <1 yr; 1.74 and 1.90 Gy cm2 for 1 to <5 yr; 2.83 and 3.22 Gy cm2 for 5 to <10 yr; and 7.34 and 8.68 Gy cm2 for 10 to <16 yr, respectively. The third quartile value obtained for the DAP/body weight ratio for the full sample of procedures was 0.17 (Gy cm2/kg) for diagnostic and therapeutic procedures. Conclusions: The data presented in this paper are an initial attempt at establishing local DRLs in pediatric interventional cardiology, from a large sample of procedures for the standard age bands used in Europe, complemented with the values of the ratio between DAP and patient weight. This permits a rough estimate of DRLs for different patient weights and the refining of these values for the age bands when there may be large differences in child size. These DRLs were obtained at the largest pediatric hospital in Chile, with an active optimization program, and could be used by other hospitals in the Latin America region to compare their current patient dose values and determine whether corrective action is appropriate. [ABSTRACT FROM AUTHOR]

Purpose: The authors describe a design for prepatient region of interest attenuators (ROIAs) to reduce dose area product (DAP) for clinical use. The authors describe a model to predict DAP values from x-ray technique parameters recorded during a clinical procedure for image sequences obtained in the presence or absence of ROIAs. The model was developed primarily to determine what the DAP to a patient undergoing cardiac catheterization with a ROIA would have been if no ROIA had been used allowing a determination of DAP reduction. Methods: Copper ROIAs with thicknesses that vary gradually so as not to cause significant image artifacts were constructed. X-ray image sequences were acquired on a clinical catheterization system with and without ROIAs with varying x-ray technique parameters. DAP values were measured for all said exposures using an ionization chamber and compared to a model the authors developed. Results: The model can predict DAP values within 3.5% on average with or without ROIAs when compared to ionization chamber measurements. Conclusions: The proposed experimental design is adequate for measuring DAP reductions on the order of 1.5-3.5 that are expected when introducing a ROIA during patient catheterization imaging. [ABSTRACT FROM AUTHOR]

Purpose: The breast cancer detection rate for digital breast tomosynthesis (DBT) is limited by the xray image quality. The limiting Nyquist frequency for current DBT systems is around 5 lp/mm, while the fine image details contained in the high spatial frequency region (>5 lp/mm) are lost. Also today the tomosynthesis patient dose is high (0.67-3.52 mGy). To address current issues, in this paper, for the first time, a high-resolution low-dose organic photodetector/amorphous In-Ga-Zn-O thin-film transistor (a-IGZO TFT) active pixel sensor (APS) x-ray imager is proposed for next generation DBT systems. Methods: The indirect x-ray detector is based on a combination of a novel low-cost organic photodiode (OPD) and a cesium iodide-based (CsI:Tl) scintillator. The proposed APS x-ray imager overcomes the difficulty of weak signal detection, when small pixel size and low exposure conditions are used, by an on-pixel signal amplification with a significant charge gain. The electrical performance of a-IGZO TFT APS pixel circuit is investigated by SPICE simulation using modified Rensselaer Polytechnic Institute amorphous silicon (a-Si:H) TFT model. Finally, the noise, detective quantum efficiency (DQE), and resolvability of the complete system are modeled using the cascaded system formalism. Results: The result demonstrates that a large charge gain of 31-122 is achieved for the proposed high-mobility (5-20 cm²/Vs) amorphous metal-oxide TFT APS. The charge gain is sufficient to eliminate the TFT thermal noise, flicker noise as well as the external readout circuit noise. Moreover, the low TFT (<10-13 A) and OPD (<10-8 A/cm²) leakage currents can further reduce the APS noise. Cascaded system analysis shows that the proposed APS imager with a 75 µm pixel pitch can effectively resolve the Nyquist frequency of 6.67 lp/mm, which can be further improved to ~101p/mm if the pixel pitch is reduced to 50µm. Moreover, the detector entrance exposure per projection can be reduced from 1 to 0.3 mR without a significant reduction of DQE. The signal-to-noise ratio of the a-IGZO APS imager under 0.3 mR x-ray exposure is comparable to that of a-Si:H passive pixel sensor imager under 1 mR, indicating good image quality under low dose. A threefold reduction of current tomosynthesis dose is expected if proposed technology is combined with an advanced DBT image reconstruction method. Conclusions: The proposed a-IGZO APS x-ray imager with a pixel pitch <75 µm is capable to achieve a high spatial frequency (>6.67 lp/mm) and a low dose (<0.4 mGy) in next generation DBT systems [ABSTRACT FROM AUTHOR]

Purpose: The authors investigated the energy response of XR-QA2 GafChromicTM film over a broad energy range used in diagnostic radiology examinations. The authors also made an assessment of the most suitable functions for both reference and relative dose measurements. Methods: Pieces of XR-QA2 film were irradiated to nine different values of air kerma in air, following reference calibration of a number of beam qualities ranging in HVLs from 0.16 to 8.25 mm Al, which corresponds to effective energy range from 12.7 keV to 56.3 keV. For each beam quality, the authors tested three functional forms (rational, linear exponential, and power) to assess the most suitable function by fitting the delivered air kerma in air as a function of film response in terms of reflectance change. The authors also introduced and tested a new parameter ? = netΔR · em netΔR that linearizes the inherently nonlinear response of the film. Results: The authors have found that in the energy range investigated, the response of the XR-QA2 based radiochromic film dosimetry system ranges from 0.222 to 0.420 in terms of netΔR at Kair air = 8 cGy. For beam qualities commonly used in CT scanners (4.03-8.25 mm Al), the variation in film response (netΔR at Kair air = 8 cGy) amounts to ± 5%, while variation in Kair air amounts to ± 14%. Conclusions: Results of our investigation revealed that the use of XR-QA2 GafChromicTM film is accompanied by a rather pronounced energy dependent response for beam qualities used for x-ray based diagnostic imaging purposes. The authors also found that the most appropriate function for the reference radiochromic film dosimetry would be the power function, while for the relative dosimetry one may use the exponential response function that can be easily linearized. [ABSTRACT FROM AUTHOR]

Purpose: The Vero4DRT system has the capability for dynamic tumor-tracking (DTT) stereotactic irradiation using a unique gimbaled x-ray head. The purposes of this study were to develop DTT conformal arc irradiation and to estimate its geometric and dosimetric accuracy. Methods: The gimbaled x-ray head, supported on an O-ring gantry, was moved in the pan and tilt directions during O-ring gantry rotation. To evaluate the mechanical accuracy, the gimbaled x-ray head was moved during the gantry rotating according to input command signals without a target tracking, and a machine log analysis was performed. The difference between a command and a measured position was calculated as mechanical error. To evaluate beam-positioning accuracy, a moving phantom, which had a steel ball fixed at the center, was driven based on a sinusoidal wave (amplitude [A]: 20 mm, time period [T]: 4 s), a patient breathing motion with a regular pattern (A: 16 mm, average T: 4.5 s), and an irregular pattern (A: 7.2-23.0 mm, T: 2.3-10.0 s), and irradiated with DTT during gantry rotation. The beam-positioning error was evaluated as the difference between the centroid position of the irradiated field and the steel ball on images from an electronic portal imaging device. For dosimetric accuracy, dose distributions in static and moving targets were evaluated with DTT conformal arc irradiation. Results: The root mean squares (RMSs) of the mechanical error were up to 0.11 mm for pan motion and up to 0.14 mm for tilt motion. The RMSs of the beam-positioning error were within 0.23 mm for each pattern. The dose distribution in a moving phantom with tracking arc irradiation was in good agreement with that in static conditions. Conclusions: The gimbal positional accuracy was not degraded by gantry motion. As in the case of a fixed port, the Vero4DRT system showed adequate accuracy of DTT conformal arc irradiation. [ABSTRACT FROM AUTHOR]

Purpose: New technology has been developed to treat age-related macular degeneration (AMD) using 100 kVp pencil-beams that enter the patient through the radio-resistant sclera with a depth of interest between 1.6 and 2.6 cm. Measurement of reference and relative dose in a kilovoltage x-ray beam with a 0.42 cm diameter field size and a 15 cm source to axis distance (SAD) is a challenge that is not fully addressed in current guidelines to medical physicists. AAPMˈs TG-61 gives dosimetry recommendations for low and medium energy x-rays, but not all of them are feasible to follow for this modality. Methods: An investigation was conducted to select appropriate equipment for the application. PTWˈs Type 34013 Soft X-Ray Chamber (Freiburg, Germany) and CIRSˈs Plastic Water LR (Norfolk, VA) were found to be the best available options. Attenuation curves were measured with minimal scatter contribution and thus called Low Scatter Tissue Air Ratio (LSTAR). A scatter conversion coefficient (Cscat) was derived through Monte Carlo radiation transport simulation using MCNPX (LANL, Los Alamos, NM) to quantify the difference between a traditional TAR curve and the LSTAR curve. A material conversion coefficient (Cmat) was determined through experimentation to evaluate the difference in attenuation properties between water and Plastic Water LR. Validity of performing direct dosimetry measurements with a source to detector distance other than the treatment distance, and therefore a different field size due to a fixed collimator, was explored. A method-Integrated Tissue Air Ratio (ITAR)-has been developed that isolates each of the three main radiological effects (distance from source, attenuation, and scatter) during measurement, and integrates them to determine the dose rate to the macula during treatment. Results: LSTAR curves were determined to be field size independent within the range explored, indicating that direct dosimetry measurements may be performed with a source to detector distance of 20 cm even though the SAD is 15 cm during treatment. Cscat varied from 1.102 to 1.106 within the range of depths of interest. The experimental variance among repeated measurements of Cmat was larger than depth dependence, so Cmat was estimated as1.019 for all depths of interest. Conclusions: Equipment selection, measurement techniques, and formalism for the determination of dose rate to the macula during stereotaxy for AMD have been determined and are strongly recommended by the authors of this paper to be used by clinical medical physicists. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the usefulness of a six-degrees-of freedom (6D) correction using ExacTrac robotics system in patients with head-and-neck (HN) cancer receiving radiation therapy. Methods: Local setup accuracy was analyzed for 12 patients undergoing intensity-modulated radiation therapy (IMRT). Patient position was imaged daily upon two different protocols, cone-beam computed tomography (CBCT), and ExacTrac (ET) images correction. Setup data from either approach were compared in terms of both residual errors after correction and punctual displacement of selected regions of interest (Mandible, C2, and C6 vertebral bodies). Results: On average, both protocols achieved reasonably low residual errors after initial correction. The observed differences in shift vectors between the two protocols showed that CBCT tends to weight more C2 and C6 at the expense of the mandible, while ET tends to average more differences among the different ROIs. Conclusions: CBCT, even without 6D correction capabilities, seems preferable to ET for better consistent alignment and the capability to see soft tissues. Therefore, in our experience, CBCT represents a benchmark for positioning head and neck cancer patients. [ABSTRACT FROM AUTHOR]

Purpose: In x-ray mammography, flattening of the breast improves image quality and reduces absorbed dose. Current mammographic compression guidelines are based on applying a standardized force to each breast. Because breast size is not taken into consideration, this approach leads to large variations in applied pressure (force applied per unit contact area). It is the authors' hypothesis that a pressure-controlled compression protocol, which takes contact area into account, (1) improves standardization across the population in terms of physiological conditions in the compressed breast (blood pressure), and (2) reduces discomfort and pain, particularly the number of severe pain complaints, (3) with limited effects on image quality and absorbed glandular dose (AGD). Methods: A prospective observational study including 291 craniocaudal (CC) and 299 mediolateral oblique (MLO) breast compressions in 196 women following the authors' hospital's standard compression protocol with 18 decanewton (daN) target force was performed. Breast thickness, applied force, area of contact between breast and compression paddle, and mean pressure were recorded during the entire compression. Pain scores before and after breast compressions were obtained using an 11-point numerical rating scale (NRS). Scores of 7 and higher were considered to indicate severe pain. The authors analyzed differences between the CC and MLO compressions, correlation coefficients (ρ) between compression parameters, and odds-ratios (OR) for all parameters as possible predictors for experiencing severe pain using multivariate logistic regression. The observed data were used in two models to estimate what breast thickness, required force, and pain score would be for pressure-controlled compression protocols with target pressures ranging from 4 to 28 kilopascal (kPa). For a selection of 79 mammograms having a 10% or more thickness difference with respect to the prior mammogram, the authors performed a retrospective observer study to assess whether such thickness differences have significant effects on image quality or AGD. Results: In a standard 18 daN force-controlled compression protocol, the authors observed an average pressure of 21.3 kPa ± 54% standard deviation for CC compressions and 14.2 kPa ± 32% for MLO compressions. Women with smaller breasts endured higher pressures and experienced more pain, as indicated by a significant negative correlation (ρ = -0.19, p < 0.01) between contact area and pain score. Multivariate regression showed that contact area is a strong and significant predictor for severe pain (ORNRS≥7CC=0.10/dm2, p < 0.05), as is the case with any pain already present before compression (ORNRS≥7CC=1.61 per NRS-point, p < 0.05). Model estimations showed that mammographic breast compression with a standardized pressure of 10 kPa, corresponding with normal arterial blood pressure, may significantly reduce the number of severe pain complaints with an average increase in breast thickness of 9% for small breasts and 2% for large breasts. For an average 16.5% thickness difference in prior-current mammogram pairs, the authors found no differences in image quality and AGD Conclusions: Model estimations and an observer study showed that pressure-controlled mammographic compression protocols may improve standardization and reduce discomfort with limited effects on image quality and AGD. [ABSTRACT FROM AUTHOR]

Purpose: Anode heel effect renders large-scale background nonuniformities in digital radiographs. Conventional offset/gain calibration is performed at mono source-to-image distance (SID), and disregards the SID-dependent characteristic of heel effect. It results in a residual nonuniform background in the corrected radiographs when the SID settings for calibration and correction differ. In this work, the authors develop a robust and efficient computational method for digital x-ray detector gain correction adapted to SID-variant heel effect, without resorting to physical filters, phantoms, complicated heel effect models, or multiple-SID calibration and interpolation. Methods: The authors present the Duo-SID projection correction method. In our approach, conventional offset/gain calibrations are performed only twice, at the minimum and maximum SIDs of the system in typical clinical use. A fast iterative separation algorithm is devised to extract the detector gain and basis heel patterns from the min/max SID calibrations. The resultant detector gain is independent of SID, while the basis heel patterns are parameterized by the min- and max-SID. The heel pattern at any SID is obtained from the min-SID basis heel pattern via projection imaging principles. The system gain desired at a specific acquisition SID is then constructed using the projected heel pattern and detector gain map. Results: The method was evaluated for flat field and anatomical phantom image corrections. It demonstrated promising improvements over interpolation and conventional gain calibration/correction methods, lowering their correction errors by approximately 70% and 80%, respectively. The separation algorithm was able to extract the detector gain and heel patterns with less than 2% error, and the Duo-SID corrected images showed perceptually appealing uniform background across the detector. Conclusions: The Duo-SID correction method has substantially improved on conventional offset/gain corrections for digital x-ray imaging in an SID-variant environment. The technique is relatively simple, and can be easily incorporated into multiple-point gain calibration/correction techniques. It offers a potentially valuable tool for preprocessing digital x-ray images to boost image quality of mammography, chest and cardiac radiography, as well as automated computer aided diagnostic radiology. [ABSTRACT FROM AUTHOR]

Purpose: With recently introduced technical innovations for CT systems, the dose of CT scan acquisitions has been substantially reduced; even effective dose values below 1 mSv have been reported. Due to this development, dose of the localizer radiograph may contribute substantially to dose of the whole CT examination. Since there are only limited data in the literature regarding patient dose for the different types of localizer radiographs, patient dose values were estimated in our study by measurements and Monte Carlo simulations and compared to dose values of typical CT examinations. Methods: First, dose distributions were measured in anthropomorphic phantoms for three different body regions (head, thorax, abdomen-pelvic) and three positions of the x-ray tube (AP, PA, and lateral views); measured values were compared to simulated data using Monte Carlo techniques for validation purposes. Second, organ and effective dose values for the various investigated localizer radiograph scenarios were calculated and compared with published dose values for standard CT and low-dose CT examinations. Results: For the anthropomorphic phantom, deviations of the dose values between measured and calculated results were in the range of 15%. Organ and effective dose values showed a strong dependence on the tube position. The largest differences were observed for chest localizer radiographs in the female phantom for the dose to the breast (AP: 1.01 mGy vs PA: 0.24 mGy). Overall effective dose values were in the range of 0.04-0.42 mSv per localizer radiograph acquisition. Conclusions: In view of the technical dose-reducing innovations in CT, localizer radiographs may substantially contribute to the total dose of the whole CT examination, particularly in the case of dedicated low-dose scans used, e.g., for young patients or screening purposes. Optimization of dose in localizer radiographs should be pursued further in the same way as it was done in CT. [ABSTRACT FROM AUTHOR]

Purpose: Wireless flat panel detectors are gaining increased usage in portable medical imaging. Two such detectors were evaluated and compared with a conventional flat-panel detector using the formalism of the International Electrotechnical Commission (IEC 62220-1) for measuring modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) using two different filtration schemes. Methods: Raw images were acquired for three image receptors (DRX-1C and DRX-1, Carestream Health; Inc., Pixium 4600, Trixell) using a radiographic system with a well-characterized output (Philips Super80 CP, Philips Healthcare). Free in-air exposures were measured using a calibrated radiation meter (Unfors Mult-O-Meter Type 407, Unfors Instruments AB). Additional aluminum filtration and a new alternative combined copper-aluminum filtration were used to conform the x ray output to IEC-specified beam quality definitions RQA5 and RQA9. Using the IEC 62220-1 formalism, each detector was evaluated at XN/2, XN, and 2XN, where the normal exposure level to the detector surface (XN) was set to 8.73 μGy (1.0 mR). The prescribed edge test device was used to evaluate the MTF, while the NNPS was measured using uniform images. The DQE was then calculated from the MTF and NNPS and compared across detectors, exposures, and filtration schemes. Results: The three DR systems had largely comparable MTFs with DRX-1 demonstrating lower values above 1.0 cycles/mm. At each exposure, DRX-1C and Pixium detectors demonstrated better noise performance than that of DRX-1. Zero-frequency DQEs for DRX-1C, Pixium, and DRX-1 detectors were approximately 74%, 63%, and 38% for RQA5 and 50%, 42%, and 28% for RQA9, respectively. Conclusions: DRX-1C detector exhibited superior DQE performance compared to Pixium and DRX-1. In terms of filtration, the alternative filtration was found to provide comparable performance in terms of rank ordering of different detectors with the added convenience of being less bulky for in-the-field measurements. [ABSTRACT FROM AUTHOR]

Purpose: Digital breast tomosynthesis (DBT) differs from conventional mammography in target/filter, kVp range, and imaging geometry. The aim of this study was to assess the breast input exposure of a DBT system by completing a workload survey of DBT installations, and to determine the parameters α, β, and γ in the Archer equation for the primary radiation generated by the clinical workload distributions. Methods: The authors conducted a retrospective survey of the x-ray breast imaging performed between September 2011 and September 2012 in three clinical DBT rooms equipped with Selenia Dimensions systems (Hologic Inc., Bedford, MA). A total of 343 examinations were analyzed to calculate the workload (mA-minute) and the primary air kerma at 1 m from the source (K1). Transmission curves were calculated for the primary radiation generated by the workload distributions of the DBT rooms, and were fitted to the Archer equation. Results: There were large variations in patient volume and workload in the three examination rooms. In all these rooms, the average tube voltage (kVp) was about 31, the average K1 per patient was 16-21 mGy, and the average mA-minute per patient was 1.4-2.2 times higher than that of the mammography room described in NCRP Report No. 147. Most DBT screening examinations consisted of four two-dimensional mammographic views plus four tomosynthesis scans; the numbers of views acquired in diagnostic examinations varied widely. Tomosynthesis scans contributed about 30% of total mA-minute and about 50% of K1. For the primary radiation generated by the clinical workload distributions, α was similar to that of 40-45 kVp W/Al (target/filter), and α + β was similar to that of 30 kVp W/Al. Conclusions: The workload (mA-minute and K1) distributions of mammographic examinations with DBT differ from conventional mammography. A field survey of patient volume and x-ray tube usage is important for the shielding design of DBT facilities. The clinical workloads and transmission data presented in this paper may be useful for clinical medical physicists. [ABSTRACT FROM AUTHOR]

Purpose: The performance of various x-ray converters, employed in medical imaging systems, has been widely examined by several methodologies (experimental, analytical, and Monte Carlo techniques). The x-ray converters most frequently employed in energy integrating digital radiology detectors are the Gd2O2S:Tb granular phosphor, the CsI:Tl structured phosphor, and the a-Se photoconductor. The imaging characteristics of an x-ray converter are affected by its x-ray detection properties. However, various definitions of x-ray detection have been used in the literature, leading to different results for the quantum detection efficiency (QDE) for the same type of x-ray converter. For this reason, there is a need for accurate determination of the x-ray detection and, in particular, its relation to detector response. Methods: The present article reports on the performance of the three aforementioned x-ray converters in terms of the QDE and the x-ray statistical factor Ix and examines the effect of the x-ray detection, directly related to converter output signal, on the zero-frequency DQE. For the purposes of this study, Monte Carlo simulation was used to model the x-ray interactions within the x-ray converter. Simulations were carried out in the energy range from 10 keV up to 80 keV and considering two layers of different coating weights (50 and 100 mg/cm2). The prediction and comparison of zero-frequency DQE were based on two different approaches for x-ray detection, i.e., (a) fraction of interacting photons and (b) fraction of photons leading to energy deposition. In addition, the effect of energy deposition through Compton scattering events on the DQE values was estimated. Results: Our results showed discrepancies between Monte Carlo techniques (based on energy deposition events) and analytical calculations (based on x-ray attenuation) on QDE. Discrepancies were found to range up to 10% for Gd2O2S:Tb (100 mg/cm2), 7.7% for CsI:Tl (50 mg/cm2), and 8.2% for a-Se (50 mg/cm2). Discrepancies were analyzed by examining the scattering effects (elastic and inelastic) within the converters and led to further analysis of scattering events on Ix as well. Significant overestimations were found for both factors (QDE and Ix) on the zero-frequency DQE. Conclusions: Considering that the highest overestimation was found in the thin layer (50 mg/cm2), Monte Carlo evaluation showed that the overestimation (%) between DQE values (based on either x-ray interacting events or energy impartation events) was more significant at 20 keV for CsI:Tl (approximately 2.1%), at 40 keV for Gd2O2S:Tb (approximately 8.1%), and finally at 60 and 80 keV for a-Se converter (approximately 4.8 and 8.2%, respectively). Finally, the overestimation due to the effect of Compton scattering on DQE was found more significant for the a-Se converter and especially above 40 keV reaching approximately the value of 8.9% at 80 keV. [ABSTRACT FROM AUTHOR]

Purpose: Noise characterization through estimation of the noise power spectrum (NPS) is a central component of the evaluation of digital x-ray systems. Extensive works have been conducted to achieve accurate and precise measurement of NPS. One approach to improve the accuracy of the NPS measurement is to reduce the statistical variance of the NPS results by involving more data samples. However, this method is based on the assumption that the noise in a radiographic image is arising from stochastic processes. In the practical data, the artifactuals always superimpose on the stochastic noise as low-frequency background trends and prevent us from achieving accurate NPS. The purpose of this study was to investigate an appropriate background detrending technique to improve the accuracy of NPS estimation for digital x-ray systems. Methods: In order to achieve the optimal background detrending technique for NPS estimate, four methods for artifactuals removal were quantitatively studied and compared: (1) Subtraction of a low-pass-filtered version of the image, (2) subtraction of a 2-D first-order fit to the image, (3) subtraction of a 2-D second-order polynomial fit to the image, and (4) subtracting two uniform exposure images. In addition, background trend removal was separately applied within original region of interest or its partitioned sub-blocks for all four methods. The performance of background detrending techniques was compared according to the statistical variance of the NPS results and low-frequency systematic rise suppression. Results: Among four methods, subtraction of a 2-D second-order polynomial fit to the image was most effective in low-frequency systematic rise suppression and variances reduction for NPS estimate according to the authors' digital x-ray system. Subtraction of a low-pass-filtered version of the image led to NPS variance increment above low-frequency components because of the side lobe effects of frequency response of the boxcar filtering function. Subtracting two uniform exposure images obtained the worst result on the smoothness of NPS curve, although it was effective in low-frequency systematic rise suppression. Subtraction of a 2-D first-order fit to the image was also identified effective for background detrending, but it was worse than subtraction of a 2-D second-order polynomial fit to the image according to the authors' digital x-ray system. Conclusions: As a result of this study, the authors verified that it is necessary and feasible to get better NPS estimate by appropriate background trend removal. Subtraction of a 2-D second-order polynomial fit to the image was the most appropriate technique for background detrending without consideration of processing time. [ABSTRACT FROM AUTHOR]

Purpose: Quality management for any use of medical x-ray imaging should include monitoring of radiation dose. Fluoroscopically guided interventional (FGI) procedures are inherently clinically variable and have the potential for inducing deterministic injuries in patients. The use of a conventional diagnostic reference level is not appropriate for FGI procedures. A similar but more detailed quality process for management of radiation dose in FGI procedures is described. Methods: A method that takes into account both the inherent variability of FGI procedures and the risk of deterministic injuries from these procedures is suggested. The substantial radiation dose level (SRDL) is an absolute action level (with regard to patient follow-up) below which skin injury is highly unlikely and above which skin injury is possible. The quality process for FGI procedures collects data from all instances of a given procedure from a number of facilities into an advisory data set (ADS). An individual facility collects a facility data set (FDS) comprised of all instances of the same procedure at that facility. The individual FDS is then compared to the multifacility ADS with regard to the overall shape of the dose distributions and the percent of instances in both the ADS and the FDS that exceed the SRDL. Results: Samples of an ADS and FDS for percutaneous coronary intervention, using the dose metric of reference air kerma (Ka,r) (i.e., the cumulative air kerma at the reference point), are used to illustrate the proposed quality process for FGI procedures. Investigation is warranted whenever the FDS is noticeably different from the ADS for the specific FGI procedure and particularly in two circumstances: (1) When the facility's local median Ka,r exceeds the 75th percentile of the ADS and (2) when the percent of instances where Ka,r exceeds the facility-selected SRDL is greater for the FDS than for the ADS. Conclusions: Analysis of the two data sets (ADS and FDS) and of the percent of instances that exceed the SRDL provides a means for the facility to better manage radiation dose (and therefore both deterministic and stochastic radiation risk) to the patient during FGI procedures. [ABSTRACT FROM AUTHOR]

Purpose: To generalize and experimentally validate a novel algorithm for reconstructing the 3D pose (position and orientation) of implanted brachytherapy seeds from a set of a few measured 2D cone-beam CT (CBCT) x-ray projections. Methods: The iterative forward projection matching (IFPM) algorithm was generalized to reconstruct the 3D pose, as well as the centroid, of brachytherapy seeds from three to ten measured 2D projections. The gIFPM algorithm finds the set of seed poses that minimizes the sum-of-squared-difference of the pixel-by-pixel intensities between computed and measured autosegmented radiographic projections of the implant. Numerical simulations of clinically realistic brachytherapy seed configurations were performed to demonstrate the proof of principle. An in-house machined brachytherapy phantom, which supports precise specification of seed position and orientation at known values for simulated implant geometries, was used to experimentally validate this algorithm. The phantom was scanned on an ACUITY CBCT digital simulator over a full 660 sinogram projections. Three to ten x-ray images were selected from the full set of CBCT sinogram projections and postprocessed to create binary seed-only images. Results: In the numerical simulations, seed reconstruction position and orientation errors were approximately 0.6 mm and 5°, respectively. The physical phantom measurements demonstrated an absolute positional accuracy of (0.78±0.57) mm or less. The θ and φ angle errors were found to be (5.7±4.9)° and (6.0±4.1)°, respectively, or less when using three projections; with six projections, results were slightly better. The mean registration error was better than 1 mm/6° compared to the measured seed projections. Each test trial converged in 10-20 iterations with computation time of 12-18 min/iteration on a 1 GHz processor. Conclusions: This work describes a novel, accurate, and completely automatic method for reconstructing seed orientations, as well as centroids, from a small number of radiographic projections, in support of intraoperative planning and adaptive replanning. Unlike standard back-projection methods, gIFPM avoids the need to match corresponding seed images on the projections. This algorithm also successfully reconstructs overlapping clustered and highly migrated seeds in the implant. The accuracy of better than 1 mm and 6° demonstrates that gIFPM has the potential to support 2D Task Group 43 calculations in clinical practice. [ABSTRACT FROM AUTHOR]

Purpose: Fluoroscopic x-ray imaging systems are used extensively in spatio-temporal detection tasks and require a spatio-temporal description of system performance. No accepted metric exists that describes spatio-temporal fluoroscopic performance. The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient 'dose efficiency.' It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. However, the use of a temporally-corrected DQE does not provide system temporal information and it is only valid under specific conditions, many of which are not likely to be satisfied by suboptimal systems. The authors propose a spatio-temporal DQE that describes performance in both space and time and is applicable to all spatio-temporal quantum-based imaging systems. Methods: The authors define a spatio-temporal DQE (two spatial-frequency axes and one temporal-frequency axis) in terms of a small-signal spatio-temporal modulation transfer function (MTF) and spatio-temporal noise power spectrum (NPS). Measurements were made on an x-ray image intensifier-based bench-top system using continuous fluoroscopy with an RQA-5 beam at 3.9 μR/frame and hardened 50 kVp beam (0.8 mm Cu filtration added) at 1.9 μR/frame. Results: A zero-frequency DQE value of 0.64 was measured under both conditions. Nonideal performance was noted at both larger spatial and temporal frequencies; DQE values decreased by ∼50% at the cutoff temporal frequency of 15 Hz. Conclusions: The spatio-temporal DQE enables measurements of decreased temporal system performance at larger temporal frequencies analogous to previous measurements of decreased (spatial) performance. This marks the first time that system performance and dose efficiency in both space and time have been measured on a fluoroscopic system using DQE and is the first step toward the generalized use of DQE on clinical fluoroscopic systems. [ABSTRACT FROM AUTHOR]

Purpose: Monte Carlo simulation is a very useful tool for radiotherapy and diagnostic radiology. Yet even with the latest PCs, simulation of photon spectra emitted by an x-ray tube is a time-consuming task, potentially reducing the possibility to obtain relevant data such as dose evaluations, simulation of geometric settings, or monitor detector efficiency. This study developed and validated a method to generate random numbers for realistic beams in terms of photon spectrum and intensity to simulate x-ray tubes via Monte Carlo algorithms. Methods: Starting from literature data, the most common semiempirical models of bremsstrahlung are analyzed and implemented, adjusting their formulation to describe a large irradiation area (i.e., large field of view) and to take account of the heel effect as in common practice during patient examinations. Results: Simulation results show that Birch and Marshall’s model is the fastest and most accurate for the aims of this work. Correction of the geometric size of the beam and validation of the intensity variation (heel effect) yielded excellent results with differences between experimental and simulated data of less than 6%. Conclusions: The results of validation and execution time showed that the tube simulator calculates the x-ray photons quickly and efficiently and is perfectly capable of considering all the phenomena occurring in a real beam (total filtration, focal spot size, and heel effect), so it can be used in a wide range of applications such as industry, medical physics, or quality assurance. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate the variability in quantitation of positron emission tomography (PET) data acquired within the context of a multicenter consortium. Methods: PET quantitation phantoms designed by American Association of Physicists in Medicine/Society of Nuclear Medicine Task Group 145 were sent to the ten member sites of the Pediatric Brain Tumor Consortium (PBTC), a NIH-funded research consortium investigating the biology and therapies for brain tumors in children. The phantoms were water-filled cylinders (18.6 cm inside height and 20.4 cm inside diameter) based on the standard ACR phantom with four small, “hot” cylinders of varying diameters (8, 12, 16, 25 mm, all with 38 mm height), consisting of an equilibrium mixture of 68Ge/68Ga in an epoxy matrix. At each site, the operator added the appropriate amount of 18F to the water in the background in order to attain a feature-to-background ratio of roughly 4:1. The phantom was imaged and reconstructed as if it were a brain PET scan for the PBTC. An approximately 12 mm circular region of interest (ROI) was placed over each feature and in a central area in the background. The mean and maximum pixel values for each ROI were requested from local sites in units of activity concentration (Bq/ml) and the standard uptake value (SUV) (g/mL) based on bodyweight. The activity concentration was normalized by the decay-corrected known activity concentration for the features, and reported as the absolute recovery coefficient (RC). In addition, central analyses were performed by two observers. Results: The ten sites successfully imaged the phantom within 5 months and submitted the quantitative results and the phantom image data to the PBTC Operations and Biostatistics Center. The local site-based and central analyses yielded similar mean values for RC. Local site-based SUV measurements of the hot cylindrical features yielded greater variability than central analysis (COV range of 29.9%–42.8% compared to 7.7%–23.2%). Correcting for miscalculations in the local site reported SUVs substantially reduced the variation to levels similar to the central analysis (COV range of 8.8%–18.4%) and also led to the local sites providing a similar mean of the SUV values to those from the central analysis. In the central analysis, the use of mean SUV in place of maximum SUV for an ROI of fixed size substantially reduced the variation in the SUV values (COV ranges of 7.7%–11.3% vs 9.3%–23.2%). Conclusions: Based on this investigation, a SUV variability in the range of 10%–25% due solely to instrument and analysis factors can be expected in the context of a multicenter consortium if a central reading is used and quality assurance and quality control procedures are followed. The overall SUV variability can be expected to be larger than this due to biological and protocol factors. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate Gd2O2S:Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. Gd2O2S:Eu is nonhygroscopic, emitting red light with decay time close to that of Gd2O2S:Tb. Methods: The light intensity emitted per unit of x-ray exposure rate (absolute luminescence efficiency) was measured for laboratory prepared screens with coating thicknesses of 33.1, 46.4, 63.1, 78.3, and 139.8 mg/cm2 and tube voltages ranging from 50 to 140 kVp. Parameters related to image quality such as the modulation transfer function (MTF) and the detective quantum efficiency (DQE) were also experimentally examined. In addition, a previously validated Monte Carlo code was used to estimate intrinsic x-ray absorption and optical properties, as well as the MTF and the Swank factor (I) of the Gd2O2S:Eu scintillators. Results: Gd2O2S:Eu light intensity was found higher than that of single CsI:Tl crystal for tube voltages up to 100 kVp. The MTF and the DQE were found to be comparable with those of Gd2O2S:Tb and CsI:Tl screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. Gd2O2S:Eu showed peak emission in the wavelength range 620–630 nm. Its emission spectrum was excellently matched to various optical detectors (photodiodes, photocathodes, CCDs, and CMOS) employed in flat panel detectors. Conclusions: Gd2O2S:Eu is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light. [ABSTRACT FROM AUTHOR]

Purpose: In the past decade, phase-contrast imaging (PCI) has been applied to study different kinds of tissues and human body parts, with an increased improvement of the image quality with respect to simple absorption radiography. A technique closely related to PCI is phase-retrieval imaging (PRI). Indeed, PCI is an imaging modality thought to enhance the total contrast of the images through the phase shift introduced by the object (human body part); PRI is a mathematical technique to extract the quantitative phase-shift map from PCI. A new phase-retrieval algorithm for the in-line phase-contrast x-ray imaging is here proposed. Methods: The proposed algorithm is based on a mixed transfer-function and transport-of-intensity approach (MA) and it requires, at most, an initial approximate estimate of the average phase shift introduced by the object as prior knowledge. The accuracy in the initial estimate determines the convergence speed of the algorithm. The proposed algorithm retrieves both the object phase and its complex conjugate in a combined MA (CMA). Results: Although slightly less computationally effective with respect to other mixed-approach algorithms, as two phases have to be retrieved, the results obtained by the CMA on simulated data have shown that the obtained reconstructed phase maps are characterized by particularly low normalized mean square errors. The authors have also tested the CMA on noisy experimental phase-contrast data obtained by a suitable weakly absorbing sample consisting of a grid of submillimetric nylon fibers as well as on a strongly absorbing object made of a 0.03 mm thick lead x-ray resolution star pattern. The CMA has shown a good efficiency in recovering phase information, also in presence of noisy data, characterized by peak-to-peak signal-to-noise ratios down to a few dBs, showing the possibility to enhance with phase radiography the signal-to-noise ratio for features in the submillimetric scale with respect to the attenuation-based imaging. Conclusions: It has been shown that phase-retrieved radiographies can be used both to have quantitative phase information about soft tissues, complementary to the attenuation information, and to enhance the visibility of details inside soft tissues, with higher efficiency with respect to phase radiography. [ABSTRACT FROM AUTHOR]

Purpose: The image registration literature comprises many methods for 2D-3D registration for which accuracy has been established in a variety of applications. However, clinical application is limited by a small capture range. Initial offsets outside the capture range of a registration method will not converge to a successful registration. Previously reported capture ranges, defined as the 95% success range, are in the order of 4–11 mm mean target registration error. In this article, a relatively computationally inexpensive and robust estimation method is proposed with the objective to enlarge the capture range. Methods: The method uses the projection-slice theorem in combination with phase correlation in order to estimate the transform parameters, which provides an initialization of the subsequent registration procedure. Results: The feasibility of the method was evaluated by experiments using digitally reconstructed radiographs generated from in vivo 3D-RX data. With these experiments it was shown that the projection-slice theorem provides successful estimates of the rotational transform parameters for perspective projections and in case of translational offsets. The method was further tested on ex vivo ovine x-ray data. In 95% of the cases, the method yielded successful estimates for initial mean target registration errors up to 19.5 mm. Finally, the method was evaluated as an initialization method for an intensity-based 2D-3D registration method. The uninitialized and initialized registration experiments had success rates of 28.8% and 68.6%, respectively. Conclusions: The authors have shown that the initialization method based on the projection-slice theorem and phase correlation yields adequate initializations for existing registration methods, thereby substantially enlarging the capture range of these methods. [ABSTRACT FROM AUTHOR]

Purpose: In this study, five different units based on three different technologies—traditional computed radiography (CR) units with granular phosphor and single-side reading, granular phosphor and dual-side reading, and columnar phosphor and line-scanning reading—are compared in terms of physical characterization and contrast detail analysis. Methods: The physical characterization of the five systems was obtained with the standard beam condition RQA5. Three of the units have been developed by FUJIFILM (FCR ST-VI, FCR ST-BD, and FCR Velocity U), one by Kodak (Direct View CR 975), and one by Agfa (DX-S). The quantitative comparison is based on the calculation of the modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Noise investigation was also achieved by using a relative standard deviation analysis. Psychophysical characterization is assessed by performing a contrast detail analysis with an automatic reading of CDRAD images. Results: The most advanced units based on columnar phosphors provide MTF values in line or better than those from conventional CR systems. The greater thickness of the columnar phosphor improves the efficiency, allowing for enhanced noise properties. In fact, NPS values for standard CR systems are remarkably higher for all the investigated exposures and especially for frequencies up to 3.5 lp/mm. As a consequence, DQE values for the three units based on columnar phosphors and line-scanning reading, or granular phosphor and dual-side reading, are neatly better than those from conventional CR systems. Actually, DQE values of about 40% are easily achievable for all the investigated exposures. Conclusions: This study suggests that systems based on the dual-side reading or line-scanning reading with columnar phosphors provide a remarkable improvement when compared to conventional CR units and yield results in line with those obtained from most digital detectors for radiography. [ABSTRACT FROM AUTHOR]

Purpose: The authors describe a new technique to determine the system presampled modulation transfer function (MTF) in digital radiography using only the detector noise response. Methods: A cascaded-linear systems analysis was used to develop an exact relationship between the two-dimensional noise power spectrum (NPS) and the presampled MTF for a generalized detector system. This relationship was then utilized to determine the two-dimensional presampled MTF. For simplicity, aliasing of the correlated noise component of the NPS was assumed to be negligible. Accuracy of this method was investigated using simulated images from a simple detector model in which the “true” MTF was known exactly. Measurements were also performed on three detector technologies (an x-ray image intensifier, an indirect flat panel detector, and a solid state x-ray image intensifier), and the results were compared using the standard edge-response method. Flat-field and edge images were acquired and analyzed according to guidelines set forth by the International Electrotechnical Commission, using the RQA 5 spectrum. Results: The presampled MTF determined using the noise-response method for the simulated detector system was in close agreement with the true MTF with an averaged percent difference of 0.3% and a maximum difference of 1.1% observed at the Nyquist frequency (fN). The edge-response method of the simulated detector system also showed very good agreement at lower spatial frequencies (less than 0.5 fN) with an averaged percent difference of 1.6% but showed significant discrepancies at higher spatial frequencies (greater than 0.5 fN) with an averaged percent difference of 17%. Discrepancies were in part a result of noise in the edge image and phasing errors. For all three detector systems, the MTFs obtained using the two methods were found to be in good agreement at spatial frequencies less than 0.5 fN with an averaged percent difference of 3.4%. Above 0.5 fN, differences increased to an average of 20%. Deviations of the experimental results largely followed the trend seen in the simulation results, suggesting that differences between the two methods could be explained as resulting from the inherent inaccuracies of the edge-response measurement technique used in this study. Aliasing of the correlated noise component was shown to have a minimal effect on the measured MTF for the three detectors studied. Systems with significant aliasing of the correlated noise component (e.g., a-Se based detectors) would likely require a more sophisticated fitting scheme to provide accurate results. Conclusions: Results indicate that the noise-response method, a simple technique, can be used to accurately measure the MTF of digital x-ray detectors, while alleviating the problems and inaccuracies associated with use of precision test objects, such as a slit or an edge. [ABSTRACT FROM AUTHOR]

Radiography or computed tomography is the most widely available imaging tool for foreign body detection. However, the detectability of low-density substances by x ray is very poor when located in soft tissues. Various dielectric loss factors of foreign bodies contribute great microwave absorption heterogeneity compared with the surrounding tissue. A fast thermoacoustic tomography system at 1.2 and 6 GHz was developed to detect foreign targets in small animals. The 6 GHz system had a much higher signal-to-noise ratio in near-surface imaging but smaller imaging depth than the 1.2 GHz system. The effects of microwave distribution inhomogeneity on nonuniform excitation of acoustic pressure were studied and a corresponding calibration algorithm for image distortion was provided and experimentally examined. Thermoacoustic images of radiolucent objects including glass fiber, wood, and bamboo hidden in phantom and residual in living mice were compared with radiography and ultrasonography. Good contrast was obtained between the foreign bodies and the tissue surrounding it, and the location and size of the lesion targets in thermoacoustic images were in good agreement with the actual sample. The experimental results demonstrate that thermoacoustic tomography may become the ideal modality for radiolucent foreign body detection and imaging in animals and human. [ABSTRACT FROM AUTHOR]

The response of indirect x-ray digital imaging sensors is often not homogenous on the entire surface area. In this case, calibration is needed to build offset and gain maps, which are used to correct the sensor output. The sensors of new generation are equipped with an on-board memory, which serves to store these maps. However, because of its limited dimension, the maps have to be compressed before saving them. This step is critical because of the extremely high compression rate required. The authors propose here a novel method to achieve such a high compression rate, without degrading the quality of the sensor output. It is based on quad tree decomposition, which performs an adaptive sampling of the offset and gain maps, matched with a RBF-based interpolation strategy. The method was tested on a typical intraoral radiographic sensor and compared with traditional compression techniques. Qualitative and quantitative results show that the method achieves a higher compression rate and produces images of superior quality. The method can be adopted also in different fields where a high compression rate is required. [ABSTRACT FROM AUTHOR]

The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10-7–10-2 R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct interaction of x rays in the gain region. Thus, HARP-AMFPI is a promising flat-panel imager structure that enables high-resolution fully quantum noise limited x-ray imaging over a wide exposure range. [ABSTRACT FROM AUTHOR]

The H operator represents the deterministic performance of any imaging system. For a linear, digital imaging system, this system operator can be written in terms of a matrix, H, that describes the deterministic response of the system to a set of point objects. A singular value decomposition of this matrix results in a set of orthogonal functions (singular vectors) that form the system basis. A linear combination of these vectors completely describes the transfer of objects through the linear system, where the respective singular values associated with each singular vector describe the magnitude with which that contribution to the object is transferred through the system. This paper is focused on the measurement, analysis, and interpretation of the H matrix for digital x-ray detectors. A key ingredient in the measurement of the H matrix is the detector response to a single x ray (or infinitestimal x-ray beam). The authors have developed a method to estimate the 2D detector shift-variant, asymmetric ray response function (RRF) from multiple measured line response functions (LRFs) using a modified edge technique. The RRF measurements cover a range of x-ray incident angles from 0° (equivalent location at the detector center) to 30° (equivalent location at the detector edge) for a standard radiographic or cone-beam CT geometric setup. To demonstrate the method, three beam qualities were tested using the inherent, Lu/Er, and Yb beam filtration. The authors show that measures using the LRF, derived from an edge measurement, underestimate the system’s performance when compared with the H matrix derived using the RRF. Furthermore, the authors show that edge measurements must be performed at multiple directions in order to capture rotational asymmetries of the RRF. The authors interpret the results of the H matrix SVD and provide correlations with the familiar MTF methodology. Discussion is made about the benefits of the H matrix technique with regards to signal detection theory, and the characterization of shift-variant imaging systems. [ABSTRACT FROM AUTHOR]

In order to improve the safety and efficacy of percutaneous aortic valve replacement procedures, a closed bore hybrid x-ray/MRI (CBXMR) system is proposed in which an x-ray C-arm will be positioned with its isocenter ≈1 m from the entrance of a clinical MRI scanner. This system will harness the complementary strengths of both modalities to improve clinical outcome. A key component of the CBXMR system will be a rotating anode x-ray tube to produce high-quality x-ray images. There are challenges in positioning an x-ray tube in the magnetic fringe field of the MRI magnet. Here, the effects of an external magnetic field on x-ray tube induction motors of radiography x-ray tubes and the corresponding reduction of x-ray tube heat loadability are investigated. Anode rotation frequency fanode was unaffected when the external magnetic field Bb was parallel to the axis of rotation of the anode but decreased when Bb was perpendicular to the axis of rotation. The experimental fanode values agreed with predicted values to within ±3% over a Bb range of 0–30 mT. The MRI fringe field at the proposed location of the x-ray tube mounted on the C-arm (≈4 mT) reduced fanode by only 1%, so x-ray tube heat loadability will not be compromised when using CBXMR systems for percutaneous aortic valve replacement procedures. Eddy current heating power in the rotor due to an MRI fringe field was found to be two orders of magnitude weaker than the heating power produced on the anode due to a fluoroscopic exposure, so eddy current heating had no effect on x-ray tube heat loadability. [ABSTRACT FROM AUTHOR]

An x-ray light valve (XLV) coupled with an optical scanner has the potential to meet the need for a low-cost, high quality digital imaging system for general radiography. The XLV/scanner concept combines three well-established, and hence, low-cost technologies: An amorphous selenium (a-Se) layer as an x-ray-to-charge transducer, a liquid crystal (LC) cell as an analog display, and an optical scanner for image digitization. The XLV consists of an a-Se layer and LC cell in a sandwich structure which produces an optical image in the LC layer upon x-ray exposure. The XLV/scanner system consists of an XLV in combination with an optical scanner for image readout. Here, the effect of each component on the spatial resolution of an XLV/scanner system is investigated. A theoretical model of spatial resolution of an XLV is presented based on calculations of the modulation transfer function (MTF) for a-Se and a LC cell. From these component MTFs, the theoretical MTF of the XLV is derived. The model was validated by experiments on a prototype XLV/scanner system. The MTF of the scanner alone was obtained by scanning an optical test target and the MTF of the XLV/scanner system was measured using x rays. From the measured MTF of the scanner, the theoretical MTF of the XLV/scanner system was established and compared with the experimental results. Good general agreement exists between experimental and theoretical results in the frequency range of interest for general radiography, although the theoretical curves slightly overstate the measured MTFs. The experimental MTF of the XLV was compared with the MTF of two clinical systems and was shown to have the capability to exceed the resolution of flat-panel detectors. From this, the authors can conclude that the XLV has an adequate resolution for general radiography. The XLV/scanner also has the potential to eliminate aliasing while maintaining a MTF that exceeds that of a flat-panel imager. [ABSTRACT FROM AUTHOR]

Radiographic techniques are devised on the basis of anatomic dimensions. Inaccurate dimensions can cause radiographs to be exposed inappropriately and patient radiation exposures to be calculated incorrectly. The source of anatomic dimensions in common usage dates back to 1948. The objective of this study was to compare traditional and modern anthropometric data, use modern dimensions to estimate potential errors in patient exposure, and suggest modified technique guidelines. Anthropometry software was used to derive modern anatomic dimensions. Data from routine annual testing were analyzed to develop an x-ray generator output curve. Published tabulated data were used to determine the relationship between tissue half-value layer and kilovoltage. These relationships were used to estimate entrance skin exposure and create a provisional technique guide. While most anatomic regions were actually larger than previously indicated, some were similar, and a few were smaller. Accordingly, exposure estimates were higher, similar, or lower, depending on the anatomic region. Exposure estimates using modern dimensions for clinically significant regions of the trunk were higher than those calculated with traditional dimensions. Exposures of the postero-anterior chest, lateral chest, antero-posterior (AP) abdomen, male AP pelvis, and female AP pelvis were larger by 48%, 31%, 54%, 52%, and 112%, respectively. The dimensions of bony regions of the anatomy, such as the joints and skull, were unchanged. These findings are consistent with the idea that anatomic areas where fat is deposited are larger in the modern U.S. population than they were in previous years. Exposure techniques for manual radiography and calculations of patient dose for automatic exposure control radiography should be adjusted according to the modern dimensions. Population radiation exposure estimates calculated in national surveys should also be modified appropriately. [ABSTRACT FROM AUTHOR]

A self-consistent approach for the Monte Carlo calculation of free-air chamber (FAC) correction factors needed to convert the chamber reading into the quantity air-kerma at the point of measurement is introduced, and its implementation in the new EGSnrc user code egs_fac is discussed. To validate the method, comparisons between computed and measured FAC correction factors for attenuation Ax, scatter (Ascat), and electron loss (Aeloss) are performed in the medium energy range where the experimental determination is believed to be accurate. The Monte Carlo calculations utilize a full simulation of the x-ray tube with BEAMnrc and a detailed model of the parallel-plate FAC. Excellent agreement between the computed Ascat and Aeloss and the measured values for these correction factors currently used in the National Research Council (NRC) of Canada primary FAC standard is observed. Our simulations also agree with previous Monte Carlo results for Ascat and Aeloss for the 135 and 250 kVp Consultative Committee for Ionizing Radiation reference beam qualities. The computed attenuation correction agrees with the measured Aatt within the stated uncertainties, although the authors’ simulations demonstrate that the evacuated-tube technique employed at NRC to measure the attenuation correction slightly overestimates Aatt in the medium energy range. The newly introduced corrections for backscatter, beam geometry, and lack of charged particle equilibrium along the beam axis are found to be negligible. On the other hand, the correction for photons leaking through the FAC aperture, currently ignored in the NRC standard, is shown to be significant. [ABSTRACT FROM AUTHOR]

The measurement of the modulation transfer function (MTF) of an imaging device is a common requirement in evaluating radiographic detector performance. Such measurements are considered mandatory in detector development research, and may also be carried out as part of routine quality assurance (QA) checks of image quality. Traditionally, MTF measurement has been performed by imaging either a narrow slit or a sharp edge in order to generate a line spread function, whose Fourier transform provides the MTF on a near-continuous frequency domain. Much less commonly employed is the method of square-wave line-pair modulations, in which the modulation response to bar resolution targets contained in a bar pattern is used to estimate the MTF at discrete spatial frequencies. While the slit and edge methods offer advantages of accuracy and a well-known standardized protocol for measurement based on several decades of development, their major limitation is the difficult and time-consuming experimental setup that is necessary to ensure accurate measurements. On the other hand, the bar pattern offers the advantage of a quick, simple, and easy measurement without the need for a complex experimental setup, with the main disadvantages of the technique being a pseudo-normalization that may lead to an overestimated MTF, and corrections for removing higher-order frequency harmonics that require interpolating between discrete spatial frequencies. Therefore, bar patterns are traditionally used for qualitative imaging applications like detector QA in terms of relative and arbitrarily defined spatial resolution metrics, while slit and edge methods are preferred for quantitative MTF measurements. Compared to diagnostic x rays, MTF measurements using megavoltage x rays are further complicated by low x-ray attenuation and excessive Compton scattering. In this work, a method to measure the MTF of megavoltage x-ray detectors based on imaging square-wave line pairs with improved near-zero-frequency normalization was developed as an adaptation to previously reported methods. Monte Carlo simulations were used to identify an improved normalization condition with which the accuracy of the MTF determined from line-pair modulations could be enhanced considerably compared to previously used techniques. Slit, edge, and bar-pattern measurements were performed to obtain the MTF of commercial megavoltage imaging devices including portal film and electronic portal imaging devices. A comparison of the MTF measurements from the three techniques was used to ascertain the validity of the proposed bar-pattern method for accurate and reliable measurement of MTF for megavoltage imagers. Statistical analyses revealed no significant differences between the bar-pattern method and the standard slit and edge techniques, indicating very good agreement (mean difference within ±3%). These results indicated the potential for line-pair bar patterns to be used more effectively than in the past for traditional QA imaging as well as for quantitative MTF measurement in detector development research. [ABSTRACT FROM AUTHOR]

The stationary grid commonly used with a digital x-ray detector causes a moiré interference pattern due to the inadequate sampling of the grid shadows by the detector pixels. There are limitations with the previous methods used to remove the moiré such as imperfect electromagnetic interference shielding and the loss of image information. A new method is proposed for removing the moiré pattern by integrating a carbon-interspaced high precision x-ray grid with high grid line uniformity with the detector for frequency matching. The grid was aligned to the detector by translating and rotating the x-ray grid with respect to the detector using microcontrolled alignment mechanism. The gap between the grid and the detector surface was adjusted with micrometer precision to precisely match the projected grid line pitch to the detector pixel pitch. Considering the magnification of the grid shadows on the detector plane, the grids were manufactured such that the grid line frequency was slightly higher than the detector sampling frequency. This study examined the factors that affect the moiré pattern, particularly the line frequency and displacement. The frequency of the moiré pattern was found to be sensitive to the angular displacement of the grid with respect to the detector while the horizontal translation alters the phase but not the moiré frequency. The frequency of the moiré pattern also decreased with decreasing difference in frequency between the grid and the detector, and a moiré-free image was produced after complete matching for a given source to detector distance. The image quality factors including the contrast, signal-to-noise ratio and uniformity in the images with and without the moiré pattern were investigated. [ABSTRACT FROM AUTHOR]

A practical method to determine the heating and cooling curves of x-ray tube assemblies with rotating anode x-ray tube is proposed. Available procedures to obtain these curves as described in the literature are performed during operation of the equipment, and the precision of the method depends on the knowledge of the total energy applied in the system. In the present work we describe procedures which use a calorimetric system and do not require the operation of the x-ray equipment. The method was applied successfully to a x-ray tube assembly that was under test in our laboratory. [ABSTRACT FROM AUTHOR]

Polychromatic phase-contrast radiography differs from traditional (absorption-only) radiography in that the method requires at least a partially coherent x-ray source and the resulting images contain information about the phase shifts of x-rays in addition to the traditional absorption information. In a typical embodiment, this effect results in a measurable enhancement in image contrast at the edges of objects. In this study, a phase-contrast imaging system was adapted to allow an object to be imaged at multiple projections, and these projections were used to generate phase-contrast computed tomography images. The images obtained with this technique show edge enhancements surrounding the objects within the image. [ABSTRACT FROM AUTHOR]