Search

This work compares the detector performance and image quality of the new Kodak Min-R EV mammography screen-film system with the Fuji CR Profect detector and with other current mammography screen-film systems from Agfa, Fuji and Kodak. Basic image quality parameters (MTF, NPS, NEQ and DQE) were evaluated for a 28 kV Mo/Mo (HVL = 0.646 mm Al) beam using different mAs exposure settings. Compared with other screen-film systems, the new Kodak Min-R EV detector has the highest contrast and a low intrinsic noise level, giving better NEQ and DQE results, especially at high optical density. Thus, the properties of the new mammography film approach those of a fine mammography detector, especially at low frequency range. Screen-film systems provide the best resolution. The presampling MTF of the digital detector has a value of 15% at the Nyquist frequency and, due to the spread size of the laser beam, the use of a smaller pixel size would not permit a significant improvement of the detector resolution. The dual collection reading technology increases significantly the low frequency DQE of the Fuji CR system that can at present compete with the most efficient mammography screen-film systems.

The aim of this work was to investigate and quantify the effects of system noise, nodule location, anatomical noise and anatomical background on the detection of lung nodules in different regions of the chest x-ray. Simulated lung nodules of diameter 10 mm but with varying detail contrast were randomly positioned in four different kinds of images: 1) clinical images collected with a 200 speed CR system, 2) images containing only system noise (including quantum noise) at the same level as the clinical images, 3) clinical images with removed anatomical noise, 4) artificial images with similar power spectrum as the clinical images but random phase spectrum. An ROC study was conducted with 5 observers. The detail contrast needed to obtain an Az of 0.80, C0.8, was used as measure of detectability. Five different regions of the chest x-ray were investigated separately. The C0.8 of the system noise images ranged from only 2% (the hilar regions) to 20% (the lateral pulmonary regions) of those of the clinical images. Compared with the original clinical images, the C0.8 was 16% lower for the de-noised clinical images and 71% higher for the random phase images, respectively, averaged over all five regions. In conclusion, regarding the detection of lung nodules with a diameter of 10 mm, the system noise is of minor importance at clinically relevant dose levels. The removal of anatomical noise and other noise sources uncorrelated from image to image leads to somewhat better detection, but the major component disturbing the detection is the overlapping of recognizable structures, which are, however, the main aspect of an x-ray image.

The purpose of this study is to present a strategy to define the reference dose levels for fluoroscopic, dose-intensive examinations. This work is a part of the project of the Federal Office of Public Health of Switzerland to translate the guidelines of the International Commission on Radiological Protection and the European Union into action. The study will also be used to set reference dose levels on the basis of a national survey. All the fluoroscopic units, involved in the survey, were equipped with a KAP (kerma-area product) meter. All KAP meters were first calibrated to ensure the comparability of the dose measurements. The doses and the dose rates together with subjective image quality measurements were acquired in all the centres. Eight types of examination were chosen by a panel of radiologists, and each of the five centres involved agreed to monitor 20 patients per examination type. A wide variation in the dose and the image quality in fixed geometry was observed. For example, the skin dose rate for abdominal examinations varied in the range of 12-42 mGy min(-1) for comparable image quality. Average KAP values of 67, 178, 106, 102, 473, 205, 307 and 316 Gy cm2 were recorded for barium meal, abdominal angiography, cerebral angiography, barium enema, hepatic embolisation, biliary drainage, cerebral embolisation and femoral stenting, respectively. The values obtained in this limited study are generally higher than the ones available in the literature and strategies to optimise these studies have to be discussed. A strict control concerning the denomination of the examination type involved in such a study is mandatory to obtain reliable data. This can only be done through a close collaboration between physicians, radiographers and medical physicists.

In mammography, the imagecontrast and dose delivered to the patient are determined by the x-ray spectrum and the scatter to primary ratio S/P. Thus the quality of the mammographic procedure is highly dependent on the choice of anode and filter material and on the method used to reduce the amount of scatteredradiation reaching the detector.Synchrotron radiation is a useful tool to study the effect of beam energy on the optimization of the mammographic process because it delivers a high flux of monochromatic photons. Moreover, because the beam is naturally flat collimated in one direction, a slot can be used instead of a grid for scatter reduction. We have measured the ratio S/P and the transmission factors for grids and slots for monoenergetic synchrotron radiation. In this way the effect of beam energy and scatter rejection method were separated, and their respective importance for image quality and dose analyzed. Our results show that conventional mammographic spectra are not far from optimum and that the use of a slot instead of a grid has an important effect on the optimization of the mammographic process. We propose a simple numerical model to quantify this effect.

The assessment of image quality in mammography often relies on the subjective evaluation of films produced with test-objects containing structures such as masses, micro-calcifications and filaments. If the methodology is adequate to control the stability of a mammography unit, its use in a context of system optimization (from the x-ray spectrum to the detector response) is limited. Thus, a test-object which allows measurements of the detectability index d' from the non-prewhitening matched filter (NPWE) observer, was developed and tested. The test-object is 45 mm thick and allows the assessment of d' in areas of different glandular/fat compositions (i.e image quality evaluation taking into account the dynamic range parameter). To simulate the absorption of the skin, a 100% fat equivalent tissue, with a thickness of 5 mm, is placed on each side of the test-object. On a conventional unit, it is possible to assess the image parameters at three optical density levels (i.e. 0.5 - 0.8 ; 1.5 - 1.6 and 2.3 - 2.6) in one exposure. The imaging of this test object on digital units has also been tested satisfactorily.

s / Physica Medica 30 (2014) e123ee145 e126 IMPACT OF THE RECONSTRUCTION PLAN ON IMAGE QUALITY FOR CT IMAGES J.G. Ott , E. Dugert , F. Becce , P. Omoumi , F.R. Verdun a a Institut de Radiophysique, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland; b Service de radiodiagnostic et radiologie interventionnelle, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland Introduction: Images acquired with Computed Tomography (CT) are traditionally reconstructed and interpreted in the axial plan. However, in clinical practice there are several situations where images have to be visualised in the axial, sagittal and coronal plan. Moreover, recent introduction of iterative algorithms allowed a significant diminish of the delivered dose, but this also goes along with repercussions on image quality. This impact has beenwidely studied in the axial plan but work still needs to be done for the coronal and sagittal plan. Material and method: Images were acquired on a HD 750 GE CT, in the 3 plans and with a CTDIvol of 7.3mGy. Each acquisition was reconstructed with a bone filter, as well as different reconstruction algorithms: the classical Filtered Back Projection (FBP) and iterative algorithms (ASIR (40% and 80%) and MBIR). Image quality assessment was done using phantoms. The MTF (Modulation Transfer Function) and the NPS (Noise Power Spectrum) were calculated in order to estimate the noise as well as the spatial resolution of the images. Image quality was also assessed through an additional metric called Task Transfer Function (TTF). It was estimated using a phantom containing cylindrical inserts composed of materials surrounded by water. TTF is obtained by measuring contrast difference between the inserts and the water and then applying mathematical treatment to the data. This allows us to estimate spatial resolution when taking contrast transfer into account. Results: Results show that images acquired and reconstructed in the same plan exhibit significantly different spatial resolution depending if it was estimated through TTF or MTF. This demonstrates a dependency of the contrast on the resolution due to the non linearity of the different filters and reconstruction algorithms we used. Furthermore, a significant reduction of both spatial resolution and noise is observed in coronal and sagittal plan compared to axial plan. Conclusion: The results suggest that CT images acquired in the same conditions but reconstructed in different plans will exhibit differences in spatial resolution as well as in noise power spectra. Those parameters having a direct influence on image quality, this means that lesion detection and characterization by the radiologist is modified. In the end, the visualization of the clinical examinations in different plans has repercussions in diagnostic imaging. http://dx.doi.org/10.1016/j.ejmp.2014.10.015 MONTE CARLO SOFTWARE FOR DOSE CALCULATION IN CT EXAMINATIONS C. Adrien , A. Croc De Suray , J.-C. Garcia-Hernandez , S. Dreuil , J. Plagnard , B. Poumarede , C. Le Loirec , J.-M. Bordy a CEA LIST, CEA/ DRT/LIST, Gif sur Yvette, France; b Institut Gustave Roussy, Paris, France Introduction: The significant rise of medical imaging exams in the past few years has led to an increase of collective doses. Despite the numerous tools already available, most of them only provide common dose index (CTDI, PDL) and effective dose rather than absorbed dose to organs. To obtain organ doses, a Monte Carlo (MC) tool, PENELOPE-C++, based on the PENELOPE simulator developed by Salvat et al is adapted. Our finale goal is to develop a predictive tool to obtain the best compromise solution for a CT exam exposure between low organ absorbed doses and high image quality. Material and methods: Due to the lack of information available in the technical note, the GE VCT Lightspeed 64 tube was modeled using the method proposed by Turner et al. Thanks to HVL and profile measurements, equivalent spectra, inherent filtrations and bowtie filter shapes are obtained. Measurements were then performed in static mode with a CdTe detector associated with an unfolding method developed by the LNHB to achieve experimental spectra and validate the tube model. Ultimately, the axial and helical rotation was implemented in the MC tool. To improve the efficiency of the simulation, two variance reduction techniques were used: a circular and a translational splitting. To validate the calculation, simulated sinograms are compared with the expected ones and the particle distribution along the gantry path is checked. The MC tool and the X-ray tube model were then validated for dosimetric purposes. Measured doses were first obtained in a static mode with a calibrated pencil ionization chamber in a PMMA phantom and compared with simulations. Validations for rotational modes are in progress. Results: Computed and measured spectra show acceptable discrepancies attributable to a misalignment during measurements. Bowtie filter shapes are in agreement with theoretical expectations. The geometric validations are consistent with the theoretical expectations. Comparisons between measured and simulated integrated doses are good enough, with less than 6% discrepancies for all different acquisition parameters. Summary: The first validations obtained for the use of PENELOPE-C++ for CT dose estimations are encouraging. The validation of the rotation motion implementation is part of ongoing research on several phantoms and for several examination procedures in CT exams. http://dx.doi.org/10.1016/j.ejmp.2014.10.016 DEVELOPMENT OF SOFTWARE HELPING IN OPTIMIZING COMPUTED TOMOGRAPHY PROTOCOLS: INITIAL RESULTS F. Gardavaud , H. Pasquier , H. Baroukh , A. Rahmouni , A. Luciani a,c,d AP-HP, Groupe Henri Mondor Albert Chenevier, Imagerie Medicale, France; General Electric Medical Systems [Buc] (GE Healthcare), France; Universit e Paris-Est Cr eteil, Facult e de M edecine de Cr eteil, UMRS955, France; d INSERM, Unit e U955, Equipe 17, France Introduction: A simulation tool was developed to enable the visualization of the effect of CT protocol optimization on Image Quality (IQ) and radiation dose. Material and methods: A database of reference Computed Tomography (CT) protocols, adapted to Discovery CT 750HD (GE Healthcare, Wisconsin), for the most encountered clinical indications in CT was established by collecting reference protocols from the American Association of Physicists in Medicine (AAPM) and from optimized and clinically validated protocols in multicentric radiological departments. By adjusting the tube current modulation, three different IQ protocols (low dose, standard, high quality) were defined, for each reference protocol. For these, CT images were acquired on an anthropomorphic phantom (PBU-60®, KYOTO KAGAKU) using the three derived IQ protocols. A software, named ProtoEnhance, was developed to help to optimize CT protocols by displaying the anthropomorphic images and associated volume Computed Tomography Dose Index (CTDIvol). We compared our clinically used hepatic helical acquisition without contrast medium to the standard optimization proposed in ProtoEnhance, qualitatively validated by a senior radiologist, by determining the CTDIvol, by measuring the Signal-Noise Ratio (SNR) in liver and the Contrast-Noise Ratio (CNR) between liver and spleen both on the anthropomorphic phantom and on patient of similar body mass index. Results: We observed significant dose reductions with the optimized protocol versus our routine protocol on the PBU-60 phantom (CTDIvol 1⁄4 5.1 mGy vs 6.9 mGy), and on patient (CTDIvol 1⁄4 5.2 mGy vs 6.6 mGy). SNR and CNR of anthropomorphic phantom images were similar to those of patient images. Conclusion: ProtoEnhance can help medical staff to optimize CT protocols according to IQ preferences.

The state of the art to describe image quality in medical imaging is to assess the performance of an observer conducting a task of clinical interest. This can be done by using a model observer leading to a figure of merit such as the signal-to-noise ratio (SNR). Using the non-prewhitening (NPW) model observer, we objectively characterised the evolution of its figure of merit in various acquisition conditions. The NPW model observer usually requires the use of the modulation transfer function (MTF) as well as noise power spectra. However, although the computation of the MTF poses no problem when dealing with the traditional filtered back-projection (FBP) algorithm, this is not the case when using iterative reconstruction (IR) algorithms, such as adaptive statistical iterative reconstruction (ASIR) or model-based iterative reconstruction (MBIR). Given that the target transfer function (TTF) had already shown it could accurately express the system resolution even with non-linear algorithms, we decided to tune the NPW model observer, replacing the standard MTF by the TTF. It was estimated using a custom-made phantom containing cylindrical inserts surrounded by water. The contrast differences between the inserts and water were plotted for each acquisition condition. Then, mathematical transformations were performed leading to the TTF. As expected, the first results showed a dependency of the image contrast and

Purpose: EOS (EOS imaging S.A, Paris, France) is an x-ray imaging system that uses slot-scanning technology in order to optimize the trade-off between image quality and dose. The goal of this study was to characterize the EOS system in terms of occupational exposure, organ doses to patients as well as image quality for full spine examinations. Methods: Occupational exposure was determined by measuring the ambient dose equivalents in the radiological room during a standard full spine examination. The patient dosimetry was performed using anthropomorphic phantoms representing an adolescent and a five-year-old child. The organ doses were measured with thermoluminescent detectors and then used to calculate effective doses. Patient exposure with EOS was then compared to dose levels reported for conventional radiological systems. Image quality was assessed in terms of spatial resolution and different noise contributions to evaluate the detector's performances of the system. The spatial-frequency signal transfer efficiency of the imaging system was quantified by the detective quantum efficiency (DQE). Results: The use of a protective apron when the medical staff or parents have to stand near to the cubicle in the radiological room is recommended. The estimated effective dose to patients undergoing a full spine examination with the EOS system was 290μSv for an adult and 200 μSv for a child. MTF and NPS are nonisotropic, with higher values in the scanning direction; they are in addition energy-dependent, but scanning speed independent. The system was shown to be quantum-limited, with a maximum DQE of 13%. The relevance of the DQE for slot-scanning system has been addressed. Conclusions: As a summary, the estimated effective dose was 290μSv for an adult; the image quality remains comparable to conventional systems.

The display of low-contrast structures and fine microcalcifications is essential for the early diagnosis of breast cancer. In order to achieve a high image quality level with a minimum amount of radiation delivered to the patient, the use of different spectra (Mo or Rh anode and filters) was introduced. The European Synchrotron Radiation Facility is able to produce a monochromatic beam with a high photon flux. It is thus a powerful tool to study the effect of beam energy on image quality and dose in mammography. Our image quality assessment is based on the calculation of the size of the smallest microcalcification detectable on a radiograph, derived from the statistical decision theory. The mean glandular dose is simultaneously measured. Compared with conventional mammography units, the monochromaticity of synchrotron beams improves contrast and the use of a slit instead of an anti-scatter grid leads to a higher primary beam transmission. The relative contribution of these two effects on image quality and dose is discussed.

This work monitors the radiation doses to a radiologist during supervision of automatic contrast media injections during helical-CT examinations of the chest and abdomen. Forty consecutive standard helical-CT examinations of adult's chest and/or abdomen were monitored with five dosimeters worn by the radiologist supervising the entire injection with the hand on the injection site. Mean doses per examination measured at chest, thyroid gland, and hand levels were 11, 16, and 130 microGy, respectively, during chest examinations, and 5, 7, and 55 microGy during abdominal examinations. According to the high number of CT examinations performed, wearing lead apron, special lead glove protection, and thyroid shield is highly recommended.

A novel approach to patient dose and image quality optimization was developed and implemented for chest and lumbar spine radiography. A Monte Carlo model of the imaging chain, including an anthropomorphic voxel-phantom to simulate the patient, was utilized. Detector noise and system unsharpness were modeled and their influence on image quality considered. Image quality was quantified by the contrast ((Delta) OD) and the ideal observer signal-to-noise (SNR) for a number of relevant image details at various positions in the anatomy and measures of dynamic range (DR). Among systems evaluated in a clinical trial, a reference system, acknowledged to yield acceptable image quality, was selected. A large variety of other imaging conditions were simulated and compared to the reference system. Some of the simulated systems were found to give as good imaging performance but at substantially reduced patient doses: 35% and 50% reduction in the lumbar spine AP and the chest PA view, respectively. The model was also used to define a single-valued 'figure-of- merit,' the physical image quality score, PIQS, with the aim to make possible ranking of the imaging systems. By comparing the ranking according to PIQS with radiologists' ranking it was possible to analyze the features in the images which are clinically important.

Normal tissue structure in a radiological image, called anatomical noise, can prevent radiologists from seeing the pathology they are looking for. The goal of this paper is to show the importance of this noise component compared to the system one (quantum mottle, screen structure and film noises) in the particular case of mammography. Two normal mammographic images are digitized in order to provide an anatomical structure. On this background, an object simulating a microcalcification (a sphere) or a tumor (a spherical lens) is filtrated by the modulation transfer function of the imaging system representative of a mammographic unit and superimposed. A two alternative forced choice experiment is effected on these synthesized images in which the amount of object contrast and system noise is varied. The images are presented on a high resolution screen to five observers used for this kind of experiment. The experimental results are then compared to the signal to noise ratios given by the non-prewhitening matched filter model in which the human visual transfer function is taken into account. When comparing the experimental results with the model in which the anatomical noise is considered as a noise or as a signal, it is observed that the experimental results are in-between. This means that the anatomical background has a component that can be considered as a noise and another that can be recognized as signal. At the present time, there is no observer model who takes the anatomical noise effect into account. The use of a homogeneous test object without anatomical structure to qualify the system performance or to optimize the radiological procedure then appears questionable.

BACKGROUND: The frequency of CT procedures has registered a significant increase over the last decade, which led at the international level to an increasing concern on the radiological risk associated with the use of CT especially in paediatrics. This work aimed at investigating the use of computed tomography in Switzerland, following the evolution of CT frequency and dose data over a decade and comparing it to data reported in other countries. METHODS: The frequency and dose data related to CT are obtained by means of a nationwide survey. National frequencies were established by projecting the collected data, using the ratio of the number of CT units belonging to the respondents to the total number of CT units in the country. The effective doses per examination were collected during an auditing campaign. RESULTS: In 2008 about 0.8 Million CT procedures (~ 100 CT examinations / 1000 population) were performed in the country, leading to a collective effective dose of more than 6000 man.Sv (0.8 mSv/caput). In a decade the frequency of CT examinations averaged over the population and the associated average effective dose per caput increased by a factor of 2.2 and 2.9 respectively. CONCLUSIONS: Although the contribution of CT to the total medical X-rays is 6% in terms of the frequency, it represents 68% in terms of the collective effective dose. These results are comparable to those reported in a number of countries in Europe and America with similar health level.

Purpose: The number and complexity of interventional cardiology (IC) procedures has been steadily increasing over the last twenty years. This implies an increased risk of stochastic and even deterministic effects to the patient, as well as an increased exposure of IC staff. Radiation protection must thus become of prime importance and should be promoted by all possible means. Methods: We are currently developing a mobile application that will help the physician to evaluate his/her current state of practice regarding radiation protection. The key elements to achieve this goal would be:‐Comparing his/her patient delivered doses to the local diagnostic reference levels (DRL).‐Estimate the risk and severity of potential radiation‐induced skin burns and the necessity of patient follow‐up.‐Estimate one's average personal dose.‐Give advice in order to reduce patient and staff exposure.‐Give general information about radiation protection. Results: As radiation‐induced erythema occurs several days or weeks the X‐ray exposure, it can be easily diagnosed as being caused by another factor, such as medication or allergy. Giving the patient more information about his/her personal risk would greatly improve his/her follow‐up to minimize negative side effects of a high dose IC procedure. As for the staff, it will help them with their daily practice by giving them useful tips aiming to reduce the dose delivered to the patient and, as a consequence, their own personal dose. Conclusion: The promotion of radiation protection must be done using all available means. The tremendous growth of mobile devices in the recent years called for a gap to be filled. When ready, our mobile application will help the physician to reach the lowest dose possible while still keeping diagnostic accuracy by estimating his/her practice with respect to the local diagnostic reference levels and giving useful working tips.

Quality assurance programmes are becoming a common practice in the field of mammography. At the present time several recommendations exist and different test objects are used to optimize this radiological procedure. The goal of this study was to check if geographically distant centres using different quality control procedures were comparable when using a common objective way of assessing image quality. The results show that consensus still needs to be found among radiologists to reach a satisfactory level of harmony between patient doses and image quality in Europe. The benefits of early detection of breast cancer have caused an increase in the use of mammography. Mass screening campaigns are becoming a common practice which can be seen as an improvement from the public health point of view, but also leads to an increase of the population irradiation. It is well established that mammography is one of the most technically demanding radiographic procedures. A small change in technique or processing factors can have a significant effect on image quality and radiation dose. It is necessary to consider carefully the selection of equipment, imaging techniques and positioning to produce mammograms at the lowest dose consistent with high diagnostic sensitivity and specificity [1] .

Image quality and dose produced by a spiral CT with various pitch values were investigated on the basis of test-object images and measurements of CT dose indexes. No major difference in image quality or dose was observed when comparing sequential and spiral mode acquisition with a pitch of one. Increase in pitch value produces a loss of contrast which leads to a loss of detectability. Nevertheless, in realistic protocls the image quality in the transverse plane remains acceptable up to pitch values of 1.3 – 1.6.

Radiological image quality can be objectively quantified by the statistical decision theory. This theory is commonly applied with the noise of the imaging system alone (quantum, screen and film noises) whereas the actual noise present on the image is the 'anatomical noise' (sum of the system noise and the anatomical texture). This anatomical texture should play a role in the detection task. This paper compares these two kinds of noises by performing 2AFC experiments and computing the area under the ROC-curve. It is shown that the 'anatomical noise' cannot be considered as a noise in the sense of Wiener spectrum approach and that the detectability performance is the same as the one obtained with the system noise alone in the case of a small object to be detected. Furthermore, the statistical decision theory and the non- prewhitening observer does not match the experimental results. This is especially the case in the low contrast values for which the theory predicts an increase of the detectability as soon as the contrast is different from zero whereas the experimental result demonstrates an offset of the contrast value below which the detectability is purely random. The theory therefore needs to be improved in order to take this result into account.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Introduction : Tomographic techniques in diagnostic and interventional radiology or radiation therapy are in rapid development. The CTDI formalism that is currently used to assess dose has been challenged by several groups. The goal of this contribution is to evaluate the required scan length to reach equilibrium on various MDCT units and estimate the average dose delivered within a slice when using systems having a cone beam geometry. Method and Materials:Measurements were performed on three MDCT systems (GEMS 8, 16 and 64‐row), a flat panel fluoroscopy (Allura — Philips), an IGRT (Synergy, Elekta ltd) and on a tomotherapy (TomoTherapy Inc.) using two standard CTDI phantoms and a home made phantoms (PMMA cylinder of 30 cm filled with water) with a conventional small volume ion chamber (0.6 cc Farmer type) and a standard pencil ion chamber.Dose profiles were also recorded at various positions within the slice to study the impact of scatter as a function of the distance between the centre of the phantom and its periphery. Results: For CT units a theoretical length of 400 mm is required to reach the equilibrium at the center of the phantom. The measurements show that a dose plateau was reached after 420 mm. The average dose within a slice measured in our home made phantom for standard abdominal CT (120 kV, 210 effective mAs) was 15.3 mGy; 26.9 mGy for the fluoro‐CT (122kV, 274mAs, 20.7s); 39.0mGy for IGRT system (120kV, 219mAs, 27×27cm2field size, one rotation) and 13.1 mGy for the Tomotherapy system (3.5 MV, pitch=0.8). Conclusion: The CTDI concept should be replaced by a more generic methodology, such as the one presented here, that could be used in all cone beam geometries. Measurements should be done using water equivalent phantoms.

We estimated human observer linear templates underlying the detection of a realistic, spherical mass signal with mammographic backgrounds. Five trained naïve observers participated in two-alternative forced-choice (2-AFC) detection experiments with the signal superimposed on synthetic, clustered lumpy backgrounds (CLBs) in one condition and on nonstationary real mammographic backgrounds in another. Human observer linear templates were estimated using a genetic algorithm. A variety of common model observer templates were computed, and their shapes and associated performances were compared with those of the human observer. The estimated linear templates are not significantly different for stationary CLBs and real mammographic backgrounds. The estimated performance of the linear template compared with that of the human observers is within 5% in terms of percent correct (Pc) for the 2-AFC task. Channelized Hotelling models can fit human performance, but the templates differ considerably from the human linear template. Due to different local statistics, detection efficiency is significantly higher on nonstationary real backgrounds than on globally stationary synthetic CLBs. This finding emphasizes that nonstationary backgrounds need to be described by their local statistics.

According to the Nyquist theorem, the highest signal frequency which can be represented without foldover (aliasing) in a Fourier transform frequency-domain discrete spectrum is one-half of the time-domain sampling frequency. For example, since ion cyclotron resonance (ICR) frequency is inversely related to ionic mass-to-charge ratio, m/z, the highest ICR frequency (corresponding to the lowest correctly represented m/z) in direct-mode Fourier transform ICR mass spectrometry is restricted to one-half of the maximum sampling frequency, or about m/z ≥ 18 at 3.058 tesla (T) for a maximum sampling frequency of about 5.2 MHz. In this paper, we show that interleaved addition of two digitized time-domain transient signals, one of which is delayed by one-half of one sampling period (i.e., half of one cycle of the time-domain sampling frequency) with respect to the other, generates a time-domain discrete waveform which is indistinguishable from a single waveform produced by sampling at twice the original sampling rate. Thus, provided that the two transients have (or have been normalized to) the same magnitude, one can double the Nyquist-limited frequency range. If the sampling period is divided into three or more equal parts, with interleaved addition of three or more correspondingly delayed transients, the same method can further increase the upper frequency limit. The method is applied to the experimental doubling or quadrupling of FT/ICR direct-mode frequency range, as for example in the extension of the lower mass limit to below m/z = 12 at 3.058 T with a sampling rate of only 4.0 MHz.

A frequency-domain Lorentzian spectrum can be derived from the Fourier transform of a time-domain exponentially damped sinusoid of infinite duration. Remarkably, it has been shown that even when such a noiseless time-domain signal is truncated to zero amplitude after a finite observation period, one can determine the correct frequency of its corresponding magnitude-mode spectral peak maximum by fitting as few as three spectral data points to a magnitude-mode Lorentzian spectrum. In this paper, we show how the accuracy of such a procedure depends upon the ratio of time-domain acquisition period to exponential damping time constant, number of time-domain data points, computer word length, and number of time-domain zero-fillings. In particular, we show that extended zero-filling (e.g., a “zoom” transform) actually reduces the accuracy with which the spectral peak position can be determined. We also examine the effects of frequency-domain random noise and roundoff errors in the fast Fourier transformation (FFT) of time-domain data of limited discrete data word length (e.g., 20 bit/word at single and double precision). Our main conclusions are: (1) even in the presence of noise, a three-point fit of a magnitude-mode spectrum to a magnitude-mode Lorentzian line shape can offer an accurate estimate of peak position in Fourier transform spectroscopy; (2) the results can be more accurate (by a factor of up to 10) when the FFT processor operates with floating-point (preferably double-precision) rather than fixed-point arithmetic; and (3) FFT roundoff errors can be made negligible by use of sufficiently large (> 16 K) data sets.

The FT/ICR mass spectrometer is one of the highest performance mass analyzers. However, the necessity of working in the very high vacuum region to achieve ultra-high resolution limits the use of many of the current ionization and separation techniques. To solve this, methods have been developed in the last years, to use medium/high vacuum pressure regimes with FT/ICR while still maintaining its performance. One of these is the development of the double cell FT/ICR instrument. The ion motions in this spectrometer have been studied experimentally and a method is presented to transfer ions between the two cells in cases, where ion formation and transfer cannot take place at the same time.

PURPOSE: Quantification of myocardial blood flow (MBF) with generator-produced (82)Rb is an attractive alternative for centres without an on-site cyclotron. Our aim was to validate (82)Rb-measured MBF in relation to that measured using (15)O-water, as a tracer 100% of which can be extracted from the circulation even at high flow rates, in healthy control subject and patients with mild coronary artery disease (CAD). METHODS: MBF was measured at rest and during adenosine-induced hyperaemia with (82)Rb and (15)O-water PET in 33 participants (22 control subjects, aged 30 ± 13 years; 11 CAD patients without transmural infarction, aged 60 ± 13 years). A one-tissue compartment (82)Rb model with ventricular spillover correction was used. The (82)Rb flow-dependent extraction rate was derived from (15)O-water measurements in a subset of 11 control subjects. Myocardial flow reserve (MFR) was defined as the hyperaemic/rest MBF. Pearson's correlation r, Bland-Altman 95% limits of agreement (LoA), and Lin's concordance correlation ρ (c) (measuring both precision and accuracy) were used. RESULTS: Over the entire MBF range (0.66-4.7 ml/min/g), concordance was excellent for MBF (r = 0.90, [(82)Rb-(15)O-water] mean difference ± SD = 0.04 ± 0.66 ml/min/g, LoA = -1.26 to 1.33 ml/min/g, ρ(c) = 0.88) and MFR (range 1.79-5.81, r = 0.83, mean difference = 0.14 ± 0.58, LoA = -0.99 to 1.28, ρ(c) = 0.82). Hyperaemic MBF was reduced in CAD patients compared with the subset of 11 control subjects (2.53 ± 0.74 vs. 3.62 ± 0.68 ml/min/g, p = 0.002, for (15)O-water; 2.53 ± 1.01 vs. 3.82 ± 1.21 ml/min/g, p = 0.013, for (82)Rb) and this was paralleled by a lower MFR (2.65 ± 0.62 vs. 3.79 ± 0.98, p = 0.004, for (15)O-water; 2.85 ± 0.91 vs. 3.88 ± 0.91, p = 0.012, for (82)Rb). Myocardial perfusion was homogeneous in 1,114 of 1,122 segments (99.3%) and there were no differences in MBF among the coronary artery territories (p > 0.31). CONCLUSION: Quantification of MBF with (82)Rb with a newly derived correction for the nonlinear extraction function was validated against MBF measured using (15)O-water in control subjects and patients with mild CAD, where it was found to be accurate at high flow rates. (82)Rb-derived MBF estimates seem robust for clinical research, advancing a step further towards its implementation in clinical routine.

To assess the technical feasibility of multi-detector row computed tomographic (CT) angiography in the assessment of peripheral arterial bypass grafts and to evaluate its accuracy and reliability in the detection of graft-related complications, including graft stenosis, aneurysmal changes, and arteriovenous fistulas.Four-channel multi-detector row CT angiography was performed in 65 consecutive patients with 85 peripheral arterial bypass grafts. Each bypass graft was divided into three segments (proximal anastomosis, course of the graft body, and distal anastomosis), resulting in 255 segments. Two readers evaluated all CT angiograms with regard to image quality and the presence of bypass graft-related abnormalities, including graft stenosis, aneurysmal changes, and arteriovenous fistulas. The results were compared with McNemar test with Bonferroni correction. CT attenuation values were recorded at five different locations from the inflow artery to the outflow artery of the bypass graft. These findings were compared with the findings at duplex ultrasonography (US) in 65 patients and the findings at conventional digital subtraction angiography (DSA) in 27.Image quality was rated as good or excellent in 250 (98%) and in 252 (99%) of 255 bypass segments, respectively. There was excellent agreement both between readers and between CT angiography and duplex US in the detection of graft stenosis, aneurysmal changes, and arteriovenous fistulas (kappa = 0.86-0.99). CT angiography and duplex US were compared with conventional DSA, and there was no statistically significant difference (P.25) in sensitivity or specificity between CT angiography and duplex US for both readers for detection of hemodynamically significant bypass stenosis or occlusion, aneurysmal changes, or arteriovenous fistulas. Mean CT attenuation values ranged from 232 HU in the inflow artery to 281 HU in the outflow artery of the bypass graft.Multi-detector row CT angiography may be an accurate and reliable technique after duplex US in the assessment of peripheral arterial bypass grafts and detection of graft-related complications, including stenosis, aneurysmal changes, and arteriovenous fistulas.

The goal of this paper is to present a methodology to compare the performances of new screen-film systems by means of different approaches. The first method is based on a subjective evaluation of films produced with two mammographic test objects. The second method is based on an objective image quality assessment applying the quasi-ideal observer model. Finally, a clinical comparison was performed on two particular systems. The results show a very good correlation between the different approaches.

BackgroundBecause of a presumably increased incidence of long-term malignancy in interventional cardiologists, radiation exposure of the operator (ORE) during coronary interventions is of rising concern. A few studies comparing femoral to radial or right to left radial access have been published, but no data comparing the three access sites are available to our knowledge.PurposeWe sought to compare ORE by right femoral (RFA), right radial (RRA) and left radial (LRA) access during percutaneous catheterization for diagnostic coronary angiography (CA) with or without coronary angioplasty (PCI).MethodsFrom September 2014 to February 2015, all consecutive patients undergoing elective or emergency CA/PCI were prospectively included. Selection of the access site was left to the discretion of the cardiologist. ORE was measured using individual electronic radiation dosimeter badges positioned externally on the sternum. Radioprotection materials and equipment was similar for all procedures. Primary endpoint was ORE quantified as cumulative dose (CD) per dose-area product (DAP), in order to adjust for the administered radiation dose.ResultsIn total 692 consecutive procedures, 386CA (56%) and 306PCI (44%) were performed, 380 (55%) via RFA, 232 (34%) via RRA and 80 (11%) via LRA. The CD was lower in the RFA (6.9±11.8∞Sv vs. RRA 26.4±54.1 μSv, p