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The dominant powder scintillator in most medical imaging modalities for decades is Gd2O2S:Tb due to the very good intrinsic properties and overall efficiency. Except Gd2O2S:Tb there are alternative powder phosphor scintillators like Lu2SiO5:Ce and Gd2O2S:Eu that has been suggested for use in various medical imaging modalities. Gd2O2S:Eu emits red light and can be combined mainly with digital detectors like CCDs and wavelength selective detectors. Lu2SiO5:Ce emits blue light and can be combined with blue sensitivity films, photocathodes and some photodiodes. For the purpose of this study two Lu2SiO5:Ce and Gd2O2S:Eu powder phosphor scintillators with screen coating thicknesses of 25 and 33 mg/cm2 respectively, were prepared by the method of sedimentation in our laboratory. The output efficiency of the phosphor screens were evaluated with respect to incident exposure rate and the spatial frequency dependent Modulation Transfer Function (MTF). Furthermore the spectral compatibility of those materials with various detectors was evaluated. Results were compared to published data for the commercially employed dasiaKodak Min-R film-screen systempsila, based on a 31.7 mg/cm2 thick Gd2O2S:Tb phosphor. For Gd2O2S:Eu, MTF data were found comparable to those of Gd2O2S:Tb, while the MTF of Lu2SiO5:Ce was even higher. The different spectral compatibility of these phosphors could be interesting for application based on red and blue sensitive optical sensors respectively.

Magnification is a special technique applied to symptomatic women, usually following a screening mammogram. In this case small focal spots are necessary in order to reduce the geometrical unsharpness caused by the extended distance between the breast and the detector. Especially when combined with Gaussian x-ray intensity distributions with small standard deviation (sigma), small foci can lead to high values of spatial resolution. However, this spatial resolution is degraded from the blurring of the detector utilized. The x-ray photons exiting the irradiated phantom do not necessarily interact at the point of intersection with the detector, and furthermore the generated image formation particles may spread inside the detector and be recorded at a distance from the interaction site. This causes a blurring of the initial image that can be studied by means of the Point Spread Function (PSF) and the subsequent Full Width at Half of the Maximum (FWHM) of the detector. Several authors have studied this effect theoretically. However, no studies have been performed towards the quantification of this blurring under magnification conditions. In this study Monte Carlo simulation techniques were utilized to study the effect of the detector blurring on spatial resolution in magnification mammography, for several focal spot sizes and intensity distributions.

An ordinary difficulty in assessing the severity of medical data is the confined ability to structurally organize the ensemble of different cases into semantically relevant classes. A conceivable visualization scheme of the entire set can potentially reveal critical data similarities and help the physicians to ocular estimate their initial diagnosis. In this paper, a novel method for efficient organization of hip joint osteoarthritis data in a low-dimensional space is presented. A collection of 57 radiographic images are utilized and characteristic features are extracted using a standard texture-based methodology. The management of all individual cases is pursued using a well-suited data analysis methodology. The final outcome is a 2-dimensional point-diagram that visually reflects the intrinsic organization of the ensemble of available data. The proposed framework can be used to detect putative clustering tendencies, examine the presence of data similarities and potentially indicate the existence of possible false alarms in the initial perceptual estimation.

The aim of this study was to investigate the feasibility of texture analysis in characterizing endometrial tissue as depicted in two-dimensional (2D) grayscale transvaginal ultrasonography. Digital transvaginal ultrasound endometrial images were acquired from 65 perimenopausal and post-menopausal women prior to gynaecological operations; histology revealed 15 malignant and 50 benign cases. Images were processed with a wavelet-based contrast enhancement technique. Three regions of interest (ROIs) were identified (endometrium, endometrium plus adjacent myometrium, layer containing endometrial-myometrial interface) on each original and processed image. 32 textural features were extracted from each ROI employing first and second order statistics texture analysis algorithms. Textural features-based models were generated for differentiating benign from malignant endometrial tissue using stepwise logistic regression analysis. Models' performance was evaluated by means of receiver operating characteristic (ROC) analysis. The best logistic regression model comprised seven textural features extracted from the ROIs determined on the processed images; three features were extracted from the endometrium, while four features were extracted from the layer containing the endometrial-myometrial interface. The area under the ROC curve (A(z)) was 0.956+/-0.038, providing 86.0% specificity at 93.3% sensitivity using the cut-off level of 0.5 for probability of malignancy. Texture analysis of 2D grayscale transvaginal ultrasound images can effectively differentiate malignant from benign endometrial tissue and may contribute to computer-aided diagnosis of endometrial cancer.

Diagnostic and interventional radiology, are an essential part of present day medical practice. Advances in X-ray imaging technology, together with developments in digital imaging have had a significant impact on the practice of radiology. This includes improvement in image quality, reduction in dose and a broader range of available applications resulting to better patient diagnosis and treatment. X-rays have the potential for damaging healthy cells and tissues, therefore all medical procedures employing X-ray equipment must be carefully managed. In all facilities and for all equipment types, procedures must be in place in order to ensure that exposures to patients, staff and the public are kept as low as reasonably achievable. Commonly used construction materials such as, ceramic tiles and plasterboards can provide a certain degree of protection against X-radiation. In this study, the secondary radiation transmission through common building materials is investigated, in the case of narrow shaped X-ray fields. Double plasterboard and double reinforced in thickness ceramic tile provided better radiation protection results.

The aim of the present study was to assess the contrast to noise ratio (CNR) of PET scanners through a thin layer chromatography (TLC) plane source. The source was simulated using a previously validated Monte Carlo model. The model was developed by using the GATE MC package and reconstructed images obtained with the STIR software for tomographic image reconstruction. The PET scanner simulated was the GE DiscoveryST. A plane source consisted of a TLC plate, was simulated by a layer of silica gel on aluminum (Al) foil substrates, immersed in 18F-FDG bath solution. Image quality was assessed in terms of the CNR. CNR was estimated from coronal reconstructed images of the plane source. Images were reconstructed by the maximum likelihood estimation (MLE)-OSMAPOSL. OSMAPOSL reconstruction was assessed by using various subsets (3, 15 and 21) and various iterations (2 to 20). CNR values were found to decrease when both iterations and subsets increase. Two (2) iterations were found to be optimal. The simulated PET evaluation method, based on the TLC plane source, can be useful in image quality assessment of PET scanners.

In the current study preliminary results on the luminescence efficiency (LE) of toluene dissolved Cadmium Selenide/Zinc Sulfide (CdSe/ZnS, Sigma-Aldrich, Lumidot 694622) quantum dot samples (QDs) after exposure to X-rays of variable radiation flux are shown. The distinctive influence of the weight over volume (w/v) concentration of the samples in LE was investigated. The light emission of the QDs was additionally measured after UV irradiation. The distribution of the emitted light was symmetrical with a maximum at 590 nm. The w/v concentration of the QDs varied between 7.1×10-5 mg/mL to 28.4×10-5 mg/mL. The samples were handled in a cubic 12.5×12.5×45mm3 quartz cuvette. Each sample was excited under X-ray irradiation, in the energy range from 50 to 130 kVp using a BMI General Medical Merate tube with rotating Tungsten anode and inherent filtration equivalent to 2 mm Al. The X-ray LE, induced by the 28.4×10-5 mg/mL QDs found higher, however, the distinction was vague in the highly concentrated samples. The maximum efficiency was obtained at the 90 kVp for QDs with 21.3×10-5 mg/mL w/v concentration. In the high energy range (120-130 kVp) all concentration levels exhibited comparable X-ray induced LE. The luminescence properties of the investigated QDs appear promising for X-ray detection applications.

The aim of the present study was to examine the image quality performance of a CMOS digital imaging optical sensor coupled to custom made gadolinium oxysulfide powder scintillators, doped with praseodymium, cerium and fluorine (Gd2O2S:Pr,Ce,F) screens. The screens, with coating thicknesses 35.7 and 71.2 mg/cm2, were prepared in our laboratory from Gd2O2S:Pr,Ce,F powder (Phosphor Technology, Ltd) by sedimentation on silica substrates and were placed in direct contact with the optical sensor. Image quality was determined through a single index image quality parameter (information capacity). The CMOS sensor/Gd2O2S:Pr,Ce,F screens combinations were irradiated under the RQA-5 (IEC 62220-1) beam quality. The detector response function was linear for the exposure range under investigation. Under the general radiography conditions, both Gd2O2S:Pr,Ce,F screen/CMOS combinations exhibited comparable overall imaging properties, in terms of the information capacity, to previously published scintillators, such as Gd2O2S:Eu.

The aim of the present study was to assess image quality of PET scanners through a thin layer chromatography (TLC) plane source. The source was simulated using a previously validated Monte Carlo model. The model was developed by using the GATE MC package and reconstructed images obtained with the STIR software for tomographic image reconstruction. The simulated PET scanner was the GE DiscoveryST. A plane source consisted of a TLC plate, was simulated by a layer of silica gel on aluminum (Al) foil substrates, immersed in 18F-FDG bath solution (1MBq). Image quality was assessed in terms of the modulation transfer function (MTF). MTF curves were estimated from transverse reconstructed images of the plane source. Images were reconstructed by the maximum likelihood estimation (MLE)-OSMAPOSL, the ordered subsets separable paraboloidal surrogate (OSSPS), the median root prior (MRP) and OSMAPOSL with quadratic prior, algorithms. OSMAPOSL reconstruction was assessed by using fixed subsets and various iterations, as well as by using various beta (hyper) parameter values. MTF values were found to increase with increasing iterations. MTF also improves by using lower beta values. The simulated PET evaluation method, based on the TLC plane source, can be useful in the resolution assessment of PET scanners.

Component based normalization is a well-established method to calculate correction factors for unbiased and reliable PET reconstruction. Several methods have been studied and validated for cylindrical PET scanners. In this work we adapted a method already presented for cylindrical scanners to rotating dual head PET scanners. The model included corrections for detector efficiency, axial and transaxial geometric effects, crystal interference and attenuation corrections. Results from a simulated realistic dual head PET showed that the adaptation is valid. The images are significantly improved in terms of homogeneity, resolution and background contribution.

The mammographic spectrum is one of the major factors affecting image quality in mammography. In this study, a Monte Carlo (MC) simulation model was used to evaluate image quality characteristics of various mammographic spectra. The anode/filter combinations evaluated, were those traditionally used in mammography, for tube voltages between 26 and 30 kVp. The imaging performance was investigated in terms of Contrast to Noise Ratio (CNR) and Contrast Detail (CD) analysis, by involving human observers, utilizing a mathematical CD phantom. Soft spectra provided the best characteristics in terms of both CNR and CD scores, while tube voltage had a limited effect. W-anode spectra filtered with k-edge filters demonstrated an improved performance, that sometimes was better compared to softer x-ray spectra, produced by Mo or Rh anode. Regarding the filter material, k-edge filters showed superior performance compared to Al filters.

Magnification mammography is a special technique used in the cases where breast complaints are noted by a woman or when an abnormality is found in a screening mammogram. The carcinogenic risk in mammography is related to the dose deposited in the glandular tissue of the breast rather than the adipose, and average glandular dose (AGD) is the quantity taken into consideration during a mammographic examination. Direct measurement of the AGD is not feasible during clinical practice and thus, the incident air KERMA on the breast surface is used to estimate the glandular dose, with the help of proper conversion factors. Additional conversion factors adapted for magnification and tube voltage are calculated, using Monte Carlo simulation. The effect of magnification degree, tube voltage, various anode/filter material combinations and glandularity on AGD is also studied, considering partial breast irradiation. Results demonstrate that the estimation of AGD utilizing conversion factors depends on these parameters, while the omission of correction factors for magnification and tube voltage can lead to significant underestimation or overestimation of AGD. AGD was found to increase with filter material's k-absorption edge, anode material's k-emission edge, tube voltage and magnification. Decrease of the glandularity of the breast leads to higher AGD due to the increased penetrating ability of the photon beam in thick breasts with low glandularity.

The luminescence of LuYSiO/sub 5/:Ce (LYSO:Ce) and Gd/sub 2/SiO/sub 5/:Ce (GSO:Ce) crystals was studied for use in tomographic medical X-ray imaging. Both crystals were compared to CsI:Tl scintillator, used in X-ray and gamma-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/cm/sup 3/ and 6.71 g/cm/sup 3/ respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. CsI:Tl is a slightly hygroscopic, high light yield (/spl ges/10/sup 4/ photons/MeV) scintillator but of relatively slow decay time (>200 ns). Evaluation was performed by determining: 1) the absolute luminescence efficiency (emitted light flux over incident X-ray exposure) in X-ray energies employed in general X-ray imaging (40-140 kV) and in mammographic X-ray imaging (22-49 kV), 2) the light emission spectrum, determined at various X-ray energies (22-140 kV), and 3) the spectral compatibility to optical photon detectors incorporated in medical imaging systems. The light emission performance of the three scintillation materials studied, were found adequately high for X-ray imaging. LYSO:Ce and GSO:Ce were found most efficient (between 8 and 12/sub /spl mu/W/spl times/m//sup -2/) in the range from 40 to 60 kV. LYSO:Ce and GSO:Ce were found adequately most compatible with the S-20 photocathode (0.902 and 0.903 respectively against 0.763 of CsI:Tl) and adequately compatible to a-Si photodiode (0.705 and 0.737 respectively against 0.851 of CsI:Tl).

This work investigates the light emission efficiency of Lu2SiO5:Ce (LSO) powder scintillator under X-ray radiographic imaging conditions. Powder LSO scintillator has never been previously used in X-ray imaging. For the purposes of the present study three scintillating screens with coating thickness of 63.4, 108.4 and 172.5 mg/cm2, were prepared by sedimentation of LSO powder. Absolute luminescence efficiency (AE) measurements were performed in the radiographic X-ray tube voltages (40-140 kVp) range. Parameters related to X-ray detection, i.e. energy absorption efficiency and quantum detection efficiency were calculated. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of the intrinsic conversion efficiency and the light attenuation coefficients of the scintillating screens. The spectral compatibility of the LSO powder scintillator to various radiographic optical detectors was determined by performing light emission spectrum measurements and by taking into account the spectral sensitivity of the optical sensors used in digital radiography detectors. LSO was found to exhibit higher X-ray energy absorption than currently employed scintillators (CsI:Tl and Gd2O2S:Tb) in the range from 40 to 70 kVp. AE was found to increase with X-ray tube voltage up to 110 kVp. Maximum AE (8.2 times 10-6 W middot s/mR middot m2) was observed for the screen of 172.5 mg/cm2.

LYSO:Ce and LuYAP:Ce are single crystal scintillators of high density, non-hydroscopic, high light yield and short decay time and have been successfully used in small animal PET imagers. In our study, the luminescence emission properties of (Lu0.9,Y0.1)2SiO5:Ce (LYSO:Ce) and (Lu0.7,Y0.3)AlO3:Ce (LuYAP:Ce) crystals were investigated for use in medical X-ray imaging. Both crystal studied had dimensions of 2 times 2 times 8 mm3, with all surface polished. Evaluation was performed by determining the absolute luminescence efficiency (emitted light flux over incident X-ray exposure) in a wide range of X-ray energies employed in mammography (22-49 kVp) and in general X-ray imaging (50-140 kVp). Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The emission spectrum under UV and X-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility to optical photon detectors incorporated in medical imaging systems. Additionally, the optical characteristics such as transmission and absorption spectra were investigated and correlated with the scintillation properties. The light emission performance of the two scintillation materials studied was found adequately high for X-ray imaging.

Selenium is among the materials under investigation that may form effective detectors and provide a major contribution to digital mammography. Till the final image formation, there is an intervention of the x-ray photons transformation to primary electrons and their subsequent ionizing drift towards the electrodes that collect them. The characteristics of the generated primary electrons inside a-Se material such as their angular, spatial and energy distribution affect the characteristics of the final image. A Monte Carlo based model has been developed that simulates the x-ray irradiation of an a-Se detector plate, including primary photon interactions (photoelectric absorption, coherent and incoherent scattering), as well as secondary ones, such as fluorescence (Kalpha, Kbeta) and emission of Auger electrons. The angular, spatial and energy distributions for the generated primary electrons inside a-Se have been produced for various mammographic x-ray spectra and their usefulness in designing and optimizing a detector made of a-Se for digital mammography is discussed.

The aim of this study was to examine the angular distribution of the light emitted from radiation-excited scintillators in medical imaging detectors. This distribution diverges from Lambert's cosine law and affects the light emission efficiency of scintillators, hence it also affects the dose burden to the patient. In the present study, the angular distribution was theoretically modeled and was used to fit experimental data on various scintillator materials. Results of calculations revealed that the angular distribution is more directional than that predicted by Lambert's law. Divergence from this law is more pronounced for high values of light attenuation coefficient and thick scintillator layers (screens). This type of divergence reduces light emission efficiency and hence it increases the incident X-ray flux required for a given level of image brightness.

Presence of dense parenchyma in mammographic images masks lesions resulting in either missed detections or mischaracterizations, thus decreasing mammographic sensitivity and specificity. The aim of this study is evaluating the effect of a wavelet enhancement method on dense parenchyma for a lesion contour characterization task, using simulated lesions. The method is recently introduced, based on a two-stage process, locally adaptive denoising by soft-thresholding and enhancement by linear stretching. Sixty simulated low-contrast lesions of known image characteristics were generated and embedded in dense breast areas of normal mammographic images selected from the DDSM database. Evaluation was carried out by an observer performance comparative study between the processed and initial images. The task for four radiologists was to classify each simulated lesion with respect to contour sharpness/unsharpness. ROC analysis was performed. Combining radiologists’ responses, values of the area under ROC curve (A z ) were 0.93 (95% CI 0.89, 0.96) and 0.81 (CI 0.75, 0.86) for processed and initial images, respectively. This difference in A z values was statistically significant (Student’s t-test, P

Dosimetric studies in mammography are addressed by means of a Monte Carlo simulation program. The core of this program (DOSIS: dosimetry simulation studies) is a simulation model developed using FORTRAN 90, enriched with a graphical user interface developed in MS Visual Basic. User defined mammographic technique parameters affecting breast dose are imported to the simulation model and the produced results are provided by means of both absolute (surface dose, exposure at detector plane) and relative quantities (percentage depth dose, isodose curves). The program functionality has been demonstrated in the evaluation of various mammographic examination techniques. Specifically, the influence of tube voltage and filtration on the surface dose and the exposure at detector plane has been studied utilizing a water phantom. Increase of tube voltage from 25 to 30 kVp for a Mo/Mo system resulted in a 42% decrease of the surface dose for a thick breast (6 cm), without changing the exposure at the detector plane. Use of 1.02 mm Al filter for a W anode system operating at 30 kVp resulted in a 19.1% decrease of the surface dose delivered to a 5 cm water equivalent breast. Overall, W/Al systems appear to have improved dosimetric performance, resulting up to a 65% decrease of surface dose compared to Mo/Mo systems, for identical exposures at the detector plane and breast thicknesses.

Monte Carlo techniques were applied to evaluate the performance of YAP scintillator for use in medical imaging applications. The energy range considered was from 50 to 800 keV and the thickness range from 5 to 30 mm. The absorption efficiency of YAP decreases rapidly in the energy range from 50 up to 200 keV. For higher energies up to 800 keV, slow variation with energy is exhibited. In the energy range 200-800 keV the scintillator absorbs energy mainly through Compton recoil electrons while at the 50-200 keV energy range the photoelectric process dominates even following a scatter event.

The purpose of this work was to model and compare the zero-frequency detective quantum efficiency (DQE(0)) of Gd2O2S:Tb, Gd2O2S:Eu Gd2O2S:Pr, Gd2O2S: Pr, Ce, F and YTaO4:Nb granular scintillators for use X-ray medical imaging detectors. The work uses a mathematical model based on a photon diffusion differential equation. X-ray tube voltage was considered to vary from 10 and 200 kV while phosphor screen thickness ranged between 10 and 160 mg/cm2 coating.

Image transfer characteristics (MTF, DQE) of Y/sub 2/O/sub 2/S:Eu, Y/sub 2/O/sub 3/:Eu, and YVO/sub 4/:Eu image receptors were evaluated. These materials were used in the form of laboratory prepared screens. MTF was experimentally determined by the square wave response method and theoretically evaluated by a diffusion equation model. DQE was calculated using experimentally determined optical data of the scintillators. Light spectra were measured and their compatibility to the spectral sensitivity of various photodetectors was calculated. The MTF and DQE of Y/sub 2/O/sub 2/S:Eu were better than those of Y/sub 2/O/sub 3/:Eu, which was superior to YVO/sub 4/:Eu. The spectral compatibility of the three scintillators was very good to excellent (0.7 to 0.95), being better than that of some commercially used scintillators.

Signal conversion and propagation in image receptors were studied employing laboratory prepared Gd/sub 2/O/sub 2/S:Tb and La/sub 2/O/sub 2/S:Tb phosphor screens. The optical signal emitted by the screens per unit of X-ray exposure was experimentally and theoretically evaluated in the mammographic energy range. Parameters related to signal propagation (light absorption, scattering, reflection, and optical pulses statistical distribution), intrinsic X-ray to light conversion efficiency, and electron signal generated by the photodetector were studied. Image receptors employing Gd/sub 2/O/sub 2/S:Tb screens produce higher optical and electron signal intensities whereas receptors with La/sub 2/O/sub 2/S:Tb screens give better optical pulse statistics, resulting in noise reduction.

We have developed a model for Monte Carlo simulation of the function of the mammographic unit to be used as a research tool for the optimization of the mammographic procedure. A software phantom of a compressed breast has been designed and all possible physical interactions between X-rays and matter have been taken into account. Preliminary test results are presented. The expectations from this simulation are also discussed.

A software package using Monte Carlo methods has been developed for the simulation of X-ray mammography. A simplified geometry of the mammographic apparatus has been considered along with a software phantom of compressed breast. This phantom may contain inhomogeneities of various compositions and sizes at any point. Using this model one can produce mammograms resulted from simulating various mammographic conditions. First comparisons between true mammographic images with images produced from Monte Carlo simulation of mammography are very encouraging. The applications of the production of such images are discussed.

The authors are studying the design of collimated gamma ray sources of energies below 1 MeV for a variety of applications. In medical imaging such sources are very important in the laboratory for the study and characterization of scintillator detectors and also collimators. For the purpose of this study the authors have developed a Monte Carlo based simulation model, to follow up the interactions of a photon from the source. Initial results on the spatial, angular, and energy distribution characteristics of the surviving gamma rays that arrive at a 'detector' plane at a given distance from the source have been studied and presented here. Such information will be very useful in the design of an optimum gamma ray source which has to meet certain specifications regarding spot size, angular spread, and Compton tail.

An integrated model describing the signal and noise transfer characteristics of the objective image quality and information content in phosphor-produced images is presented. In the context of this model, important imaging parameters, namely optical gain, modulation transfer function, noise transfer function, detective quantum efficiency and information capacity were experimentally evaluated using seven laboratory-prepared CdPO3Cl:Mn test phosphor screens of varying coating thickness. This phosphor has been previously shown to exhibit high spectral compatibility properties with the films and optical sensors used in digital imaging systems. Experiments were performed using 50-120 kVp X-rays produced by a medical X-ray unit. Results showed that, for thick screens, optical gain attained peak values close to 200 optical photons per incident X-ray at 50 kVp. The noise transfer function was higher than the modulation transfer function. For the thin screen of 21 mg cm-2, the modulation transfer function was 0.25 at 100 line pairs mm-1, and the corresponding noise transfer function was 0.4. The detection quantum efficiency peak value was 0.22 at 50 kVp. These values are within acceptable performance limits, and, given the phosphor material's high spectral compatibility and medium temporal response, CdPO3Cl:Mn could be considered for use in X-ray detectors of static radiography imaging.

The aim of the present study was to propose a comprehensive method for PET scanners image quality assessment, by the simulation of a thin layer chromatography (TLC) flood source with a previous validated Monte-Carlo (MC) model. The model was developed by using the GATE MC package and reconstructed images were obtained using the STIR software, with cluster computing. The PET scanner simulated was the GE Discovery-ST. The TLC source was immersed in 18F-FDG bath solution (1MBq) in order to assess image quality. The influence of different scintillating crystals on PET scanner's image quality, in terms of the MTF, the NNPS and the DQE, was investigated. Images were reconstructed by the commonly used FBP2D, FPB3DRP and the OSMAPOSL (15 subsets, 3 iterations) reprojection algorithms. The PET scanner configuration, incorporating LuAP crystals, provided the optimum MTF values in both 2D and 3DFBP whereas the corresponding configuration with BGO crystals was found with the higher MTF values after OSMAPOSL. The scanner incorporating BGO crystals were also found with the lowest noise levels and the highest DQE values after all image reconstruction algorithms. The plane source can be also useful for the experimental image quality assessment of PET and SPECT scanners in clinical practice.

Use of high contrast film-screen systems in mammography, in combination with the fact that exposure parameters are selected to ensure good visualization of the mammary gland, results in overexposure of the film area corresponding to the breast periphery, therefore decreasing image quality. The aim of this work was to provide a quantitative evaluation of image quality at the breast periphery compared with the mammary gland. To deal with the difficulties in quantification of image quality introduced by low contrast encountered at the breast periphery, wavelet analysis has been used for derivation of a contrast indicator (CI) and a noise indicator (NI), taking into account local grey level variations. Gradient magnitude coefficients corresponding to region of interest (ROI) grey level values are the basis of CI definition. Mammary gland and breast periphery were sampled by equally spaced ROIs, the quantity of which was determined by a heuristic method. For NI definition, the power values of gradient magnitude coefficients corresponding to the ROI were utilized. Image quality at the breast periphery compared with the mammary gland was evaluated using 150 craniocaudal images from the Digital Database for Screening Mammography. Measurements were carried out using a tool developed in our department. A 50% contrast decrease at the breast periphery was observed, while noise decreased by approximately 2%.

Medical film digitizers play an important transitory role as digital-to-analogue bridges in radiology. Their use requires performance evaluation to assure medical image quality. A complete quality control protocol is presented, based on a set of test objects adaptable to the specification of various digitizers. The protocol includes parameters such as uniformity, input- output response, noise, geometric distortion, spatial resolution, low contrast discrimination, film slippage and light leakage, as well as associated measurement methods. The applicability of the protocol is demonstrated with two types of medical film digitizers; a charge-coupled device (CCD) digitizer and a laser digitizer. The potential value of the protocol is also discussed. Although digital imaging represents the current trend in radiology, most of the workload in a radiology department is still performed by analogue systems. Medical image digitizers have been introduced to enable the transformation of analogue radiological images to digital images. There are three main categories of digitizers used clinically: video cameras, charge-coupled device

Objective: to study various phosphors used in detectors of medical imaging systems by the gain transfer function (GTF), defined in terms of X-ray luminescence efficiency, light spectrum and modulation transfer function. Materials and methods: four phosphor materials, La2O2S:Tb, Y2O2S:Tb, Y2O2S:Eu and Y2O3:Eu were used in the form of fluorescent layers prepared in the laboratory. The GTF was determined at 30 kVp and 80 kVp X-ray tube voltages for various phosphor coating weights. Results: La2O2S:Tb, which was the highest density and effective atomic number phosphor used, was found to exhibit the best GTF performance at 80 kVp. At 30 kVp, the yttrium based phosphors were found of increased performance. This is mainly due to the proximity of the X-ray energy to the K-absorption edge of yttrium at 17 keV. Europium activated phosphors were found to perform very well when combined with the red sensitive film and the silicon photodiode. Conclusion: The GTF may be a useful method for comparing and selecting phosphor materials for use in various medical imaging applications.

Currently, medical digital imaging systems are characterized by the introduction of additional modules such as digital display, image compression and image processing, as well as film printing and digitization. These additional modules require performance evaluation to ensure high image quality. A tool for designing computer-generated test objects applicable to performance evaluation of these modules is presented. The test objects can be directly used as digital images in the case of film printing, display, compression and image processing, or indirectly as images on film in the case of digitization. The performance evaluation approach is quality control protocol based. Digital test object design is user-driven according to specifications related to the requirements of the modules being tested. The available quality control parameters include input/output response curve, high contrast resolution, low contrast discrimination, noise, geometric distortion and field uniformity. The tool has been designed and implemented according to an object oriented approach in Visual C++ 5.0, and its user interface is based on the Microsoft Foundation Class Library version 4.2, which provides interface items such as windows, dialog boxes, lists, buttons, etc. The compatibility with DICOM 3.0 part 10 image formats specifications allows the integration of the tool in the existing software framework for medical digital imaging systems. The capability of the tool is demonstrated by direct use of the test objects in case of image processing, and indirect use of the test objects in case of film digitization.

An anatomical filter based exposure equalization technique in mammography is evaluated quantitatively using a phantom. The evaluation is carried out by a comparative observer performance study, comparing the equalization technique with a conventional one based on visualization of low contrast, 6 mm circular details and high contrast, 0.5 mm and 0.25 mm small size details. These details are situated at the phantom edge, simulating the breast periphery. Visualization of these details is studied with respect to the parameters of tube voltage, optical density, detail location and phantom thickness. Phantom images are interpreted independently by three observers using a four-point grading scale. Use of the Wilcoxon signed ranks test for paired data shows statistically highly significant improvement (p0.0001) in the visualization of details for the equalization technique for all values of the parameters studied. The improvement is independent of tube voltage but dependent on optical density, detail location and phantom thickness. Optimal performance is obtained for detail location closer to the outer border of the simulated breast periphery and/or further away from the film, as well as for a greater phantom thickness simulating both thick and dense breast.

In this study a method to assess the information content of medical images produced by phosphors is described. The optical signal emitted by the phosphor after X-ray excitation, the detective quantum efficiency (DQE), expressing the signal-to-noise ratio (SNR) transfer efficiency, and the information capacity were experimentally determined. The method was based on light flux and modulation transfer function (MTF) measurements and was used to assess the imaging performance of the Zn2SiO4:Mn phosphor. The latter was employed in the form of laboratory prepared phosphor layers (test screens). Results showed that high values for optical signal emission and DQE were obtained for medium thickness phosphor layers (56 and 89 mg/cm2) at 20 kVp X-ray tube voltage. The information capacity was found to decrease continuously with phosphor coating weight.

We present the results of calculations concerning the modulation transfer function (MTF) of the thin transparent foils used in the radiographic cassettes between the phosphor material of the screen and the film. For these calculations we have taken into account the real spatial distribution of the light emitted from a phosphor screen which diverges from the Lambert law depending on the characteristics and the structure of the screen.

The poor detectability of diagnostic mammographic features, due to their low contrast, is dealt with by a software visualization tool. The tool is domain specific to medical imaging and consequently mammographic imaging, and it is envisaged as part of medical image visualization and manipulation stations. Domain specificity is served by the tool conformance to DICOM 3.0 part 10 image format specifications, specifically PAPYRUS 3.0, window width/level display adjustments of image dynamic range of up to 16 bits, and application of visualization operations to user-defined regions of interest in addition to global operations. The software has been designed and implemented according to an object oriented approach in Visual C++. The tool user interface is friendly, based on a widely used windowing paradigm, the Microsoft Foundation Class library version 4.2, which provides interface items, such as windows, dialogue boxes, lists, slide bars, buttons, etc. The visualization functionality offered by the tool relies on the following three categories of image processing algorithms: dynamic range adjustments by pixel intensity transformations, contrast enhancement and noise suppression by spatial domain direct manipulation of image pixels or by manipulation of wavelet coefficients. The first two categories of algorithms are implemented in real time. Initial use of the tool has demonstrated its potential in improving the detectability of diagnostic mammographic image features.

The capability of interactive multimedia and Internet technologies is investigated with respect to the implementation of a distance learning environment. The system is built according to a client-server architecture, based on the Internet infrastructure, composed of server nodes conceptually modelled as WWW sites. Sites are implemented by customization of available components. The environment integrates network-delivered interactive multimedia courses, network-based tutoring, SIG support, information databases of professional interest, as well as course and tutoring management. This capability has been demonstrated by means of an implemented system, validated with digital image processing content, specifically image enhancement. Image enhancement methods are theoretically described and applied to mammograms. Emphasis is given to the interactive presentation of the effects of algorithm parameters on images. The system end-user access depends on available bandwidth, so high-speed access can be achieved via LAN or local ISDN connections. Network based training offers new means of improved access and sharing of learning resources and expertise, as promising supplements in training.

The potential of interactive multimedia and Internet technologies is investigated with respect to the implementation of a distance learning system in medical imaging. The system is built according to a client-server architecture, based on the Internet infrastructure, composed of server nodes conceptually modelled as World Wide Web (WWW) sites. Sites are implemented by integration and customization of available components. The system evolves around network-delivered interactive multimedia courses and network-based tutoring, which constitute its main learning features. This potential has been demonstrated by means of an implemented system, validated with digital image processing content, specifically image enhancement. Image enhancement methods are theoretically described and applied on mammograms. Emphasis is given in the interactive presentation of the effects of algorithm parameters on images. The system end-user access depends on available bandwidth, so high speed access can be achieved via LAN or local ISDN connections.

Silicon photomultiplier (SiPMs) detectors are attractive candidates for replacing position sensitive photomultipliers in nuclear imaging. They are compact, they provide high gain with low bias voltage and show better response. The development of dedicated imaging prototypes based on SiPMs possesses several design challenges, since it is necessary to optimize scintillator and SiPM coupling, as well as signal amplification and digitization. In this work, we have investigated the performance of three SiPM modules constructed by SensL coupled on three scintillators (CsI:Tl, BGO, LYSO:Ce), which are used in SPECT and PET imaging. Irradiation was carried out using different sources, which covered a wide range of energies from 88 to 1275 keV. The parameters measured were output pulses' width and height, energy resolution and linearity as a function of bias voltage and sources energy.

In this paper we present the performance evaluation results, in the planar and tomographic modes, of a low-cost positron emission tomography camera dedicated to small-animal imaging. The system consists of two pixelated Lu2SiO5 crystals, two Hamamatsu H8500 position sensitive photomultiplier tubes, fast amplification electronics and an FPGA-USB-based read-out system. The parameters that have been studied are (i) saturation as a function of the head distance and photon acceptance angle, (ii) effect of the number of projections and half or complete head's rotation, (iii) spatial resolution as a function of the head distance, (iv) spatial resolution as a function of acceptance angle, (v) system's sensitivity as a function of these parameters and (vi) performance in small mice imaging. Image reconstruction has been carried out using open source software developed by our group (QSPECT), which is designed mainly for SPECT imaging. The results indicate that the system has a linear response for activities up to at least 2 MBq, which are typical in small-animal imaging. Best tomographic spatial resolution was measured to be ~2 mm. The system has been found suitable for imaging of small mice both in the planar and tomographic modes.

Materials like a-Se, a-As2Se3, GaSe, GaAs, Ge, CdTe, CdZnTe, Cd0.8Zn0.2Te, ZnTe, PbO, TlBr, PbI2 and HgI2 are possible photoconductors for direct conversion digital mammography detectors. The physical characteristics of primary electrons, such as their number, energies, direction angles and spatial distributions, strongly affect the characteristics of the final signal and hence image quality. In previous work, a Monte Carlo model has been developed that simulates the generation of primary electrons inside these materials for x-ray spectra in the mammographic energy range. Using this model the energy, angular and spatial distributions of primary electrons have been studied. For the case of CdTe, CdZnTe, Cd0.8Zn0.2Te and ZnTe, an investigation was also made concerning the dependence of the primary electron production on the incident x-ray energy. In this paper, this investigation has been extended to include the rest of the photoconducting materials. The investigation is realized studying the number of primary electrons produced along with the escaping of photons (both incident and fluorescent) and the number of fluorescent photons emitted for 39 monoenergetic x-ray spectra with energies between 2 and 40 keV. The information obtained from the overall investigation of the primary signal in the various photoconductors gives some good indications of the suitability of PbI2 and HgI2.

An anatomical filter has been designed, tested and subsequently used in clinical practice to equalize optical density over the entire mammographic image, thus eliminating the need for dual exposure whenever both the mammary gland and the peripheral structures of the breast must be clearly visualized. The use of the filter results in a reduction of the optical density, at the peripheral structures of the breast, with a simultaneous increase of the contrast, without causing deterioration of the mammary gland image. Improved visualization of the connective tissue, the skin, the nipple and the subcutaneous adipose tissue is achieved, as well as minimization of the radiation dose to the breast for patients with an indication of peripheral breast lesions.

An image analysis method is proposed for the monitoring of the regeneration of the tibial bone. For this purpose, 130 digitized radiographs of 13 patients, who had undergone tibial lengthening by the Ilizarov method, were studied. For each patient, 10 radiographs, taken at an equal number of postoperative successive time moments, were available. Employing available software, 3 Regions Of Interest (ROIs), corresponding to the: (a) upper, (b) central, and (c) lower aspect of the gap, where bone regeneration was expected to occur, were determined on each radiograph. Employing custom developed algorithms: (i) a number of textural features were generated from each of the ROIs, and (ii) a texture-feature based regression model was designed for the quantitative monitoring of the bone regeneration process. Statistically significant differences (p < 0.05) were derived for the initial and the final textural features values, generated from the first and the last postoperatively obtained radiographs, respectively. A quadratic polynomial regression equation fitted data adequately (r2 = 0.9, p < 0.001). The suggested method may contribute to the monitoring of the tibial bone regeneration process.

A visualization-based, computer-oriented, classification scheme is proposed for assessing the severity of hip osteoarthritis (OA) using dimensionality reduction techniques. The introduced methodology tries to cope with the confined ability of physicians to structurally organize the entire available set of medical data into semantically similar categories and provide the capability to make visual observations among the ensemble of data using low-dimensional biplots. In this work, 18 pelvic radiographs of patients with verified unilateral hip OA are evaluated by experienced physicians and assessed into Normal, Mild and Severe following the Kellgren and Lawrence scale. Two regions of interest corresponding to radiographic hip joint spaces are determined and representative features are extracted using a typical texture analysis technique. The structural organization of all hip OA data is accomplished using distance and topology preservation-based dimensionality reduction techniques. The resulting map is a low-dimensional biplot that reflects the intrinsic organization of the ensemble of available data and which can be directly accessed by the physician. The conceivable visualization scheme can potentially reveal critical data similarities and help the operator to visually estimate their initial diagnosis. In addition, it can be used to detect putative clustering tendencies, examine the presence of data similarities and indicate the existence of possible false alarms in the initial perceptual evaluation.

The statistical nature of single photon emission computed tomography (SPECT) imaging, due to the Poisson noise effect, results in the degradation of image quality, especially in the case of lesions of low signal-to-noise ratio (SNR). A variety of well-established single-scale denoising methods applied on projection raw images have been incorporated in SPECT imaging applications, while multi-scale denoising methods with promising performance have been proposed. In this paper, a comparative evaluation study is performed between a multi-scale platelet denoising method and the well-established Butterworth filter applied as a pre- and post-processing step on images reconstructed without and/or with attenuation correction. Quantitative evaluation was carried out employing (i) a cardiac phantom containing two different size cold defects, utilized in two experiments conducted to simulate conditions without and with photon attenuation from myocardial surrounding tissue and (ii) a pilot-verified clinical dataset of 15 patients with ischemic defects. Image noise, defect contrast, SNR and defect contrast-to-noise ratio (CNR) metrics were computed for both phantom and patient defects. In addition, an observer preference study was carried out for the clinical dataset, based on rankings from two nuclear medicine clinicians. Without photon attenuation conditions, denoising by platelet and Butterworth post-processing methods outperformed Butterworth pre-processing for large size defects, while for small size defects, as well as with photon attenuation conditions, all methods have demonstrated similar denoising performance. Under both attenuation conditions, the platelet method showed improved performance with respect to defect contrast, SNR and defect CNR in the case of images reconstructed without attenuation correction, however not statistically significant (p > 0.05). Quantitative as well as preference results obtained from clinical data showed similar performance of the denoising methods studied. In conclusion, the multi-scale platelet denoising method applied on raw projection images provides more efficient noise reduction while preserving image quality in a myocardial phantom SPECT imaging as compared to the Butterworth filter applied either on projection or reconstructed images. However, this trend in favour of the platelet denoising method was not observed on clinical data reconstructed either without or with attenuation correction.

The dominant powder scintillator in most medical imaging modalities for decades has been Gd2O2S:Tb due to the very good intrinsic properties and overall efficiency. Apart from Gd2O2S:Tb, there are alternative powder phosphor scintillators such as Lu2SiO5:Ce and Gd2O2S:Eu that have been suggested for use in various medical imaging modalities. Gd2O2S:Eu emits red light and can be combined mainly with digital mammography detectors such as CCDs. Lu2SiO5:Ce emits blue light and can be combined with blue sensitivity films, photocathodes and some photodiodes. For the purposes of the present study, two scintillating screens, one from Lu2SiO5:Ce and the other from Gd2O2S:Eu powders, were prepared using the method of sedimentation. The screen coating thicknesses were 25.0 and 33.1 mg cm−2 respectively. The screens were investigated by evaluating the following parameters: the output signal, the modulation transfer function, the noise equivalent passband, the informational efficiency, the quantum detection efficiency and the zero-frequency detective quantum efficiency. Furthermore, the spectral compatibility of those materials with various optical detectors was determined. Results were compared to published data for the commercially employed 'Kodak Min-R film-screen system', based on a 31.7 mg cm−2 thick Gd2O2S:Tb phosphor. For Gd2O2S:Eu, MTF data were found comparable to those of Gd2O2S:Tb, while the MTF of Lu2SiO5:Ce was even higher resulting in better spatial resolution and image sharpness properties. On the other hand, Gd2O2S:Eu was found to exhibit higher output signal and zero-frequency detective quantum efficiency than Lu2SiO5:Ce.

An image analysis system is proposed for the assessment of hip osteoarthritis (OA) severity. Sixty four hips (18 normal, 46 osteoarthritic), corresponding to 32 patients of unilateral or bilateral hip OA were studied. Employing custom developed software, 64 Region Of Interest (ROI) images of Hip Joint Spaces (HJSs) were delineated on patients' digitized radiographs. The Fourier spectrum of each HJS-ROI was computed and expressed in polar coordinates. Spectral signatures, quantifying the radial and angular distribution of HJS spectral energy were formed. Signature descriptors were generated and utilized in the design of a two-level hierarchical decision tree, used for the grading of the severity of the disease. Accordingly, at Level 1, implemented by a multiple classifier system, the discrimination between normal and osteoarthritic hips was performed. At Level 2, the hips that had been successfully characterized as osteoarthritic at Level 1, were further characterized as of ``Mild / Moderate'' or ``Severe'' OA, by the Bayes classifier. A signature descriptors based regression model was designed, so as to quantify OA-severity. The system graded OA reliably, given that the accomplished classification accuracies for Level 1 and Level 2 were 98.4% and 100%, respectively. OA-severity values, expressed by HJS-narrowing, correlated highly (r = 0.9, p < 0.001) with values predicted by the model. The system may contribute to OA-patient management.

Phosphor materials are used in medical X-ray imaging combined with various pho- todetectors suitable for conventional and digital radiogr aphy and fluoroscopy. A prerequisite for these combinations is good optical spectral matching, which results in patient dose minimiza- tion. In the present work, a recently introduced factor, named OGTE, which accounts for optical gain signal-to-noise ratio transfer efficiency, is utilize d for the evaluation of various phosphor- photodetector combinations. The optical photon spectrum of the phosphor materials studied was either determined experimentally, or obtained from literature. These phosphors were examined in conjunction with various photodetectors, which may be suitable for digital imaging. The corre- sponding optical response functions of the photodetectors were obtained from literature. It was found that there are numerous combinations exhibiting OGTE values above 0.80, which contribute to patient dose minimization.