Mammographic Phantom Research Articles

Detecting Breast Cancer with a Dual-Modality Device.

Although mammography has been the gold standard for the early detection of breast cancer, if a woman has dense breast tissue, a false negative diagnosis may occur. Breast ultrasound, whether hand-held or automated, is a useful adjunct to mammography but adds extra time and cost. The primary aim was to demonstrate that our second-generation Aceso system, which combines full-field digital mammography (FFDM) and automated breast ultrasound (ABUS) in a single platform, is able to produce improved quality images that provide clinically meaningful results. Aceso was first tested using two industry standards: a Contrast Detail Mammography (CDMAM) phantom to assess the FFDM images, and the CIRS 054GS phantom to evaluate the ABUS images. In addition, 25 women participated in a clinical trial: 14 were healthy volunteers, while 11 were patients referred by the breast clinic at Groote Schuur Hospital. The CDMAM phantom results showed the FFDM results were better than the European Reference (EUREF) standard of “acceptable” and were approaching “achievable”. The ABUS results showed a lateral and axial spatial resolution of 0.5 mm and an adequate depth penetration of 80 mm. Our second-generation Aceso system, with its improved quality of clinical FFDM and ABUS images, has demonstrated its potential for the early detection of breast cancer in a busy clinic.

Comparison of Image Quality between Mammography Dedicated Monitor and UHD 4K Monitor, Using Standard Mammographic Phantom: A Preliminary Study

Comparison of Image Quality between Mammography Dedicated Monitor and UHD 4K Monitor, Using Standard Mammographic Phantom: A Preliminary Study

Characterization of paraffin based breast tissue equivalent phantom using a CdTe detector pulse height analysis.

In this study, paraffin was selected as a base material and mixed with different amounts of CaSO4·2H2O and H3BO3 compounds in order to mimic breast tissue. Slab phantoms were produced with suitable mixture ratios of the additives in the melted paraffin. Subsequently, these were characterized in terms of first half-value layer (HVL) in the mammographic X-ray range using a pulse-height spectroscopic analysis with a CdTe detector. Irradiations were performed in the energy range of 23-35kVp under broad beam conditions from Mo/Mo and Mo/Rh target/filter combinations. X-ray spectra were acquired with a CdTe detector without and with phantom material interposition in increments of 1cm thickness and then evaluated to obtain the transmission data. The net integral areas of the spectra for the slabs were used to plot the transmission curves and these curves were fitted to the Archer model function. The results obtained for the slabs were compared with those of standard mammographic phantoms such as CIRS BR series phantoms and polymethylmethacrylate plates (PMMA). From the evaluated transmission curves, the mass attenuation coefficients and HVLs of some mixtures are close to those of the commercially available standard mammography phantoms. Results indicated that when a suitable proportion of H3BO3 and CaSO4·2H2O is added to the paraffin, the resulting material may be a good candidate for a breast tissue equivalent phantom.

Quantification of breast lesion compositions using low-dose spectral mammography: A feasibility study.

The positive predictive power for malignancy can potentially be improved, if the chemical compositions of suspicious breast lesions can be reliably measured in screening mammography. The purpose of this study is to investigate the feasibility of quantifying breast lesion composition, in terms of water and lipid contents, with spectral mammography. Phantom and tissue samples were imaged with a spectral mammography system based on silicon-strip photon-counting detectors. Dual-energy calibration was performed for material decomposition, using plastic water and adipose-equivalent phantoms as the basis materials. The step wedge calibration phantom consisted of 20 calibration configurations, which ranged from 2 to 8 cm in thickness and from 0% to 100% in plastic water density. A nonlinear rational fitting function was used in dual-energy calibration of the imaging system. Breast lesion phantoms, made from various combinations of plastic water and adipose-equivalent disks, were embedded in a breast mammography phantom with a heterogeneous background pattern. Lesion phantoms with water densities ranging from 0% to 100% were placed at different locations of the heterogeneous background phantom. The water density in the lesion phantoms was measured using dual-energy material decomposition. The thickness and density of the background phantom were varied to test the accuracy of the decomposition technique in different configurations. In addition, an in vitro study was also performed using mixtures of lean and fat bovine tissue of 25%, 50%, and 80% lean weight percentages as the background. Lesions were simulated by using breast lesion phantoms, as well as small bovine tissue samples, composed of carefully weighed lean and fat bovine tissues. The water densities in tissue samples were measured using spectral mammography and compared to measurement using chemical decomposition of the tissue. The thickness of measured and known water contents was compared for various lesion configurations. There was a good linear correlation between the measured and the known values. The root-mean-square errors in water thickness measurements were 0.3 and 0.2 mm for the plastic phantom and bovine tissue backgrounds, respectively. The results indicate that spectral mammography can be used to accurately characterize breast lesion composition in terms of their equivalent water and lipid contents.

Comparison of two psychometric functions in analyzing 4-AFC detection results using a task-based structured phantom for digital mammography

Introduction Detectability of spiculated and non-spiculated mass models and microcalcifications, in a structured background phantom of acrylic spheres and water, was studied for digital mammography via the four-alternative forced-choice (4-AFC) paradigm. Purpose To compare the threshold diameters for mass and microcalcification detection using two types of psychometric curves applied on the contrast-detail data. Material and methods Ten images of the structured phantom were acquired on 23 digital mammography systems under automatic exposure control. The 4-AFC study was performed with in-house developed software and 5 medical physicists as observers. Percentage correctly detected lesions (PC) was obtained for each target type. Two psychometric curves (Weibull and Logistic functions) were applied to determine the threshold diameters and number of detected targets (at PC = 62.5%). Results Both fitting procedures were successfully applied on all systems. After averaging over 23 systems, the threshold diameters for spiculated and non-spiculated masses and microcalcifications, with the Weibull psychometric curves, were 4.0 ± 0.3 mm (R2 = 0.61 ± 0.08), 4.6 ± 0.7 mm (R2 = 0.51 ± 0.11), and 0.114 ± 0.003 mm (R2 = 0.91 ± 0.03) respectively, and the values of 4.0 ± 0.4 mm (R2 = 0.61 ± 0.08), 4.7 ± 0.6 mm (R2 = 0.50 ± 0.11), and 0.114 ± 0.003 mm (R2 = 0.91 ± 0.03) were obtained with the Logistic function. The numbers of detected targets assessed from the two functions were not different (3–4 spiculated masses, 1–2 non-spiculated masses, and 4 groups of microcalcifications). If the PC values were not completely covering the lower and upper than 62.5%, there will be possibility different results occurred from these two functions. Conclusion Weibull and Logistic curve fits gave similar and reproducible threshold diameters for the structured phantom.

Contrast and depth resolution of breast lessions in a digital breast tomosynthesis system

Introduction Digital breast tomosynthesis (DBT) provides a quasi-three-dimensional structural information of the breast, solving the issue of overlapping mammographic parenchyma in breast lesion visualization. Purpose This study investigates the effect of lesion position along the z-axis and breast thickness on image quality of DBT reconstructed images. Materials and methods Mass objects (size: 3 mm) of varying nominal contrast values (1.5%, 2%, 3% and 4%) and microcalcification objects (size ∼300 μm) at two different nominal contrast values, of a mammographic phantom (Leeds, TORMAM), were imaged with a DBT system (Hologic, Selenia Dimensions) at clinical settings. Four object positions along the z-axis were investigated by increasing test object distance from the detector, considering a breast thickness of 45 mm. In addition, for a specific phantom position along the z-axis, four breast thickness values (17, 30, 45, 65 mm) were investigated. Image quality metrics considered are CNR at focal plane and depth resolution, estimated using the full-width-at-half maximum (FWHM) of the artifact spread function (ASF) of lesion objects. Results Lesion CNR at focal plane remained constant for increasing object-detector distance, while increasing with objects’ nominal contrast, as expected. CNR decreased for increasing phantom thickness, for both lesion types. Depth Z-resolution differed with respect to lesion size at detector plane, as estimated by ASF, yielding 30.5 ± 4.3 mm for masses and 3.3 ± 0.4 mm for microcalcifications. Finally, lesion depth resolution was not affected by position along z-axis or phantom thickness. Conclusion Breast thickness and lesion size should be considered when assessing DBT image quality.

Optimizing quality of digital mammographic imaging using Taguchi analysis with an ACR accreditation phantom

ABSTRACTThis work demonstrated the improvement of the visualization of lesions by modulating the factors of an X-ray mammography imaging system using Taguchi analysis. Optimal combinations of X-ray operating factors in each group of level combination were determined using the Taguchi method, in which all factors were organized into only 18 groups, yielding analytical results with the same confidence as if each factor had been examined independently. The 4 considered operating factors of the X-ray machine were (1) anode material (target), (2) kVp, (3) mAs and (4) field of view (FOV). Each of these factors had 2 or 3 levels. Therefore, 54 (2×3×3×3 = 54) combinations were generated. The optimal settings were Rh as the target, 28 kVp, 80 mAs and 19×23 cm2 FOV. The grade of exposed mammographic phantom image increased from the automatic exposure control (AEC) setting 70.92 to 72.00 under the optimal setting, meeting the minimum standard (70.00) set by Taiwan's Department of Health. The average glandular dose (AGD) of the exposed phantom, 0.182 cGy, was lower than that, 0.203 cGy, under the AEC setting. The Taguchi method was extremely promising for the design of imaging protocols in clinical diagnosis.

Low dose high energy x-ray in-line phase sensitive imaging prototype: Investigation of optimal geometric conditions and design parameters.

The objective of this study was to investigate the optimization of a high energy in-line phase sensitive x-ray imaging prototype under different geometric and operating conditions for mammography application. A phase retrieval algorithm based on phase attenuation duality (PAD) was applied to the phase contrast images acquired by the prototype. Imaging performance was investigated at four magnification values of 1.67, 2, 2.5 and 3 using an acrylic edge, an American College of Radiology (ACR) mammography phantom and contrast detail (CD) phantom with tube potentials of 100, 120 and 140 kVp. The ACR and CD images were acquired at the same mean glandular dose (MGD) of 1.29 mGy with a computed radiography (CR) detector of 43.75 μm pixel pitch at a fixed source to image distance (SID) of 170 cm. The x-ray tube focal spot size was kept constant as 7 μm while a 2.5 mm thick aluminum (Al) filter was used for beam hardening. The performance of phase contrast and phase retrieved images were compared with computer simulations based on the relative phase contrast factor (RPF) at high x-ray energies. The imaging results showed that the x-ray tube operated at 100 kVp under the magnification of 2.5 exhibits superior imaging performance which is in accordance to the computer simulations. As compared to the phase contrast images, the phase retrieved images of the ACR and CD phantoms demonstrated improved imaging contrast and target discrimination. We compared the CD phantom images acquired in conventional contact mode with and without the anti-scatter grid using the same prototype at 1.295 mGy and 2.59 mGy using 40 kVp, a 25 μm rhodium (Rh) filter. At the same radiation dose, the phase sensitive images provided improved detection capabilities for both the large and small discs, while compared to the double dose image acquired in conventional mode, the observer study also indicated that the phase sensitive images provided improved detection capabilities for the large discs. This study therefore validates the potential of using high energy phase contrast x-ray imaging to improve lesion detection and reduce radiation dose for clinical applications such as mammography.

Testing a dual-modality system that combines full-field digital mammography and automated breast ultrasound

PurposeThe aim of this study was to test a novel dual-modality imaging system that combines full-field digital mammography (FFDM) and automated breast ultrasound (ABUS) in a single platform. Our Aceso system, named after the Greek goddess of healing, was specifically designed for the early detection of cancer in women with dense breast tissue. Materials and MethodsAceso was first tested using two industry standards: a Contrast Detail Mammography (CDMAM) phantom as endorsed by European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services was used to assess the FFDM images; and the CIRS 040GSE ultrasound phantom was imaged to evaluate the quality of the ABUS images. In addition, 58 women participated in a clinical trial: 51 were healthy volunteers aged between 40 and 65, while 7 were patients referred by the breast clinic, 6 of whom had biopsy-proven breast cancer. ResultsThe CDMAM tests showed that the FFDM results were “acceptable” but fell short of “achievable” which was attributed to the low dose used. The ABUS images had good depth penetration (80 mm) and adequate axial resolution (0.5 mm), but the lateral resolution of 2 mm was judged to be too coarse. In a 42-year-old volunteer with extremely dense breast tissue, the ABUS modality detected a lesion (a benign cyst) that was mammographically occult in the FFDM image. For a 73-year-old patient with fatty breasts, a malignant lesion was successfully detected and co-registered in the FFDM and ABUS images. On average, each woman spent less than 11 min in the acquisition room. ConclusionsWhile there is room for improvement in the quality of both the FFDM and ABUS images, Aceso has demonstrated its ability to acquire clinically meaningful images for a range of women with varying breast densities and, therefore, has potential as a screening device.

Breast dose in mammography is about 30% lower when realistic heterogeneous glandular distributions are considered.

Current dosimetry methods in mammography assume that the breast is comprised of a homogeneous mixture of glandular and adipose tissues. Three-dimensional (3D) dedicated breast CT (bCT) data sets were used previously to assess the complex anatomical structure within the breast, characterizing the statistical distribution of glandular tissue in the breast. The purpose of this work was to investigate the effect of bCT-derived heterogeneous glandular distributions on dosimetry in mammography. bCT-derived breast diameters, volumes, and 3D fibroglandular distributions were used to design realistic compressed breast models comprised of heterogeneous distributions of glandular tissue. The bCT-derived glandular distributions were fit to biGaussian functions and used as probability density maps to assign the density distributions within compressed breast models. The MCNPX 2.6.0 Monte Carlo code was used to estimate monoenergetic normalized mean glandular dose "DgN(E)" values in mammography geometry. The DgN(E) values were then weighted by typical mammography x-ray spectra to determine polyenergetic DgN (pDgN) coefficients for heterogeneous (pDgNhetero) and homogeneous (pDgNhomo) cases. The dependence of estimated pDgN values on phantom size, volumetric glandular fraction (VGF), x-ray technique factors, and location of the heterogeneous glandular distributions was investigated. The pDgNhetero coefficients were on average 35.3% (SD, 4.1) and 24.2% (SD, 3.0) lower than the pDgNhomo coefficients for the Mo-Mo and W-Rh x-ray spectra, respectively, across all phantom sizes and VGFs when the glandular distributions were centered within the breast phantom in the coronal plane. At constant breast size, increasing VGF from 7.3% to 19.1% lead to a reduction in pDgNhetero relative to pDgNhomo of 23.6%-27.4% for a W-Rh spectrum. Displacement of the glandular distribution, at a distance equal to 10% of the compressed breast width in the superior and inferior directions, resulted in a 37.3% and a -26.6% change in the pDgNhetero coefficient, respectively, relative to the centered distribution for the Mo-Mo spectrum. Lateral displacement of the glandular distribution, at a distance equal to 10% of the compressed breast width, resulted in a 1.5% change in the pDgNhetero coefficient relative to the centered distribution for the W-Rh spectrum. Introducing bCT-derived heterogeneous glandular distributions into mammography phantom design resulted in decreased glandular dose relative to the widely used homogeneous assumption. A homogeneous distribution overestimates the amount of glandular tissue near the entrant surface of the breast, where dose deposition is exponentially higher. While these findings are based on clinically measured distributions of glandular tissue using a large cohort of women, future work is required to improve the classification of glandular distributions based on breast size and overall glandular fraction.

Average glandular dose in digital mammography and digital breast tomosynthesis: comparison of phantom and patient data

For the evaluation of the average glandular dose (AGD) in digital mammography (DM) and digital breast tomosynthesis (DBT) phantoms simulating standard model breasts are used. These phantoms consist of slabs of polymethyl methacrylate (PMMA) or a combination of PMMA and polyethylene (PE). In the last decades the automatic exposure control (AEC) increased in complexity and became more sensitive to (local) differences in breast composition. The question is how well the AGD estimated using these simple dosimetry phantoms agrees with the average patient AGD. In this study the AGDs for both dosimetry phantoms and for patients have been evaluated for 5 different x-ray systems in DM and DBT modes. It was found that the ratios between patient and phantom AGD did not differ considerably using both dosimetry phantoms. These ratios averaged over all breast thicknesses were 1.14 and 1.15 for the PMMA and PMMA-PE dosimetry phantoms respectively in DM mode and 1.00 and 1.02 in the DBT mode. These ratios were deemed to be sufficiently close to unity to be suitable for dosimetry evaluation in quality control procedures. However care should be taken when comparing systems for DM and DBT since depending on the AEC operation, ratios for particular breast thicknesses may differ substantially (0.83–1.96). Although the predictions of both phantoms are similar we advise the use of PMMA + PE slabs for both DM and DBT to harmonize dosimetry protocols and avoid any potential issues with the use of spacers with the PMMA phantoms.

SU-D-204-04: Average Glandular Dose (AGD) Measurement of GE Contrast-Enhanced Spectral Mammography (CESM) Using a ACR Mammography Accreditation Phantom

Purpose: To investigate a practical approach to measure the average glandular dose (AGD) for GE Contrast-Enhanced Spectral Mammography (CESM) using a ACR mammography accreditation phantom Methods: This study used a GE Senographe Essential unit with SenoBright CESM, a Gammex ACR mammography accreditation phantom, an Unfors RaySafe X2 mammography detector, and a Radcal 10×9−6M ion chamber. Five AUTO CESM exposures were done on the ACR phantom with 5 daN compression to select the target/filter combination, kVp, and mAs. These techniques were used for the following manual CESM exposures, and the regular mammography to simulate the low energy exposure of a CESM run. Both Unfors and Radcal detectors are positioned near the phantom as the regular AGD measurement of mammography. The unfors detector measured the high energy exposure of the CESM run directly. The Radcal detector was set to accumulated mode and measured the total output from a CESM run. For Radcal, the high energy exposure was determined by subtracting the output of the regular mammography which simulated the low energy run of CESM from the total output. We also measured the HVLs of the low and high energy exposure respectively. The measured entrance skin air Kerma was then converted to the AGD using two Methods: one was based on the tables provided by GE; the other was introduced by D R Dance and K C Young (2014). Results: The AGD from the AUTO CESM on a ACR mammography phantom is approximately 1.75 mGy, 13.5% higher than that of the regular CNT AUTO mode, and 94% higher than that of the regular STD AUTO mode of this GE unit. The high energy exposure contributes about 18% of the total AGD. The AGD results from two methods are agreed to each other within 2%. Conclusion: We provide a practical approach to measure the AGD of GE CESM.

Evaluating clinical implications of 15-mega-sub-pixel liquid-crystal display in phase-contrast mammography

Phase-contrast mammography (PCM) systems characteristically yield sharp images with edge enhancement and high-resolution 25-μm/pixel mammograms. However, not all PCM image information can be shown on the display at a resolution of 5-megapixel (5-MP), although 5-MP monitors are recommended for interpretation of digital mammograms. Therefore, we investigated the potential utility of a 15-mega-sub-pixel (15-MsP) display for PCM images. We used a monitor that offered both 5-MP and 15-MsP displays by using a sub-pixel drive (SPD) technique to increase the spatial resolution of the monitor by threefold in the direction of the sub-pixels. Contrast-detail mammography phantom images were evaluated visually by four radiologic technologists. In this study, four display magnification ratios were used and the calculated image quality figures (IQFs) were compared with those of a 5-MP display. The detection capability of the 15-MsP display was significantly better than that of the 5-MP display at magnification ratios of 49 and 100%. At other magnification ratios, the detection capability of the 15-MsP display was higher than that of the 5-MP display, but the difference was not significant. A 15-MsP display has the potential to provide better detection than that provided by conventional 5-MP displays. A 15-MsP display using SPD technology is suitable for high-resolution digital mammograms, such as those produced by PCM systems.

Use of low-energy contrast-enhanced spectral mammography (CESM) as diagnostic mammography-proof of concept

Rationale and objectivesTo prove the diagnostic potential of low-energy images from contrast enhanced spectral mammography (CESM) by comparing low-energy CESM with full-field digital mammography (FFDM) with a contrast detail phantom and in patients. Materials and methodsLow-energy CESM and FFDM images of a contrast detail mammography phantom (CDMAM) were performed at different simulated breast thicknesses and automatically analysed with respect to contrast detail visibility, sensitivity, specificity, positive and negative predictive value and accuracy by two different software tools. Results from phantom studies were confirmed by comparing the detection of benign and suspicious findings of the breast in FFDM and low-energy CESM of 20 patients with breast cancer. Pearson correlation was calculated and agreement between measured sizes of benign and suspicious findings with FFDM and low-energy CESM was evaluated with Bland–Altman analysis. ResultsContrast-detail threshold of the low-energy CESM was equal to FFDM and below the acceptable and achievable limits given by the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF). Sensitivity, specificity, positive and negative predictive value and accuracy of low-energy CESM were equal, or even better as FFDM. Size measurements of masses, parenchymal asymmetries, micro- and macrocalcifications with low-energy CESM significantly correlated with FFDM. No significant over- or underestimation of size of mammographic finding was seen using low-energy CESM compared to FFDM. ConclusionThese data prove the concept to use the low-energy CESM image as diagnostic mammography.

Electron density of Rhizophora spp. wood using Compton scattering technique at 15.77, 17.48 and 22.16keV XRF energies

Abstract Compton (incoherently) scattered photons which are directly proportional to the electron density of the scatterer, have been employed in characterizing Rhizophora spp. as breast tissue equivalent. X-ray fluorescent scattered incoherently from Rhizophora spp. sample was measured using Si-PIN detector and three XRF energy values 15.77, 17.48 and 22.16 keV. This study is aimed at providing electron density information in support of the introduction of new tissue substitute materials for mammography phantoms.

Abstract 4299: Comparison of high-resolution 3D X-ray microCT and tomosynthesis imaging: A breast phantom study

Abstract We have demonstrated the feasibility of imaging a mammographic accreditation phantom using high-resolution 3D X-ray microCT as an alternative to tomosynthesis. While both X-ray microCT and tomosynthesis produce high-resolution 3D images, tomosynthesis requires compression of the specimen and yields asymmetrical voxels, resulting in high spatial resolution along two axes and more limited resolution along the third axis. MicroCT imaging, however, does not require compression and provides uniform, high resolution in all directions. The limited angular range of tomosynthesis is advantageous for pre-operative screening tasks, while the increased spatial and full angular range of microCT has been increasingly applied to the assessment of surgically excised breast tissue during breast conserving surgery. Rapid and accurate assessment of excised tissues is desirable to minimize risk of recurrence, which is highest in the first two years after surgery. We employed a 35-80 kV, 7.6-15W scan protocol in X-ray microCT to image the breast phantom. We also tested the ability to detect the phantom target features (2.00-0.16 mm) in long (25 minute) and short (5-6 minute) scans. The phantom was designed to simulate the X-ray attenuation of a slab of compressed human breast consisting of glandular and adipose tissue. Both X-ray microCT and tomosynthesis were able to capture the smallest features (0.16 mm) of the phantom. Both long- and short-duration microCT scans enabled detection of the smallest (0.16mm) features of the phantom. The results obtained here suggest that (1) microCT could be used, as an alternative to tomosynthesis, to identify and localize features on the order of 100-200 microns in ex vivo tumor specimens and (2) microCT could be used to detect features of this size on an intra-operative basis (in 5-6 minute scans). This study shows the feasibility of using microCT for intra-operative 3D examination of surgical specimens, an application which could aid clinical decision-making in assessment of excision margins. Additionally, if high-resolution 3D imaging techniques can distinguish between features of tumor and non-tumor areas of tissues, as is suggested by these results, then these imaging modalities could hold promise for identification of biomarkers and elucidation of the gross anatomy of breast tumor types, such as ductal carcinoma in situ. There is not yet an accepted phantom for testing the detection limits of 3D high-resolution X-ray imaging. The phantom used here is a validated tool for calibration of mammography instruments, but it seems that digital X-ray imaging technologies, such as microCT, can quite easily capture the features of this phantom. Therefore, while microCT performed as well as tomosynthesis in detection of features in this breast phantom study, there is a need for the development and validation of new phantoms to assess the ability of tomosynthesis and microCT to resolve features in the <100 micron range. Citation Format: Jolene M. Singh, Anthony H. Bui, James S. Michaelson. Comparison of high-resolution 3D X-ray microCT and tomosynthesis imaging: A breast phantom study. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4299. doi:10.1158/1538-7445.AM2014-4299

Fast one-dimensional wave-front propagation for x-ray differential phase-contrast imaging.

Numerical wave-optical simulations of X-ray differential phase-contrast imaging using grating interferometry require the oversampling of gratings and object structures in the range of few micrometers. Consequently, fields of view of few millimeters already use large amounts of a computer's main memory to store the propagating wave front, limiting the scope of the investigations to only small-scale problems. In this study, we apply an approximation to the Fresnel-Kirchhoff diffraction theory to overcome these restrictions by dividing the two-dimensional wave front up into 1D lines, which are processed separately. The approach enables simulations with samples of clinically relevant dimensions by significantly reducing the memory footprint and the execution time and, thus, allows the qualitative comparison of different setup configurations. We analyze advantages as well as limitations and present the simulation of a virtual mammography phantom of several centimeters of size.

SU-E-I-04: A Mammography Phantom to Measure Mean Glandular Dose and Image Quality

Purpose: To evaluate mean glandular dose (MGD) and image quality in a selection of mammography systems using a novel phantom based on thermoluminescent dosemeters and the ACR wax insert. Methods: The phantom consists of two acrylic, 19 cm diameter, 4.5 cm thick, semicircular modules, used in sequence. The image quality module contains the ACR insert and is used to obtain a quality control image under automatic exposure conditions. The dosimetric module carries 15 TLD-100 chips, some under Al foils, to determine air kerma and half-value-layer. TL readings take place at our laboratory under controlled conditions. Calibration was performed using an ionization chamber and a Senographe 2000D unit for a variety of beam qualities, from 24 to 40 kV, Mo and Rh anodes and filters. Phantom MGD values agree, on the average, within 3% with ionization chamber data, and their precision is better than 10% (k=1). Results: MGD and image quality have been evaluated in a selection of mammography units currently used in Mexican health services. The sample includes analogic (screen/film), flexible digital (CR), and full-field digital image receptors. The highest MDG are associated to the CR technology. The most common image quality failure is due to artifacts (dust, intensifying screen scratches, and processor marks for film/screen, laser reader defects for CR). Conclusion: The developed phantom permits the MGD measurement without the need of a calibrated ionization chamber at the mammography site and can be used by a technician without the presence of a medical physicist. The results indicate the urgent need to establish quality control programs for mammography.

Should processed or raw image data be used in mammographic image quality analyses? A comparative study of three full-field digital mammography systems

The purpose of this study is to compare a number of measured image quality parameters using processed and unprocessed or raw images in two full-field direct digital units and one computed radiography mammography system. This study shows that the difference between raw and processed image data is system specific. The results have shown that there are no significant differences between raw and processed data in the mean threshold contrast values using the contrast-detail mammography phantom in all the systems investigated; however, these results cannot be generalised to all available systems. Notable differences were noted in contrast-to-noise ratios and in other tests including: response function, modulation transfer function , noise equivalent quanta, normalised noise power spectra and detective quantum efficiency as specified in IEC 62220-1-2. Consequently, the authors strongly recommend the use of raw data for all image quality analyses in digital mammography.

An assessment of reference exposure in analogic and digital mammographic units

Abstract In this study, the incident air kerma ( K i,a ), half-value layer (HVL), output and voltage accuracy for 28 mammography services were evaluated. All mammographs had high frequency rectification, a focus-film distance greater than 60 cm, automatic exposure control, a Mo–Mo anode-filter combination, and compression system. Twenty-three evaluations were made of analogic imaging systems and 21 of digital imaging systems, two of which were full field digital mammography units. The K i,a was measured in the beam radiation with a 6 cm 3 ionization chamber, calibrated for a mammography range of energy. A standard American College of Radiology mammographic phantom simulated a skull caudal incidence. The average, minimum, and maximum K i,a values were 10.13 mGy, 3.92 mGy, and 30.41 mGy, respectively. However, when the analogic and digital systems are analyzed separately in two subsets, the values were 8.13 mGy, 3.92 mGy, and 11.78 mGy for the analogic systems and 12.33 mGy, 5.21 mGy, and 30.41 mGy for the digital systems, respectively. The results show that the K i,a values found in digital systems were higher than those in analogic systems, highlighting the differences between these acquisition systems. All HVL values, measured in the primary beam at 28 kV were found between 0.33 mm Al and 0.43 mm Al. Although the manufacture time of the equipment was approximately 146 months (~12 years) prior, the variation in output was between 0.071 mGy/mAs and 0.164 mGy/mAs for the entire sample.