Ranging from 20 kV to 640 kV, 621 x-ray spectra were produced and are available at 1 kV tube potential intervals. The spectra are tabulated at 1 keV intervals. TASMICS spectra were shown to be largely equivalent to published spectral models and are available in spreadsheet format for interested users by emailing the corresponding author (JMB).

Purpose: 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. Methods: 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 (pDgN hetero ) and homogeneous (pDgN homo ) 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. Results: The pDgN hetero coefficients were on average 35.3% (SD, 4.1) and 24.2% (SD, 3.0) lower than the pDgN homo 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 pDgN hetero relative to pDgN homo 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 pDgN hetero 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 pDgN hetero coefficient relative to the centered distribution for the W-Rh spectrum. Conclusions: 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. C 2015 American Association of Physicists in Medicine.

Purpose To develop tables of normalized glandular dose coefficients DgN for a range of anode–filter combinations and tube voltages used in contemporary breast imaging systems. Methods Previously published mono-energetic DgN values were used with various spectra to mathematically compute DgN coefficients. The tungsten anode spectra from TASMICS were used; Molybdenum and Rhodium anode-spectra were generated using MCNPx Monte Carlo code. The spectra were filtered with various thicknesses of Al, Rh, Mo or Cu. An initial HVL calculation was made using the anode and filter material. A range of the HVL values was produced with the addition of small thicknesses of polymethyl methacrylate (PMMA) as a surrogate for the breast compression paddle, to produce a range of HVL values at each tube voltage. Using a spectral weighting method, DgN coefficients for the generated spectra were calculated for breast glandular densities of 0%, 12.5%, 25%, 37.5%, 50% and 100% for a range of compressed breast thicknesses from 3 to 8 cm. Results Eleven tables of normalized glandular dose (DgN) coefficients were produced for the following anode/filter combinations: W + 50 μm Ag, W + 500 μm Al, W + 700 μm Al, W + 200 μm Cu, W + 300 μm Cu, W + 50 μm Rh, Mo + 400 μm Cu, Mo + 30 μm Mo, Mo + 25 μm Rh, Rh + 400 μm Cu and Rh + 25 μm Rh. Where possible, these results were compared to previously published DgN values and were found to be on average less than 2% different than previously reported values. Conclusion Over 200-pages of DgN coefficients were computed for modeled x-ray system spectra that are used in a number of new breast imaging applications. The reported values were found to be in excellent agreement when compared to published values.

Purpose The purpose of this work was to develop and make available x-ray spectra for some of the most widely used digital mammography (DM), breast tomosynthesis (BT), and breast CT (bCT) systems in North America. Methods The Monte Carlo code MCNP6 was used to simulate minimally-filtered (only beryllium) x-ray spectra at 8 tube potentials from 20 to 49 kV for DM/BT, and 9 tube potentials from 35 to 70 kV for bCT. Vendor-specific anode compositions, effective anode angles, focal spot sizes, source-to-detector distances, and beryllium filtration were simulated. For each 0.5 keV energy bin in all simulated spectra, the fluence was interpolated using cubic splines across the range of simulated tube potentials to produce spectra in 1 kV increments from 20 to 49 kV for DM/BT and from 35 to 70 kV for bCT. The HVL of simulated spectra with conventional filtration (at 35 kV for DM/BT and 49 kV for bCT) was used to assess spectral differences resulting from variations in: (1) focal spot size (0.1 and 0.3 mm IEC), (2) solid angle at the detector (i.e. small and large FOV size), and (3) geometrical specifications for vendors that employ the same anode composition. Results Averaged across all DM/BT vendors, variations in focal spot and FOV size resulted in HVL differences of 2.2% and 0.9%, respectively. Comparing anode compositions separately, the HVL differences for Mo (GE, Siemens) and W (Hologic, Philips, and Siemens) spectra were 0.3% and 0.6%, respectively. Both the commercial Koning and prototype “Doheny” (UC Davis) bCT systems utilize W anodes with a 0.3 mm focal spot. Averaged across both bCT systems, variations in FOV size resulted in a 2.2% difference in HVL. In addition, the Koning spectrum was slightly harder than Doheny with a 4.2% difference in HVL. Therefore to reduce redundancy, a generic DM/BT system and a generic bCT system were used to generate the new spectra reported herein. The spectral models for application to DM/BT were dubbed the Molybdenum, Rhodium, and Tungsten Anode Spectral Models using Interpolating Cubic Splines (MASMICSM-T, RASMICSM-T, and TASMICSM-T ; subscript “M-T” indicating mammography and tomosynthesis). When compared against reference models (MASMIPM, RASMIPM, and TASMIPM; subscript “M” indicating mammography), the new spectral models were in close agreement with mean differences of 1.3%, −1.3%, and −3.3%, respectively, across tube potential comparisons of 20, 30, and 40 kV with conventional filtration. TASMICSbCT-generated bCT spectra were also in close agreement with the reference TASMIP model with a mean difference of −0.8%, across tube potential comparisons of 35, 49, and 70 kV with 1.5 mm Al filtration. Conclusions The Mo, Rh, and W anode spectra for application in DM and BT (MASMICSM-T, RASMICSM-T, and TASMICSM-T) and the W anode spectra for bCT (TASMICSbCT) as described in this study should be useful for individuals interested in modeling the performance of modern breast x-ray imaging systems including dual energy mammography which extends to 49 kV. These new spectra are t...

Myocardial metabolic and perfusion imaging is a vital tool for understanding the physiologic consequences of heart failure. We used PET imaging to examine the longitudinal kinetics of 18F-FDG and 14(R,S)-18F-fluoro-6-thia-heptadecanoic acid (18F-FTHA) as analogs of glucose and fatty acid (FA) to quantify metabolic substrate shifts with the spontaneously hypertensive rat (SHR) as a model of left ventricular hypertrophy (LVH) and failure. Myocardial perfusion and left ventricular function were also investigated using a newly developed radiotracer 18F-fluorodihydrorotenol (18F-FDHROL). Methods Longitudinal dynamic electrocardiogram-gated small-animal PET/CT studies were performed with 8 SHR and 8 normotensive Wistar-Kyoto (WKY) rats over their life cycle. We determined the myocardial influx rate constant for 18F-FDG and 18F-FTHA (KiFDG and KiFTHA, respectively) and the wash-in rate constant for 18F-FDHROL (K1FDHROL). 18F-FDHROL data were also used to quantify left ventricular ejection fraction (LVEF) and end-diastolic volume (EDV). Blood samples were drawn to independently measure plasma concentrations of glucose, insulin, and free fatty acids (FFAs). Results KiFDG and KiFTHA were higher in SHRs than WKY rats (P < 3 × 10−8 and 0.005, respectively) independent of age. A decrease in KiFDG with age was evident when models were combined (P = 0.034). The SHR exhibited higher K1FDHROL (P < 5 × 10−6) than the control, with no age-dependent trends in either model (P = 0.058). Glucose plasma concentrations were lower in SHRs than controls (P < 6 × 10−12), with an age-dependent rise for WKY rats (P < 2 × 10−5). Insulin plasma concentrations were higher in SHRs than controls (P < 3 × 10−3), with an age-dependent decrease when models were combined (P = 0.046). FFA levels were similar between models (P = 0.374), but an increase with age was evident only in SHR (P < 7 × 10−6). Conclusion The SHR exhibited alterations in myocardial substrate use at 8 mo characterized by increased glucose and FA utilizations. At 20 mo, the SHR had LVH characterized by decreased LVEF and increased EDV, while simultaneously sustaining higher glucose and similar FA utilizations (compared with WKY rats), which indicates maladaptation of energy substrates in the failing heart. Elevated K1FDHROL in the SHR may reflect elevated oxygen consumption and decreased capillary density in the hypertrophied heart. From our findings, metabolic changes appear to precede mechanical changes of LVH progression in the SHR model.

Purpose: To present a dataset of computational digital breast phantoms derived from high-resolution three-dimensional (3D) clinical breast images for the use in virtual clinical trials in two-dimensional (2D) and 3D x-ray breast imaging. Acquisition and validation methods: Uncompressed computational breast phantoms for investigations in dedicated breast CT (BCT) were derived from 150 clinical 3D breast images acquired via a BCT scanner at UC Davis (California, USA). Each image voxel was classified in one out of the four main materials presented in the field of view: fibroglandular tissue, adipose tissue, skin tissue, and air. For the image classification, a semi-automatic software was developed. The semi-automatic classification was compared via manual glandular classification performed by two researchers. A total of 60 compressed computational phantoms for virtual clinical trials in digital mammography (DM) and digital breast tomosynthesis (DBT) were obtained from the corresponding uncompressed phantoms via a software algorithm simulating the compression and the elastic deformation of the breast, using the tissue's elastic coefficient. This process was evaluated in terms of glandular fraction modification introduced by the compression procedure. The generated cohort of 150 uncompressed computational breast phantoms presented a mean value of the glandular fraction by mass of 12.3%; the average diameter of the breast evaluated at the center of mass was 105 mm. Despite the slight differences between the two manual segmentations, the resulting glandular tissue segmentation did not consistently differ from that obtained via the semi-automatic classification. The difference between the glandular fraction by mass before and after the compression was 2.1% on average. The 60 compressed phantoms presented an average glandular fraction by mass of 12.1% and an average compressed thickness of 61 mm. Data format and access: The generated digital breast phantoms are stored in DICOM files. Image voxels can present one out of four values representing the different classified materials: 0 for the air, 1 for the adipose tissue, 2 for the glandular tissue, and 3 for the skin tissue. The generated computational phantoms datasets were stored in the Zenodo public repository for research purposes (http://

Purpose The purpose of this work was to generate uncompressed heterogeneous breast phantom models using size‐dependent fibroglandular distributions derived from a large cohort of breast CT (bCT) datasets, and to compare differences in normalized glandular dose coefficients for bCT “DgNCT” when the realistic heterogeneous model is considered relative to the simple, homogeneous model used in the past. Methods A cohort of 274 segmented bCT datasets were used to quantify the fibroglandular tissue distribution within the breast parenchyma. Each dataset was interpolated to an isotropic voxel size of 0.25 mm and the breast center‐of‐mass was aligned for all coronal slices. Each aligned dataset was converted into two binarized volumes representing voxels containing only glandular tissue “G(x,y,z)” and voxels containing glandular or adipose tissue “AG(x,y,z)”. The datasets were classified by volume in accordance with previously reported size‐dependent, breast‐shaped phantoms. Within the five groups — each containing on average 55 datasets, all G(x,y,z) and AG(x,y,z) volumes were summed separately representing the cumulative distribution of glandular tissue or breast parenchyma (glandular + adipose), respectively. G(x,y,z) was divided by AG(x,y,z) on a voxel‐by‐voxel basis resulting in a glandular fraction “GF(x,y,z)” distribution for each phantom size. The GF(x,y,z) distributions were used to construct heterogeneous mathematical phantoms for the small, median, and large breast sizes with a 1.5 mm skin thickness — based on previously reported measurements from bCT, and a 5 mm skin thickness for comparison with outdated assumptions of skin thickness. A subset of 15 bCT datasets from the cohort (five for each breast size) were used to construct voxelized patient models for validation of the heterogeneous phantom models. Monte Carlo techniques were used to estimate monoenergetic DgN(E)CT values for photon energies from 9 to 70 keV (in 1 keV intervals) using the mathematical phantoms composed of either heterogeneous or homogeneous breast parenchyma. Polyenergetic (pDgNCT) coefficients were determined by weighting the DgN(E)CT values by x‐ray spectra tuned to the beam characteristic of breast CT. Dose coefficients were compared between the two breast compositions for each volume class, breast density, and skin thickness. Results For photon energies ≲45 keV, the homogeneous model overestimates DgN(E) values relative to the realistic heterogeneous model sorted into five volume classes. The 5 mm skin thickness underestimates DgN(E) values relative to the realistic 1.5 mm thickness for lower energies and the differences diminish up to 70 keV. Averaged across all phantom sizes the homogeneous model overestimates pDgNCT by 5.7% and 23.3% for the 60 kV W/Cu and 49 kV W/Al spectra, respectively. The heterogeneous model was also found to be in agreement with the voxelized bCT patient models with pDgNCT differences less than 2.3% and 5.2% for the 60 kV W/Cu and 49 kV W/Al spectra, respectively, across all phantom sizes. Conclusion Anatom...

Purpose A modular phantom for dosimetry and imaging performance evaluation in cone‐beam computed tomography (CBCT) is reported, providing a tool for quantitative technical assessment that can be adapted to a broad variety of CBCT imaging configurations and clinical applications. Methods The phantom presents a set of modules that can be ordered in various configurations suitable to a particular CBCT system. Modules include slabs containing a uniform medium, low‐contrast inserts, line‐spread features, and disk features suitable to measurement of image uniformity, noise, noise‐power spectrum (NPS), contrast, contrast‐to‐noise ratio (CNR), Hounsfield (HU) accuracy, linearity, spatial resolution modulation transfer function (MTF), and magnitude of cone‐beam artifact. Automated software recognizes the phantom configuration in DICOM images and provides structured reporting of such test measures. In any modular configuration, the phantom permits measurement of air kerma in central and peripheral locations with an air ionization chamber (e.g., Farmer chamber). The utility and adaptability of the phantom were demonstrated across a spectrum of CBCT systems, including scanners for orthopaedic imaging (Carestream OnSight 3D, Rochester NY), breast imaging (Doheny prototype, UC Davis), image‐guided surgery (IGS, Medtronic O‐arm, Littleton MA), angiography (Siemens Artis Zeego, Forcheim Germany), and image‐guided radiation therapy (IGRT, Elekta Synergy XVI, Stockholm Sweden). Results The phantom provided a consistent platform for quantitative assessment of dose and imaging performance compatible with a broad spectrum of CBCT systems. The purpose of the survey was not to obtain head‐to‐head performance comparison of systems designed for such distinct clinical applications. Rather, the survey demonstrated the suitability of the phantom to a broad spectrum of systems in a manner that provides characterization pertinent to disparate applications and imaging tasks. For example: the orthopaedic CBCT system (pertinent clinical tasks relating to high‐resolution bone imaging) was shown to achieve MTF consistent with imaging of high‐contrast trabecular bone structures (i.e., the MTF reduced to 10% at spatial frequency, f10 = 1.2 mm−1); the breast system (even higher‐resolution imaging of microcalcifications) exhibited f10 = 2.2 mm−1; the IGS system (tasks including both bone and soft‐tissue contrast resolution) provided f10 = 0.9 mm−1 and soft‐tissue CNR = 1.64; the angiography system (soft‐tissue body interventions) demonstrated CNR = 1.2 in soft tissues approximating liver lesions; and the IGRT system (pertinent tasks emphasizing HU linearity and image uniformity) showed linear response with HU values (R2 = 1), with a cupping artifact (tcup = 5.8%) due to x‐ray scatter. Conclusions The phantom provides an adaptable, quantitative basis for CBCT dosimetry and imaging performance evaluation suitable to a broad variety of CBCT systems. The dosimetry and image quality metrics are consistent with up‐to‐date methods for rigorous, quantitative,...