Generation and analysis of clinically relevant breast imaging x-ray spectra

Abstract

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...

Investigating energy deposition in glandular tissues for mammography using multiscale Monte Carlo simulations

“…Furthermore, as part of the sensitivity analysis described at the end of the previous section, we consider two additional mammography photon spectra: a 20 kVp spectrum with molybdenum target and 0.0386 mm‐thick molybdenum filter (Mo/Mo), and a 30 kVp spectrum with tungsten target and 0.05 mm‐thick rhodium filter (W/Rh). These spectra were obtained from the MASMICS and TASMICS models developed by Hernandez et al …”

“…Furthermore, as part of the sensitivity analysis described at the end of the previous section, we consider two additional mammography photon spectra: a 20 kVp spectrum with molybdenum target and 0.0386 mm-thick molybdenum filter (Mo/Mo), and a 30 kVp spectrum with tungsten target and 0.05 mm-thick rhodium filter (W/Rh). These spectra were obtained from the MASMICS and TASMICS models developed by Hernandez et al 40 Dose distributions within the voxelized breast tissue models for part 1 (based on phantoms 012204, 012804 and 062204 as described in Section 2.A) are computed with egs_brachy 35 (2017 distribution). In part 1, only a compressed breast thickness of 5 cm is considered.…”

Direct measurement of clinical mammographic x-ray spectra using a CdTe spectrometer

“…Due to the aforementioned limitations, the most common method for obtaining mammography x‐ray spectra is by means of mathematical models . However, in some cases, not all parameters that characterize the x‐ray spectra are available in these models .…”

“…Due to the aforementioned limitations, the most common method for obtaining mammography x-ray spectra is by means of mathematical models. [7][8][9][10][11] However, in some cases, not all parameters that characterize the x-ray spectra are available in these models. 4 Indirect methods to obtain a representation of x-ray spectra can also be found in the literature, for example, the reconstruction of measured scattered x-ray spectra 12,13 and nonclinical spectra.…”

Average glandular dose coefficients for pendant‐geometry breast CT using realistic breast phantoms

“…HVL measurements were made at tube voltages of 50, 60, and 70 kV with 0.2 mm Cu filtration. The previously reported tungsten anode spectral model using interpolating cubic splines for application in bCT (TASMICS bCT ) was then used in conjunction with the HVL measurements to model the Doheny scanner's x‐ray spectrum. TASMICS bCT provides minimally filtered (0.8 mm beryllium) x‐ray spectra from 35 to 70 kV, and the Monte Carlo model used for generating these x‐ray spectra makes use of the specific geometry employed in breast CT.…”