X-Ray Scatter in Differential Phase-Contrast Breast Imaging Using Gratings-Based Interferometer
S Vedantham*, L Shi, A Karellas, University of Massachusetts Medical School, Worcester, MAWE-G-103-4 Wednesday 4:30PM - 6:00PM Room: 103
Purpose: To determine the x-ray scatter content in differential phase-contrast imaging of the breast using a gratings-based interferometer.
Methods: X-ray scatter during small field-of-view (9.6x5-cm) differential phase-contrast breast imaging with a gratings-based interferometer (25-keV design) was determined using GEANT4 Monte Carlo (MC) toolkit. The duty-cycles of source (G0), phase (G1) and analyzer (G2) gratings were 0.25, 0.5 and 0.5, respectively. All gratings were planar and fabricated from 0.675-mm thick silicon wafers. MC estimated transmission efficiencies of the gratings in parallel-beam geometry were validated with theoretical estimates. After validation, their transmission efficiencies were determined in cone-beam geometry. Position-independent estimates of scatter and primary photons at the detector plane were obtained with 2 to 8 cm thick adipose and fibroglandular breasts and without the breast in the x-ray beam. The recorded x-ray scatter was analyzed after classification as photons that underwent at least one Compton interaction (incoherent scatter) and as photons that underwent Rayleigh interaction alone (coherent scatter). While G2 is needed in practice, simulations were conducted without G2 to determine its role in scatter reduction.
Results: In parallel-beam geometry, Monte Carlo estimated transmission efficiencies showed good correspondence (r2>0.99) with theory. In cone-beam geometry, the transmission efficiencies of G0, G1 and G2 gratings were 0.16, 0.7 and 0.25, respectively. Position-independent estimates of scatter-to-primary ratio were 0.08 without the breast, and increased from 0.13 (0.15) to 0.25 (0.31) for 2 to 8 cm thick adipose (fibroglandular) breasts. Coherent scatter was the dominant contributor to total scatter with coherent-to-incoherent scatter ratio ranging from 1.65 (1.94) to 1.8 (2.04) for adipose (fibroglandular) breasts. The G2 grating reduced incoherent scatter by ~5% to 24% for 2 to 8-cm breasts.
Conclusion: The 0.675-mm thick silicon wafer contributed to ~30% reduction in transmission efficiency for each grating. The G2 grating reduces the incoherent scatter at the detector plane.
Funding Support, Disclosures, and Conflict of Interest: Supported in part by the National Institutes of Health (NIH) grants R01 CA128906 and R21 CA134128. The contents are solely the responsibility of the authors and do not represent the official views of the NIH or NCI.