Comparison of Scatter/Primary Measurements with GATE Simulations for X-Ray Spectra in Cone Beam CT Mammography

It is commonly understood that scattered radiation in CT degrades the reconstructed image. Scatter correction relies on precise measurements or Monte Carlo simulation results in experimental conditions. Previous studies on both experimental measurements and Monte Carlo simulations have been reported in diagnostic radiology and conventional mammography. Rapidly developed cone beam CT mammography significantly differs from conventional mammography in breast shape, geometry, etc. aspects, which are amongst the most important factors that impact the scatter fraction. The Geant4 based Monte Carlo simulation package GATE has been successful in the application of PET and SPECT with its implemented precise modeling of various physics processes. However, there exist little reports in the literature about the GATE application in X-ray CT. We present some preliminary results on the experimental measurements of the scatter to primary ratios in cone beam CT mammography setting using the beam stop and aperture methods. The measurements were used to compare and validate the performance of the GATE simulations by choosing the low energy or standard physics models for electromagnetic processes including Compton and Rayleigh scatterings. Aided by precise GATE simulations, we discovered a significant scatter component from sources other than the studied object in scatter measurement using conventional methods. We developed a new strategy of measurement to subtract this background scatter.