Abstract ID: 159 Contribution of coherent and incoherent scatter in grating-based phase-contrast imaging

Abstract

Aim Grating-based phase-contrast imaging (GB-PCI) is a recent development in X-ray imaging. Using three gratings, a highly periodic intensity pattern is created and measured. The amplitude (visibility) of this pattern is an important system parameter that determines image quality and scatter degrades this system visibility. Two GB-PCI setup aspects are expected to reduce the scatter fraction in the image: grating G2 can be considered an anti-scatter grid while large object-to-detector distances (D) will limit large angle scatter contributions. The aim was to quantify the efficiency with which these two aspects reduce both coherent and incoherent scatter in GB-PCI. Method PENELOPE Monte Carlo simulations were used with a realistic GB-PCI imaging geometry: gratings G1 and G2 had pitches of 4 and 2 μm, respectively, heights of 35 and 26 μm and duty cycles of 0.5. The trenches of the silicon gratings were filled with air in G1 and gold in G2. The G1-to-detector distance was 4.53 cm, while G2 was fixed to the detector. A 40 kVp X-ray tube was simulated in a plane wave geometry. Three different cases were evaluated for two objects, a finger imaged in air and a 5 cm thick PMMA slab. Case 1 had G2 in place and D was 9.5 cm, G2 was removed for case 2 and D was 9.5 cm, while case 3 had G2 removed and D was 4 cm. Results and conclusion Coherent scatter-to-primary ratio (SPRcoh) for the finger was 1.63%, 0.56% and 0.77% for cases 1,2,3 respectively. Similarly the incoherent SPR (SPRincoh) was 0.29%, 0.20% and 0.67%. For the PMMA slab, SPRcoh was 6.65%, 7.67% and 10.50% for cases 1, 2 and 3, while SPRincoh was respectively 2.26%, 3.05% and 7.86%. The uncertainty was 5%. Increasing D from 4 to 9.5 cm reduces both scatter-to-primary ratios (SPRcoh by 27% and SPRincoh by 65%). G2 will only reduce scattered radiation for larger objects with higher exit scatter fractions(consistent with [1] ) due to absorption of primaries and the creation of scatter in the grating.