OBJECTIVE: The purpose of this study was to utilize a dedicated breast CT
system using a 2D beam stop array to physically evaluate the scatter to primary ratios
(SPRs) of different geometric phantoms and prospectively acquired clinical patient
data.
METHODS: Including clinically unrealizable compositions of 100% glandular
and 100% fat, projection images were acquired using three geometrically different phantoms
filled with fluids simulating breast tissue. The beam stop array method was used for
measuring scatter in projection space, and creating the scatter corrected primary images.
2D SPRs were calculated. Additionally, a new figure of merit, the 3D normalized scatter
contribution (NSC) volumes were calculated.
RESULTS: The 2D SPR values (0.52–1.10) were primarily dependent on phantom
geometry; a secondary dependence was due to their uniform density; 2D SPRs were low
frequency and smoothly varying in the uniformly filled phantoms. SPRs of clinical patient
data followed similar trends as phantoms, but with noticeable deviations and high
frequency components due to the heterogeneous distribution of glandular tissue. The
maximum measured patient 2D SPRs were all <0.6, even for the largest diameter breast.
These results demonstrate modest scatter components with changing object geometries and
densities; the 3D NSC volumes with higher frequency components help visualize scatter
distribution throughout the reconstructed image volumes. Furthermore, the SPRs in the
heterogeneous clinical breast cases were underestimated by the equivalent density,
uniformly filled phantoms.
CONCLUSIONS: These results provide guidance on the use of uniformly
distributed density and differently shaped phantoms when considering simulations. They
also clearly demonstrate that results from patients can vary considerably from 2D SPRs of
uniformly simulated phantoms.
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