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A novel cone-beam CT (CBCT) system has been developed with promising capabilities for musculoskeletal imaging
(e.g., weight-bearing extremities and combined radiographic / volumetric imaging). The prototype system demonstrates
diagnostic-quality imaging performance, while the compact geometry and short scan orbit raise new considerations for
scatter management and dose characterization that challenge conventional methods. The compact geometry leads to
elevated, heterogeneous x-ray scatter distributions - even for small anatomical sites (e.g., knee or wrist), and the short
scan orbit results in a non-uniform dose distribution. These complex dose and scatter distributions were investigated via
experimental measurements and GPU-accelerated Monte Carlo (MC) simulation. The combination provided a powerful
basis for characterizing dose distributions in patient-specific anatomy, investigating the benefits of an antiscatter grid,
and examining distinct contributions of coherent and incoherent scatter in artifact correction. Measurements with a 16
cm CTDI phantom show that the dose from the short-scan orbit (0.09 mGy/mAs at isocenter) varies from 0.16 to 0.05
mGy/mAs at various locations on the periphery (all obtained at 80 kVp). MC estimation agreed with dose measurements
within 10-15%. Dose distribution in patient-specific anatomy was computed with MC, confirming such heterogeneity
and highlighting the elevated energy deposition in bone (factor of ~5-10) compared to soft-tissue. Scatter-to-primary
ratio (SPR) up to ~1.5-2 was evident in some regions of the knee. A 10:1 antiscatter grid was found earlier to result in
significant improvement in soft-tissue imaging performance without increase in dose. The results of MC simulations
elucidated the mechanism behind scatter reduction in the presence of a grid. A ~3-fold reduction in average SPR was
found in the MC simulations; however, a linear grid was found to impart additional heterogeneity in the scatter
distribution, mainly due to the increase in the contribution of coherent scatter with increased spatial variation. Scatter
correction using MC-generated scatter distributions demonstrated significant improvement in cupping and streaks.
Physical experimentation combined with GPU-accelerated MC simulation provided a sophisticated, yet practical
approach in identifying low-dose acquisition techniques, optimizing scatter correction methods, and evaluating patientspecific
dose.
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