Analysis of Dependence of Detector Position on Detected Scatter Distribution in Dedicated Breast SPECT

In SPECT, scattered photons contribute to the detected signal, reducing contrast and quantification accuracy. Several methods exist to correct scatter, including the dual-energy window technique, but have not been fully evaluated on non-traditional SPECT trajectories. Using MCNP5, a Monte Carlo study was performed to analyze how incident scatter is affected by detector position for breast SPECT. An ideal detector was positioned at various azimuthal and polar angles relative to a pendant breast geometry. Detected scatter from the breast, heart, liver, torso, and lesion was linearly fit; the slope was used to characterize the distribution. Typical photopeak and scatter energy window ratios were calculated. Results indicate detected scatter depends upon detector position and its vantage of major uptake organs; however, the effect is minimal for non-direct views, with a ratio of 0.37. A single coefficient for dual-energy window scatter correction should suffice for breast imaging trajectories ignoring direct views of the heart/liver.