A dual-photopeak window method for scatter correction.

The imaging of scattered photons degrades contrast and is a major source of error in the quantitation of activity. It was hypothesized that, if the photopeak was divided into two nonoverlapping energy windows, a regression relation could be obtained between the ratio of counts within these windows and the scatter fraction for counts within the total region. This idea was tested by acquiring dual photopeak window acquisitions of a 99mTc point source in an elliptical attenuator, and at the same locations in air. From these, a regression between the scatter fraction and window ratio was determined. When this regression was applied to estimate the scatter distribution for acquisitions in both uniform and nonuniform elliptical attenuators, the residual scatter fraction was reduced approximately ten-fold and the estimated scatter line spread functions matched very closely the tails of the total line spread functions. In SPECT acquisitions, dual-photopeak window scatter correction was observed to significantly increase the contrast of "cold" spheres, improve the accuracy of estimating activity at the center of "hot" spheres, and return the three-dimensional modulation transfer function for point sources in an elliptical attenuator to near their in-air shape.