A TRANSMISSION-DEPENDENT METHOD FOR SCATTER CORRECTION IN SPECT

A method of scatter compensation has been developed that incorporates planar transmission measurements in the estimation of photopeak scatte r in SPECT. Methods: The scatter distribution is first estimated by co nvolving the planar projections with a monoexponential scatter functio n. The number of scattered events that subsequently reach the detector as a proportion of total events (i.e., scatter fraction) is then dete rmined for each point in the projections based on narrow-beam transmis sion values, obtained using an external source. The assumptions of the method were tested using (TC)-T-99m and (TI)-T-201 point and line sou rces. The quantitative and qualitative impact of transmission-dependen t scatter correction was assessed in realistic phantom experiments sim ulating blood-pool, lung and myocardial perfusion studies. Results: Th e method accurately predicts the scatter distribution from Tc-99m and (TI)-T-201 line sources in a phantom with variable density. Reconstruc ted counts are artificially enhanced in regions of high tissue density when scattered events are not removed from the projections prior to a ttenuation correction. Using convolution-subtraction with a constant s catter fraction (k = 0.4), scatter is underestimated in the heart and overestimated in the lungs, whereas transmission-dependent scatter cor rection enables activity to be quantified with greater than or equal t o 95% accuracy in heart and lung regions. Conclusion: We conclude that incorporating transmission data enables accurate scatter compensation in objects with nonuniform density.