Dual-window scatter correction and energy window setting in cerebralblood flow SPECT: a Monte Carlo study

Abstract

The image quality in SPECT studies of the regional cerebral blood flow (rCBF)performed with 99mTc-HMPAO is degraded by scattered photons. Thefinite energy resolution of the gamma camera makes the detection of scatteredphotons unavoidable, and this is observed in the image as an impaired contrastbetween grey and white matter structures.In this work, a Monte Carlo simulated SPECT study of a realistic voxel-basedbrain phantom was used to evaluate the resulting contrast-to-noise ratio for anumber of energy window settings, with and without the dual-window scattercorrection. Values of the scaling factor k, used to obtain the fraction ofscattered photons in the photopeak window, were estimated for each energywindow.The use of a narrower, asymmetric, energy discrimination window improved thecontrast, with a subsequent increase in statistical noise due to the lowernumber of counts. The photopeak-window setting giving the best contrast-to-noiseratio was found to be the same whether or not scatter correction was applied.Its value was 17% centred at 142 keV. At the optimum photopeak-window setting,the contrast was improved by using scatter correction, but the contrast-to-noiseratio was made worse.