Simultaneous dual-isotope technetium-99m/thallium-201 cardiac SPET imaging using a projection-dependent spilldown correction factor.

A spilldown correction method is proposed for the thallium-201 window image in simultaneous dual-isotope technetium-99m/thallium-201 single-photon emission tomographic (SPET) imaging based on a single acquisition into three energy windows. In this method, images are simultaneously acquired in two standard energy windows over the 99mTc and 201Tl photopeak regions and a third spilldown window adjacent to the 201Tl window. Using a Monte Carlo simulation of SPET, the fractional amount of 99mTc and 201Tl spilldown in the 201Tl window with respect to the total counts from the spilldown window, k12, was calculated for simulated images of point sources at varying depths within a water-filled elliptical tub phantom. When applied to experimental acquisitions, k12, multiplied by the total counts from the spilldown window, is then subtracted from the 201Tl window image to produce the corrected image. However, for successful applications in SPET, k12 must be determined on a projection-by-projection basis since k12 is depth dependent. Thus, a regression relation was obtained between k12 and the total count ratio of the spilldown to 99mTc windows, k23. The spilldown correction method was applied to 201Tl photopeak images of an extended source distribution in uniform and nonuniform attenuating media with dual-isotope 99mTc/201Tl and single-isotope 201Tl. A marked improvement in image contrast was observed between the corrected and uncorrected 201Tl window images. The average count ratio of uncorrected dual-isotope 201Tl/single-isotope 201Tl was 3.08 for uniform and 2.99 for non-uniform attenuating media.(ABSTRACT TRUNCATED AT 250 WORDS)