Abstract
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 the99mTc and201Tl photopeak regions and a third spilldown window adjacent to the201Tl window. Using a Monte Carlo simulation of SPET, the fractional amount of99mTc and201Tl spilldown in the201Tl 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 the201Tl 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 to99mTc windows, k23. The spilldown correction method was applied to201T1 photopeak images of an extended source distribution in uniform and nonuniform attenuating media with dual-isotope99mTc/201Tl and single-isotope201Tl. A marked improvement in image contrast was observed between the corrected and uncorrected201Tl window images. The average count ratio of uncorrected dual-isotope201Tl/single-isotope201Tl was 3.08 for uniform and 2.99 for non-uniform attenuating media. When corrected, this value approached unity (0.97 and 1.08) and the corrected dual-isotope images were visually similar The presented method in which spilldown correction for the201Tl photopeak window is performed in a single acquisition on a projection-by-projection basis in simultaneous dual-isotope SPET imaging could form the basis for a rapid and accurate clinical dual-isotope protocol independent of radiotracer administration.
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Hademenos, G.J., Dahlbom, M. & Hoffman, E.J. Simultaneous dual-isotope technetium-99m/thallium-201 cardiac SPET imaging using a projection-dependent spilldown correction factor. Eur J Nucl Med 22, 465–472 (1995). https://doi.org/10.1007/BF00839061
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DOI: https://doi.org/10.1007/BF00839061