Dual-isotope brain SPECT imaging with technetium-99m and iodine-123: Clinical validation using xenon-133 SPECT

Our phantom studies indicate that the energy resolution (9.7% FWHM) of a new three-headed single-photon tomograph (PRISM-3000) separates the distribution of ^99mTc from ¹²³I for 10% asymmetric or 15% or 10% centered ^99mTc windows when combined with a 10% asymmetric ¹²³I window. This technique is now applied to the simultaneous measurement of resting rCBF and changes induced by vasodilation (1 g acetazolamide) in 10 subjects with cerebrovascular disease. Resting and vasodilated ¹³³Xe SPECT images were obtained first. Within 48 hr, ^99mTc HMPAO was given at rest, acetazolamide injected, and after 20 min either [¹²³I] IMP or [¹²³I] HIPDM was administered. Subjects were scanned for ^99mTc and ¹²³I simultaneously using 10% asymmetric windows. Regression analyses demonstrated a linear relationship between ¹³³Xe SPECT and dual-isotope SPECT measurements of lesion-to-cerebellum ratios in baseline (r = 0.92), vasodilated (r = 0.86) and rest-minus-vasodilated data (r = 0.85). Technetium-99m and ¹²³I images obtained through dual-isotope imaging are by definition in perfect anatomic registration.