QUANTITATIVE ASSESSMENT OF REGIONAL MYOCARDIAL BLOOD-FLOW WITH TL-201AND SPECT

Thallium-201 has been used extensively as a myocardial perfusion agent and to assess myocardial viability. Unlike other Tc-99m-labeled agent s such as Tc-99m-sestamibi and Tc-99m-tetro-fosmine, the regional conc entration of Tl-201 varies with time, and its kinetics make it a poten tial candidate for estimating absolute physiologic parameters with kin etic model analysis. This article outlines a strategy for quantitative assessment of regional myocardial blood flow in man using Tl-201 and dynamic single photon emission computed tomography (SPECT), Quantitati vely accurate SPECT images that are proportional to the true radioacti vity distribution are prerequisites for model-based kinetic analysis. Our technique for quantitative SPECT includes ordered-subset maximum l ikelihood-expectation maximization (ML-EM) reconstruction with transmi ssion data-based attenuation correction and transmission-dependent con volution subtraction scatter correction. A three-compartment model was found to reproduce the observed regional time-activity curves well, a nd dog experiments demonstrated that influx rate constant (K-1) values estimated from the dynamic SPECT data correlated well with absolute m yocardial blood flow determined by in vitro microspheres for a physiol ogically wide range of flows. Several possible strategies for simplify ing the study procedures, without compromising accuracy, are also pres ented, which should make absolute quantitation of regional myocardial blood flow feasible using Tl-201 and a conventional SPECT camera in a clinical setting.