Myocardial clearance kinetics of technetium-99m-SQ30217: A marker of regional myocardial blood flow

SQ30217 is a new, technetium-99m- (^99mTc) labeled perfusion agent introduced for cardiac imaging. To evaluate the myocardial tracer kinetics, ^99mTc-SQ30217 was injected intracoronarily in open-chested dogs under baseline conditions and after administration of intravenous (i.v.) dipyridamole. Myocardial first-pass retention fraction averated 0.90 ± 0.04. Clearance of the tracer occurred in a biexponential manner. Sixty-seven percent of retained activity cleared with a half-time of 2.3 ± 0.6 min, while the residual activity demonstrated slow clearance. The clearance rate of the rapid phase correlated with myocardial blood flow (r = 0.72, p < 0.001). Myocardial SQ30217 clearance rate following i.v. injection as determined by dynamic imaging with tomography (SPRINT) averaged 21 ± 4 min and increased to 13 ± 4 min following dipyridamole. Thus, ^99mTc-SQ30217 is a promising flow tracer with high initial myocardial retention and rapid tissue clearance, which allow repeated flow determinations within short time intervals using advanced SPECT technology.