Assessment of coronary flow reserve using a combination of planar first-pass angiography and myocardial SPECT: Comparison with myocardial ¹⁵O-water PET

Coronary flow reserve (CFR), defined as the ratio of maximum coronary flow increase from baseline resting blood flow, is one of the most sensitive parameters to detect early signs of coronary arteriosclerosis at the microvascular level. Myocardial perfusion PET is a well-established technology for CFR measurement, however, availability is still limited. The aim of this study is to introduce and validate myocardial flow reserve measurement by myocardial perfusion SPECT. Methods Myocardial perfusion SPECT at rest and ATP stress (0.16 mg/Kg/min) was performed in 10 patients with known coronary artery disease. Immediately after the injection of Tc-99m sestamibi (MIBI), left ventricular (LV) dynamic planar angiographic data were obtained for 90s. Coronary flow reserve index as measured by MIBI SPECT (CFR_MIBI) was calculated as follows: CFR_MIBI = Cm_sSbm_b / Cm_bSbm_s, where subscripts _b, _s, Cm, and Sbm indicate baseline, during stress, myocardial counts with MIBI SPECT, and integral of LV counts with first pass angiography, respectively. Additionally, standard stress/rest ¹⁵O-water PET to estimate CFR was performed in all patients as standard of reference. Results CFR_MIBI increased in conjunction with CFR, but underestimated blood flow at high flow rates. The relationship between CFR_MIBI (Y) and CFR_PET (X) was well fitted as follows: Y = 1.40x(1-exp(1.79/x)) (r = 0.84). Conclusions The index of CFR_MIBI reflects the CFR by ¹⁵O-water PET but underestimates flow at high flows, maybe as a reflection of pharmacokinetic limitations of MIBI.