Pilot Measurements of Coronary Flow Reserve (CFR) and Comparison to Myocardial Perfusion Imaging (MPI) using Dynamic and Gated Stress/Rest ^99mTc-SESTAMIBI CZT-SPECT

Introduction: Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) often underestimates the presence of multi-vessel coronary artery disease (CAD) in cases where the myocardium is homogenously hypoperfused. Absolute measurements of coronary flow reserve (CFR) have been shown to provide incremental diagnostic and prognostic information in this regard. Recently, such measurements have become feasible in SPECT systems utilizing CZT detectors. We have acquired such a system and began a pilot study to clinically assess this new method in the detection of multi-vessel CAD.

Methods: An initial cohort of 7 randomly selected CAD patients underwent a CFR acquisition protocol using ^99mTc-SESTAMIBI. This protocol is similar to the standard MPI protocol (including the total patient dose); however, the injection is performed within the apparatus, thus recording the radiotracer’s dynamic passage through the left ventricle and transient perfusion in the myocardium. CFR below 2.0 is an established indicator of CAD, while severe ischemia in MPI studies is diagnosed when ischemic total perfusion deficit (ITPD) > 10%. We hypothesized that the two indicators should be correlated.

Results: The findings in 6 out of 7 patients were consistent with our hypothesis: (1) Three patients with "negative ischemia" (ITPD < 10%) correspond to "negative CAD" (CFR > 2.0), and (2) "positive ischemia" correspond to "positive CAD" in the other three patients. Interestingly, the 7^th patient scored "negative ischemia" (ITPD = 3%) but "positive CAD" (CFR = 1.88). Subsequent review of the patient`s medical records revealed a three-vessel CAD diagnosis according to recent coronary angiography, illustrating the unique advantage of CFR over MPI in the detection of multi-vessel CAD.

Conclusion: These initial promising results demonstrate the feasibility of CFR measurements using ^99mTc-SESTAMIBI CZT-SPECT. Currently, a much larger population study is being initiated with diverse CAD pathologies.