Background: This research was undertaken to investigate the ability of dynamic single-photon emission computed tomographic (SPECT) imaging to quantify myocardial perfusion in vivo with 99mTc-labeled teboroxime. The objectives of this experiment were (1) to determine the reproducibility of the model parameters fv, K1, and k2 (volume fraction of blood in the tissue and wash-in and wash-out of 99mTc-labeled teboroxime in the myocardium, respectively), (2) to determine if the kinetics of 99mTc-labeled teboroxime correlate with an independent measure of myocardial blood perfusion, and (3) to determine the amount of extravascular activity in the arterial blood time-activity curve generated from the dynamic SPECT images.
Methods and results: Twenty-nine studies were performed on 10 dogs. The dogs were divided into three groups: reproducibility, occlusion, and vasodilation. In the reproducibility protocol, the physiology was kept as constant as possible. In the occlusion and vasodilation protocols, myocardial perfusion was either decreased by occluding the left anterior descending coronary artery or increased by continuous adenosine infusion, respectively. In all studies an independent measure of myocardial perfusion was obtained with either radiolabeled microspheres or a flow probe, and the activity of 99mTc-labeled teboroxime in the arterial blood was monitored continuously. The root-mean-square errors calculated with data from the reproducibility group were 19.9% +/- 8.5%, 14.0% +/- 5.7%, and 14.5% +/- 5.0% for fv, K1, and k2, respectively. The occlusion group data showed that K1 demonstrated a higher correlation (r = 0.887) with microsphere myocardial perfusion than did k2 (r = 0.689). The results from the vasodilation group showed that K1 demonstrated a stronger relationship to myocardial blood flow (MBF) measured with a flow probe (K1 = 0.237 + 0.629 MBF [r = 0.935] and k2 = 0.177 + 0.263 MBF [r = 0.904]). Finally, the amount of extravascular activity in the blood time-activity curve generated from the dynamic SPECT images was determined to be 45.5% +/- 16.4%.
Conclusions: The wash-in parameter K1 correlates with myocardial perfusion in dogs; therefore dynamic SPECT imaging of 99mTc-labeled teboroxime has the potential for measuring regional myocardial perfusion in patients.