Reproducibility of Thallium-201 Myocardial Perfusion Study in Rat Model with MicroSPECT

Gated myocardial perfusion Single Photon Emission Computed Tomography (SPECT) is a non-invasive diagnostic medical imaging test and one of the most commonly used medical procedures for assessing myocardial perfusion and left ventricular functions in the same study. Serial imaging with SPECT is used to study heart diseases in small animals and thereby can play a role in developing new therapies and new radiotracers and also can follow disease progression inside the subject. In vivo measurement using microSPECT allows the evaluation of cardiac factors like end diastolic volume (EDV), end systolic volume (ESV), ejection fraction (EF) and perfusion homogeneity (PH). Serial imaging reduces the unnecessary sacrifice of small animals and improves the power of small-animal studies. The goal of our study is to determine the intra- and inter-subject reproducibility of left ventricular functional measurements with T1-201 thallium-chloride for cardiac microSPECT imaging in a rat model. Eight normal Sprague-Dawley rats underwent electrocardiogram-gated SPECT scanning weekly for 5 weeks and eight rats with a surgically induced myocardial infarction underwent imaging for 2 weeks at 2-3 day intervals. The rats were injected with 0.5 mCi of T1-201 and scanned with a mciroSPECT scanner. The microSPECT was a 4-headed scanner with 9 pinholes/head (36 pinholes in total). The scan was started just after the injection and continued for 30 minutes. We used 4DM-SPECT, a clinical software package, to analyse the data. We found the values of EDV, ESV, EF and PH and the intra- and inter-subject variance in these values for both normal and MI rats for 10 minute, 20 minute and 30 minute scanning durations. There were no significant differences found between myocardial infarcted and normal rats with respect to the intra-subject variability, but there were significant differences in the inter-rat variability. This study provides a baseline reproducibility of T1-201 for cardiac microSPECT small-animal imaging.