Quantification of Myocardial Perfusion Defect Size in Rats: Comparison between Quantitative Perfusion SPECT and Autoradiography

Ultra-high resolution single-photon emission computed tomography (SPECT) system, using multiple pinhole collimators, has been applied to the imaging of small rodents. We aimed to compare the myocardial infarction (MI) area on quantitative perfusion single-photon emission computed tomography (QPS; Cedars-Sinai Medical Center, USA) with that on high-resolution autoradiography in rat model to determine the accuracy of perfusion defect measurement by QPS. After thoracotomy, rats (n = 9) had their left coronary arteries occluded and reperfused before injection with 185 MBq [Tc-99m] methoxyisobutylisonitrile ([Tc-99m]MIBI) for SPECT and autoradiography. Healthy rats (n = 28) were similarly scanned to create a normal database on which to base QPS. The MI area on SPECT images was analysed automatically by QPS software. For the autoradiography images, regions of interest for MI were set at 1 mm intervals. In normal rats, [Tc-99m]MIBI accumulated throughout the left ventricles, and a polar map of ventricular perfusion showed the lowest and highest uptakes in the inferior (68 % +/- 4 %) and anterior (92 % +/- 5 %) walls, respectively. In the rat MI model, the percentage of polar map with reduced [Tc-99m]MIBI uptake correlated strongly with the percentage of left ventricle with MI on autoradiography (r (2) = 0.90). QPS can quantitatively evaluate MI severity on myocardial perfusion images in rats, with comparable results to autoradiography. This widely available software could promote the development of new techniques for analysing cardiac images in small animals.