LABORATORY INVESTIGATION SINGLE-PHOTON EMISSION TOMOGRAPHY Quantitation of size of relative myocardial perfusion defect by single-photon emission computed tomography

The purpose of this study was to validate a semiautomatic method for quantitating the size of relative myocardial perfusion defects from single-photon emission computed tomographic (SPECT) images. We compared the size of the image defect in vivo, expressed as percent of involved left ventricle, as determined by this method with the anatomic size of the defect in vitro in 19 dogs. To test the method under optimal conditions, we first labeled the left ventricular myocardium in nine dogs by left atrial injection of 99mTc-labeled macroaggregated albumin particles after acute occlusion of one coronary artery. The "defect volume" was defined as the volume of the left ventricular myocardium for which counts fell 2 or more SDs below the distribution of counts in the myocardium supplied by a normal coronary artery in a series of animals. The relative in vivo defect volume by SPECT occupied 26.46 + 12.7% of the left ventricular volume (mean SD), compared with a relative defect size in vitro of 33.3 + 13.7% (p = NS) of left ventricular volume as determined by well counting of myocardial samples. There was a close correlation between the two measurements (r .92). However, myocardial relative defect volumes involving less than 5% of myocardium were not identified by SPECT. The defect volume weighted for the relative reduction in flow within the defect zone or the relative "reduced perfusion volume" was also determined. The correlation between the estimates by SPECT and those made in vitro for relative reduced perfusion volume was also high (r = .94). The method was then evaluated under conditions simulating the clinical imaging situation by injecting 201Ti intravenously into 10 resting dogs. Relative defect volume in vivo by SPECT was 29.38 + 13.3% of left ventricular volume compared with a relative defect volume in vitro of 35.09 ± 10.73% of left ventricular myocardial volume (p = .09). The correlation between the two was .70. The tomographic relative reduced perfusion volume occupied 11.4 + 7.8% of the left ventricular volume compared with 16.9 ± 9.3% (p = .003) for the measure in vitro. Correlation between the SPECT and anatomic estimates of relative reduced perfusion volume was high (r = .88). We conclude that the size of a relative myocardial perfusion defect can be accurately quantitated by single-photon tomography. The techniques described may prove useful in the assessment in vivo of interventions directed at altering myocardial infarct size, in the determination of extent of ischemic myocardium, or in the diagnostic evaluation of patients with suspected coronary artery disease. Circulation 70, No. 6, 1048-1056, 1984. THE SEARCH FOR accurate noninvasive methods for determining the size of myocardial infarction has been the aim of many investigations.1"'° The use of therapeutic interventions designed to decrease infarct size has been an impetus for the development of measurements of size that might be applied clinically. Several From the Cardiovascular Disease Section, Department of Medicine and the Department of Radiology, VA Medical Center and the University of Washington, Seattle. Supported by the General Medical Research Service of the Veterans Administration and an American Heart Association-Washington grantin-aid. Address for correspondence: James H. Caldwell, M.D., Division of Cardiology (III), VA Medical Center, 1660 South Columbian Way, Seattle, WA 98108. Received Oct. 31, 1983; revision accepted Aug. 23, 1984. 1048 imaging modalities have been proposed to define myocardial perfusion defects.4 SO In this study, we employed single-photon emission computed tomography (SPECT) to externally quantitate myocardial perfusion defects. For imaging of this type a standard gamma camera that rotates about the subject and readily available radionuclides are used, and it is thus relatively inexpensive and potentially widely applicable. A prior study in our laboratory has established that the visual analysis of SPECT images improves the ability to detect myocardial infarction when compared with conventional planar imaging. "I The purpose of this study was to test, in instrumented dogs, a semiautomatic method for quantitating relative myocardial perfusion CIRCULATION by gest on A ril 4, 2017 http://ciajournals.org/ D ow nladed from LABORATORY INVESTIGATION SINGLE-PHOTON EMISSION TOMOGRAPHY abnormalities and to validate it by direct tissue counting. We studied both an idealized preparation using intra-atrial 9smTc-labeled particles and a more clinically relevant preparation in which intravenous 201T1 was used.