Abstract
Thallium-201 myocardial scintigraphy during exercise test is used for diagnosis of ischemic heart disease. Recently, quantitative analysis by computer is performed instead of visual analysis. For quantitative analysis there are ROI and Circumferential Prolile Method, furthermore, the latter are classified into Count and Density Circumferential Profile Curve. When initial image (immediately after exercise) shows lower perfusion or perfusion defect (less than 50% according to Density Profile), these finding are due to myocardial infarction or transient myocardial ischemia.
The lower perfusion or perfusion defect are filled up at 3-4 hours after exercise. This phenomenon is due to redistribution. The redistribution is observed in cases of transient ischemia, however it is not seen in cases of myocardial infarction. For quantitative determination of filling up in lower perfusion or perfusion defect, washout rate is calculated by Count Profile. Washout rate is as follow: Washout rate=(-Initial Count-Delayed Count)/Initial Count. Washout rate are more than 20%(no redistribution), these segments are located in the area of normal myocardium or myocardial infarction. They are less than 20% (redistribution) in transient ischemia. The distinction between normal myocardium, transient myocardial ischemia and myocardial infarction are possible by using quantitative analysis as Density and Count Prolile. By these methods, the three vessel disease and old myocardial infarction with transient ischemia are diagnosed correctly.
