Quantification of the extent of myocardial infarction by thallium-201 single photon emission computed tomography

The diagnostic capability of a circumferential profile analysis with a two-dimensional representation of Tl-201 myocardial SPECT depends on the normal range of thallium distribution. The present study was thus to determine the lower normal limits useful for assessing the precise extent of myocardial infarction (MI). The quantitative analysis of Tl-201 myocardial SPECT was correlated with pathological findings of the heart in 50 autopsy cases (28 with MI; 22 without MI). The lower normal limits were 2.5 standard deviations below the mean values calculated using profiles normalized to the maximum pixel count observed in each profile. Using this lower normal limit, the sensitivity was 63.8%; specificity was 87.4%; and accuracy was 80.7% for determining the extent of ischemic lesions. However, for detecting MI, the sensitivity by quantitative analysis was 97%, which was higher than that by visual analysis. Non-transmural infarction 2.5 cm in size, undetectable by visual analysis, was detected by two-dimensional polar representation. However, the specificity of detecting MI was low (59%). The detectability of MI extent varied from site to site; false negative lesions were frequent in the septal region, and false positive lesions in the posterolateral region of the dilated hypertrophic heart. In conclusion, Tl-201 myocardial SPECT is useful for evaluating MI automatically, although possible false positive diagnosis must be taken into accounts in cases of dilated hypertrophic heart. (N.K.)