[Evaluation of ischemic heart disease by thallium-201 washout-rate map using SPECT]

In thallium-201 myocardial perfusion scintigraphy, washout rate (WR) has been used for the evaluation of the severity of ischemic heart disease (IHD). The WR was calculated from the polar map (Bull's-eye display) of myocardial perfusion using SPECT. To analyze the abnormality of WR map, we computed the extent and severity scores of WR. Applications of two types of standards, absolute and relative standards from control group (n = 16), were compared. The multiple regression analysis showed that the global WR was a function of the severity of coronary artery stenosis and exercise level, i.e. WR (%) = -2.38 X (number of stenotic artery) + 0.093 X (rate-pressure product/100) + 19.7 (n = 62, r = 0.63). Thus in evaluating the severity of IHD by absolute WR, the correction of WR was necessary according to the exercise level. Whereas, to evaluate the score of WR abnormality in polar map, the relative standard separated each group with different number of stenotic artery better than absolute standard did. In conclusion, calculation of WR score from relative standard is recommended for the analysis of polar WR map, although absolute global WR is useful for the evaluation of severity of coronary artery disease.