[A fundamental study of 99mTc-HMPAO double injection method and clinical application to stress scintigraphy in orthostatic hypotension].

Double injection method using brain perfusion 99mTc-HMPAO SPECT is popular one for evaluating stress scintigraphy. For appropriate evaluation of this method 555 MBq (15 mCi) of 99mTc-HMPAO was injected twice in sequence at the resting state. The first and second SPECT images were obtained 5 min after each injection. Twenty-five ROIs of 8 x 8 pixels were placed on in various regions of the first images, and calculate each counts (C1). Then the counts of the same region of the second scan were calculated (C2). One hundred and fifty ROIs/6 patients were examined. We derived the linear relationship as C2 = 1.66 x C1 + 106 (r = 0.97), where C1 and C2 represents counts of the first scan, and second scan, respectively. This results suggests that the counts of the second scan is derived from the counts of the first scan without second scanning if they are obtained in the same condition. When we applied this method to stress scintigraphy, it may be useful for evaluating the regional brain perfusion changes before and after loading instead of using subtraction technique.