Characteristics of the myocardial SPECT images of 99mTc-MIBI and 99mTc-Teboroxime

Characteristics of the myocardial distribution of 99mTc-Teboroxime was compared with the myocardial distibution of 201Tl. We made summed myocardial images, in which central three short-axis SPECT slices were added. Rectagular region of interest (ROI) was set on each myocardial segment, and mean counts of each myocardial region was obtained using summed short-axis images. The ratio of inferior-to-anterior mean counts (I/A) was 0.69±0.20 in 99mTc-MIBI and 0.62±0.16 in 201Tl. The ratio of inferior-to-lateral mean counts was 0.70±0.18 and 0.65±0.13, respectively. Both ratios in 99mTc-MIBI were significantly higher than those in 201Tl (p<0.05). 201Tl to 929mTc-MIBI ratios of these two values were 1.11±0.17 (I/A) and 1.08±0.16 (I/L). The ratios of I/A and I/L of 99mTc-MIBI were about 10 percent higher than those of 201Tl. 99mTc-Teboroxime dynamic short-axis SPECT images of every three-minute were obtained. The ratios of counts in each wall were calculated similarly. After about 8 minutes, gradual increase in hepatic activity can be a cause of quatitative error in the assessment of SPECT images. We obtained the data with a human cardiac phantom. The myocardial phantom filled with 99mTc or 201Tl was placed in the mediastinal portion that is surrounded by the lung (saw dust) and vertebra (plastic bar). The ratio of I/A was 0.79 and I/L was 0.85 in 201Tl. The I/A ratio was 0.93 and I/L was 0.97 in 99mTc. Both ratios in 99mTc were about 15 percent higher than those in 201Tl. When we assess images quantitatively using these new 99mTc-labeled myocardial agents, it is necessary to interpret the images taking account of the characteristics, because the radiopharmaceutical distribution of these new agents are different from that of 201Tl. (author)