Effect of radiochemical purity of Tc-99(m)-Q12 on myocardial SPET image quality

In myocardial perfusion SPET studies with Tc-99(m)-Q12, we observed that so me patients had high liver uptake that interfered significantly in the asse ssment of the inferior wall. The aim of this study was to assess the effect s of the radiochemical purity of Tc-99(m)-Q12 on liver uptake. Thirty-one p atients undergoing routine myocardial infarction perfusion studies were eva luated. The radiochemical purity of Tc-99(m)-Q12 was determined using HPLC. Venous blood samples taken 50 min after injection of Tc-99(m)-Q12 during p eak exercise were also analysed. Liver uptake was expressed as the liver-to -heart ratio. In addition, the SPET images were classified by two experienc ed nuclear medicine specialists into three groups representing high-quality images (n = 7), images with high general background activity (n = 13) and images with high liver and/or intestinal uptake (n = 11). The liver-to-hear t ratio correlated inversely with the radiochemical purity of Tc-99(m)-Q12 (r = -0.65, P < 0.001) and unchanged Tc-99(m)-Q12 in plasma (r = -0.44, P < 0.02). The radiochemical purity of Tc-99(m)-Q12 was significantly lower in the group with high liver uptake (60.1 +/- 4.2%) than in the group with go od-quality images (81.8 +/- 5.6%, P < 0.01) or with high background activit y (82.3 +/- 2.5%, P < 0.03). In conclusion, the radiochemical purity of Tc- 99(m)-Q12 has a significant inverse correlation with the liver-to-heart rat io; thus, the high radiochemical purity of Tc-99(m)-Q12 should be confirmed to prevent interference by liver uptake. ((C) 1999 Lippincott Williams & W ilkins).