Effect of radiochemical purity of ⁹⁹tc^m-q12 on myocardial spet image quality

In myocardial perfusion SPET studies with ⁹⁹Tc^m-Q12, we observed that some patients had high liver uptake that interfered significantly in the assessment of the inferior wall. The aim of this study was to assess the effects of the radiochemical purity of ⁹⁹Tc^m-Q12 on liver uptake. Thirty- one patients undergoing routine myocardial infarction perfusion studies were evaluated. The radiochemical purity of ⁹⁹Tc^m Q12 was determined using HPLC. Venous blood samples taken 50 min after injection of ⁹⁹Tc^m-Q12 during peak exercise were also analysed. Liver uptake was expressed as the liver-to-heart ratio. In addition, the SPET images were classified by two experienced 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- heart ratio correlated inversely with the radiochemical purity of ⁹⁹Tc^m - Q12 (r= -0.65, P < 0.001) and unchanged ⁹⁹Tc^m -Q12 in plasma (r = -0.44, P < 0.02). The radiochemical purity of ⁹⁹Tc^m-Q12 was significantly lower in the group with high liver uptake (60.1 ± 4.2%) than in the group with good- quality images (81.8 ± 5.6%, P < 0.01) or with high background activity (82.3 ± 2.5%, P < 0.01). In conclusion, the radiochemical purity of ⁹⁹Tc^m-Q12 has a significant inverse correlation with the liver-to-heart ratio; thus, the high radiochemical purity of ⁹⁹Tc^m-Q12 should be confirmed to prevent interference by liver uptake.