[A useful method to evaluate 11C-methionine uptake using positron emission tomography: determination of the optimal scanning time for evaluation and a comparison between the tumor-to-muscle ratio and the distribution absorption ratio].

We determined the optimal scanning time for evaluating 11C-methionine uptake and then compared the usefulness of the tumor-to-muscle ratio (TMR) with the distribution absorption ratio (DAR) using positron emission tomography. Forty-two PET studies were performed to examine 42 tumorous lesions, 25 normal lung tissues, 23 normal bone marrow and 39 blood pool. In the 42 lesions examined, the TMR at 5, 10-20, 20-32 and 32-40 minutes after 11C-methionine injection, compared with that at 45-60 minutes, was 96 +/- 23%, 91 +/- 8.6%, 94 +/- 6.9% and 96 +/- 6.9%, respectively. A correlation study between the TMR and the DAR demonstrated good results in both the normal tissue (r = 0.96) and the tumorous lesions (r = 0.93). In conclusion, the 11C-methionine uptake can be evaluated at any time from 10 minutes after the injection of 11C-methionine and both the TMR and the DAR are considered to be useful methods for evaluating 11C-methionine uptake using positron emission tomography.