Evaluation of C-11-methionine-PET/MRI in primary hyperparathyroidism.

1026 Objectives: C-11-methionine-PET/CT is a highly sensitive method for the preoperative localization of parathyroid adenomas causing primary hyperparathyroidism. However, the correlation between PET findings and corresponding anatomical structures in CT is often difficult. PET/MRI is a promising method in this respect by combining the advantages of excellent soft tissue contrast and functional imaging in MRI with the superior sensitivity of molecular imaging with PET with less radiation exposure compared to PET/CT. Thus, we evaluated the performance of C-11-methionine PET/MRI for localization of parathyroid adenomas in patients with hyperparathyroidism. Methods: 12 PET/MRI scans (Siemens Biograph mMR, 3 T) of patients with laboratory evidence of primary hyperparathyroidism were evaluated retrospectively (7F, 5M, median age 54 years). The scans were acquired 20 min after i. v. application of C-11-methionine (approx. 500 MBq, skull base to diaphragm, native + contrast enhanced, Gadovist 0.1 ml / kg BW, scan time approx. 40 min). The protocol consisted of the following sequences: axial T1-Flash CAIPI, T2-Haste STIR, T2-TSE, DWI, dynamic contrast enhanced T1-Flash; sagittal + coronal: T2-TSE Dixon. The level of certainty of findings in PET alone and for the combined analysis of PET and MRI were rated on the Likert scale from 1 to 5 (1 = uncertain diagnosis, 5 = certain diagnosis). Results: In all cases PET scans showed at least one suspicious finding for a parathyroid adenoma. One patient presented with two suspicious findings. In PET alone, 10/13 results were rated with 4, 1/13 with 5 and 2/13 with 3. By combining MRI with PET, the ratings improved to 5 in 11/13, mainly due to a typical morphological correlate which was most often identified by early arterial enhancement in the dynamic contrast enhanced sequence. In 2/13 cases there was no change by combined PET and MRI analysis and in 1/13 no clear anatomical correlate was detectable in MRI. For 6 cases the diagnosis could be confirmed histopathologically after operation without false positive findings. Compared to equivalent PET/CT protocols, a reduction in radiation exposure from 65-80 % can be achieved. Conclusions: C-11-methionine-PET/MRI is a promising method for preoperative localization of parathyroid adenomas in primary hyperparathyroidism with a high detection rate of adenomas combined with excellent anatomical correlation and a substantial reduction of radiation exposure compared to PET/CT.