This study was designed to evaluate the ability of PET/MRI, using 18 F-FDG and 68 Ga-DOTATATE as tracers, to detect hormoneproducing pituitary microadenoma when diagnosis is difficult using MRI alone. Methods: We recruited 37 patients with elevated hormone levels, including 19 with undiagnosable primary pituitary adenoma and 18 with suspected recurrent pituitary adenoma. 18 F-FDG PET/MRI and 68 Ga-DOTATATE PET/MRI were performed within 1 wk of each other in all patients. Within 2 wk afterward,

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... 7 of the 37 patients underwent transsphenoidal adenomectomy, 3 underwent sella region radiotherapy, 1 underwent somatostatin therapy, and 6 had only clinical follow-up. The image characteristics and uptake levels were correlated with the surgical findings and pathologic results. Receiver-operating-characteristic curves were analyzed to determine the optimal cutoff to differentiate adenoma from normal pituitary tissue. The area under the receiver-operating-characteristic curve was calculated to compare diagnostic performance. Results: The PET/MR images were of diagnostic quality and without obvious image artifacts. The high contrast of the PET images provided complementary information to the fine anatomic display of the MR images. Increased 18 F-FDG uptake was clearly observed in all patients. MRI enhanced using a 0.05 mmol/kg dose of gadopentetate dimeglumine showed suggestive findings in only 47% of the patients with primary adenoma and 39% of those with recurrent adenoma; when a 0.1 mmol/kg dose was used, the respective percentages were 37% and 50%. The 18 F-FDG SUV max of the 16 primary adenomas that underwent transsphenoidal adenomectomy (6.8 6 3.7) was significantly higher than that of normal pituitary tissue (3.2 6 1.