Diagnostic Value of F-18-FACBC PET/MRI in Brain Metastases

Purpose The study aims to evaluate whether combined F-18-FACBC PET/MRI could provide additional diagnostic information compared with MRI alone in brain metastases. Patients and Methods Eighteen patients with newly diagnosed or suspected recurrence of brain metastases received dynamic F-18-FACBC PET/MRI. Lesion detection was evaluated on PET and MRI scans in 2 groups depending on prior stereotactic radiosurgery (SRS group) or not (no-SRS group). SUVs, time-activity curves, and volumetric analyses of the lesions were performed. Results In the no-SRS group, 29/29 brain lesions were defined as "MRI positive." With PET, 19/29 lesions were detected and had high tumor-to-background ratios (TBRs) (D-max MR, >= 7 mm; SUVmax, 1.2-8.4; TBR, 3.9-25.9), whereas 10/29 lesions were undetected (D-max MR, <= 8 mm; SUVmax, 0.3-1.2; TBR, 1.0-2.7). In the SRS group, 4/6 lesions were defined as "MRI positive," whereas 2/6 lesions were defined as "MRI negative" indicative of radiation necrosis. All 6 lesions were detected with PET (D-max MR, >= 15 mm; SUVmax, 1.4-4.2; TBR, 3.6-12.6). PET volumes correlated and were comparable in size with contrast-enhanced MRI volumes but were only partially congruent (mean DSC, 0.66). All time-activity curves had an early peak, followed by a plateau or a decreasing slope. Conclusions F-18-FACBC PET demonstrated uptake in brain metastases from cancer of different origins (lung, gastrointestinal tract, breast, thyroid, and malignant melanoma). However, F-18-FACBC PET/MRI did not improve detection of brain metastases compared with MRI but might detect tumor tissue beyond contrast enhancement on MRI. F-18-FACBC PET should be further evaluated in recurrent brain metastases.