Focal uptake of the heart on (18)F-FDG PET images is a characteristic feature of patients with sarcoidosis. Furthermore, (18)F-FDG PET has the potential to detect cardiac sarcoidosis that cannot be diagnosed by (67)Ga or (99m)Tc-MIBI scintigraphy.

Both 18F-FDG PET and MRI provided high sensitivity for diagnosing cardiac sarcoidosis in patients with suspected cardiac involvement, but the specificity of (18)F-FDG PET was not as high as previously reported. The different distributions of the findings in the two modalities suggest the potential of 18F-FDG PET and MRI in detecting different pathological processes in the heart.

Because of its higher soft-tissue contrast, whole-body integrated PET/MR offers potential advantages over PET/CT for evaluation of bone lesions. However, unlike PET/CT, PET/MR ignores the contribution of cortical bone in the attenuation map. Thus, the aims of this study were to evaluate the diagnostic performance of wholebody integrated 18 F-FDG PET/MR specifically for bone lesions and to analyze differences in standardized uptake value (SUV) quantification between PET/MR and PET/CT. Methods: One hundred nineteen patients with 18 F-FDG-avid primary malignancies underwent a single-injection, dual-imaging protocol using 18 F-FDG on a PET/ CT scanner and a subsequent PET/MR scan with a T1-weighted volumetric interpolated breath-hold examination (VIBE) Dixon sequence for attenuation correction and an unenhanced coronal T1-weighted turbo spin-echo (TSE) sequence for bone analysis. Three sets of images (CT with PET [from PET/CT; set A], T1-weighted VIBE Dixon with PET [set B], and T1-weighted TSE with PET [both from PET/MR; set C]) were analyzed. Two readers rated every lesion using a 4-point scale for lesion conspicuity on PET, a 4-point scale for anatomic allocation of PET-positive lesions, and a 5-point scale for the nature of every lesion based on its appearance on morphologic imaging and uptake on PET. For all lesions and for representative regions of normal bone, SUV analysis was performed for PET/ MR and PET/CT. Results: In total, 98 bone lesions were identified in 33 of 119 patients, and 630 regions of normal bone were analyzed. Visual lesion conspicuity on PET was comparable for PET/CT (mean rating, 2.82 6 0.45) and PET/MR (2.75 6 0.51; P 5 0.3095). Anatomic delineation and allocation of suggestive lesions was significantly superior with T1-weighted TSE MRI (mean rating, 2.84 6 0.42) compared with CT (2.57 6 0.54, P 5 0.0001) or T1-weighted VIBE Dixon MRI (2.57 6 0.54, P 5 0.0002). No significant difference in correct classification of malignant bone lesions was found among sets A (85/90), B (84/90), and C (86/90). For bone lesions and regions of normal bone, a highly significant correlation existed between the mean SUVs for PET/MR and PET/CT (R 5 0.950 and 0.917, respectively, each P , 0.001). However, substantially lower mean SUVs were found for PET/MR than for PET/CT both for bone lesions (12.4% 6 15.5%) and for regions of normal bone (30.1% 6 27.5%). Conclusion: Compared with PET/CT, fully integrated whole-body 18 F-FDG PET/MR is technically and clinically robust for evaluation of bone lesions despite differences in attenuation correction. PET/MR, including diagnostic T1-weighted TSE sequences, was superior to PET/CT for anatomic delineation and allocation of bone lesions. This finding might be of clinical relevance in selected cases-for example, primary bone tumors, early bone marrow infiltration, and tumors with low uptake on PET. Thus, a diagnostic T1-weighted TSE sequence is recommended as a routine protocol for oncologic PET/MR.