Objective Hybrid whole-body magnetic resonance/positron emission tomography (MR/PET) systems are a new diagnostic tool enabling the simultaneous acquisition of morphologic and multiple functional data and thus allowing for a diversified characterization of oncological diseases. The aim of this study was to investigate the image and alignment quality of MR/PET in patients with pulmonary lesions and to compare the congruency of the 2 functional measurements of diffusion-weighted imaging (DWI) in MR imaging and 2-deoxy-[18F] fluoro-2-D-glucose (FDG) uptake in PET. Materials and Methods A total of 15 patients were examined with a routine positron emission tomography/computer tomography (PET/CT) protocol and, subsequently, in a whole-body MR/PET scanner allowing for simultaneous PET and MR data acquisition. The PET and MR image quality was assessed visually using a 4-point score (1, insufficient; 4, excellent). The alignment quality of the rigidly registered PET/CT and MR/PET data sets was investigated on the basis of multiple anatomic landmarks of the lung using a scoring system from 1 (no alignment) to 4 (very good alignment). In addition, the alignment quality of the tumor lesions in PET/CT and MR/PET as well as for retrospective fusion of PET from PET/CT and MR images was assessed quantitatively and was compared between lesions strongly or less influenced by respiratory motion. The correlation of the simultaneously acquired DWI and FDG uptake in the pulmonary masses was analyzed using the minimum and mean apparent diffusion coefficient (ADC_min and ADC_mean) as well as the maximum and mean standardized uptake value (SUV_max and SUV_mean), respectively. In addition, the correlation of SUV_max from PET/CT data was investigated as well. On lesions 3 cm or greater, a voxelwise analysis of ADC and SUV was performed. Results The visual evaluation revealed excellent image quality of the PET images (mean [SD] score, 3.6 [0.5]) and overall good image quality of DWI (mean [SD] score of 2.5 [0.5] for ADC maps and 2.7 [0.5] for diffusion-weighted images, respectively). The alignment quality of the data sets was very good in both MR/PET and PET/CT without significant differences (overall mean [SD] score of MR/PET, 3.8 [0.4]; PET/CT 3.6 [0.5]). Also, the alignment quality of the tumor lesions showed no significant differences between PET/CT and MR/PET (mean cumulative misalignment of MR/PET, 7.7 mm; PET/CT, 7.0 mm; P = 0.705) but between both modalities and a retrospective fusion (mean cumulative misalignment, 17.1 mm; P = 0.002 and P = 0.008 for PET/CT and MR/PET, respectively). Also, the comparison of the lesions strongly or less influenced by respiratory motion showed significant differences only for the retrospective fusion (21.3 mm vs 11.5 mm, respectively; P = 0.043). The ADC_min and SUV_max as measures of the cell density and glucose metabolism showed a significant reverse correlation (r = −0.80; P = 0.0006). No significant correlation was found between ADC_mean and SUV_mean (r = −0.42; P = 0.1392). Also, SUV_max from the PET/CT data showed significant reverse correlation to ADC_min (r = −0.62; P = 0.019). The voxelwise analysis of 5 pulmonary lesions each showed weak but significant negative correlation between ADC and SUV. Conclusions Examinations of pulmonary lesions in a simultaneous whole-body MR/PET system provide diagnostic image quality in both modalities. Although DWI and FDG-PET reflect different tissue properties, there may very well be an association between the measures of both methods most probably because of increased cellularity and glucose metabolism of FDG-avid pulmonary lesions. A voxelwise DWI and FDG-PET correlation might provide a more sophisticated spatial characterization of pulmonary lesions.

Multiparametric PET-MRI with the amino-acid analog ¹⁸F-FET enables the simultaneous assessment of molecular, morphologic, and functional brain tumor characteristics. Although it is considered the most accurate non-invasive approach in brain tumors, its relevance for patient management is still under debate. Here we report the diagnostic performance of ¹⁸F-FET PET/MR and its impact on clinical management in a retrospective patient cohort. Methods: We retrospectively analyzed brain tumor patients who underwent ¹⁸F-FET PET/MR between 2017 and 2018. ¹⁸F-FET PET/MR examinations were indicated clinically due to equivocal standard imaging or clinical course. Histological confirmation or clinical and standard imaging follow-up served as the reference standard. We evaluated ¹⁸F-FET PET/MR accuracy in identifying malignancy in untreated suspect lesions (category new diagnosis) and true progression during adjuvant treatment (category detection of progression) in a clinical setting. Using multiple regression, we also estimated the contribution of single modalities to produce an optimal PET/MRI outcome. We assessed the recommended and applied therapies before and after ¹⁸F-FET PET/MR and noted if the treatment changed based on the ¹⁸F-FET PET/MR outcome. Results: We included 189 cases in the study. ¹⁸F-FET PET/MR allowed the identification of malignancy at new diagnosis with an accuracy of 85% and identified true progression with an accuracy of 93%. Contrast enhancement, ¹⁸F-FET PET uptake, and tracer kinetics were the major contributors to an optimal PET/MR outcome. In the previously equivocal patients, ¹⁸F-FET PET/MR changed the clinical management in 33% of the untreated lesions and 53% of the tumor progressions. Conclusion: Our results suggest that ¹⁸F-FET PET/MR helps clarify equivocal conditions and profoundly supports brain tumor patients9 clinical management. The optimal modality setting of ¹⁸F-FET PET/MR and the clinical value of a simultaneous examination need further exploration. At a new diagnosis, multiparametric ¹⁸F-FET PET/MR might help prevent unnecessary invasive procedures by ruling out malignancy; however, adding static ¹⁸F-FET PET to an already existing MR examination seems to be of equal value. At detection of progression, multiparametric ¹⁸F-FET PET/MR may increase therapy effectiveness by distinguishing between tumor progression and therapy-related imaging alterations.