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Ga-PSMA PET/CT appears to be a promising method for detecting RCC metastases. However, no additional diagnostic value in assessing the primary tumour was found.

The lower detection rate of 18 F-FDG PET/MRI than 18 F-FDG PET/CT regarding small lung nodules should be considered in the staging of malignant tumors. The purpose of this study was to evaluate the outcome of these small lung nodules missed by 18 F-FDG PET/MRI. Methods: Fifty-one oncologic patients (mean age ± SD, 56.6 ± 14.0 y; 29 women, 22 men; tumor stages, I [n 5 7], II [n 5 7], III [n 5 9], IV [n 5 28]) who underwent 18 F-FDG PET/CT and subsequent 18 F-FDG PET/MRI on the same day were retrospectively enrolled. Images were analyzed by 2 interpreters in random order and separate sessions with a minimum of 4 wk apart. A maximum of 10 lung nodules was identified for each patient on baseline imaging. The presence, size, and presence of focal tracer uptake was noted for each lung nodule detected on 18 F-FDG PET/CT and 18 F-FDG PET/MRI using a postcontrast T1-weighted 3-dimensional gradient echo volume-interpolated breath-hold examination sequence with fat suppression as morphologic dataset. Follow-up CT or 18 F-FDG PET/CT (mean time to follow-up, 11 mo; range, 3-35 mo) was used as a reference standard to define each missed nodule as benign or malignant based on changes in size and potential new tracer uptake. Nodule-to-nodule comparison between baseline and follow-up was performed using descriptive statistics. Results: Out of 134 lung nodules found on 18 F-FDG PET/CT, 18 F-FDG PET/MRI detected 92 nodules. Accordingly, 42 lung nodules (average size ± SD, 3.9 ± 1.3 mm; range, 2-7 mm) were missed by 18 F-FDG PET/MRI. None of the missed lung nodules presented with focal tracer uptake on baseline imaging or follow-up 18 F-FDG PET/CT. Thirty-three out of 42 missed lung nodules (78.6%) in 26 patients were rated benign, whereas 9 nodules (21.4%) in 4 patients were rated malignant. As a result, 1 patient required upstaging from tumor stage I to IV. Conclusion: Although most small lung nodules missed on 18 F-FDG PET/MRI were found to be benign, there was a relevant number of undetected metastases. However, in patients with advanced tumor stages the clinical impact remains controversial as upstaging is usually more relevant in lower stages.

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Our objective was to compare 18 F-FDG PET/MRI (performed using a contrast-enhanced T1-weighted fat-suppressed volume-interpolated breath-hold examination [VIBE]) with 18 F-FDG PET/CT for detecting and characterizing lung lesions in oncologic patients. Methods: In 121 oncologic patients with 241 lung lesions, PET/MRI was performed after PET/CT in a single-injection protocol (260 ± 58 MBq of 18 F-FDG). The detection rates were computed for MRI, the PET component of PET/CT, and the PET component of PET/MRI in relation to the CT component of PET/CT. Wilcoxon testing was used to assess differences in lesion contrast (4-point scale) and size between morphologic datasets and differences in image quality (4-point scale), SUV mean , SUV max , and characterization (benign/malignant) between PET/MRI and PET/CT. Correlation was determined using the Pearson coefficient (r) for SUV and size and the Spearman rank coefficient (ρ) for contrast. Results: The detection rates for MRI, the PET component of PET/CT, and the PET component of PET/MRI were 66.8%, 42.7%, and 42.3%, respectively. There was a strong correlation in size (r 5 0.98) and SUV (r 5 0.91) and a moderate correlation in contrast (ρ 5 0.48). Image quality was better for PET/CT than for PET/MRI (P , 0.001). Lesion measurements were smaller for MRI than for CT (P , 0.001). SUV max and SUV mean were significantly higher for PET/MRI than for PET/CT (P , 0.001 each). There was no significant difference in lesion contrast (P 5 0.11) or characterization (P 5 0.076). Conclusion: In the detection and characterization of lung lesions 10 mm or larger, 18 F-FDG PET/MRI and 18 F-FDG PET/CT perform comparably. Lesion size, SUV and characterization correlate strongly between the two modalities. However, the overall detection rate of PET/MRI remains inferior to that of PET/CT because of the limited ability of MRI to detect lesions smaller than 10 mm. Thus, thoracic staging with PET/MRI bears a risk of missing small lung metastases. Pul monary lesion detection and characterization play a key role in cancer staging, as the presence of lung metastases influences therapy regimens and patient survival (1-3). CT, offering high spatial resolution of pulmonary tissue, has been regarded as the reference standard for lung lesion detection (4,5). However, because morphologic CT-based criteria have a relatively low specificity for malignant versus benign character, there has been a need for a more robust diagnostic standard. Over the last decade, 18 F-FDG PET/CT has proven successful not only in detecting pulmonary lesions but also in discriminating benign from malignant findings, taking advantage of the accurate anatomic information from CT and the functional characterization from PET in a onestop-shop examination (6-8). Yet, a major drawback of 18 F-FDG PET/CT is the low sensitivity of the PET component in pulmonary lesions smaller than 10 mm, because of motion artifacts, partialvolume effects, and the limited spatial resolution of PET (9). MRI has played only a minor role in radiologic asses...