Comparative Performance of ¹⁸F-FDG PET/MRI and ¹⁸F-FDG PET/CT in Detection and Characterization of Pulmonary Lesions in 121 Oncologic Patients

Abstract

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...

PET/MRI: Where might it replace PET/CT?

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