Lung visualisation on PET/MRI: implementing a protocol with a short echo-time and low flip-angle volumetric interpolated breath-hold examination sequence

Aim: To assess the diagnostic performance in detecting lung lesions of a short echo-time (TE) and low flip-angle (FA) volumetric interpolated breath-hold examination (VIBE) sequence included in the integrated positron-emission tomography (PET)/magnetic resonance imaging (MRI) protocol.

Method and materials: Thirty-seven oncological patients who underwent computed tomography (CT) and PET/MRI, including both a dedicated short TE, low FA VIBE (modified VIBE) and a standard VIBE of the lung, were enrolled. Modified VIBE images were reviewed retrospectively and independently by three raters, to detect pulmonary nodules, parenchymal consolidation, and bands. Three other groups examined standard VIBE, PET, and CT images. MRI and PET findings were compared to CT using Krippendorff's alpha using patient-based and a lesion-based analysis. Krippendorff's alpha was calculated to assess the interobserver agreement among the three raters of the modified VIBE.

Results: In the patient-based analysis (positivity ≥1 lesion), the comparison of modified VIBE with CT showed an alpha of 0.54 for nodules <6 mm (versus 0.41 for standard VIBE and 0.09 for PET) and an alpha of 0.88 for nodules ≥6 mm (versus 0.74 for standard VIBE and 0.42 for PET). On a lesion-based analysis (presence/absence of each lesion), modified VIBE compared to CT showed an alpha of0.58 for nodules <6 mm (versus 0.44 for standard VIBE and 0.09 for PET) and an alpha of 0.90 for nodules ≥6 mm (versus 0.79 for standard VIBE and 0.50 for PET). The alpha value for the interobserver agreement was 0.90 for nodules <6 mm, 0.91 for nodules ≥6 mm, 1.00 for consolidations, and 0.95 for bands in the patient-based analysis and 0.89, 0.93, 1.00, and 0.95 in the lesion-based analysis.

Conclusions: Modified VIBE proved to be reproducible, showed better accuracy than standard VIBE and PET, and very good concordance with CT in assessing lung nodules ≥6 mm, whereas the agreement was less satisfactory for smaller nodules.