Diagnostic Accuracy of a Fluid-attenuated Inversion-Recovery Sequence with Fat Suppression for Assessment of Peripatellar Synovitis: Preliminary Results and Comparison with Contrast-enhanced MR Imaging

Purpose To determine the agreement of fat-suppressed (FS) fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging and contrast material-enhanced (CE) T1-weighted MR imaging for the assessment of peripatellar synovitis. Materials and Methods The institutional review board approved this retrospective study and waived the requirement for patient informed consent. Thirty-three patients with knee pain underwent 3-T MR imaging. The protocol consisted of routine clinical sequences followed by the FLAIR FS sequence (inversion time, 2200 msec) and CE T1-weighted imaging. Visibility of the synovium, synovial thickness, and severity of synovitis in five peripatellar regions were assessed with both sequences. Hoffa synovitis on unenhanced MR images was also analyzed. Then, correlations and agreements between FLAIR FS and CE T1-weighted imaging were evaluated. Diagnostic performance statistics of FLAIR FS and Hoffa synovitis were calculated by using CE T1-weighted imaging as the reference standard. Results Peripatellar synovitis on FLAIR FS images was found in 14 patients by reader 1 and in 17 patients by reader 2. Strong correlations were found between FLAIR FS and CE T1-weighted imaging in the assessment of peripatellar synovitis by both readers (correlation coefficient, 0.675-0.973). With CE T1-weighted imaging as the reference standard, FLAIR FS showed relatively good diagnostic performance for the detection of synovitis of any severity (accuracy of 92.1%-93.9% at the site level and 90.9% at the patient level), while Hoffa synovitis on unenhanced MR images showed moderate sensitivity (78.9%-87.5%) and low specificity (47.1%-64.3%) for the detection of peripatellar synovitis. There was good agreement between the two readers for the synovial visibility (weighted κ = 0.81-0.88) and synovitis assessments (intraclass correlation coefficient = 0.95, weighted κ = 0.72-0.79) on FLAIR FS and CE T1-weighted images. Conclusion Our preliminary study shows that FLAIR FS imaging can potentially enable evaluation of inflamed synovium with high sensitivity and specificity, without the injection of a contrast agent.