Comprehensive assessment of knee joint synovitis at 7?T MRI using contrast-enhanced and non-enhanced sequences

摘要

Background: Seven T ultra-high field MRI systems have recently been approved for clinical use by the U.S. andEuropean regulatory agencies. These systems are now being used clinically and will likely be more widely availablein the near future. One of the applications of 7 T systems is musculoskeletal disease and particularly peripheralarthritis imaging. Since the introduction of potent anti-rheumatic therapies over the last two decades MRI hasgained increasing importance particularly for assessment of disease activity in early stages of several rheumaticdisorders. Commonly gadolinium-based contrast agents are used for assessment of synovitis. Due to potential sideeffectsof gadolinium non-enhanced techniques are desirable that enable visualization of inflammatory diseasemanifestations. The feasibility of 7 T MRI for evaluation of peripheral arthritis has not been shown up to now. Aim ofour study was to evaluate the feasibility of contrast-enhanced (CE) and non-enhanced MRI at 7 T for the assessmentof knee joint synovitis.Method: Seven T MRI was acquired for 10 patients with an established diagnosis of psoriatic or rheumatoid arthritis.The study pulse sequence protocol was comprised of a sagittal intermediate-weighted fat-suppressed (FS), axialfluid-attenuated inversion recovery (FLAIR) FS, sagittal 3D T1-weighted dynamic contrast enhanced (DCE) and anaxial static 2D T1-weighted FS contrast-enhanced sequence (T1-FS CE). Ordinal scoring on non-enhanced (Hoffaandeffusion-synovitis) and enhanced MRI (11-point synovitis score), and comparison of FLAIR-FS with static T1-FSCE MRI using semiquantitative (SQ) grading and volume assessment was performed. For inter- and intra-readerreliability assessment weighted kappa statistics for ordinal scores and intraclass correlation coefficients (ICC) forcontinuous variables were used.Results: The total length of study protocol was 15 min 38 s. Different amounts of synovitis were observed in allpatients (mild: n = 3; moderate: n = 5; severe: n = 2). Consistently, SQ assessment yielded significantly lowerperipatellar summed synovitis scores for the FLAIR-FS sequence compared to the CE T1-FS sequence (p 0.01).FLAIR-FS showed significantly lower peripatellar synovial volumes (p 0.01) compared to CE T1-FS imaging with anaverage percentage difference of 18.6 ± 9.5%. Inter- and intra-reader reliability for ordinal SQ scoring ranged from0.21 (inter-reader Hoffa-synovitis) to 1.00 (inter-reader effusion-synovitis). Inter- and intra-observer reliability of SQ3D-DCE parameters ranged from 0.86 to 0.99.Conclusions: Seven T FLAIR-FS ultra-high field MRI is a potential non-enhanced imaging method able to visualizesynovial inflammation with high conspicuity and holds promise for further application in research endeavors andclinical routine by trained readers.