MRI lesions in the sacroiliac joints of patients with spondyloarthritis: an update of definitions and validation by the ASAS MRI working group.

OBJECTIVES: The Assessment of SpondyloArthritis international Society (ASAS) MRI working group (WG) was convened to generate a consensus update on standardised definitions for MRI lesions in the sacroiliac joint (SIJ) of patients with spondyloarthritis (SpA), and to conduct preliminary validation. METHODS: The literature pertaining to these MRI lesion definitions was discussed at three meetings of the group. 25 investigators (20 rheumatologists, 5 radiologists) determined which definitions should be retained or required revision, and which required a new definition. Lesion definitions were assessed in a multi-reader validation exercise using 278 MRI scans from the ASAS classification cohort by global assessment (lesion present/absent) and detailed scoring (inflammation and structural). Reliability of detection of lesions was analysed using kappa statistics and the intraclass correlation coefficient (ICC). RESULTS: No revisions were made to the current ASAS definition of a positive SIJ MRI or definitions for subchondral inflammation and sclerosis. The following definitions were revised: capsulitis, enthesitis, fat lesion and erosion. New definitions were developed for joint space enhancement, joint space fluid, fat metaplasia in an erosion cavity, ankylosis and bone bud. The most frequently detected structural lesion, erosion, was detected almost as reliably as subchondral inflammation (κappa/ICC:0.61/0.54 and 0.60/0.83) . Fat metaplasia in an erosion cavity and ankylosis were also reliably detected despite their low frequency (κappa/ICC:0.50/0.37 and 0.58/0.97). CONCLUSION: The ASAS-MRI WG concluded that several definitions required revision and some new definitions were necessary. Multi-reader validation demonstrated substantial reliability for the most frequently detected lesions and comparable reliability between active and structural lesions.

Susceptibility-weighted MR imaging to improve the specificity of erosion detection: a prospective feasibility study in hand arthritis.

OBJECTIVE: To evaluate the diagnostic potential of susceptibility-weighted imaging (SWI) for the detection of erosions of the hand, compared to T1-weighted (T1w) magnetic resonance imaging (MRI). Computed tomography (CT) was used as a reference standard. MATERIALS AND METHODS: We prospectively investigated 37 patients with suspected arthritic activity of the hand. All patients underwent T1w, SWI, and CT on the same day. Patients were randomized to MRI or CT first. CT, T1w, SWI, and T1w/SWI were scored for erosions according to OMERACT RAMRIS guidelines. Specificity, sensitivity, and diagnostic accuracy were separately calculated for T1w, SWI, and T1w/SWI on a per-patient and per-bone basis using CT as reference. The one-tailed McNemar test was performed to test the number of erosion-positive patients in T1w, SWI, and T1w/SWI for non-inferiority. Measured erosion sizes were compared using Pearson's test. RESULTS: CT was positive for erosions in 16 patients and 55 bones. SWI and T1w/SWI had superior diagnostic accuracy (91.2 and 93.8%) compared to T1w (87.8%) driven by a higher specificity (93.8 and 96.5%) compared to T1w (88.8%). On the patient level, SWI and T1w/SWI showed non-inferiority (p = 0.11 and p = 0.38) but not T1w alone (p < 0.0001). The lesion size on CT correlated better with SWI (Pearson's r = 0.92) compared to T1w (r = 0.69). CONCLUSIONS: Adding SWI to a standard MRI protocol has the potential to improve erosion detection in hands by increasing specificity. SWI depicts bony erosions more accurately compared to standard MRI techniques.

Iterative Reconstruction May Improve Diagnosis of Gout: An Ex Vivo (Bio)Phantom Dual-Energy Computed Tomography Study.

OBJECTIVES: We hypothesize that, compared with filtered back projection (FBP), iterative reconstruction (IR) increases the detected volume of uric acid, which serves as a measure of the sensitivity of the method, and therefore allows examinations with lower radiation exposure. Thus, the aim of our study was to evaluate the role of IR in dual-energy computed tomography (DECT) for gout assessment and volumetry in an ex vivo gout model using an epoxy phantom and a biophantom. MATERIALS AND METHODS: We prepared specimens with different concentrations of monosodium uric acid in ultrasound gel (30%-50%) and inserted them into an epoxy-based phantom and a porcine foreleg. Computed tomography scanning was performed on a 320-row single-source DECT scanner in volume mode with an ascending order of tube currents. Image data sets were reconstructed using FBP and IR with 2 iteration levels (IR1 and IR2). Measurements in regions of interest (ROIs) and volumetric measurements were performed using either fixed parameters for the analysis software (epoxy phantom) or parameters specifically adapted for each data set (porcine phantom). Seven retrospectively identified clinical data sets were used for validation in patients. Rm-ANOVA was used for statistical analysis. No institutional review board approval was required. RESULTS: We found no differences in Hounsfield units between the different reconstruction algorithms (P = 0.09 and 0.05 for 80 and 135 kVp, respectively) and the calculated dual-energy gradient (P = 0.27). Filtered back projection detected less uric acid compared with IR (with fixed parameters: 6.0 ± 0.3 cm for FBP and 6.1 ± 0.2 for IR1 and IR2; with adapted thresholds: 1.2 ± 0.3 cm for FBP and 1.8 ± 0.1 and 2.0 ± 0.1 for IR1 and IR2, respectively). The differences were significant for all measurements (P = 0.0003). Also in the test cases, FBP detected significantly fewer tophi (mean volume, 1.38 ± 2.1 cm) compared with IR1 (1.86 ± 2.9) and IR2 (2.07 ± 3.1) (P = 0.04). CONCLUSIONS: Iterative reconstruction has the potential to improve the sensitivity of a DECT scan for gouty tophi, to decrease radiation exposure, or to combine both options.