Diffusion kurtosis imaging in sacroiliitis to evaluate the activity of ankylosing spondylitis

BACKGROUND: Conventional magnetic resonance (MR) imaging is limited in providing sufficient information on microstructure or in quantitatively evaluating certain inflammation processes. Functional MR sequences such as diffusion kurtosis imaging (DKI) might help to evaluate the sacroiliac joint in ankylosing spondylitis (AS) patients. PURPOSE: To explore the application of DKI in evaluating the disease activity of AS. STUDY TYPE: Prospective. POPULATION: Forty-four patients with a diagnosis of AS according to the Assessment in SpondyloArthritis International Society (ASAS) criteria. FIELD STRENGTH/SEQUENCE: 3.0T MRI including the DKI sequence (b = 0, 500, 1000, 1500, 2000 s/mm2 ). STATISTICAL TESTS: Two-independent-samples t-test and one-way analysis of variance (ANOVA) were used to compare the DKI parameters among different groups, and post-hoc Scheffe's method was adopted. Receiver operating characteristic (ROC) analysis and Spearman's rank correlation were performed to test the diagnostic performance of DKI parameters in distinguishing different activity grades and the correlation between them, respectively. ASSESSMENT: AS disease activity was evaluated according to the Ankylosing Spondylitis Disease Activity Score (ASDAS), and four disease activity states were chosen by consensus: inactive disease and moderate, high, and very high disease activity. The three cutoffs selected to separate these states were: 1.3, 2.1, and 3.5 units, respectively. RESULTS: The corrected ADC (D) and apparent diffusion coefficient (ADC) values of sacroiliac joints in the active group were significantly higher, while the the kurtosis of diffusion (K value) value was significantly lower than those of the inactive group (all P < 0.001). The D value performed best in distinguishing different activity grades (all P < 0.001). The D and ADC values correlated positively, while the K value correlated negatively, with activity grade significantly (r = 0.918, 0.798, and -0.765, respectively; all P < 0.001). DATA CONCLUSION: DKI of sacroiliac joints might be useful to evaluate the disease activity of AS. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:101-108.