Improved Performance of Compartments in Detecting the Activity of Axial Spondyloarthritis Based on IVIM DWI with Optimized Threshold b Value

Abstract

Purpose. To explore the diagnostic performance of the optimized threshold $b$ values on IVIM to detect the activity in axial spondyloarthritis (axSpA) patients. Method. 40 axSpA patients in the active group, 144 axSpA patients in the inactive group, and 20 healthy volunteers were used to evaluate the tissue diffusion coefficient ( $D_{\text{slow}}$ ), perfusion fraction ( $f$ ), and pseudodiffusion coefficient ( $D_{\text{fast}}$ ) with $b$ thresholds of 10, 20, and 30 s/mm2. The Kruskal-Wallis test and one way ANOVA test was used to compare the different activity among the three groups in axSpA patients, and receiver operating characteristic (ROC) curve analysis was applied to evaluate the performance for $D_{\text{slow}}$ , $f$ , and $D_{\text{fast}}$ to detect the activity in axSpA patients, respectively. Results. $D_{\text{slow}}$ demonstrated a statistical difference between two groups ( $P<0.05$ ) with all threshold $b$ values. With the threshold b value of 30 s/mm2, $f$ could discriminate the active from control groups ( $P<0.05$ ). $D_{\text{slow}}$ had similar performance between the active and the inactive groups with threshold $b$ values of 10, 20, and 30 s/mm2 (AUC: 0.877, 0.882, and 0.881, respectively, all $P<0.017$ ). Using the optimized threshold $b$ value of 30 s/mm2, $f$ showed the best performance to separate the active from the inactive and the control groups with AUC of 0.613 and 0.738 (both $P<0.017$ ) among all threshold $b$ values. Conclusion. $D_{\text{slow}}$ and $f$ exhibited increased diagnostic performance using the optimized threshold $b$ value of 30 s/mm2 compared with 10 and 20 s/mm2, whereas $D_{\text{fast}}$ did not.