Comparing the accuracy and reliability of detecting intensity of spinal inflammation on STIR sequence with ADC values in axial spondyloarthritis

Objective To compare the accuracy and reliability of detecting the intensity of spinal inflammation on short tau inversion recovery (STIR) with the apparent diffusion coefficient (ADC) values of the active MRI lesions in axial spondyloarthritis (axSpA). Materials and methods Fifty active lesions in STIR sequence of spinal MRI were identified. With reference to sites of active lesions in STIR, the corresponding region of interest (ROI) on ADC map was drawn to determine the maximum ADC (ADCmax), mean ADC (ADCmean), normalized maxium (nADCmax) and mean (nADCmean). Four independent readers scored the identified active lesions as “intense” or “non-intense” according to the SPARCC MRI index. They were compared to various ADC parameters for assessment of accuracy and reliability. Regression analyses were used to adjust potential factors that could affect ADC. Results Significant differences were found in ADCmax between “intense” and “non-intense” lesions scored by 3 of the 4 readers (1405.7±271.4 vs 1165.8±223.8, p=0.01; 1420.7±272.1 vs 1209.0±248.5, p=0.01; 1438.0±307.2 vs 1213.6±231.0, p=0.01). Only 1 reader could differentiate a difference in “intense” and “non-intense” lesions with respect to ADCmean (899.2±248.3 vs 711.0±222.6, p=0.01) and nADCmean (4.4±2.1 vs 3.4±1.4, p=0.05). Inter-reader agreements were slight to moderate (Kappa=0.07-0.45). Reliability substantially improved when only the lowest and highest 25th percentiles of ADC values were included (Kappa=0.17-0.75). Regression analyses showed the “intense” lesions were associated with higher ADC values after adjustment for confounders. Conclusion Reading of STIR MRI is limited by the lack of ability in differentiating subtle differences of spinal inflammation. ADC could be an alternative method.