Diffusion-weighted magnetic resonance imaging in differentiating acute infectious spondylitis from degenerative Modic type 1 change; the role of b-value, apparent diffusion coefficient, claw sign and amorphous increased signal.

Objective: To examine the effect of using different b-values on the utility of diffusion-weighted (DW) MRI in differentiating acute infectious spondylitis from Modic type 1 and the discriminative accuracy of related apparent diffusion coefficient (ADC), claw-sign and amorphous increased signal. Methods: 43 patients with equivocal diagnosis of acute infectious spondylitis/Modic type 1 by using MR images were prospectively studied. The discriminative accuracy of DWMRI using three b-values of 50, 400, 800s mm(-2), ADC, claw sign and amorphous increased signal was examined. Results: DW MRI differentiated infectious spondylitis from Modic type 1 change most accurately when a b-value of 800s mm(-2) was chosen [sensitivity, 91.7%; specificity, 96.8%; positive-predictive value (PPV), 91.7%; negative-predictive value (NPV), 96.8%; and accuracy, 95.3%]. The optimal cut-off ADC value was 1.5231023 mm(-2) s(-1) (sensitivity, 91.7%; specificity, 100%; PPV, 100%; NPV, 96.9%; and accuracy, 97.7%). Best visualized at a b-value of 50s mm(-2), claw sign (for degeneration) and amorphous increased signal (for infection) were 100% accurate. Conclusion: Should DW MRI be used in differentiating acute infectious spondylitis from degeneration, large b-values are required. With low b-values, however, claw sign and amorphous increased signal are very accurate in this regard. Advances in knowledge: DW MRI using large b-values could be used in differentiating acute infectious spondylitis from Modic type I.