Reliability and Repeatability of Diffusion Tensor Imaging in Healthy and Pathological Patellar Tendons

Patellar tendinopathy and bone-patellar tendon-bone autograft harvest for anterior cruciate ligament reconstruction are tendon injuries that impact long-term knee health. Diffusion tensor imaging (DTI) is a non-invasive magnetic resonance imaging (MRI) based approach with the potential to assess tendon microstructure. This study aimed to determine the inter-rater reliability of segmentations and test-retest repeatability of DTI metrics in pathological and contralateral patellar tendons. Ten participants received two bilateral knee MRI scans within a 7-day period. 3D CUBE proton density weighted images and DTI were acquired. Two raters segmented each of the first scans, and one rater segmented the second scans. Tendon masks were then bisected into proximal and distal regions of equal length and trisected into medial, lateral, and central regions of equal width. From the DTI acquisition, diffusivities and fractional anisotropy averages were extracted. Intraclass correlations (ICCs) for inter-rater reliability and test-retest repeatability were calculated for each metric separated by limb (pathological vs contralateral tendon). Excellent inter-rater reliability was observed for all DTI scalar metrics in all regions (ICCs from 0.920 to 0.994). Repeatability was poor to moderate in pathological tendons (0.164 to 0.709) and moderate to good in contralateral tendons (0.566 to 0.842). Statement of Clinical Significance: While clinical implications of altered DTI scalar metrics in pathological tendons require further investigation, findings from this study provide clinicians and researchers with a reliable method for capturing patellar tendon microstructure.