Tissue-Specific T2* Biomarkers in Patellar Tendinopathy by Subregional Quantification Using 3D Ultrashort Echo Time MRI

Background Quantitative MRI of patellar tendinopathy (PT) can be challenging due to spatial variation of T-2* relaxation times. Purpose 1) To compare T-2* quantification using a standard approach with analysis in specific tissue compartments of the patellar tendon. 2) To evaluate test-retest reliability of different methods for fitting ultrashort echo time (UTE)-relaxometry data. Study Type Prospective. Subjects Sixty-five athletes with PT. Field Strength/Sequence 3D UTE scans covering the patellar tendon were acquired using a 3.0T scanner and a 16-channel surface coil. Assessment Voxelwise median T-2* was quantified with monoexponential, fractional-order, and biexponential fitting. We applied two methods for T-2* analysis: first, a standard approach by analyzing all voxels covering the proximal patellar tendon. Second, within subregions of the patellar tendon, by using thresholds on biexponential fitting parameter percentage short T-2* (0-30% for mostly long T-2*, 30-60% for mixed T-2*, and 60-100% for mostly short T-2*). Statistical Tests Average test-retest reliability was assessed in three athletes using coefficients-of-variation (CV) and coefficients-of-repeatability (CR). Results With standard image analysis, we found a median [interquartile range, IQR] monoexponential T-2* of 6.43 msec [4.32-8.55] and fractional order T-2* 4.39 msec [3.06-5.78]. The percentage of short T-2* components was 52.9% [35.5-69.6]. Subregional monoexponential T-2* was 13.78 msec [12.11-16.46], 7.65 msec [6.49-8.61], and 3.05 msec [2.52-3.60] and fractional order T-2* 11.82 msec [10.09-14.44], 5.14 msec [4.25-5.96], and 2.19 msec [1.82-2.64] for 0-30%, 30-60%, and 60-100% short T-2*, respectively. Biexponential component short T-2* was 1.693 msec [1.417-2.003] for tissue with mostly short T-2* and long T-2* of 15.79 msec [13.47-18.61] for mostly long T-2*. The average CR (CV) was 2 msec (15%), 2 msec (19%) and 10% (22%) for monoexponential, fractional order and percentage short T-2*, respectively. Data Conclusion Patellar tendinopathy is characterized by regional variability in binding states of water. Quantitative multicompartment T-2* analysis in PT can be facilitated using a voxel selection method based on using biexponential fitting parameters. Level of Evidence 1 Technical Efficacy Stage 1