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

Abstract

BackgroundQuantitative MRI of patellar tendinopathy (PT) can be challenging due to spatial variation of T2* relaxation times.Purpose1) To compare T2* 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 TypeProspective.SubjectsSixty‐five athletes with PT.Field Strength/Sequence3D UTE scans covering the patellar tendon were acquired using a 3.0T scanner and a 16‐channel surface coil.AssessmentVoxelwise median T2* was quantified with monoexponential, fractional‐order, and biexponential fitting. We applied two methods for T2* 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 T2* (0–30% for mostly long T2*, 30–60% for mixed T2*, and 60–100% for mostly short T2*).Statistical TestsAverage test–retest reliability was assessed in three athletes using coefficients‐of‐variation (CV) and coefficients‐of‐repeatability (CR).ResultsWith standard image analysis, we found a median [interquartile range, IQR] monoexponential T2* of 6.43 msec [4.32–8.55] and fractional order T2* 4.39 msec [3.06–5.78]. The percentage of short T2* components was 52.9% [35.5–69.6]. Subregional monoexponential T2* 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 T2* 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 T2*, respectively. Biexponential component short T2* was 1.693 msec [1.417–2.003] for tissue with mostly short T2* and long T2* of 15.79 msec [13.47–18.61] for mostly long T2*. The average CR (CV) was 2 msec (15%), 2 msec (19%) and 10% (22%) for monoexponential, fractional order and percentage short T2*, respectively.Data ConclusionPatellar tendinopathy is characterized by regional variability in binding states of water. Quantitative multicompartment T2* analysis in PT can be facilitated using a voxel selection method based on using biexponential fitting parameters.Level of Evidence1Technical Efficacy Stage1 J. Magn. Reson. Imaging 2020;52:420–430.