Tissue-Specific T * 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 * relaxation times.

PURPOSE

1. To compare T * 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 * was quantified with monoexponential, fractional-order, and biexponential fitting. We applied two methods for T * 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 * (0-30% for mostly long T *, 30-60% for mixed T *, and 60-100% for mostly short T *).

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 * of 6.43 msec [4.32-8.55] and fractional order T * 4.39 msec [3.06-5.78]. The percentage of short T * components was 52.9% [35.5-69.6]. Subregional monoexponential T * 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 * 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 *, respectively. Biexponential component short T * was 1.693 msec [1.417-2.003] for tissue with mostly short T * and long T * of 15.79 msec [13.47-18.61] for mostly long T *. The average CR (CV) was 2 msec (15%), 2 msec (19%) and 10% (22%) for monoexponential, fractional order and percentage short T *, respectively.

DATA CONCLUSION

Patellar tendinopathy is characterized by regional variability in binding states of water. Quantitative multicompartment T * 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 J. Magn. Reson. Imaging 2020;52:420-430.