Ultra-high field magnetic resonance imaging of the quadriceps tendon enthesis in healthy subjects

Purpose Although enthesitis is a hallmark of several rheumatologic conditions, current imaging methods are still unable to characterize entheses changes because of the corresponding short transverse relaxation times ( T 2). A growing number of MR studies have used Ultra-High Field (UHF) MRI in order to assess low- T 2 tissues e.g., tendon but never in humans. The purpose of the present study was to assess in vivo the enthesis of the quadriceps tendon in healthy subjects using UHF MRI. Methods Eleven healthy subjects volunteered in an osteoarthritis imaging study. The inclusion criteria were: no knee trauma, Lequesne index = 0, less than 3 h of sport activities per week, and Kellgren and Lawrence grade = 0. 3D MR images were acquired at 7 T using GRE sequences and a T 2* mapping. Regions of interest i.e., trabecular bone, subchondral bone, enthesis, and tendon body were identified, and T 2* values were quantified and compared. Results Quadriceps tendon enthesis was visible as a hyper-intense signal. The largest and the lowest T 2* values were quantified in the subchondral bone region and the tendon body respectively. T 2* value within subchondral bone was significantly higher than T 2* value within the enthesis. T 2* in subchondral bone region was significantly higher than the whole tendon body T 2*. Conclusion A T 2* gradient was observed along the axis from the enthesis toward the tendon body. It illustrates different water biophysical properties. These results provide normative values which could be used in the field of inflammatory rheumatologic diseases and mechanical disorders affecting the tendon.