The rotator cuff tendon (RCT) is the primary dynamic stabilizer of the glenohumeral joint. However magic angle effect decrease the sensitivity of MRI in assessment of RCT. The purpose of our study is to utilize the 3D ultrashort echo time Cones sequence with magnetization transfer preparation (UTE-Cones-MT) and two-pool quantitative MT modeling to assess the RCT.
The rotator cuff tendon (RCT) is the primary dynamic stabilizer of the glenohumeral joint. RCT dysfunction can lead to abnormal joint kinematics through loss of force couples, deterioration of shoulder function, and ultimately cartilage degeneration and cuff arthropathy. Magnetic resonance imaging (MRI) is widely considered as the gold standard for evaluation of the RCT. Although high accuracy has been shown for the assessment of tearing, conventional MRI demonstrates a low sensitivity of 13-50% for RCT tendinopathy compared with surgical findings with exceedingly poor interobserver reliability1. A major confounding factor for the assessment of tendon is the magic angle effect. Unlike other tendons, such as the Achilles, which have a more constant orientation in clinical imaging scenarios, the RCT orientation is varied and always courses through the magic angle. Such large signal intensity changes may exceed those produced by disease. Recently the ultrashort echo time magnetization transfer(UTE-MT) technique with two-pool modeling has shown promise as a clinically compatible quantitative technique which is resistant to the magic angle effect2. However, to date, evaluation has only been performed using 2D UTE sequences on Achilles tendons. The purpose of our study is to utilize the 3D ultrashort echo time Cones sequence with magnetization transfer preparation (UTE-Cones-MT) and two-pool quantitative MT modeling to assess the RCT.
Figure 2 shows the results of both UTE-MT modeling and multiple-TE T2 fitting for a selected sample. The measured T1 value of this sample was 648 ms. The results for the five angle orientations between fiber direction and B0 are shown in the different rows. The two-pool UTE-MT modeling provides excellent fitting (all residuals were less than 0.6%) of signal changes over five MT powers and five off-resonance frequencies. Figure 3 shows graphs of the T2 values derived by fitting multiple-TE data and macromolecular proton fractions in a selected sample. Using the CPMG sequence, T2 ranged from 16.6 ms to 45.4 ms at 0° to 55° relative to B0, representing a 173% increase. However, macromolecular fraction remains relatively consistent ranging from 19.5 to 21.7%, representing an 11% difference. Several other UTE-MT modeling parameters, including T2 value of macromolecular protons (T2m) and exchange rate from macromolecular protons to water protons (RM0w) also demonstrated minimal angular dependence(Table 1). These results suggest that f, T2m and RM0w can be used as magic angle insensitive biomarkers of the RCT.
[1] Robertson PL, Schweitzer ME, Mitchell DG, Schlesinger F, Epstein RE, Frieman BG, Fenlin JM. Rotator cuff disorders: interobserver and intraobserver variation in diagnosis with MR imaging. Radiology. 1995;194(3):831-5
[2] Ma YJ, Shao H, Du J, Chang EY. Ultrashort echo time magnetization transfer (UTE-MT) imaging and modeling: magic angle independent biomarkers of tissue properties. NMR Biomed. 2016 Nov;29(11):1546-1552.