Rotator cuff tendon assessment using magic‐angle insensitive 3D ultrashort echo time cones magnetization transfer (UTE‐Cones‐MT) imaging and modeling with histological correlation

Abstract

Background: Rotator cuff tendons (RCTs) are challenging to image due to the "magic angle effect" and their short T 2 . Purpose: To assess the degree of magic angle sensitivity of human RCTs and to utilize a 3D ultrashort echo time Cones sequence with magnetization transfer preparation (UTE-Cones-MT) and two-pool quantitative MT modeling with histological correlation. We hypothesized that MT parameters would be less sensitive to the magic angle compared with conventional T 2 measurements. Study Type: Prospective imaging pathologic correlation. Specimen: Twenty cadaveric rotator cuff tendons were imaged at five sample orientations ranging from 0-908 relative to the B 0 field. Field Strength/Sequence: 3T/3D UTE-Cones-MT and Carr-Purcell-Meiboom-Gill (CPMG). Assessment: Two-pool quantitative MT modeling parameters and T 2 values were calculated in regions of interest drawn by a medical physicist. Histopathological analysis was performed and mild and severe tendinopathy groups were assigned by a histopathologist and histotechnician. Statistical Tests: Coefficients of variations (CVs) were calculated for measures between the different orientations and group means were compared for each measure. Results: CVs of T 2 and macromolecular fractions between orientations were 26.14 6 16.82% and 6.18 6 2.77% (mean 6 SD), respectively. T 2 measurements at 08, 278, 708, and 908 showed significant differences between the two histological groups (P 5 0.004, 0.008, 0.003, and 0.015, respectively), but not at 558 (P 5 0.611). Mean T 2 value ranges between orientations for the mild and severe tendinopathy groups were 15.27-30.32 msec and 20.81-35.85 msec, respectively, showing overlap despite statistically significant differences (P 5 0.003). Macromolecular fractions at all angles showed significant differences between the two groups (P < 0.0001). Mean fraction ranges between orientations for the mild and severe tendinopathy groups were 14.32-17.17% and 10.00-13.75% respectively (P < 0.0001) with no overlap. Data Conclusion: Compared with T 2 , macromolecular fraction obtained with the 3D UTE-Cones-MT technique is resistant to the magic angle effect and is more sensitive to RCT degeneration. Level of Evidence: 1 Technical Efficacy: Stage 2

Age-related decrease in collagen proton fraction in tibial tendons estimated by magnetization transfer modeling of ultrashort echo time magnetic resonance imaging (UTE-MRI)

“…Magnetization transfer (MT) modeling combined with UTE-MRI has recently been used to indirectly measure the macromolecular protons fraction (MMF) in different tissues 20,21,23–28 . Interestingly, two-pool UTE-MT modeling has demonstrated promise as a clinically compatible quantitative technique that is resistant to the magic angle effect 20,21 .…”

“…Magnetization transfer (MT) modeling combined with UTE-MRI has recently been used to indirectly measure the macromolecular protons fraction (MMF) in different tissues 20,21,23–28 . Interestingly, two-pool UTE-MT modeling has demonstrated promise as a clinically compatible quantitative technique that is resistant to the magic angle effect 20,21 . Specifically, UTE-MT modeling has been recently implemented on cadaveric Achilles and rotator cuff tendons in order to assess MMF, and showed roughly no orientation angle sensitivity 20,21 .…”

“…Interestingly, two-pool UTE-MT modeling has demonstrated promise as a clinically compatible quantitative technique that is resistant to the magic angle effect 20,21 . Specifically, UTE-MT modeling has been recently implemented on cadaveric Achilles and rotator cuff tendons in order to assess MMF, and showed roughly no orientation angle sensitivity 20,21 . UTE-MT modeling relies on the phenomenon of magnetization transfer to quantify protons, including directly detected water protons (both free and restricted) and indirectly detected macromolecular protons, which possess T2* values too short for direct imaging, even with UTE sequences.…”

“…UTE-MT modeling relies on the phenomenon of magnetization transfer to quantify protons, including directly detected water protons (both free and restricted) and indirectly detected macromolecular protons, which possess T2* values too short for direct imaging, even with UTE sequences. This technique provides multiple parameters, including MMF, macromolecular relaxation time (T2 MM ), and exchange rates 20,21 .…”

Quantitative MRI Musculoskeletal Techniques: An Update

“…Recent studies using the UTE MT technique on rotator cuff tendons have shown promising results that are much less sensitive to magic angle effects compared with transverse relaxation times [103,104] (Fig. 6).…”