Background

Rotator cuff tendons (RCTs) are challenging to image due to the "magic angle effect" and their short T₂ .

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 T₂ measurements.

Study type

Prospective imaging pathologic correlation.

Specimen

Twenty cadaveric rotator cuff tendons were imaged at five sample orientations ranging from 0-90° relative to the B₀ field.

Field strength/sequence

3T/3D UTE-Cones-MT and Carr-Purcell-Meiboom-Gill (CPMG).

Assessment

Two-pool quantitative MT modeling parameters and T₂ 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 T₂ and macromolecular fractions between orientations were 26.14 ± 16.82% and 6.18 ± 2.77% (mean ± SD), respectively. T₂ measurements at 0°, 27°, 70°, and 90° showed significant differences between the two histological groups (P = 0.004, 0.008, 0.003, and 0.015, respectively), but not at 55° (P = 0.611). Mean T₂ 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 = 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 T₂ , 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 J. Magn. Reson. Imaging 2017.