Quantitative MRI of visually intact rotator cuff muscles by multiecho Dixon-based fat quantification and diffusion tensor imaging.

Background: Quantitative MRI allows assessment of shoulder rotator cuff (RC) muscles by Dixon MR sequences with calculation of fractional fat content (FF%) maps and diffusion tensor imaging (DTI) including tractography.

Purpose: To compare FF% and DTI derived parameters among visually intact RC muscles, to compare 2D with 3D DTI measurements and to establish normative values.

Study Type: Prospective.

Subjects: Forty patients aged >18 years undergoing shoulder MR arthrography were included.

Field Strength/sequence: MR arthrography of the shoulder including 3D multiecho Dixon and 3D echo-planar DTI sequences (15 gradient encoding directions, b-value 600 s/mm ) was performed at 3.0T.

Assessment: Muscles affected by RC tears or fatty infiltration of Goutallier grade ≥1 were excluded. Two independent radiologists measured FF%, apparent diffusion coefficient (ADC), and fractional anisotropy (FA) by region-of-interest (ROI) placements at the Y-position of the scapula and 3D tractography of each muscle with qualitative evaluation was performed.

Statistical Tests: Intraclass correlation coefficients (ICCs) and Cohen's kappa were used for interreader agreement and Pearson correlation coefficient to correlate quantitative measures with each other and age, independent-samples t-test, one-way analysis of variance (ANOVA), and Kruskal-Wallis test were performed to investigate differences between genders and muscles.

Results: Qualitative and quantitative measurements showed moderate (κ = 0.41-0.56) to almost perfect (ICC = 0.75-0.99) agreement. There were weak but significant positive correlations of FF% with age (r = 0.273, P < 0.05) and FA-2D (r = 0.319-0.383, P < 0.05). Significant differences were found among RC muscles for ADC, radial diffusivity (RD), and tract homogeneity (all P < 0.05) but not between genders (all P ≥ 0.05). High correlations of 2D with 3D measurements for ADC (r = 0.639, P < 0.001) and FA (r = 0.628, P < 0.001) were seen.

Data Conclusion: Quantitative MRI with estimation of FF% and DTI parameters shows significant age-associated changes and differences among visually intact RC muscles. High reproducibility and correlations of 2D with 3D DTI measurements can be expected.

Level Of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:109-117.