Magnetization Transfer Saturation Imaging of Human Calf Muscle: Reproducibility and Sensitivity to Regional and Sex Differences.

BACKGROUND: Magnetization transfer saturation (MTsat ) derives a semiquantitative index of magnetization transfer in faster acquisition times than quantitative magnetization transfer; the potential of MTsat for muscle imaging has not yet been explored.

PURPOSE: To evaluate the potential of MTsat to identify regional and sex differences in calf muscle.

STUDY TYPE: Prospective cohort study.

PHANTOM/SUBJECTS: Vials with different agar and nickel nitrate concentrations providing a range of macromolecular fraction and T1 . Seven male subjects (25 ± 7 years) and seven female subjects (28 ± 14 years); three subjects were scanned in three separate sessions to assess reproducibility.

FIELD STRENGTH/SEQUENCE: 3T, 3D fast low angle shot (FLASH) sequence with and without a magnetization transfer pulse; acquisition time of 4.12 minutes.

ASSESSMENT: The effectiveness of two methods of fat suppression was evaluated using the fat unsuppressed sequence as the reference and MTsat maps derived with and without transmit field inhomogeneity corrections were compared. Statistical evaluation of MTsat differences between calf muscles and between male and female cohorts was made.

STATISTICAL TESTS: Bland-Altman plots were used to assess fat suppression and B1+ correction. The coefficient of variation (CV) and the repeatability coefficient (RC) were calculated from the repeat sessions. Sex and regional differences were assessed using two-way factorial analyses of variance (ANOVAs) with Bonferroni-adjusted independent sample t-tests for post-hoc analyses.

RESULTS: In phantoms, MTsat increased linearly with agar concentration and MTsat was independent of T1 (P = 0.229) evaluated in phantoms with two T1 s. The CV and RC of MTsat ranged between 2.65 to 5.03% and 0.13 to 0.38, respectively, in the different calf muscles. MTsat of the tibialis anterior was significantly higher than other muscles (P < 0.05). MTsat in male subjects was significantly higher than in female subjects (P = 0.009).

DATA CONCLUSION: MTsat maps of calf muscle acquired under 5 minutes may have the potential to detect regional and sex differences.

LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019.