Magnetization transfer saturation imaging of human calf muscle: Reproducibility and sensitivity to regional and sex differences

Abstract

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 T1s. 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;50:1227–1237.

On the fat saturation effect in quantitative ultrashort TE MR imaging

“…In our study, we found that, similar to what was seen with , T 1ρ values decreased when FatSat was used. Decreased MTR values were obtained from the FatSat UTE MRI sequence, similar to a human calf muscle study that used the MT saturation technique 32 . The MMF values increased when FatSat was applied in our study.…”

“…Decreased MTR values were obtained from the FatSat UTE MRI sequence, similar to a human calf muscle study that used the MT saturation technique. 32 The MMF values increased when FatSat was applied in our study. A simulation study was performed by Li K. et al to investigate the effect of different fat fractions on MMF calculation using a two-pool MT model.…”

A model‐based framework for correcting inhomogeneity effects in magnetization transfer saturation and inhomogeneous magnetization transfer saturation maps

“…11 The results from the empirical factor and the proposed model-based correction were very similar in the +2 kHz protocol, despite a change in MT-pulse duration from 4 ms to 12 ms. The empirical correction factor as presented in Equation ( 1) has been used in other work in the brain, 14 and in muscle, 13 although using slightly different imaging parameters. While the present study found good agreement between the model-based and empirical correction methods with minimal changes to the saturation protocol, it would be of interest to see if the correction factor differs significantly as Δf shifts closer to zero.…”

“…12 Equation 1 was derived for a specific imaging protocol, 11 and while it can be adapted to different protocols by collecting data at multiple saturation levels, 10 it has been applied as is to data collected using various saturation parameters. 13,14 Calculating the empirical factor requires an MR sequence with an adjustable saturation pulse flip angle, which may not be available on all scanners. The empirical correction accounts for all remnant ΔB + 1 effects in MT sat maps arising from saturation and excitation pulses.…”

Rotator cuff muscle fibrosis can be assessed using ultrashort echo time magnetization transfer MRI with fat suppression

“…[8][9][10][11][12] Magnetization transfer (MT) measures, which provide information on the macromolecular and free water pools, have also been used on muscles. [13][14][15][16][17][18][19] However, the specificity of the MT measurements is unclear because some have shown significant correlations with intramuscular fat 19 and others have shown significant correlations with protein concentrations. 15 Fat suppression (FS) techniques have been suggested by some authors to disambiguate measurements of the macromolecular pool in the presence of fatty infiltration.…”