Quantitative muscle water T2 mapping using RF phase-modulated 3D gradient echo imaging | JoVE Visualize

Area of Science:

Magnetic Resonance Imaging
Biomedical Engineering
Musculoskeletal Imaging

Background:

Water T2 relaxation time is a crucial biomarker for skeletal muscle tissue characterization.
Accurate T2 estimation is challenging in skeletal muscles due to motion and B1 field inhomogeneities.
Existing methods often lack the speed and robustness required for in vivo applications.

Purpose of the Study:

To develop and validate a motion-robust 3D magnetic resonance imaging (MRI) sequence for accurate water T2 estimation in skeletal muscles.
To assess the sequence's performance in phantoms and in vivo, including its ability to account for confounding factors like B1 variations and fat content.

Main Methods:

A partially spoiled gradient echo (pSPGR) sequence was employed, acquiring 10 image volumes with varied RF phase-cycling and flip angles.
A bi-component water/fat model was used to fit the complex signal evolution, extracting T2 values while correcting for B1 and fat fraction.
The sequence was implemented in both Cartesian and radial trajectories, with validation through numerical simulations, phantom studies, and in vivo experiments on thigh and tongue muscles.

Main Results:

Phantom studies showed high correlation (R² > 0.8) between the proposed method and reference spectroscopy/multi-spin echo techniques.
In vivo, T2 values correlated well with reference methods in healthy (R² = 0.69) and pathological muscles (R² = 0.87), demonstrating robustness to B1 inhomogeneities (R² = 0.06).
The radial implementation significantly reduced the standard deviation of T2 values in the tongue muscle by 28% compared to the Cartesian approach.

Conclusions:

The proposed 3D sequence enables efficient and accurate water T2 estimation in skeletal muscles, including small, moving structures like the tongue.
This technique expands the potential for characterizing heterogeneous muscle impairments.
The method's compatibility with clinical research durations makes it a valuable tool for muscle tissue assessment.