Parameter optimization for proton density fat fraction quantification in skeletal muscle tissue at 7 T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Radiology

Background:

• High-field MRI at 7 Tesla (7T) offers enhanced signal-to-noise ratio for improved tissue characterization.
• Accurate quantification of fat in muscle tissue is crucial for diagnosing and monitoring various metabolic and neuromuscular diseases.
• Proton density fat fraction (PDFF) is a reliable biomarker for assessing intramuscular adipose tissue.

Purpose of the Study:

• To develop and validate an optimized image acquisition and post-processing workflow for determining proton density fat fraction (PDFF) in calf muscle tissue at 7 Tesla (7T).
• To compare PDFF measurements at 7T with those obtained at 3T in both healthy individuals and patients with fatty muscle replacement.

Main Methods:

• Optimization of echo times (TEs) for a multi-echo gradient echo sequence at 7T, guided by simulations of the effective number of signal averages (NSA*).
• Validation of optimized parameters through phantom and in vivo measurements in healthy calf muscle (n=12).
• Evaluation of methods to mitigate phase errors at 7T, including phase demodulation with B0 mapping and TE shifting.

Main Results:

• Optimized TEs are critical for accurate fat-water separation at 7T, reducing fat-water swaps.
• Phase demodulation or longer TEs effectively addressed phase errors.
• PDFF values measured at 7T in calf muscles were comparable to those obtained at 3T in healthy subjects (n=9) and patients (n=3).

Conclusions:

• Proton density fat fraction (PDFF) determination in calf muscle tissue is feasible and accurate at 7T.
• The established chemical shift-based approach, with optimized acquisition and post-processing, provides reliable fat quantification at ultra-high field strengths.
• This workflow facilitates advanced musculoskeletal imaging and research applications at 7T.