Water-Fat Separation for the Knee on a 50 mT Portable MRI Scanner

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• The Dixon method is a standard for fat suppression in MRI due to its robustness against magnetic field inhomogeneity and signal-to-noise ratio (SNR) preservation.
• Very-low-field (VLF) MRI (< 100 mT) is experiencing a resurgence, but water-fat separation techniques for VLF remain underexplored.
• Existing Dixon methods require adaptation for the unique challenges of VLF imaging.

Purpose of the Study:

• To develop and validate a modified two-point Dixon method for effective water-fat separation in VLF MRI.
• To assess the performance of this method on a portable 50 mT MRI scanner.
• To demonstrate the potential of VLF MRI for detailed anatomical imaging through water-fat separation.

Main Methods:

• A modified two-point Dixon method was implemented, incorporating T2* effects and prior information.
• Regional iterative phasor extraction (RIPE) was utilized to determine the error phasor.
• Least squares solutions were applied to calculate water and fat signal fractions using data from a homemade 50 mT portable MRI scanner with spin-echo and gradient-echo sequences.

Main Results:

• Phantom studies yielded accurate fat signal fractions (0.94 and 0.93).
• Knee imaging clearly distinguished cartilage, muscle, and fat tissues.
• Water-only images enhanced visualization of structures like cartilage, which are difficult to discern otherwise.

Conclusions:

• The modified Dixon method is feasible for water-fat separation at 50 mT.
• This represents the first reported instance of water-fat separation using a 50 mT portable MRI scanner.
• The findings support the utility of VLF MRI for advanced imaging applications.