Ultra-low-field magnetization transfer imaging at 0.055T with low specific absorption rate

Area of Science:

• Magnetic Resonance Imaging
• Biophysics
• Medical Physics

Background:

• Magnetization transfer (MT) imaging is crucial for enhancing tissue contrast in MRI.
• Conventional MT techniques often require high specific absorption rate (SAR), limiting their application, especially on ultra-low-field (ULF) systems.
• ULF MRI offers cost-effectiveness and portability but faces challenges with B0 homogeneity.

Purpose of the Study:

• To demonstrate effective Magnetization Transfer (MT) effects using low specific absorption rate (SAR) on ultra-low-field (ULF) MRI.
• To validate the feasibility of MT imaging on a shielding-free 0.055T ULF head scanner.
• To assess the impact of MT preparation on brain tissue contrast and lesion detection.

Main Methods:

• Implementation of MT imaging using sinc-modulated RF pulse train (SPT) modules for off-resonance irradiation.
• Integration of SPT modules into 3D gradient echo (GRE) and fast spin echo (FSE) protocols on a 0.055T ULF MRI scanner.
• Verification of MT effects in phantoms and subsequent brain imaging in healthy subjects and patients.

Main Results:

• Clear MT effects observed in phantoms and brain tissues (gray matter, white matter, muscle) with low SAR (0.0024 and 0.0008 W/kg).
• MT preparation significantly enhanced tissue contrasts in T2-weighted and FLAIR-like images.
• Improved delineation of brain lesions was achieved with MT preparation.
• Fat, CSF, and blood showed weaker MT effects.

Conclusions:

• Robust MT effects are achievable at ULF MRI with extremely low SAR, overcoming B0 inhomogeneity challenges.
• Flexible MT pulse design is enabled on low-cost ULF MRI platforms.
• This technique holds potential for augmenting the clinical utility of ULF MRI for brain imaging and beyond.