Detection of tiny oscillatory magnetic fields using low-field MRI: A combined phantom and simulation study

Area of Science:

• Medical Imaging
• Biophysics

Background:

• Blood-oxygen-level-dependent (BOLD) effects can interfere with low-field magnetic resonance (MR) imaging.
• Spin-lock preparation sequences offer a potential method to mitigate BOLD interference.

Purpose of the Study:

• To demonstrate the feasibility of spin-lock preparation sequences in low-field MR imaging.
• To analyze magnetization dynamics and validate experimental findings with theoretical models.

Main Methods:

• Utilized two spin-lock preparations: spin-lock Mz (SL-Mz) and stimulus-induced rotary saturation (SIRS).
• Analyzed magnetization dynamics using the Bloch equation.
• Conducted phantom experiments with a loop coil to assess MR signal changes.
• Performed curve fittings to account for radio frequency effects.

Main Results:

• Experimental results showed good agreement with Bloch equation predictions.
• Investigated the relationship between MR signal change, target signal strength, and phase.
• The SL-Mz sequence successfully detected a magnetic field signal strength of 2.34 nT.

Conclusions:

• Spin-lock preparation sequences are feasible for low-field MR imaging, effectively preventing BOLD interference.
• The study validates the use of the Bloch equation for analyzing spin-lock sequence dynamics.
• Demonstrated the sensitivity of SL-Mz in detecting low magnetic field strengths.