Efficient imaging using spiral acquisitions on a portable 50-mT MR head scanner

Area of Science:

• Medical Imaging
• Biophysics
• Electrical Engineering

Background:

• Ultralow-field (ULF) magnetic resonance imaging (MRI) systems offer portability but face challenges with low signal-to-noise ratio (SNR), leading to inferior image quality.
• Spiral acquisition techniques show promise for efficient k-space coverage and improved SNR efficiency in ULF MRI.
• Addressing noise and blurring is critical for enhancing ULF MRI diagnostic capabilities.

Purpose of the Study:

• To develop and evaluate a spiral-out MRI sequence for brain imaging on a portable 50-mT system.
• To improve SNR efficiency and reduce noise and blurring artifacts in ULF MRI.
• To investigate the effectiveness of electromagnetic interference (EMI) cancelation and field map acquisition within the ULF context.

Main Methods:

• A novel spiral-out sequence was designed, incorporating three modules: noise calibration for EMI cancelation, embedded field map acquisition for phase error correction, and imaging with optimized low bandwidth sampling.
• Image reconstruction leveraged system imperfections like gradient delays and concomitant fields.
• The proposed method was compared against Cartesian acquisition and a state-of-the-art EMI cancelation algorithm using phantom and in vivo experiments.

Main Results:

• The spiral-out sequence demonstrated higher SNR efficiency compared to Cartesian counterparts.
• Temporal SNR improvements of 23%-44% were achieved in phantom and in vivo experiments.
• The technique yielded distortion-free images with approximately 80% noise suppression, outperforming a comparative EMI cancelation algorithm.

Conclusions:

• The proposed spiral-out sequence effectively enhances SNR efficiency and suppresses noise in ULF MRI brain imaging.
• This approach offers a viable solution for improving image quality on portable 50-mT MRI systems.
• Future research can explore diverse image contrasts using this method to expand ULF MRI applications.