MS student Yaokun Shi with Advisor K. Haran

Magnetic resonance imaging (MRI) is widely recognized for its non-invasive nature and ability to generate high-quality, multi-contrast images.  Traditionally, enhancing image quality has relied on increasing field strength, but this approach comes with significant costs, high energy demands, and the need for a homogeneous base magnetic field to ensure proper operation. In contrast, low-field MRI systems provide a more affordable and energy-efficient alternative, but face challenges related to signal-to-noise ratio (SNR), which is critical for clinical use. More innovative approaches have explored leveraging inhomogeneities in the base magnetic field to develop a compact MRI system.

Building on this concept, we propose a novel spatial encoding strategy using three sets of magnet arrays to generate an inhomogeneous base magnetic field.  During scanning, this pre-recorded field is dynamically perturbed by adjusting the angles of the magnet arrays with high-torque motors to encode spatial information. An in-house solenoid RF coil and amplifier circuit, integrated with a Red Pitaya controller, facilitate RF pulse transmission and signal reception across various center frequencies and field map steps.  The free induction decay (FID) signal is acquired for each field map step, with its magnitude recorded before repeating the process for subsequent steps.  A prototype was built, and initial acquisition results closely align with simulations, reinforcing the feasibility of achieving full-image reconstruction.  Future advancements will focus on implementing higher torque-density motors (PMVM), designing planar RF coils, and leveraging machine learning for denoising and super-resolution to enhance image quality for clinical applications.

Figure 15. Top: prototype assembly and test setup. Bottom: result from 12 acquisitions at one encoding step compared to simulated results.

Figure 16. Simulated image reconstruction with top being true image and bottom being reconstructed images.