SQUID-based instrumentation for ultra-low-field MRI

TL;DR

This paper presents a seven-channel SQUID system for ultra-low-field MRI and demonstrates its capability to produce 3D images of a sheep brain at microtesla-range fields, comparing favorably with high-field MRI.

Contribution

The work introduces a multi-channel SQUID-based ULF MRI system with detailed design and demonstrates its imaging performance on biological tissue.

Findings

Successful 3D imaging of a sheep brain at 46 microtesla

Achieved spatial resolution of approximately 2.5 mm x 2.5 mm x 5 mm

Compared ULF MRI images with high-field MRI showing comparable quality

Abstract

Magnetic resonance imaging at ultra-low fields (ULF MRI) is a promising new imaging method that uses SQUID sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at a microtesla-range measurement field. In this work, a seven-channel SQUID system designed for simultaneous 3D ULF MRI and magnetoencephalography (MEG) is described. The system includes seven second-order SQUID gradiometers, characterized by magnetic field resolutions of 1.2 - 2.8 fT/rtHz. It is also equipped with five sets of coils for 3D Fourier imaging with pre-polarization. Essential technical details of the design are discussed. The system's ULF MRI performance is demonstrated by multi-channel 3D images of a preserved sheep brain acquired at 46 microtesla measurement field with pre-polarization at 40 mT. The imaging resolution is 2.5 mm x 2.5 mm x 5 mm. The ULF MRI images are compared to images of the same brain acquired using conventional high-field MRI. Different ways to improve imaging SNR are discussed.