Enhancing B0 Homogeneity in Low-Field MRI: Experimental Study on the Thermal Dependence of Halbach Permanent Magnets

Motivation: Temperature-dependent B0 drift limits the use of sequences (e.g. bSSFP) in low-field MRI, preventing the full utilization of the system's potential. Goal(s): The temperature of the used NdFeB-magnets is stabilized through active water cooling in a Halbach slice, with B0-drift measured and simulated. Approach: A Halbach slice prototype with water-cooled magnets and heating capabilities was designed. The magnetic field was mapped with Hall sensors, while temperature, pressure, and flow sensors characterized the cooling performance. Results: Experimental results confirmed expected homogeneity changes with temperature, while identifying a feasible variant of cooling method for future Halbach MRI systems. Impact: Dynamic temperature-dependent B0-drift of permanent magnet-based low-field MRI represents a significant challenge, especially with bSSFP sequences. Our experimental study, complemented by the construction of a prototype, demonstrates a solution to this problem through active water cooling of the magnets themselves.