Slug-Mapper: Magnetic Scanner for Ultra Low-Field MRI Scanners

Ultra-Low Field (ULF) MRI scanners offer a portable and cost-effective alternative to conventional MRI systems, but require careful calibration to compensate for reduced magnetic field strength and signal quality. In this paper, we present Slug-Mapper, a low-cost, open-source magnetic field scanner designed to map the static field $B_0$ voxel-by-voxel within the bore of a ULF MRI system. Built using a repurposed 3D printer, a Raspberry Pi, and off-the-shelf components, Slug-Mapper enables high-resolution magnetic field characterization for both passive and active shimming. We provide a detailed overview of MRI physics, the engineering challenges of ULF systems, and the architecture and operation of Slug-Mapper. This tool bridges the gap between hardware prototyping and precise system calibration, supporting the development of accessible and portable MRI technology.