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ABSTRACT The goal of the MRI4ALL hackathon, which took place in October 2023, was to develop a functional low‐field MRI scanner in just one week and to release all created source code and resources as open‐source packages. The event was attended by 52 participants from 16 institutions who assembled the scanner on the last day of the hackathon. The scanner's magnetic B₀field with a strength of 43 mT and a target field‐of‐view size of 11 cm³was created with a Halbach array made from 990 N40UH permanent magnets, held in place using 3D printed ring formers. Gradient coils were fabricated by gluing enameled copper wire onto 3D printed holders with imprinted wire patterns. A solenoid coil for RF transmission and reception was built by winding 20 turns of Litz wire around a 3D printed cylinder. A Red Pitaya FPGA prototyping board running the MaRCoS framework was used to control the scanner components, and a GPA‐FHDO amplifier board was used to drive the gradients. To simplify the scanner's operation, console software with an intuitive graphical user interface was developed in Python using the PyPulseq package for sequence calculations. Furthermore, the scanner was equipped with a cooling system, as well as options for passive and active shimming. After resolving several technical issues that arose during the assembly, the scanner is now able to acquire MR images with different sequences. While not suitable for real‐world clinical applications, it can be utilized for educational purposes or as a low‐cost prototyping platform. Moreover, it may serve as a reference design for future MRI development projects. All source code and resources are available on the project websitemri4all.org, allowing other groups to replicate the scanner. Evidence Leveln/a Technical EfficacyStage 1. 

PurposeAn MRI scanner is equipped with global shim systems for shimming one region of interest (ROI) only. However, it often fails to reach state‐of‐the‐art when shimming two isolated regions of interest simultaneously, even though the two‐area shimming can be essential in scan scenarios, such as bilateral breasts or dyadic brains. To address these challenges, a hybrid active and passive local shimming technique is proposed to simultaneously shim two isolated region‐of‐interest areas within the whole FOV. MethodsA local passive shimming system is constructed by optimized bilateral ferromagnetic chip arrays to compensate for the magnet's significant high‐order B₀inhomogeneities at the boundary of the manufacturer's specified homogeneous volume, thus locally improving the available FOV. The local active shimming consists of 40‐channel DC loops powered by 64‐channel current amplifiers. With the optimized current distribution, active shimming can correct the residual low‐order B₀inhomogeneities and subject‐specific field inhomogeneities. In addition, active shimming is used to homogenize the center frequencies of the two regions. ResultsWith the implementation of the hybrid active and passive local shimming, the 95% peak‐to‐peak was reduced from 1.92 to 1.12 ppm by 41.7%, and RMS decreased from 0.473 to 0.255 ppm by 46.1% in a two‐phantom experiment. The volume ratio containing MR voxels within a 0.5‐ppm frequency span increased from 64.3% to 81.3% by 26.3%. ConclusionThe proposed hybrid active and passive local shimming technique uses both passive and active local shimming, and it can efficiently shim two areas simultaneously, which is an unmet need for a commercial MRI scanner.