Lightweight, compact, and high-performance 3T MR system for imaging the brain and extremities.

PURPOSE: To build and evaluate a small-footprint, lightweight, high-performance 3T MRI scanner for advanced brain imaging with image quality that is equal to or better than conventional whole-body clinical 3T MRI scanners, while achieving substantial reductions in installation costs. METHODS: A conduction-cooled magnet was developed that uses less than 12 liters of liquid helium in a gas-charged sealed system, and standard NbTi wire, and weighs approximately 2000 kg. A 42-cm inner-diameter gradient coil with asymmetric transverse axes was developed to provide patient access for head and extremity exams, while minimizing magnet-gradient interactions that adversely affect image quality. The gradient coil was designed to achieve simultaneous operation of 80-mT/m peak gradient amplitude at a slew rate of 700 T/m/s on each gradient axis using readily available 1-MVA gradient drivers. RESULTS: In a comparison of anatomical imaging in 16 patients using T2 -weighted 3D fluid-attenuated inversion recovery (FLAIR) between the compact 3T and whole-body 3T, image quality was assessed as equivalent to or better across several metrics. The ability to fully use a high slew rate of 700 T/m/s simultaneously with 80-mT/m maximum gradient amplitude resulted in improvements in image quality across EPI, DWI, and anatomical imaging of the brain. CONCLUSIONS: The compact 3T MRI system has been in continuous operation at the Mayo Clinic since March 2016. To date, over 200 patient studies have been completed, including 96 comparison studies with a clinical 3T whole-body MRI. The increased gradient performance has reliably resulted in consistently improved image quality.

Development of a 3 T-250 mm Bore MgB2 Magnet System.

The authors had reported components' development of 3 T-250 mm bore MgB2 magnet system. Pre-reacted MgB2 tape wire with copper lamination had n-value related problem due to raw Boron particle size inequality, but it had been corrected. Long MgB2 wires over 3 km had been supplied. All six component coils were made with a wet winding procedure. They were tested individually with the same cooling scheme of conduction cooling as the actual magnet assembly. Though all coils could be ramped to some extent, some coils showed fairly large remnant voltage. Since the voltage distribution over the coil was not even, the uniformity along the wire length may not be good enough. The stability of the coil was verified by its no training performance even with fast ramping. The magnet assembly and its test with conduction cooling were planned. I c of the superconducting joint with this pre-reacted wire was doubled during past one year's development.