Development of MR imaging system with 0.2-T permanent magnets

MR imaging has been shown to have significant advantage in clinical use. However, the usual MR imaging system with superconductive and resistive magnets involves many problems with facilities, operations, and system cost. To solve these problems, the authors have developed a cost-effective MR imaging system using high-energy permanent magnets. The static magnetic fields are materialized Nd-Fe-B permanent magnets, which have a high B-H product. The static 0.2-T field is formed in a vertical direction. To improve image quality the authors have developed many techniques such as use of highly sensitive receiving coils, optimization of band width, and ultra-low-noise amplifiers. The temperature coefficient of the magnet is about - 900 ppm/degree C. The authors have assembled a heat control system in a gantry to eliminate the environmental temperature fluctuation