Magnetic resonance imaging (MRI) is a method to visualize the information obtained by nuclear magnetic resonance of Hydrogen (mainly water in vivo) using magnetism and microwave. MRI can acquire images in any directions, free from irradiation of X-ray , although it has relatively long imaging time and produces loud scanning noise. MRI machines are broadly used in clinics mainly for medical imaging diagnosis, and more than five thousand MRI scanners have been actively installed in hospitals and research institutes in Japan. MRI can provide high contrast and spatial resolutions, applied to image not only the brain but also the body and limbs. MRI use a very strong magnetic field, and 3T (=30000 gauss) is common in clinics.