Because the imaging principle of MR is that molecular relaxation is caused by a high-field magnetic field, the higher the field strength, the clearer the image will be. Of course, this is not absolute. At present, major medical equipment manufacturers at home and abroad have developed low-field MR (such as 0.35T MR) for some special examinations and treatments.
In fact, there is little difference in the field strength of 1T and 1.5T between the skull and the brain.