A magnet structure for an MRI apparatus utilizing a permanent magnet, which apparatus has an inverted U shape with two essentially parallel opposed pole pieces, which are supported at a predetermined distance from each other by an inverted U-shaped magnetic yoke, which pole pieces and/or at least a portion of which yoke delimit a cavity for receiving at least a part of the patient's body, whereas a partial volume is generated in the volume of said cavity, which has such magnetic field values as to provide MRI images of a sufficient quality to enable the use thereof as diagnostic images, i.e. a so-called imaging volume. According to the invention, the distance (D1) between the pole pieces (1, 2) of the magnet structure is of 36 to 42 cm, and the pole pieces (1, 2) have a surface area of 4500 to 5500 cm2. The invention also relates to an MRI imaging apparatus, particularly designed for the spine region, or a part thereof, and which has a magnet structure as described above.