Examination of the sacroiliac joints must, like MRI of other joint areas, include two different scan planes. This is necessary for visualising all anatomical parts of the joints and thereby assessing abnormalities correctly. Due to the joint form and localisation a semi-coronal and a semi-axial slice orientation should be used. Certain separation of the anterior cartilaginous and the posterior ligamentous joint portion can only be obtained with a semi-axial slice orientation as illustrated in the section about normal anatomy.
The image shows the orientation of scan planes on an initial lateral scout view of the region. To the left semi-coronal and to the right semi-axial slice orientation.
MR scan planes – spine
For spinal examination sagittal slice orientation is often sufficient, but evaluation of the joints between the vertebral bodies and the ribs (costo-vertebral joints) may require supplementary axial slices.
Sagittal STIR images of the whole spine showing signs of disease activity postero-lateral in thoracic vertebral bodies and anterior in lumbar vertebral bodies (arrows). These are typical localisations of changes as part of ankylosing spondylitis.
Sagittal T1-weighted images of the whole spine shows slight chronic changes in the form of decreased bone marrow signal anteriorly at two vertebral corners (arrow), but no fatty deposition.
Axial T1 FS images after intravenous Gd. contrast corresponding to the inflammation in the thoracic region showing enhancement in the region of left-sided costo-vertebral joints (arrows) as a sign of active inflammation in these joints.