Magnetic resonance scanning (MR-scanning) or magnetic
resonance imaging (MRI) is superior to CT and radiography for detecting early
sacroiliitis because MRI can show active inflammation in addition to structural
damage. In later stages MR can provide valuable information about disease
activity corresponding to the sacroiliac joints as well as the spine. MRI is
therefore appropriate for measuring the disease activity and can be used to
monitor the disease with regard to indication for treatment and for assessing
the effect of therapy.
MRI is based on a rather complicated technique. The images can
be obtained in numerous ways related to different MR sequences and it is
possible to obtain images in arbitrary scan planes. It is
important to choose the most appropriate sequences and slice orientation for
each specific diagnostic purpose.
During image interpretation, the radiologist
must be familiar with normal MRI findings and the
appearance of diseases that can simulate sacroiliitis or spinal changes as part
of spondyloarthropathy (differential diagnoses).
Positive MRI in
a patient with normal radiographic examination (non-radiographic sacroiliitis).
The images manifest
subchondral edema (open arrows) as sign of active sacroiliitis. Besides,
erosion of the sacral joint facet (arrow).