The magnetic resonance imaging (MRI) is part of the Assessment of SpondyloArthritis international Society (ASAS) criteria for diagnosis of axial spondyloarthritis. However, the MRI protocol in patients with sacroiliitis is usually reduced to a few proven sequences. The T1 spin echo (T1 SE) sequence leads to an excellent anatomical depiction of the sacroiliac joints (SI-joints) and allows the detection of fatty lesions in the near by bone marrow. Short tau inversion recovery (STIR) technique is used to search for bone marrow oedema (BME) that is present for example in acute inflammation. Other sequences like gradient echo (GRE) imaging ore contrast enhanced T1 with fat suppression are optional and not part in every MRI protocol.
Despite of the simplicity of this imaging strategy there are still some disadvantages. T1-SE for example is limited to a slice thickness of 3 to 5 mm when attempting an appropriate acquisition time. Therefore, structures or lesions significantly smaller might get lost in the partial volume effect. STIR imaging is very fast and robust but the signal intensity of the BME is relatively low.
However, there are some approaches to overcome this hurdles with new MRI sequences. High-resolution 3D sequences with a slice thickness of less than 1 mm allow reconstructions in different angles out of one data set and display smallest lesions like erosions or osteophytes. Furthermore, the signal intensity of the BME can be increased by other methods of fat saturation.
This lecture will summarise the properties and applications of some of the new MRI sequences in sacroiliitis and give an overview over image interpretation, important findings and differential diagnoses.
Disclosure of Interest None declared