From the Guidelines
To evaluate the sacroiliac joint, a specialized MRI protocol is recommended that includes both T1-weighted and fluid-sensitive sequences (such as STIR or T2 fat-suppressed) with thin slices through the SI joints, as this approach has been shown to be highly sensitive and specific for detecting sacroiliitis 1. The optimal MRI protocol should include axial, coronal, and oblique coronal planes oriented along the axis of the sacrum.
- Contrast enhancement with gadolinium is not routinely necessary but may be added if infection or tumor is suspected.
- The MRI should be performed on at least a 1.5 Tesla machine for adequate resolution. This specialized protocol is important because the SI joint has a complex anatomy and standard lumbar spine MRI protocols often do not adequately visualize the joint.
- The fluid-sensitive sequences are particularly valuable for detecting bone marrow edema, which is an early sign of sacroiliitis, while T1-weighted images help evaluate structural changes like erosions, sclerosis, and ankylosis. For patients with suspected inflammatory conditions like ankylosing spondylitis, the MRI should include the entire pelvis to assess for involvement of other structures, as recommended by the American College of Radiology 1. The use of MRI in evaluating sacroiliac joints has been widely recognized as an important tool in the evaluation of patients with suspected axial spondyloarthritis, resulting in improved diagnostic confidence and yielding findings that stimulate changes in both diagnosis and treatment plans for patients 1.
From the Research
MRI Sequences for Evaluating Sacroiliac Joint
- The imaging modality of choice for suspected sacroiliitis is MRI, which should include at least four sequences: coronal oblique T1-weighted and fluid-sensitive sequences, a perpendicular axial oblique sequence, and a sequence for optimal evaluation of the bone-cartilage interface 2.
- T2-weighted multipoint Dixon sequence can be used as a single sequence in MRI of the sacroiliac joints for the diagnosis of active and chronic sacroiliitis, as it provides superior contrast-to-noise ratios (CNRs) compared to conventional MRI sequences 3.
- Zero echo time (ZTE) magnetic resonance imaging can be used to identify structural lesions in patients with enthesitis-related arthritis, and has been shown to have similar sensitivity to low-dose CT in detecting erosion 4.
Comparison of MRI Sequences
- Short tau inversion recovery (STIR) sequences alone are sufficient for establishing a reliable diagnosis and quantifying the amount of inflammation in active sacroiliitis, but a contrast-enhanced study may be beneficial to ensure maximum diagnostic confidence in early sacroiliitis 5.
- Fat-saturated T2-weighted and contrast-enhanced fat-saturated T1-weighted images can be used to detect signs of active inflammation, while T1-weighted images can be used to detect signs of chronic sacroiliitis 3.
Scoring Systems for Sacroiliac Joint Evaluation
- The Spondyloarthropathy Research Consortium of Canada scoring systems are recommended as tools for MRI evaluation of the sacroiliac joint, with fair evidence to support their use 6.
- However, limited data on criterion validity limit the assessment of scoring system accuracy, and further research is needed to evaluate the diagnostic accuracy and reliability of existing MRI-based sacroiliac joint scoring systems 6.