Recommendations for acquisition and interpretation of MRI of the spine and sacroiliac joints in the diagnosis of axial spondyloarthritis in the UK. 
To develop evidence-based recommendations on the use of MRI in the diagnosis of axial SpA (axSpA).  A working group comprising nine rheumatologists and nine musculoskeletal radiologists with an interest in axSpA was established, with support from the British Society of Spondyloarthritis (BRITSpA).  Two meetings were held.  In the first meeting, research questions were formulated.  In the second meeting, the results of a systematic literature review designed to inform the recommendations were reviewed.  An anonymized Delphi process was used to formulate the final set of recommendations.  For each recommendation, the level of evidence and strength of recommendation was determined.  The level of agreement was assessed using a 0-10 numerical rating scale.  Two overarching principles were formulated, as follows: The diagnosis of axSpA is based on clinical, laboratory and imaging features (overarching principle 1), and patients with axSpA can have isolated inflammation of either the sacroiliac joints or the spine (overarching principle 2).  Seven recommendations addressing the use of MRI in the assessment of patients with suspected axSpA were formulated, covering topics including recommended sequences, anatomical coverage, acquisition parameters and interpretation of active and structural MRI lesions.  The level of agreement for each recommendation was very high (range 8.8-9.8).  A joint rheumatology and radiology consensus on the acquisition and interpretation of MRI in axSpA diagnosis was achieved, and a research agenda formulated.  This consensus should help standardize practice around MRI and ensure a more informed, consistent approach to the diagnosis of axSpA.