The value of chemical shift imaging and T1-Dixon MRI in evaluation of structural changes in sacroiliac joint in ankylosing spondylitis

Background: The aim of this study was to assess the diagnostic value of dual gradient-echo T1-weighted sequence (in phase and out of phase) and the related Dixon images in evaluation of structural changes observed in sacroiliac joint in patients diagnosed with ankylosing spondylitis. Forty patients with low back pain were included in the study; they underwent T1-Dixon and routine MRI study on the sacroiliac joint in addition to pelvic CT. Results: This study was carried out on forty patients, 27 (67.5%) males and 13 (32.5%) females, their mean age was 34.93 +/- 11.21 years, and mean duration of symptoms was 8.1 +/- 7.4 years. The mean Ankylosing Spondylitis Disease Activity Score ASDAS value was 4.03 +/- 0.85 years. The most common structural change was subchondral fat deposition. Dixon MRI was significantly superior to T1WI in simple quantification of the amount of fat with P= 0.036 and excellent inter-rater reliability (96%), P= 0.0001. The number of erosions/backfills detected on Dixon was higher than that detected in T1WI with higher accuracy (97.5%) and excellent inter-rater reliability (95%), P= 0.0001. ASDAS showed significant positive correlation with erosion/backfill (r= 69, P= 0.0001) and with maximal fat deposition detected on Dixon (r= 32, P= 0.044). There were significant difference between the patients having high ASDAS and others having very high ASDAS scores regarding the sub-articular sclerosis (P= 0.013). Conclusion: 3D T1-based Dixon is a helpful imaging technique in proper assessment of different structural changes in sacroiliitis, its integration into routine MR protocol is recommend as it could yield a better depiction of erosive/ backfill and fat deposition.