Detailed bone assessment of the sacroiliac joint in a prospective imaging study: comparison between computed tomography, zero echo time, and black bone magnetic resonance imaging

Objectives To compare the value of zero echo time (ZTE) and gradient echo “black bone” (BB) MRI sequences for bone assessment of the sacroiliac joint (SI) using computed tomography (CT) as the reference standard. Materials and methods Between May 2019 and January 2021, 79 patients prospectively underwent clinically indicated 3-T MRI including ZTE and BB imaging. Additionally, all patients underwent a CT scan covering the SI joints within 12 months of the MRI examination. Two blinded readers performed bone assessment by grading each side of each SI joint qualitatively in terms of seven features (osteophytes, subchondral sclerosis, erosions, ankylosis, joint irregularity, joint widening, and gas in the SI joint) using a 4-point Likert scale (0 = no changes–3 = marked changes). Scores were compared between all three imaging modalities. Results Interreader agreement was largely good ( k values: 0.5–0.83). Except for the feature “gas in SI joint” where ZTE exhibited significantly lower scores than CT ( p < 0.001), ZTE and BB showed similar performance relative to CT for all other features ( p > 0.52) with inter-modality agreement being substantial to almost perfect (Krippendorff’s alpha coefficients: 0.724–0.983). When combining the data from all features except for gas in the SI joint and when binarizing grading scores, combined sensitivity/specificity was 76.7%/98.6% for ZTE and 80.8%/99.1% for BB, respectively, compared to CT. Conclusions The performance of ZTE and BB sequences was comparable to CT for bone assessment of the SI joint. These sequences may potentially serve as an alternative to CT yet without involving exposure to ionizing radiation.