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MRI-based synthetic CT: a new method for structural damage assessment in the spine in patients with axial spondyloarthritis – a comparison with low-dose CT and radiography
  1. Simone Tromborg Willesen1,2,
  2. Anna EF Hadsbjerg1,2,
  3. Jakob Møllenbach Møller3,
  4. Nora Vladimirova1,2,
  5. Bimal M K Vora4,
  6. Sengül Seven1,
  7. Susanne Juhl Pedersen1,
  8. Mikkel Østergaard1,2
  1. 1 Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Rigshospitalet, Glostrup, Denmark
  2. 2 University of Copenhagen Faculty of Health and Medical Sciences, Copenhagen, Denmark
  3. 3 Department of Radiology, Herlev Gentofte Hospital, Copenhagen, Denmark
  4. 4 Department of Diagnostic Radiology, Singapore General Hospital, Singapore
  1. Correspondence to Dr Simone Tromborg Willesen, Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Rigshospitalet, Glostrup, Denmark; simone.willesen{at}


Objective To investigate the ability of MRI-based synthetic CT (sCT), low-dose CT (ldCT) and radiography to detect spinal new bone formation (NBF) in patients with axial spondyloarthritis (axSpA).

Methods Radiography of lumbar and cervical spine, ldCT and sCT of the entire spine were performed in 17 patients with axSpA. sCT was reconstructed using the BoneMRI application (V.1.6, MRIGuidance BV, Utrecht, NL), a quantitative three-dimensional MRI-technique based on a dual-echo gradient sequence and a machine learning processing pipeline that can generate CT-like MR images. Images were anonymised and scored by four readers blinded to other imaging/clinical information, applying the Canada-Denmark NBF assessment system.

Results Mean scores of NBF lesions for the four readers were 188/209/37 for ldCT/sCT/radiography. Most NBF findings were at anterior vertebral corners with means 163 on ldCT, 166 on sCT and 35 on radiography. With ldCT of the entire spine as reference standard, the sensitivity to detect NBF was 0.67/0.13 for sCT/radiography; both with specificities >0.95. For levels that were assessable on radiography (C2–T1 and T12–S1), the sensitivity was 0.61/0.48 for sCT/radiography, specificities >0.90. For facet joints, the sensitivity was 0.46/0.03 for sCT/radiography, specificities >0.94. The mean inter-reader agreements (kappa) for all locations were 0.68/0.58/0.56 for ldCT/sCT/radiography, best for anterior corners.

Conclusion With ldCT as reference standard, MRI-based sCT of the spine showed very high specificity and a sensitivity much higher than radiography, despite limited reader training. sCT could become highly valuable for detecting/monitoring structural spine damage in axSpA, not the least in clinical trials.

  • Magnetic Resonance Imaging
  • Spondylitis, Ankylosing
  • Arthritis

Data availability statement

Data are available on reasonable request.

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Data availability statement

Data are available on reasonable request.

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  • Handling editor Josef S Smolen

  • Presented at This work has been presented at the American College of Rheumatology (ACR) Congress in November 2023.

  • Correction notice This article has been corrected since it published Online First. Reference 38 has been removed.

  • Contributors STW: conceptualisation, methodology, validation, visualisation, writing–original draft, writing–review and editing. AEFH: methodology, formal analysis, validation, writing–review and editing. JMM: conceptualisation, investigation, data curation, writing–review and editing. NV: investigation, data curation, writing–review and editing. BMKV: investigation, writing–review and editing. SS: data curation, writing–review and editing. SJP: data curation, investigation, writing–review and editing. MØ: conceptualisation, methodology, investigation, validation, writing–review and editing, visualisation, supervision, project administration, guarantor.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests STW has received grants from the Danish Rheumatism Association ('Gigtforeningen') and the PARTNER Psoriatic Arthritis Network Fellowship program. AEFH has received grants from Novartis. NV has received grants from Novartis and speaker and/or consultancy fees from MSD. JMM has no competing interests. BMKV has no competing interests. SS has no competing interests. SJP has received grants and contracts from Innovation Fund Denmark and Nordic Bioscience A/S, consulting fees, speaking fees and/or research support from AbbVie, Novartis, MSD, Pfizer and UCB. MØ has received research grants from Abbvie, BMS, Merck, Novartis and UCB, and speaker and/or consultancy fees from Abbvie, BMS, Celgene, Eli-Lilly, Galapagos, Gilead, Janssen, MEDAC, Merck, Novartis, Pfizer, Sandoz and UCB.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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