ACR Meeting Abstracts

ACR Meeting Abstracts

Abstract Number: 0906

Measurement of Vertebral Hounsfield Units in Low Dose Computed Tomography – a Reliable Methodology for Assessing Bone Mineral Density at the Vertebral Level in Patients with Radiographic Axial Spondyloarthritis

Mary Lucy Marques1, Nuno Pereira da Silva2, Désirée van der Heijde3, Floris van Gaalen1 and Sofia Ramiro1, 1Leiden University Medical Center, Leiden, Netherlands, 2Radiology Department, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal, 3Department of Rheumatology, Leiden University Medical Center, Meerssen, Netherlands

Meeting: ACR Convergence 2021

Keywords: , , , ,

Session Information

Date: Sunday, November 7, 2021

Title: Spondyloarthritis Including PsA – Diagnosis, Manifestations, & Outcomes Poster II: Imaging in Spondyloarthritis (0897–0907)

Session Type: Poster Session B

Session Time: 8:30AM-10:30AM

Background/Purpose: Bone loss paradoxically coexists with bone formation in radiographic axial spondyloarthritis (r-axSpA). Assessing bone mineral density (BMD) in r-axSpA poses challenges, namely because of possible overestimation due to ectopic bone formation. The measurement of Computed Tomography (CT) Hounsfield Units (HU) at the individual vertebral level has been shown to correlate with BMD as measured by Dual-energy X-ray absorptiometry in trauma patients.1 However, its value in r-axSpA has never been studied. Whole spine low dose CT (ldCT) has been suggested as the ideal method to assess both bone formation and bone loss in r-axSpA. By using ldCT scans, we aimed to cross-sectionally describe HU measurements and their inter-reader reliability at the vertebral level from C3 to L5 in patients with r-axSpA.

Methods: We used ldCT scans of r-axSpA patients included in the Sensitive Imaging in Ankylosing Spondylitis (SIAS) study, a multicenter (Leiden, the Netherlands and Herne, Germany) 2-year prospective cohort. A standardized protocol was applied in both centers and automatic exposure control calibration in ldCT imaging acquisition was used. For the present study, baseline ldCT scans were independently assessed by two trained readers. The HU measurement was performed as described in Figure 1 – using OsiriX software (v6.5.1). Inter-reader reliability was assessed using intraclass correlation coefficients (ICC) absolute agreement, applying two-way mixed effect models. Agreement was assessed using the smallest detectable difference (SDD = 1.96 x SDdifference /(√k), in which SDdifference is the standard deviation of the differences in status scores between two readers, and k=2 (number of readers) and Bland-Altman plots.

Results: Whole spine ldCT scans from 50 r-axSpA patients (mean (SD) age of 49 (10) years; 43 (86%) male and 42 (84%) HLA-B27 positive) were included. In total, 220 cervical, 588 thoracic and 245 lumbar vertebrae were assessed by both readers. The HU values decreased from the cervical to the lumbar spine – Table 1. For both readers, the highest mean (SD) value for HU was obtained at C3 (354 (106) and 355(108), for reader 1 and 2 respectively), and the lowest at L3 (153 (65) and 150 (65), for reader 1 and 2 respectively). Inter-reader reliability was shown to be excellent (cervical spine ICC: 0.90 to 1.00; thoracic spine ICC: 0.97 to 1.00; lumbar spine ICC: 0.89 to 0.91). SDD varied from 4 to 8. A small degree of systematic error was observed between the two readers, i.e., for the majority of vertebrae, reader 1 scored somewhat higher than reader 2 (mean difference of scores ranging from -0.6 HU to 2.9 HU). Bland-Altman plots show homoscedasticity throughout the whole spine. Representative examples from vertebrae of each segment of the spine are presented in Figure 2.

Conclusion: Low dose CT measurement of HU is a reliable method to assess BMD at each vertebra from C3 to L5. This methodology can aid the future study of bone loss in r-axSpA, a disease affecting the whole spine. Further validation and longitudinal assessment of reliability are warranted in future studies.

1Shaun P. Patel, et al. J Clin Exp Orthop. 2016;2(1:14):1–7.

Figure 1. Methodology of Hounsfield Units (HU) measurement. Using a three-dimensional curved-multiplanar reconstruction (3D Curved-MPR) we identify the curve of the spine from the spinal canal (1a). On the obtained sagittal image, the individual vertebral levels are identified. At each vertebral level, two lines of reference are positioned at the superior (yellow line A) and inferior (yellow line C) limits of the vertebra. Equidistant to A and C, the yellow line B will be positioned at the center of the vertebral body (1b). Vertebral HU measurements are taken from a reconstructed cross-sectional slice positioned at the center of the vertebra as defined by the selection process described above (1c). A circular sample region of this slice is used, centered at the body origin and having a diameter equal to 75% of the average of distances posteroinferior-to-anteroinferior, and posterosuperior-to-anterosuperior. The density of the vertebra is calculated as the average image intensity within the sample region, reported in HU (1d).

Table 1. Descriptive statistics of Hounsfield Units (HU) per vertebral level, according to reader 1 and 2 measurements

Figure 2. Bland-Altman plots for representative examples from vertebrae of each segment of the spine: C4, T1, and L1. The scatter of differences is homoscedastic.

Disclosures: M. Marques, None; N. Pereira da Silva, ABC Company, 2; D. van der Heijde, AbbVie, 2, Amgen, 2, Astellas, 2, AstraZeneca, 2, Bayer, 2, BMS, 2, Boehringer Ingelheim, 2, Celgene, 2, Cyxone, 2, Daiichi, 2, Eisai, 2, Eli Lilly, 2, Galapagos, 2, Gilead, 2, GlaxoSmithKline, 2, Janssen, 2, Merck, 2, Novartis, 2, Pfizer, 2, Regeneron, 2, Roche, 2, Sanofi, 2, Takeda, 2, UCB Pharma, 2, Imaging and Rheumatology BV, 4; F. van Gaalen, Stichting ASAS, 5, Stichting vrienden van Sole Mio, 5, Jacobus stichting, 5, Novartis, 5, UCB, 5, Abb Vie, 12, personal fees, MSD, 12, personal fees, Bristol Myers Squibb, 12, personal fees, ASAS EC, 2, ASAS treasurer, 2; S. Ramiro, AbbVie, 2, Eli Lilly, 2, MSD, 2, Novartis, 2, Sanofi, 2, UCB, 2, MSD, 5.

To cite this abstract in AMA style:

Marques M, Pereira da Silva N, van der Heijde D, van Gaalen F, Ramiro S. Measurement of Vertebral Hounsfield Units in Low Dose Computed Tomography – a Reliable Methodology for Assessing Bone Mineral Density at the Vertebral Level in Patients with Radiographic Axial Spondyloarthritis [abstract]. Arthritis Rheumatol. 2021; 73 (suppl 9). https://acrabstracts.org/abstract/measurement-of-vertebral-hounsfield-units-in-low-dose-computed-tomography-a-reliable-methodology-for-assessing-bone-mineral-density-at-the-vertebral-level-in-patients-with-radiographic-axial/. Accessed .

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