Please cite this article in press as: Barnabe C, et al. Reproducible metacarpal joint space width measurements using 3D analysis of images acquired with high-resolution peripheral quantitative computed tomography. Med Eng Phys (2013), http://dx.doi.org/10.1016/j.medengphy.2013.04.003 ARTICLE IN PRESS G Model JJBE-2281; No. of Pages 5 Medical Engineering & Physics xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Medical Engineering & Physics jou rn al h om epage: www.elsevier.com/locate/medengphy Communication Reproducible metacarpal joint space width measurements using 3D analysis of images acquired with high-resolution peripheral quantitative computed tomography Cheryl Barnabe a,b,* , Helen Buie c , Michelle Kan c , Eva Szabo c , Susan G. Barr a,b , Liam Martin a , Steven K. Boyd c,d a Department of Medicine, University of Calgary, Canada b Department of Community Health Sciences, University of Calgary, Canada c Schulich School of Engineering, University of Calgary, Canada d Department of Radiology, University of Calgary, Canada a r t i c l e i n f o Article history: Received 8 June 2012 Received in revised form 11 February 2013 Accepted 14 April 2013 Keywords: Musculoskeletal imaging Rheumatoid arthritis a b s t r a c t Objective: Joint space narrowing is an important feature of progressive joint damage and functional impairment in rheumatoid arthritis (RA). Methods to provide a continuous measurement of joint space width have not been adopted in research or clinical settings. High-resolution peripheral quantitative computed tomography (HR-pQCT) (Scanco Medical AG, Brüttisellen, Switzerland) accurately and repro- ducibly images bone microstructure at a nominal isotropic voxel dimension of 82 m. Given the ability of HR-pQCT to detect bone margins with high precision, we developed methodology to measure a three- dimensional (3D) metacarpophalangeal (MCP) joint space width and tested the reproducibility of the scan protocol with hand repositioning. Materials and methods: Consecutive HR-pQCT scans of the 2nd and 3rd MCP joints of ten subjects with early RA (70% female, mean age 45 years), with repositioning between scans, were obtained. The periosteal edges of the metacarpal head and proximal phalanx base were detected using the CT Evaluation Program V6.0 (Scanco Medical AG). Using the method of ‘fitting maximal spheres’, the joint space width and distribution of joint space thickness was estimated. Results: The mean minimum joint space width of the 2nd MCP was 1.82 mm (SD 0.20) and of the 3rd MCP 1.84 mm (SD 0.23). Reproducibility with repositioning was reliable, with overlapping filtered histograms and a root square mean coefficient of variance of 4.8%. Conclusions: We provide reproducible methodology for evaluating the joint space width of the MCP joints. When combined with the assessment of erosions and periarticular bone density, HR-pQCT may be the ideal technology to assess disease activity and progression in RA. © 2013 IPEM. Published by Elsevier Ltd. All rights reserved. 1. Introduction Joint damage in rheumatoid arthritis (RA) results in functional impairment, disability, and a decline in quality of life. Recent analy- sis from pooled randomized controlled trial data has demonstrated that joint space narrowing, rather than erosive damage, is more clearly associated with an irreversible decline in physical function over time [1]. Joint space narrowing has been largely ignored as a sign of progression of disease in comparison to erosion develop- ment, but is clearly of critical importance to patient outcomes. * Corresponding author at: Department of Medicine, University of Calgary, Canada. Tel.: +1 403 220 7725. E-mail address: ccbarnab@ucalgary.ca (C. Barnabe). Current scoring methods for joint space narrowing using plain radiographs are characterized by low sensitivity to change. In the most widely used scoring system in randomized clinical trials in RA, an ordinal scale is used to characterize normal joint space, min- imal narrowing, generalized narrowing with either <50% or >50% of the joint space remaining, or complete loss of joint space [2]. Ordinal scales only characterize incremental steps in change, and miss small continuous measurements that represent progression. To address this limitation, methods to directly measure the joint space width with plain radiograph [3–5] or using a variety of auto- mated software programs [6–14] have been described. Additionally, joint space width measurements have been deter- mined using digital X-ray radiogrammetry (DXR), a technology used in measuring bone mineral density in the hand (Pronosco X- Posure System version 2.0; Sectra Pronosco A/S, Denmark) [15,16]. These techniques attempt to determine the measurement using 1350-4533/$ – see front matter © 2013 IPEM. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.medengphy.2013.04.003