Template-based method to measure the 3D joint space for hand arthritis

PURPOSE: Rheumatiod arthritis (RA) of the hand is a widespread and debilitating disease with a large social and economic impact. RA damages the inter articular cartilage, causing narrowing of the joint space width (JSW.) In this study a template-based approach for measuring the 3D JSW is presented, which uses multiple projections of the joint and a comparison to 3D templates from anatomical specimens. METHODS: This study examined 20 proximal interphalangeal (PIP), and 20 metacarpophalangeal (MCP) joints. Realistic simulated radiographs with a pitch of 0.1 mm were produced from 3D data sets obtained by imaging skeletal specimens with a 0.066 trim pitch mu CT system. The technique attempted to match each bone to an anatomical template after the template had undergone transformations in virtual imaging space. For each native joint projection, the two opposing margins were delineated using a technique developed to segment bone margins on hand radiographs. The projected margins of each joint surface at each acquisition were then compared to a set of margins created by projecting rays through the surfaces of the anatomical templates, and the best-matched template was chosen. The performance was evaluated by calculating dJSW = vertical bar Native joint JSW- Template JSW vertical bar. RESULTS: The average dJSW ranged from 0.10 mm to 0.30 mm for approximately half of the average joint radius. CONCLUSIONS: A new technique for 3D imaging based on anatomical templates has been demonstrated. The work is specific to hand imaging but may be applied to other anatomical objects with regularity of shape. It may also complement previous work in digital tomosynthesis.