ARTHRITIS & RHEUMATOLOGY Vol. 68, No. 2, February 2016, pp 332–336 DOI 10.1002/art.39459 V C 2016, American College of Rheumatology BRIEF REPORT Development and Validation of a Semiautomated Method to Measure Erosion Volume in Inflammatory Arthritis by Computed Tomography Scanning Jeffrey Duryea, 1 Ruby Russell, 1 Ellen M. Gravallese, 2 Jonathan Kay, 2 Roger Han, 1 Bing Lu, 1 and Daniel H. Solomon 1 Objective. Valid measurement of erosion volume in rheumatoid arthritis (RA) will facilitate the testing of treatments that may help to heal erosion. This study was undertaken to develop and validate a software method to measure erosion volume on computed tomog- raphy (CT) scans of the hand and wrist. Methods. Duplicate CT acquisitions of both hands of 5 patients with RA were evaluated using a semiauto- mated software tool to measure erosion volume in the entire hand and wrist and in each of 6 subregions. Repro- ducibility was quantified using the intraclass correlation coefficient (ICC), root mean square standard deviation (RMSSD), and coefficient of variation (CV), and the ana- lysis was performed at the level of the hand (n 5 10) and the subject (n 5 5). Results. The ICCs between 2 repositioned acquisi- tions were excellent, ranging from 0.97 to 1.00. At the hand level, the RMSSD was 15.6 mm 3 with a CV of 7.3%, and the CVs at the 6 regions ranged from 7.6% to 21.0%. At the subject level, the RMSSD was 31.2 mm 3 with a CV of 3.7%, and the CVs at the 6 regions ranged from 0.5% to 15.8%. Conclusion. We have developed a novel semiauto- mated software method to measure erosion volume on hand and wrist CT scans. The method is reproducible and can be used to detect changes in erosion volume. This will facilitate the testing of treatments intended to reduce erosion volume. Articular bone erosions in rheumatoid arthritis (RA) are strongly associated with long-term disability and remain an important treatment target (1). With more aggressive treatment, progression of joint erosions is observed less commonly. Several biologic and small-mole- cule disease-modifying antirheumatic drugs (DMARDs) have been shown to arrest or slow erosion progression, but none has been demonstrated to reduce erosion volume impactfully (2–4). Drugs developed to alter bone metabo- lism have been tested for their effects on joint erosions, with mixed results: administration of highly potent amino- bisphosphonates has reduced erosion number in some studies (5), and denosumab treatment has produced a slight improvement in the Sharp score (6). It is possible that therapies that are anabolic for bone, in contrast to those that are antiresorptive, may reduce erosion volume. However, a more sensitive measure of erosion volume may be needed to demonstrate such change. Imaging modalities, including conventional radi- ography, computed tomography (CT), and magnetic res- onance imaging (MRI), are used extensively to assess structural consequences of RA, both in clinical and in research settings. For research purposes, 2 methods have been used to evaluate images: semiquantitative scoring and quantitative measurement. The Sharp (7) and van der Heijde (8) scoring systems both provide semiquantitative assessments of joint space width (JSW) and erosions seen on hand and wrist radiographs. Sever- al reports have described automated software used for quantitative measurement of JSW (9–12) and erosion size (13) on digital radiographs. More recently, these methods have been applied to 3-dimensional (3-D) imaging modalities, such as MRI and CT. The RAMRIS (RA MRI Scoring) system was developed to provide a semiautomated assessment of hand and wrist MRI in patients with RA (14). Several studies have measured structural changes in RA using hand or wrist CT (4,15–17); however, to our knowledge, none has used automated software to quantify true erosion volume. Supported by Eli Lilly and company. 1 Jeffrey Duryea, PhD, Ruby Russell, BA, Roger Han, MD, Bing Lu, PhD, Daniel H. Solomon, MD, MPH: Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts; 2 Ellen M. Gravallese, MD, Jonathan Kay, MD: University of Massachusetts Medical School, Worcester. Address correspondence to Jeffrey Duryea, PhD, Radiology Department, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115. E-mail: jduryea@bwh. harvard.edu. Submitted for publication May 29, 2015; accepted in revised form September 29, 2015. 332