Digital tomosynthesis for bone erosion scoring in gout: comparison with plain radiography and computed tomography

Sir, CT is the current gold standard for the assessment of bone erosion in inflammatory arthritis [1]. However, CT is costly and requires large radiation doses. Digital tomosynthesis is a recently developed imaging method in which multiple projected images obtained at different angles are collected with a digital detector [2, 3]. These cross-sectional images are used to reconstruct three-dimensional images of the scanned object. Several recent studies have reported that tomosynthesis allows low-cost, low-radiation detection of bone erosion in RA [4, 5]. Bone erosion is a frequent complication of tophaceous gout. The radiographic appearance of gouty erosions differs from that of RA, with sclerotic edges, overhanging margins and preserved periarticular bone [6]. The aim of this study was to determine the sensitivity and reproducibility of digital tomosynthesis compared with plain radiography (XR) and CT for the scoring of bone erosion in gout. Thirty-six people with gout were prospectively recruited from rheumatology outpatient clinics in Auckland, New Zealand (97% male, mean disease duration 18 years, 78% with s.c. tophi). All participants had gout according to the 1977 ARA classification criteria. XR and CT scans of the dominant wrist were obtained as previously reported [7]. Tomosynthesis was performed on the same day using a commercially available tomosynthesis unit (Volume RAD, GE Medical Systems, Pewaukee, WI, USA) (Fig. 1). A coronal projection was acquired, with the X-ray tube moving in an arc of 40° relative to a fixed solid-state detector. Focal spot size was 0.6 mm. The exposure factors were a tube voltage of 50 kV and current of 100 mA with a total exposure time of 6.3 s. The tomographic layer height was 35 mm, yielding 30 partitions of 1-mm nominal thickness. This study was approved by the New Zealand Ministry of Health Ethics Committee. All patients provided written informed consent according to the Declaration of Helsinki.