This exhibit aims to 1) Illustrate appearances of monosodium urate deposition on dual energy CT 2) Review causes of false positive findings 3) Discuss potential causes of false negative findings, and important limitations of this technique

Dual energy CT (DECT) is increasingly being employed for the diagnosis and treatment monitoring of gout (1,2). DECT scans demonstrate monosodium urate (MSU) deposition, based on the changes in attenuation of MSU crystals compared to calcium at different photon energies. The findings of DECT are typically displayed as colour coded images with MSU deposits being shaded a different colour (green in this poster), that is distinct from cortical and trabecular calcium (typically purple and blue in this poster).

MSU deposits on dual energy CT In patients with gout, MSU deposits occur within joints, tendons, bursae, fasciae, or cartilage (3). In keeping with the lower limb predilection of gout clinically, MSU deposition on DECT is more common in the lower limb (1,4). The most common lower limb sites of MSU deposition on DECT include the 1st MTP joint, ankle joint, Achilles and peroneal tendons, followed by the tendons, bursae and menisci around the knee (4). Figure 1 is a colour-coded image demonstrating intra-articular MSU...

Dual energy CT is a useful tool to demonstrate MSU deposition within the peripheral appendicular skeleton and soft tissue, which is an important feature of gout. Understanding the causes of artefacts, false positive findings and false negative findings, helps in the interpretation of dual energy CT studies. Radiologists and clinicians should be aware of the current limitations of this technique when ascribing clinical significance to positive and negative findings.

1.Chou H, Chin TY, Peh WC. Dual‐energy CT in gout–A review of current concepts and applications. Journal of medical radiation sciences. 2017 Feb 2.Yu Z, Mao T, Xu Y, Li T, Wang Y, Gao F, Sun W. Diagnostic accuracy of dual-energy CT in gout: a systematic review and meta-analysis. Skeletal radiology. 2018 May 3:1-7. 3.Lichtenstein L, Scott HW, Levin MH. Pathologic changes in gout: survey of eleven necropsied cases. The American journal of pathology. 1956 Oct;32(5):871. 4.Mallinson PI, Reagan AC, Coupal T, Munk PL, Ouellette...

The authors can be contacted at [email protected] and [email protected]. The authors will like to thank Dr Ahmed Daghir, Consultant MSK Radiologist at Brighton and Sussex University Hospitals, UK, for contribution of a number of cases used in this exhibit.