1072 AJR:194, April 2010 as well as monitoring response to treatment, is therefore highly desirable. The advent of dual-energy CT has the potential to achieve this goal for the first time. The current imaging techniques used to confirm and monitor gout include radiogra- phy [3], ultrasound [3, 4], CT [3], and MRI [3, 5]. However, these techniques are not specific enough to facilitate the diagnosis of gout. An ideal imaging technique would be highly specific for monosodium urate depo- sition. The presence of monosodium urate would confirm the diagnosis of gout, and ap- propriate therapy could be instituted earlier, thereby significantly reducing risks associat- ed with delayed diagnosis, such as joint de- struction and deformities and rupture of liga- ments and tendons. Materials and Methods The dual-energy CT system (Definition, Sie- mens Healthcare) is equipped with two x-ray tubes rather than one (Fig. 1). The dual-source scanner allows simultaneous acquisition at two different en- ergy levels (thereby eliminating errors due to mis- registration of data or patient movement between acquisitions) and creation of two different data sets that are loaded into the postprocessing software (Syngo Dual Energy, Siemens Healthcare) on a multitechnique CT workspace (SW-Version VA20, Siemens Healthcare). An image-based two-materi- al decomposition algorithm of the datasets is subse- quently performed to separate calcium from mono- sodium urate, using soft tissue as the baseline (Fig. 2A). The material-specific differences in attenua- tion between the high and low tube voltage acqui- sitions enable easy classification of the chemical Dual-Energy CT as a Potential New Diagnostic Tool in the Management of Gout in the Acute Setting Savvakis Nicolaou 1 Charlotte Jane Yong-Hing Sandro Galea-Soler Daniel J. Hou Luck Louis Peter Munk Nicolaou S, Yong-Hing CJ, Galea-Soler S, Hou DJ, Louis L, Munk P 1 All authors: ER Radiology Division, Radiology Department, Vancouver General Hospital, 899 W 12th Ave., Vancouver, BC, V5Z 1M9, Canada. Address correspondence to S. Nicolaou (savvas.nicolaou@vch.ca and savvasn@yahoo.com). -USCULOSKELETAL฀)MAGING฀s฀4ECHNICAL฀)NNOVATION AJR 2010; 194:1072–1078 0361–803X/10/1944–1072 © American Roentgen Ray Society G out results from precipitation of monosodium urate crystals with- in joints. It is the most common crystal deposition arthropathy and affects up to 6 million people in the United States [1, 2]. Peak incidence occurs in middle age, and the condition is five to seven times more common among men than wom- en, who tend to present postmenopausally [1]. Hyperuricemia does not necessarily lead to gout, and patients with gout may present with normal serum uric acid levels [1]. The classic presentation of acute gout in- volving the first metatarsophalangeal joint (podagra) is seen in approximately 50% of cases [3]. Differentiation from septic arthri- tis can be difficult, and, even in established gout, infection cannot be excluded on clin- ical grounds alone. Although peripheral joints are preferentially involved, almost any joint can be affected, and as the disease pro- gresses, there can be involvement of the axial skeleton. A polyarticular form of gout is also recognized and is most common among the elderly and among women [3]. Although clinical features can help with the diagnosis of gout, many other diseases can mimic or coexist with it. Definitive di- agnosis requires polarized light microsco- py of fluid aspirated from the involved joint showing needle-shaped negatively birefrin- gent monosodium urate crystals. Treatment is often initiated on assumption of the diag- nosis. Joint aspiration can be technically dif- ficult, and there is a risk of complications [3]. A noninvasive means of confirming gout be- fore the classic radiographic changes occur, Keywords: crystal deposition arthropathy, dual-energy CT, gout DOI:10.2214/AJR.09.2428 Received January 20, 2009; accepted after revision September 30, 2009. OBJECTIVE. Gout is the most common crystal deposition arthropathy currently diag- nosed clinically and with arthrocentesis. Dual-energy CT is a promising new imaging tech- nique offering potential new applications in a number of clinical areas. CONCLUSION. The ability of dual-energy CT to diagnose early gout and its use as a problem-solving tool is shown here. Diagnosis of subclinical gout could avert associated long- term complications, thereby reducing disease burden and improving overall quality of life. Nicolaou et al. Dual-Energy CT Diagnosis of Gout Musculoskeletal Imaging Technical Innovation Downloaded from www.ajronline.org by 139.173.54.11 on 07/11/13 from IP address 139.173.54.11. Copyright ARRS. For personal use only; all rights reserved