Gout results from precipitation of monosodium urate crystals within joints. It affects about 6 million people in the U.S. Dual-source CT (DSCT) is able to distinguish gout’s monosodium urate crystal deposits from normal bone and thus can reliably diagnose gout in its preclinical stages. This opens the door to noninvasive gout diagnosis and earlier, more effective treatment.
Gout is often difficult to diagnose
Gout can be difficult to diagnose using current methods. Clinical features can also be evoked by many other diseases. Definitive diagnosis requires polarized light microscopy of material from a joint aspiration, which can be technically difficult and includes a risk of complications. Treatment is often initiated on assumption of the diagnosis. Thus a noninvasive diagnostic method is highly desirable.
Diagnosis based on a two material decomposition algorithm
The typical scan protocol for gout diagnosis by means of Dual-source CT scanners includes settings of 140 kV and 55 mAs for tube A, and 80 kV and 243 mAs for tube B using a collimation of 0.6 mm and reconstructions of 0.75 mm. The total radiation dose is 2–3 mSv. Bilateral imaging of several peripheral joints including elbows, wrists, hands, and feet is standard. The software can separate calcium from monosodium urate deposits by using an image-based two-material decomposition algorithm, of which soft tissue is the baseline. The high and low tube voltage acquisitions create attenuation differences in the two materials that enable easy separation of monosodium urate (color-coded in red) from calcium (color-coded in blue).
An early diagnose can avoid associated risks
The ability to detect the disease at its preclinical stage by DSCT allows preventing articular and bony damage by starting treatment earlier. This may also make disease regression easier to achieve and can probably avoid associated risks, such as increased cardiovascular mortality, decreased renal function, and formation of renal calculi.
Fig.: A 45-year-old woman with swelling along lateral malleolus of right ankle but no history of trauma. Left, radiograph shows nonspecific soft-tissue swelling overlying lateral malleolus (arrow). Right, 3D volume-rendered coronal dual-energy CT image reveals that mass is composed of monosodium urate (red) consistent with tophus (arrow).
DSCT is an accurate method for the diagnosis of preclinical gout that obviates the need for risky and inconvenient invasive diagnostics. It enables an early treatment to avoid bone and joint damages or associated diseases.
Dr. Savvakis Nicolaou, Charlotte Jane Yong-Hing, and Dr. Sandro Galea-Soler, and colleagues from Vancouver General Hospital in British Columbia
Full text article
AJR, April 2010, Vol. 194:4, pp. 1072-1078
Source: Aunt Minnie.com