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Dual-Energy Computed Tomography Useful for Diagnosing Gout

VBCR - June 2013, Volume 2, No 3 - Gout

By Rosemary Frei, MSc

Montreal, Quebec—Dual-energy computed tomography (DECT) has value in gout diagnosis and management, according to a presentation at the Canadian Association of Radiologists’ 2013 annual meeting.

DECT involves the use of 2 x-ray sources, each at a different energy level, and 2 banks of detectors 90 degrees apart. The radiation dose is the same as for regular computed tomography. The result is 2 sets of images that can be compared to produce color-coded depictions of ligaments, tendons, bone edema, and uric acid (Figures 1 and 2).

Paul Mallinson, MBChB, a radiology fellow at Vancouver General Hospital, works on DECT in gout with Savvas Nicolaou, MD, an assistant professor of diagnostic radiology at the University of British Columbia. DECT is noninvasive and, therefore, has advantages over the classic test, which involves aspiration of the affected joint to determine whether monosodium urate crystals and/or infection are present.

“That means the patient has to have a needle in a joint, which is a little painful and has potential complications, plus you have to limit the number of joints you test because the patient won’t find it acceptable to have multiple joints aspirated,” Dr Mallinson explained.

Patients who are suspected to have gout undergo DECT imaging of the hands and wrists, followed by the elbows, the knees, the feet, and the ankles. Previous studies have shown the technique has a sensitivity ranging from 84% to 100% and specificity ranging from 79% to 100% (AJR Am J Roentgenol. 2012;199:S78-S86).

“You can look for gout in the joint or joints you think are symptomatic, and you can also look at other joints to see if there are gout crystals even though gout hasn’t become clinically apparent in those joints yet,” said Dr Mallinson in explaining other advantages of DECT. In addition, patients can be reimaged after urate-lowering therapy to determine whether the treatment has been effective.

The images are displayed on a specialized workstation as 3-plane cross-sectional and 3-dimensional images. The urate is shown as green areas and the calcium of the bones is blue (Figures 1 and 2).

There can be artifacts that appear green on the images that are not actually gout, but DECT users quickly learn to differentiate these from true gout, Dr Mallinson said. Tissues that commonly produce artifacts are the nails and nail beds in the feet, and areas where there is thickened skin or areas of proximate skin, such as when toes are pressed together.

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Last modified: May 21, 2015
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