Published Online:https://doi.org/10.1148/radiol.11102485

Dual-energy CT depicts uric acid crystals in gout and can add information to joint fluid aspiration, possibly replacing it in some patients with an acutely inflamed joint, and may be a diagnostic imaging modality in patients who do not undergo aspiration.

Purpose

To estimate the accuracy, sensitivity, specificity, and interobserver agreement of dual-energy computed tomography (CT) in detection of uric acid crystals in joints or periarticular structures in patients with arthralgia and patients suspected of having gout, with joint aspiration results as reference standard.

Materials and Methods

With institutional review board approval, patient consent, and HIPAA compliance, 94 patients (age range, 29–89 years) underwent dual-source, dual-energy (80 and 140 kVp) CT of a painful joint. A material decomposition algorithm was used to identify uric acid. Two blinded musculoskeletal radiologists evaluated the dual-energy CT images and classified the examination findings as positive or negative for the presence of uric acid crystals. Reference standard was the result of joint aspiration.

Results

Forty-three of 94 patients (46%) underwent attempted joint aspiration within 1 month of dual-energy CT. Aspiration was successful in 31 of 43 patients (72%). In 12 of 31 patients (39%), uric acid crystals were identified at joint aspiration; in 19 patients, they were not. Readers 1 and 2 had no false-negative findings for uric acid at dual-energy CT. Sensitivity was 100% (12 of 12; 95% confidence interval (CI): 74%, 100%) for both readers. Specificity was 89% (17 of 19; 95% CI: 67%, 99% ) for reader 1 and 79% (15 of 19; 95% CI: 54%, 94%) for reader 2, with near-perfect agreement between the readers (κ = 0.87; range, 0.70–1.00) in the 31 patients who underwent aspiration.

Conclusion

Initial retrospective assessment suggests that dual-energy CT is a sensitive, noninvasive, and reproducible method for identifying uric acid deposits in joints and periarticular soft tissues in patients suspected of having gout.

© RSNA, 2011

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Article History

Received December 20, 2010; revision requested February 21, 2011; final revision received July 6; accepted July 12; final version accepted July 13.
Published online: Nov 2011
Published in print: Nov 2011