Computed Tomography Identifies Gout by Color
Up to now, computed tomography (CT) has played a limited role in the evaluation of gout, since conventional CT systems cannot reliably verify deposits of uric acid.
According to a Canadian study at Vancouver General Hospital, doctors could use computed tomography (CT) in the future to diagnose gout much more reliably than with the joint puncture method used currently. The Siemens dual-energy computed tomography (DECT) scanner enables a noninvasive examination, which quickly and accurately localizes small deposits of uric acid and marks them in color on the CT image. The Canadian scientists used a Somatom Definition CT scanner for their DECT trials. This is the world’s only CT scanner with two X-ray tubes capable of simultaneously producing different energies.
Occurring primarily in men, gout is the most common inflammatory joint disease. The uric acid crystals deposited in the joints cause painfully swollen joints. Gout is nevertheless difficult to diagnose, since there are quite a few diseases such as arthritis with similar symptoms. Diagnostic certainty can be achieved only by verifying the presence of uric acid deposits. This is typically done by puncturing the joint with a needle and withdrawing fluid. This can be difficult and painful in the case of inflamed joints or in regions of the body that are difficult to access. The computed tomography procedure is simpler and more precise: The doctors taking part in the study reported finding more gout-afflicted sites per patient overall using DECT than with the conventional clinical examination. The scientists also achieved significantly better detection of gout in the elbow, foot, ankle and knee with DECT than with the puncture method.
The key to the new method is the software: Siemens collaborated with the Canadian radiologists to develop a dual-energy algorithm for identifying uric acid deposits. They performed CT scans at different energies to determine the levels of the deposits. From this Siemens developed a new dual-energy protocol for gout that now can be used by any physician. The algorithm is based on the realization that the CT values of uric acid deposits are lower than those for calcium, for example, when scans are performed with different energies (80 and 140 kilovolts). The different attenuation values are color-coded on the clinical CT image. The uric acid crystals, for example, are color-coded red while other bone formations and calcium are displayed in blue. Reliable diagnosis is even possible in cases with very slight clinical symptoms.
