Diagnosing gout, a nasty disease involving swollen joints and often a good deal of pain, is difficult because the symptoms are often similar to various forms of arthritis. The definitive method of diagnosis is to draw fluid from a joint and test it for the presence of uric acid crystals. CT scanners have long been considered potentially useful as a non-invasive diagnostic modality, but their ability to help identify uric acid deposits has been limited. To overcome this, Canadian researchers decided to try using a new algorithm on the SOMATOM Definition dual energy CT (DECT) scanner from Siemens. Initial findings from the researchers show that the novel technique can provide radiologists with significant help in diagnosing gout, potentially avoiding aspirations for patients in the future.
Siemens explains the findings:
In collaboration with Siemens, Dr. Savvas Nicolaou, Director of Emergency Radiology at Vancouver General Hospital and Associate Professor at the University of British Columbia in Vancouver, and both his radiology and rheumatology colleagues developed a dual-energy algorithm for identifying uric acid deposits.
The Canadian scientists used a SOMATOM Definition from Siemens for their trials. This system is the only CT scanner worldwide that features two X-ray tubes capable of simultaneously producing different energies. The team performed scans at different energies to determine the attenuation values of uric acid deposits. Siemens used this data to develop a new dual-energy protocol for gout that now can be used by any physician. The software algorithm used to detect gout via DECT is based on the realization that the CT values of uric acid deposits are lower, for instance, than those of calcium if scans are performed at different energies (80 and 140 kilovolts). Through color coding of the different attenuation values, it then becomes possible to recognize mono sodium urate crystals on the clinical CT image: The uric acid crystals indicating gout are, for example, color coded in red, while other bone formations and calcium are displayed in blue. The commercial version of the Siemens application is called Syngo DE Gout.
In a further study, Dr. Nicolaou and his colleagues investigated whether DECT can be used reliably to confirm the presence of gout tophi, whether DECT is superior to the traditional clinical examination ie detecting subclinical urate deposits, and whether this modality can clarify cases of doubt as problem solving tool. Ten patients were recruited who already had been diagnosed with gout by means of joint puncture with aspiration of synovial fluid and 10 control patients that did not have gout clinically. The patient records of all patients were analyzed and all patients underwent a complete rheumatological examination and DECT. The evaluation of the DECT images was performed by two radiologists working independently of one another.
This study showed that the DECT images of all patients proven to have gout yielded correspondingly positive findings in the aspirated joints. The DECT images of the control group all showed negative findings. “Our findings indicate that deposits of mono sodium urate crystals can be detected sub clinically more efficiently using DECT than with the traditional clinical examination,” says Dr. Nicolaou. The fact is that more areas involved with gout were found overall per DECT than through the other clinical examination ,ie 200 sites with DECT versus 53 sites clinically, ie four times more foci were revealed with DECT(p < 0.05). Furthermore, it has become evident that DECT can detect the presence of gout in hands, wrists feet, ankles, knees significantly better than the traditional clinical examination. DECT did not achieve significantly better results in the detection of gout in the elbow.
Full statement from Siemens: New diagnostic method for gout: Dual Energy Computed tomography instead of joint aspiration