Neil Lipsitz of the Healthcare Sector of Siemens Southern Africa in the Western Cape, says as one of the few Somatom Definitions installed worldwide, this leading edge scanner is the fastest machine available of its kind for cardiac computed tomography (CT).

With more applications rolling out all the time, Lipsitz says among the latest is a new method for diagnosing gout, where the conventional and most reliable method is to aspirate the joint in order to obtain fluid to verify the presence of monosodium urate crystals (uric acid).

“Up to now, CT has played a limited role in the evaluation of gout, since conventional CT systems cannot reliably verify deposits of uric acid. However, a current study at the Vancouver General Hospital in Canada gives rise to speculation that dual-energy computed tomography (DECT) could radically change the diagnosis of this disease,” he says.

DECT enables fast, non-invasive examinations and, based on initial evaluations, has the potential to surpass the invasive gold standard and clinical examination in terms of reliability.

“Investigations have confirmed the high sensitivity of the DECT method in detecting uric acid deposits. The Canadian scientists used the Siemens Somatom Definition CT scanner for their investigation as it is the only system in the world that features two X-ray tubes capable of simultaneously producing different energies,” he says.

Gout is the most widespread form of crystal arthopathy and the most common inflammatory joint disease in men. It is caused by the deposition of uric acid crystals in joints and predominantly occurs among men, with millions of people worldwide currently afflicted by this painful, destructive disease. Due to eating habits, these figures are constantly increasing.

The classical symptoms of gout are painful, visibly swollen joints. Gout is nevertheless difficult to diagnose, since quite a few diseases, for example various forms of arthritis, have similar symptoms. While imaging techniques can help to locate gout lesions, the specificity of X-ray, single-source computed tomography, magnetic resonance imaging and ultrasound is not sufficient to definitively confirm a diagnosis. Certainty can be achieved only by verifying the presence of mono sodium urate crystals, also called uric acid deposits (tophi), in and around the joint. This is done by aspirating the joint with a needle to remove the fluid, which is then microscopically analyzed under polarized light. A joint puncture may be difficult with acutely inflamed joints, since the amount of fluid available may not be sufficient for this purpose. Furthermore, some anatomical regions are difficult to access, for example in the spinal region. A non-invasive diagnostic technique is therefore extremely desirable.

The prospect of a fast, safe and noninvasive diagnosis of gout using dual-energy computed tomography (DECT) has sparked great interest in Canada. 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 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 colour 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, colour 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 i.e. detecting sub-clinical 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, i.e. 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.

In addition, the study also provided new information on the presence of sub-clinical tophi and the accumulation of monosodium urate crystal deposits in clinically challenging anatomic regions.

“To our surprise, the study showed that uric acid can be initially deposited in tendons and ligaments near and within the knee joint, ankle joint, wrist, i.e. in the collateral ligament / cruciate ligament and deep flexor tendons of the wrist,” says Dr. Nicolaou. “This is very important to know, since these deposits can increase the susceptibility of tendons and ligaments for tears. If we are able to detect the disease in an early stage, we can initiate a treatment to prevent destruction of the tendons and ligaments and joints where sub-clinical tophi are present."

"DECT is a promising new technique, that can in a reliable, non-invasive fashion confirm the presence of gout tophi sub-clinically that surpasses the sensitivity of clinical examinations, provides information on the patient's disease burden and enables differentiation from other diseases. This technique may be used for monitoring treatment success and can be used to resolve unclear cases,” says Dr. Nicolaou.

The Siemens Healthcare Sector

The Siemens Healthcare Sector is one of the largest suppliers of healthcare technology worldwide. The company is a medical solution provider with core competences and innovative strengths in diagnostic and therapeutic technologies as well as knowledge processing, including information technology and system integration. With its acquisitions in laboratory diagnostics, Siemens Healthcare is the first integrated healthcare company that combines imaging and lab diagnostics, therapy solutions and medical information technology and also supplements these with consultation and services. Siemens Healthcare offers solutions for the entire supply chain under one roof - from prevention and early detection to diagnosis and on to treatment and aftercare. In addition, Siemens Healthcare is the world market leader for innovative hearing instruments. The company employs some 49,000 employees worldwide and is present in more than 130 countries. During fiscal 2008 (ending on September 30), Siemens Healthcare achieved a total sales volume of 11.17 billion euros and incoming orders totaling 11.78 billion euros. The Sector profit from operations amounted to €1.23 billion (preliminary figures). For more information, go to: www.siemens.com/healthcare.

About Siemens Southern Africa:

Siemens has had a presence in South Africa since 1860 when the company installed the first telegraph line linking Cape Town and Simon’s Town. Today, Siemens offers a balanced portfolio of technologies focusing on the Industry, Energy and Healthcare sectors, together with the cross-sector business of Siemens IT Solutions and Services. The unique ability to offer horizontal, customised, end-to-end technology solutions enables Siemens to keep its customers one-step ahead. As a committed corporate citizen, Siemens has active corporate social investment programmes as well as a comprehensive approach to local content, manpower development, skills and training. Further information is available on the Internet at www.siemens.co.za