Public HealthNew Diagnostic Method For Gout: Dual Energy Computed Tomography Instead Of Joint Aspiration
The most reliable method of diagnosing gout is to aspirate the joint in order to obtain fluid
to verify the presence of monosodiumurate crystals (uric acid). 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. 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 management of this disease. DECT enables
fast, noninvasive examinations and, based on initial evaluations, has the potential to
surpass the clinical examination in terms of identifying subclinical disease. Investigations
have confirmed the high sensitivity of the DECT method in detecting uric acid deposits. The
Canadian scientists used the SOMATOM Definition computed tomography (CT scanner)
from Siemens for their investigation. This systemis the only CT scanner worldwide that
features two X-ray tubes capable of simultaneously producing different energies.
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 and around joints and
predominantly occurs among men. 2.1 million people in the USA and some 1.5 million people in
Germany are currently afflicted by this painful, destructive disease. Furthermore, due to our 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- 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 noninvasive 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 in
gout.
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 a 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 Siemens Healthcare Sector