Dual energy CT shows promise as new diagnostic method for gout
4 June 2009
A study at the Vancouver General Hospital in Canada shows that dual-energy computed tomography (DECT)
has potential for identifying deposits of uric acid to diagnose gout.
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.
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
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
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 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
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 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 < 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 subclinical 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 , ie 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 subclinical tophi are present."
"DECT is a promising new technique that can in a reliable,
noninvasive fashion confirm the presence of gout tophi subclinically,
provide information on the patient's disease burden and enable
differentiation from other diseases. This technique may be used for
monitoring treatment success and can be used to resolve unclear cases”,
says Dr. Nicolaou. However more research is required to more clearly
define DECT role in the management of Gout.
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