SOMATOM Definition Flash: Impressive Performance

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1 The SOMATOM Definition Flash makes a thorax scan for triple rule-out possible in less than one second.
SOMATOM Definition Flash:
Impressive Performance
In everyday clinical use, the SOMATOM Definition Flash
Dual Source CT scanner is proving to be innovative and versatile.
By Catherine Carrington
6 SOMATOM Sessions · May 2009 · www.siemens.com/healthcare-magazine
Cover Story
It’s said that experience is what separates
promise from reality. But when it comes
to the SOMATOM® Definition Flash Dual
Source CT scanner, experience shows that
promise is reality. As the innovative new
scanner is tested in daily clinical practice,
it is exceeding nearly every expectation.
Split-second thoracic scanning: proven.
Sub-milliSievert cardiac scans: confirmed.
Superb image quality: no question.
“This is the scanner that gives you all
options,” says cardiologist Stephan Achenbach, MD, a professor of medicine at
the University of Erlangen-Nuremberg in
Erlangen, Germany. “You can scan at
unprecedented low doses. You can scan
at both low and high heart rates. You can
“The SOMATOM
Definition Flash
is the scanner
that gives you all
options.”
Prof. Stephan Achenbach, MD,
Department of Cardiology,
University of Erlangen-Nuremberg,
Erlangen, Germany
scan with Dual Energy. The Definition
Flash does it all.”
Thorax and Beyond
At the University of Erlangen, radiologist
Michael Lell, MD, has used the Definition
Flash to perform thoracic imaging in
approximately 40 patients. Typically, he
is able to image the entire thorax in just
0.6 to 0.9 seconds.
“This is definitely a breakthrough,” Lell
says. “The scan is so fast, we can examine
patients who don’t hold their breath,
and we get perfect images.”
The speed of the Definition Flash translates to better patient safety and comfort.
For trauma patients, the ability to scan
the entire body in less than five seconds
not only reduces motion and breathing
artifacts, it has the potential to reduce
delays in getting to surgery. Pediatric
scanning promises to be easier and safer.
And eliminating the need for breathholding offers comfort to patients who
are very sick or injured.
“The scan speed is so fast that it’s really
unnecessary to switch a respirator on
and off in order to get sharp images,”
Lell says. “We can just keep on with the
respirator and do the fast scan, and we
get perfect image quality.”
Lell is especially pleased with both the
efficiency and effectiveness of the
Definition Flash in evaluating patients
who come from the emergency room
with chest pain. For these patients, he
uses a triple rule-out protocol. It includes
electrocardiographic gating, but avoids
the low pitch and high radiation dose
that once burdened triple rule-out studies
on single source CTs.
“We can do a single scan and rule out
three major killers from chest disease:
pulmonary embolism, aortic dissection,
and coronary occlusion,” he says. “And
with the new system, we just fly over the
heart and thorax very fast. We don’t have
redundant data anymore.”
As a result, Lell has found that the radiation dose for a triple rule-out study performed on the SOMATOM Definition
Flash amounts to just 1.6 to 1.9 mSv.
“It’s really changing thoracic imaging,”
he says. “On the one hand we have an
extremely fast scan that offers outstand-
“We can examine
patients who don’t
hold their breath,
and we get perfect
images.”
Michael Lell, MD, PD,
Department of Radiology, University
of Erlangen-Nuremberg, Erlangen,
Germany
ing image quality – and we get the coronaries for free. On the other hand, we
have the ability to perform Dual Energy
studies. That’s very exciting.”
Cardiac Imaging
Stephan Achenbach has also been scanning patients on the Definition Flash since
mid-February. So far, some 100 patients
have been imaged using the new lowdose Flash Spiral mode, that acquires data
in a single heart beat, during a 250 mspause in the cardiac cycle when the
heart is in diastole. The results have been
impressive.
“The Flash scanner is superb,” says Achenbach. “In cardiac imaging, what really
counts is temporal resolution, and this is
the fastest scanner on the market. The
image quality is excellent.”
SOMATOM Sessions · May 2009 · www.siemens.com/healthcare-magazine
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The worldwide first SOMATOM Definition Flash, installed at the University of Erlangen-Nuremberg,
Erlangen, Germany.
The Definition Flash, a second-generation
Dual Source scanner, is equipped with
two detectors and two X-ray sources set
at an angle of approximately 95 degree to
one another. With a gantry rotation time
of 0.28 s, the scanner boasts a temporal
resolution of just 75 ms. Moreover, an
innovation introduced with the Definition
Flash eliminates the need for the patient
table to slowly inch forward during data
acquisition. Instead, in low-dose Flash
Spiral mode, the scanner achieves gapless z-sampling even with the wide-open
spiral created by a pitch of 3.2 and a
table speed of more than 40 cm/s. This
is because the two detectors create two
complementary data spirals that together
include all the information that would
be found in a single spiral acquired at a
much slower table speed – but without
redundant, overlapping data and unnecessary radiation exposure.
During the first weeks of gathering clinical
experience at the University of ErlangenNuremberg, the Flash mode has been
used primarily to scan cardiac patients.
This approach has produced flawless
images free of motion artifacts. “This
scanner allows us to do cardiac imaging
at the lowest dose with the highest
image quality,” says Prof. Willi Kalender,
PhD, director of the Institute of Medical
Physics at the University of ErlangenNuremberg. “We actually measured both
spatial and temporal resolution in the
Flash mode, and they are uncompromised. For cardiac imaging, no question,
this is the best.”
Equally important, both patient examinations and physics measurements conclusively show that the Definition Flash
can scan the complete heart at an unprec-
8 SOMATOM Sessions · May 2009 · www.siemens.com/healthcare-magazine
edented radiation dose of less than 1 mSv.
Early testing focused on patients weighing less than 90 kg (200 lbs) and used
settings of 100 kV and 320 mAs. The
result was an average dose of just
0.94 mSv. Stephan Achenbach is now
evaluating whether dose can be reduced
even further in thin patients and how
settings might need to be adjusted in
heavier patients.
A sub-milliSievert radiation dose has
the potential to expand the horizons of
cardiac CT to include screening for prevention of cardiovascular disease. “We
are now at a dose for CT angiography
that is less than it used to be for calcium
scoring,” Achenbach says. “This low
dose could allow us to use cardiac CT
for screening. The question is a medical
one: Does it make sense to do screening?”
Preliminary data published in the Journal
of the American College of Cardiology
in 2007 and 2008 suggest that findings
of non-calcified, non-obstructive plaque
on CT angiography add new information
that can be used in determining a patient’s
cardiovascular risk and prognosis. But
the clinical value of cardiac CT screening
needs to be confirmed in larger studies,
Achenbach says. It is a project he and his
colleagues are already undertaking.
“It’s possible we are going to find that
there are specific patient groups who
benefit from this test – patients who
have diabetes or a strong family history
of heart disease, for example,” Achenbach
“This scanner allows
us to do cardiac
imaging at the lowest
dose with the highest
image quality.”
Prof. Willi Kalender, PhD,
Director of the Institute of Medical Physics
of the University of Erlangen-Nuremberg,
Erlangen, Germany
Cover Story
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2 With the latest DSCT technology, the heart can be visualized artifact free and with an ultra-low dose of 0.95 mSv in Flash speed.
says. “We don’t have that data yet, but we
now have a scan mode that would allow
us to use this technology for screening
if we find that it makes sense for the
patient.”
Dual Energy
Dual Energy studies are a special interest
of Hatem Alkadhi, MD, who heads both
body CT and cardiovascular imaging at
the Institute of Diagnostic Radiology,
University Hospital Zurich, Switzerland.
He has performed hundreds of Dual
Energy exams using the first-generation
Dual Source scanner, the SOMATOM
Definition, and now the new Definition
Flash scanner as well.
“Dual Energy gives radiologists additional
information that we don’t have when
making single energy scans,” says Alkadhi.
“This is a great benefit of this technique.”
Dual Energy imaging involves the simultaneous operation of two X-ray sources
at different energy levels. This enables
differentiation of fat, soft tissue and
contrast material on the basis of their
unique energy-dependent attenuation
profiles. As impressive as early versions
of Dual Energy imaging have been, the
Definition Flash brings new strengths to
the table.
An important new feature is the selective
photon shield that pre-filters high kV
X-rays, removing low-energy photons.
This improves separation of the 80 kV and
140 kV images and, therefore, improves
material differentiation by about 80%.
In addition, the photon filter consistently
reduces image noise and substantially
cuts radiation dose. “With the second
generation of Dual Energy, we’re finally
able to deliver additional diagnostic information with dose levels comparable to
a single energy scan. That’ll make the
decision to use Dual Energy even easier
for us,” Alkadhi says.
An improved ability to separate materials
has important clinical implications. It
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3 The improved ability to separate materials with Dual Energy makes it easier to characterize the composition of urinary stones.
makes it easier to characterize the composition of urinary stones, for example,
and guide clinical decisionmaking. If a
stone is composed of uric acid, the urologist has the option to try medical therapy, rather than immediately referring
the patient for shock wave lithotripsy.
“This is better for the patient,” Alkadhi
says. “And our ability to use Dual Energy
to separate materials of similar density
is what makes it possible.”
Similarly, Dual Energy imaging makes it
simple to differentiate iodinated contrast
material from bone, two materials with
similar densities on standard CT. With a
click of a button, bones can be removed
from an image, leaving only the opacified arteries for examination. In other
circumstances, iodine can be subtracted
from an image, creating virtual nonen-
hanced images without need for a separate scan prior to contrast injection. This
approach is helpful in reducing radiation
dose when performing studies that would
normally involve more than one imaging
phase.
It is also helpful when a suspicious incidental finding is noted on a contrastenhanced scan, Alkadhi says. With standard CT, it is impossible to determine in
retrospect whether the lesion is simply
a hyperdense mass or has the propensity
to take up contrast, a worrisome clue that
suggests malignancy. With Dual Energy
imaging, a virtual “do-over” is possible. By
subtracting iodine from the image, it is
possible to create a precontrast image and
evaluate lesion density in the absence of
contrast enhancement.
The SOMATOM Definition Flash is improv-
10 SOMATOM Sessions · May 2009 · www.siemens.com/healthcare-magazine
ing another important application of Dual
Energy CT – evaluation of suspected pulmonary embolism. Dual Energy imaging
enables the radiologist to not only detect
a blood clot that is cutting off blood
flow through the pulmonary artery, but
also to show the effect of the obstruction
on perfusion of the lung tissue itself.
In the past, the use of Dual Energy imaging was limited to the center of the lung
because of the smaller size of the second
detectors. A similar problem hampered
Dual Energy imaging in the liver, where
observing contrast uptake can aid in
determining whether a lesion is hepatocellular carcinoma or a hemangioma.
To realize its full potential, Dual Energy
must be able to image even lateral segments of this large organ.
“When we make a Dual Energy scan,
Cover Story
we want to cover the whole organ of
interest – the whole lung, the whole
liver, the whole abdomen,” Alkadhi says.
“If you can’t, it limits the practicability
of your technique and the willingness
of the radiologist to use it. Obviously
Siemens understood this. The Definition
Flash is a big step forward with the large
Dual Energy field of view.”
Now the Definition Flash is outfitted
with two 4-cm detectors, and the field of
view is no longer a limitation in large
organs like the lung and liver. “With the
new system the field of view is so large
we can cover the entire lung,” Alkadhi
says. “The lung parenchyma is completely
displayed with Dual Energy properties,
including the periphery.”
Dose
Dose savings are built into the SOMATOM
Definition Flash. Besides the reduced
radiation exposure that directly results
from the high table speed, the scanner
has several other dose-sparing features.
Previously, Dual Energy imaging typically
exposed patients to between 10% and
20% more radiation than a corresponding
single energy scan. Now, the photon
shield eliminates the dose penalty in most
types of Dual Energy studies, Kalender
says.
In addition, the new scanner is equipped
“With the second
generation of Dual
Energy the field of
view is so large we can
cover the entire lung.”
Hatem Alkadhi, MD, PD,
Institute of Diagnostic Radiology,
University Hospital Zurich, Switzerland
with adaptive dose shielding, which blocks
the X-rays at the beginning and end of
each spiral acquisition that will not be
used in image reconstruction. In the case
of cardiac scans, adaptive dose shielding
cuts radiation dose by as much as 25%
when the studies are performed using a
conventional pitch. However, the dose
savings are expected to be much greater
when patients are scanned using the
Flash mode.
“The percent dose reduction with the
adaptive dose shield is greater the higher
the pitch and the shorter the scan range,”
Kalender says. “That means as we go to
even higher pitch values, the effect of
shielding on dose is greater. The same
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Low dose
applies to shorter scan ranges, such as
for the heart or the brain, or in pediatric
imaging. We can expect a higher percent
reduction as compared to standard scanning.”
“For example, the radiation dose could
be reduced by as much as 50% for a scan
of the heart performed at high pitch on
the Definition Flash, when compared to
the same type of scan without the dose
shield,“ Kalender says.
Another dose-saving feature designed
for the Definition Flash is X-CARE. This
technique, which provides organ-specific
dose reduction, enables the radiologist
to turn off the X-ray tube during the portion of the gantry rotation that would
directly expose radiation-sensitive organs,
such as the breast, thyroid gland, or eye.
According to a study Kalender published
in European Radiology last year, the
X-CARE technique can cut radiation dose
to the breast by 50% during thoracic
imaging.
“It’s the best way to reduce dose to the
female breast,” Kalender says. “It’s an
exciting prospect.”
Catherine Carrington is a medical writer and
holds a master’s degree in journalism from the
University of California Berkeley. She is based
in Vallejo, CA.
Further Information
High dose
4 Direct exposure of dose sensitive organs can be significantly reduced by using X-CARE.
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somatom-definition-flash
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