Diagnostic
Imaging
November 2003
ADVANCED
CT
CT
designers dream up more specialization for future scanners
Next
generation promises more speed, more rows, and the end
of one-size-fits-all scanners
By:
Sarah Jersild
CT is the Swiss army knife of modern
imaging: fast, efficient, and capable of handling most
radiological challenges that come its way. Manufacturers,
researchers, and clinicians are working hard to beef up
CT's capabilities with faster scan times, greater numbers
of slices, increased power, and more stringent dosing
controls. But these efforts may eventually detract from
CT's all-things-for-all-imagers reputation, forcing radiologists
to choose what they need from CT.
"The power of CT is that it does everything,"
said Dr. Stanley Fox, manager of CT advanced applications
and chief clinical officer at GE Medical Systems.
CT tends to be the modality of choice
for emergency room doctors when they need a fast diagnosis,
as well as the gold standard for abdominal complaints.
The technology behind CT has advanced quickly, and radiologists
are clamoring for more. The chief measure of these technological
advances up to now has been the number of slices.
"About 30% of U.S. customers in the first
quarter of 2002 were buying eight-slice and greater CT
scanners," said Doug Ryan, director of the CT business
unit at Toshiba America Medical Systems. "As of the first
quarter of 2003 and into the second quarter, 75% of the
market or greater were buying eight- to 16-slice CT. We're
seeing this all the way down to regional 150-bed hospitals."
Despite the rapid adoption of the technology,
however, 16-slice CT may not be getting the workout it
should be. Radiologists have to change the way they look
at data, according to Dr. Elliot Fishman, director of
diagnostic radiology and body CT at Johns Hopkins University.
"If you speak to GE or Siemens, they'll
tell you that most customers don't use 16 like 16-slice
can be used: They use it like a one or a four, the same
way they've always done it," he said. "I've been in CT
for 20-plus years, and 20 years ago, we had 35 slices
per patient. Now we have 1000. If you think you're going
to look at 1000 slices the same way you looked at 30,
you're crazy."
All the major CT manufacturers are moving
to 3D rendering and are continuing to refine technologies
that assist in viewing the vast amount of data captured
by multidetector scanners.
"The big dream that customers had when
helical first came out was 'thin from thick,'" Fox said.
"They didn't always want to look at thin images, but they
wanted the ability to go back and look at the thinner
images in a problem-solving way."
'CT ULTRASOUND'
Clinicians want to be able to play "CT
ultrasound," Fox said. They want to interrogate that volume
of data at any plane, at any slice thickness, and work
around the problem area until they see what they need
to see.
Siemens Medical Solutions has introduced
Inspace real-time volume rendering to help radiologists
perform timely interpretation of data sets. By the end
of the year, the company plans to launch a new 3D workflow
system that allows clinicians to define what they want
to look at before the scan takes place, said Richard Hausmann,
president of the CT division. The system will then present
a 3D picture of those slices for evaluation.
GE's Xtream workflow engine will allow
radiologists to take a 3000-image data set and develop
it in such a way that they can look at 3D oblique and
sagittal views in the same time it takes to view 200 images
in the axial format, said Peter Arduini, general manager
of global CT business for GE Medical Systems.
Eventually, imagers may be able to select
protocols based on initial diagnosis-such as chest trauma-and
have the scanner automatically take the necessary steps
to produce 3D and 4D images. But getting scanners to deliver
this sort of functionality is just the first problem,
said Dr. Dennis Foley, chief of digital imaging at the
Medical College of Wisconsin.
"Historically, we've had the modality
development before we've had the electronic archive display
development suitable to handle data," he said. "The modality
vendors and the PACS vendors have to give us the tools
at a workstation to better evaluate the data. It's going
to take a while-PACS vendors never envisioned their platforms
as being primarily 3D displays."
Data also have to be shared outside the
radiologist's workstation. Foley suggests a thin-client
approach may be the best answer to that problem, but so
far such a solution is not available.
Another challenge vendors face is archiving
the vast amount of data collected by multidetector scanners.
As one way of attacking the problem, manufacturers are
developing advanced lossless compression algorithms that
will allow their systems to store more data in less space.
But the real breakthrough may be more philosophical.
"We're doing some think-tank work on
what you need to archive," Arduini said. "Should you save
every image you produce, or should you save only the most
pertinent data?"
The amount of data is going to keep increasing.
Suppliers are researching ways to provide 64-, 128- and
even 256-slice scanners. Toshiba is already testing a
256-slice, 0.5-mm detector in Japan, but it won't hit
the market any time soon. Computing power has yet to catch
up with the leaps in CT technology.
"It depends on Moore's Law and the cost
of computing coming down," Ryan said. "Based on the technology
evolution, we would be looking at something like the Pentium
10 to keep that system economically viable. That's not
unforeseeable. The way it's going, you could have that
as early as 2007."
The next advance won't be that long in
coming, however: Manufacturers plan to introduce 32-slice
CT in the near future. Although none of the major manufacturers
have firm dates set for the release of 32-slice CT, Fishman
predicts radiologists will start to see them at this year's
RSNA conference.
The leap forward in slices may not translate
to a comparable leap for some diagnostic situations, however.
"Looking for lung metastases or an abscess
in the abdomen-we're really good at that now," Fishman
said. "Will 32-, 64-, or 128-slice make a difference?
No. But for some applications, like cardiac imaging, it's
going to make a major difference."
Other areas that could see improvement
are oncology, interventional treatments, perfusion, and
vessel analysis. But by far the most hyped area is the
heart. Cardiovascular imaging is something of a Holy Grail
for CT. All of the major manufacturers tout their systems'
prowess at capturing images of the heart in action, and
all are planning improvements to make cardiac imaging
easier and more consistent.
"The cardiovascular market over the next
five to seven years in the U.S. will easily be a half-billion-dollar
market," said GE's Arduini. "The only real way of routinely
diagnosing disease of the coronaries with any specificity
is a cardiac cath, which is in the neighborhood of $1500
to $2000 a study. If a CT scanner gave you consistent
results, you could probably perform that for in the neighborhood
of $500."
That level of consistency is not yet
available, according to Fishman.
"Cardiac is a potential big win, but
the question is, How good are you?" he said. "If someone
comes to us with appendicitis and we say negative CT,
99.99% of the time it's negative. When can you say '(The
chest CT) is negative, stop the workup'? Even in the best
of hands, you probably could be successful in 70% to 80%
of patients."
Philips is putting much of its energy
into cardiac CT imaging. The company's cardiac CT can
track changes in heart rate and maintain a reasonable
temporal resolution throughout the study, so users don't
have to go back and readjust the phases.
Arduini predicts the release of studies
that detail different aspects of cardiac care using CT
by the end of 2003 and early 2004 and expects to see more
complete systems by early 2005 at the latest.
GE is looking at electron-beam technology
to enhance the power of its CT systems. The company plans
to release studies that show electron-beam tomography
has a 99% evaluable case rate with cardiovascular cases,
Arduini said. That is in part because electron beam allows
such high scanning speeds: up to 50 msec, or a 10-fold
increase in shutter speed over standard CT systems. He
cites one patient scanned with electron beam who had a
heart rate that varied from 40 beats per minute to 150
beats per minute. Because electron-beam tomography was
able to capture images gated to the heart rate, the studies
came out perfectly.
Speed of acquisition is only one aspect
that needs to improve, however. In order to deal with
more complex processes such as cardiovascular imaging,
CT scanners also need to develop more power and flexibility.
Siemens is concentrating on enhancing
technology beyond the number of slices. Hausmann predicts
that systems in the future will allow more flexibility
with modular systems of arrays, making it possible to
reconfigure the number and positioning of the arrays to
suit the job at hand.
"With these kinds of array detectors,
new applications are thinkable. Dynamic situations such
as perfusions of the heart or brain could be examined
by CT," he said.
Manufacturers are also working on boosting
power, in part to deal with larger patients and more complex
low-contrast situations. The push toward more power is
fostered by increasing rates of obesity in the population,
Fox said. More power is needed to image larger patients.
The increase in power provided by multidetector
scanners, along with the growing use of CT in many situations
previously covered by other modalities, is also increasing
the amount of radiation patients are exposed to. Fox pointed
out that emergency departments are scanning younger and
younger patients with a better prognosis.
"The radiation dose is not trivial,"
said Dr. Bruce McClennan, chair of diagnostic radiology
at Yale University. "The largest percentage of radiation
dose from medical treatment imaging today comes from CT
scanning. The dose from a multidetector CT scan of the
chest can be the equivalent of 10 years of mammograms."
All the manufacturers are adopting methods
such as volumetric exposure control, Fox said. Toshiba
has recently updated Real EC, a real-time exposure control
protocol, to allow radiologists to determine the percentage
of noise they will tolerate. The system automatically
runs from that level. Siemens plans to introduce additional
automated real-time dose-reduction tools that are exhibited
in 3D. Philips models its dosing regimen for pediatric
patients on a dedicated pediatric phantom. And GE has
developed a 3D dose-modulation tool that works through
the x, y, and z planes, so a scan that goes through the
shoulder and chest will update dosage parameters appropriately
for the patient's body size.
FLEXIBILITY LOST
As scanners become more complex to take
on more complicated imaging challenges, they may lose
some of the flexibility that makes CT so popular today.
Using CT for radiation therapy planning is an example.
"You'd build a wider bore, multidetector
CT scanner," Fox said. "But when you widen the bore, you
put some limitation on how fast you can rotate. A bigger
geometry, which would help radiation therapy planning,
will always be one tenth or maybe two tenths of a second
slower than a general-purpose CT scanner. It's hard for
customers to envision a situation in which a scanner doesn't
do everything and is still state of the art."
Clinicians must realize that state of
the art may not be the best option for their particular
practice, Arduini said.
"If I were a customer looking at this
product, the first thing I would say is What's my case
mix and how am I going to grow it?" he said. "How is that
going to improve my reimbursable studies, and how does
that affect my productivity?"
After evaluating those factors, radiologists
may determine that the future for their practice exists
right now.
MS. JERSILD is a freelance writer based
in Chicago.