The advent of dual-source CT scanners represents a significant step up in the
evolution of CT machines. Designed with two X-ray tubes and two detector arrays,
the dual-source scanner captures data nearly twice as fast as previous scanners.
The dual-source CT scanner is ideal for cardiac imaging, says Stefan Ruehm,
M.D., Ph.D., associate professor of radiology at UCLA Medical Center. “It’s a
rather noninvasive diagnostic tool that allows a physician, with a very high
negative predictive value, to determine whether or not the patient has coronary
artery disease,” he says.
Smart Business spoke with Ruehm about how the new scanner aids
patients and doctors alike and what further developments he expects to see in
the early detection of heart disease.
How does the dual-source CT differ from earlier CT scanners?
The main difference is that it’s about twice as fast as the previous
generation of scanners known as 64-slice CT scanners. The dual-source CT has two
X-ray sources and two 64-slice detector arrays as compared to the previous
generation, which had just one X-ray source and one detector with 64 rows. There
has been a development of CT technology from one row of detectors to four rows
to 16 rows to 64 rows. The latest development, as seen in the dual-source CT, is
putting two 64-row detectors into one scanner.
What advantages does the new scanner offer patients?
It is particularly well suited for cardiac imaging because it provides very
fast data acquisition. If your data acquisition times are too long, you will end
up with images that show motion artifacts. You want to have a very small window
to collect data during your cardiac cycle. The big advantage of the dual-source
CT is that it nearly doubles the speed that you can acquire data compared to the
previous generation of scanners. You could do cardiac CT with the previous
machines; however, you had to use beta-blockers to decrease the heart rate. With
the dual-source CT you don’t need to give beta-blockers, you can scan patients
independent of the heart rate.
How does the noninvasive nature of the dualsource CT scanners aid
doctors?
In the past, if there was a question about coronary artery disease, you would
have done a catheter angiogram study. In a certain percentage of patients, you
would have done the study for diagnostic purposes because you would have seen on
the invasive angiogram that there is no coronary artery disease. This process is
not very beneficial to the patient because it’s a rather invasive procedure and
if you do it just for diagnostic purposes it’s not appropriate. There has been a
need for an alternative, and it appears with the dual-source scanners that you
can get diagnostic information concerning the coronary arteries in a far less
invasive manner.
How useful is the dual-source scanner in helping to identify medical
problems at an early stage?
The main goal is to detect coronary artery disease at an early stage and to
adapt certain therapeutic strategies. You want to do this early, because with
certain medications, you can prevent progression of coronary artery disease. The
problem so far has been that people were reluctant undergoing the types of
invasive procedures that were previously available. With this technique, we have
a rather noninvasive tool to detect coronary artery disease. If there are signs
of disease, patients can undergo medical treatment at a very early stage and
prevent further progression or complications.
In the future, what further developments do you expect to see in the
early detection of heart disease?
One further development focuses on the exact and objective grading of the
degree of vessel narrowing. However, it has been shown that the degree of the
narrowing of the coronary arteries does not predict the likelihood of a cardiac
complication.
What appears more important is the characterization of the plaque that causes
the vessel to narrow. There may be a change of paradigm away from the
quantification of the degree of the narrowing, or stenosis, towards the
characterization of plaque. In general, there are two different types of
plaques: unstable and stable. The unstable plaques are regarded as dangerous
while stable plaque is usually calcified plaque.
With the invasive, conventional angiogram you can only see the stenosis, but
you can’t tell anything about the vessel wall itself where the plaques develop.
With these new cross-sectional techniques, you can quantify the degree of
stenosis. Eventually, we hope to differentiate between a dangerous plaque and a
stable plaque.
STEFAN RUEHM, M.D., Ph.D., is an associate professor of radiology and
director of cardiovascular CT at UCLA Medical Center. Reach him at
sruehm@mednet.ucla.edu or (310) 825- 0958.
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