Advancements
in Cardiovascular Imaging Provide
Non-Invasive Options
May / June 2004
In the recently created Cardiovascular
Imaging Section at
the Hospital of the University of Pennsylvania, radiologists
are using state-of-the-art computed tomography (CT) and Magnetic
Resonance Imaging (MRI) scanners to perform noninvasive cardiac
studies. This new equipment provides capabilities in vascular
imaging and myocardial viability imaging which may allow some
patients to avoid invasive angiography.
Penn has the only radiology department in the region to
have a dedicated cardiovascular imaging section and the
first to
offer CT coronary angiography. All studies are performed
by technologists who are dedicated to cardiology and read
by
specialty trained radiologists.
“Because we perform both CT
and MRI we are able to select the best studies for each
individual
patient and we work closely with our cardiologists, cardiovascular
surgeons, cardiothoracic surgeons, interventional radiologists
and vascular medicine specialists and surgeons,” says Harold
Litt MD, PhD, assistant professor and chief of the cardiovascular
imaging section in the Department of Radiology at the Hospital
of the University of Pennsylvania.
“In many situations, especially difficult cases such as constrictive
pericarditis or cardiomyopathy, either MRI or CT can provide
us with important clues or a diagnosis that might not be available
using other techniques. It allows physicians to look outside
the heart into the cardiopulmonary anatomy that may not be
well seen on echocardiogram or catheterization,” says Victor
A. Ferrari, MD, associate professor in the Division of
Cardiovascular Medicine at Penn. “It is also an excellent
technique when evaluating cardiac masses and assessing the
anatomy and cardiac function and the complex anatomy in patients
with congenital heart defects.”
Computed Tomography
Typically, when a patient presents with chest pain he or she
may undergo a stress test. If the stress test is abnormal,
a catheter angiogram is used to examine potential narrowing
or a blockage of the coronary arteries that may require bypass
surgery or angioplasty. Now, in some patients CT coronary
angiography can be performed, replacing the invasive catheter
angiogram for diagnosis of coronary artery stenosis. In addition
to viewing calcified plaque, CT coronary angiography provides
images of the lumen of the coronary artery to look for stenosis
and non-calcified atherosclerotic plaque. “This new technique
may be a better way of estimating risk than the coronary calcium
score that was done before without the trauma of catheterization
—a very significant improvement for the patient,” says Dr.
Litt.
Catheterization requires anesthesia, carries risks of complications
such as damage to the blood vessels, and patients are required
to lie flat for a few hours. “Catheterization is still going
to have an important role, particularly if the patient needs
an intervention such as angioplasty or placing a stent, but
we are hoping to eliminate many unnecessary, purely diagnostic
catheter angiograms performed in low-risk patients,” says
Dr. Litt.
Penn radiologists also perform coronary calcium studies utilizing
CT to measure how much calcium is in the arteries that supply
the heart. They can estimate a person’s risk for having heart
attacks or other cardiovascular disease without giving intravenous
contrast. Furthermore, cardiac CT enables studies to be performed
on people who have pacemakers or other metallic implants in
their body that make them ineligible for MRI.
MRI Stress Testing and Viability Imaging
When a patient presents with a myocardial infarction it is
difficult to assess how much of the heart muscle has been
permanently damaged and how much would recover function if
blood flow was restored. Viability imaging, a new procedure
in which contrast-enhanced MRI is utilized to look for delayed
hyperenhancement of the heart, enables cardiologists and radiologists
to determine if a damaged portion of the heart muscle is viable.
“Viability imaging is critically important, especially in
the heart failure population. It helps us understand which
patients might benefit from surgery and avoid unnecessary
bypass surgery, revascularization or other interventions,”
says Dr. Ferrari. The high resolution of MRI stress testing
and viability imaging compared to nuclear techniques allows
noninvasive imaging specialists to see smaller areas of ischemia
and to differentiate between transmural and subendocardial
ischemia or infarction.
Noninvasive Vascular Studies
There are also noninvasive alternatives for vascular studies.
By utilizing either CT angiography (CTA) or MR angiography
(MRA), physicians can view the aorta and the vessels in the
legs all the way down to the toes without requiring a catheter
angiogram. “With the addition of CTA to our vast experience
with MRA, we can provide evaluation in all types of patients
for most vascular diseases,” explains Dr. Litt. At Penn,
approximately 5,000 CTA and MRA studies are performed each
year.
Vascular studies assist the diagnosis and treatment of claudication,
peripheral vascular disease, dissections and renal artery
stenosis. Another important procedure that is performed with
CT assistance is stent graft treatment for aortic aneurysms.
This is another example of a minimally invasive technique
replacing a very invasive surgery. CT angiograms are performed
to plan the stent graft placement and make the measurements
for the device. They are also used after the placement of
the stent graft to monitor possible complications.
Research
A new research study at Penn involves performing coronary
CT angiography on patients who present in the emergency
department
(ED) with chest pain. Each year, there are more than 5 million
visits to EDs for evaluation of acute chest pain; although
in most cases, the pain is not related to their heart or
coronary
arteries, many patients are admitted to the hospital and
undergo extensive testing to be certain the heart or coronary
arteries
are not involved.
“In collaboration with cardiology, emergency
medicine and radiology, a state-of-the-art 16 detector CT
scanner, one of the first in the United States with a special
X-ray tube and gantry designed specifically for cardiac imaging,
was installed in the ED at the Hospital of the University
of Pennsylvania. A coronary CT angiogram will be performed
on eligible patients within one hour of coming to the ED.
Our hope is to determine quickly if the coronary arteries
are normal or not normal and then decide if further cardiac
testing is necessary,” explains Dr. Litt. “This has the potential
to completely change the way we evaluate people who present
with acute chest pain.”
Currently in the research phase at Penn, a future potential
capability of both CT and MRI is characterizing atherosclerotic
plaques which exist in coronary arteries, not only viewing
the degree of narrowing in the vessels but actually looking
at the vessel walls. The technology can be used to evaluate
the structure of a plaque, including its lipid core and
collagen
cap. This information may allow physicians to determine which
plaques are more “vulnerable” and likely to rupture in the
future, which may lead to aggressive treatment before a
patient
experiences chest pain or a disabling myocardial infarction.
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