Imaging the Heart: The New Frontier
MRI Heart Scans continued...
No radiation is used with MRI; however, powerful magnets are used to create
images -- so certain people cannot have an MRI, like those who wear a pacemaker
or defibrillator. The contrast medium is not iodine-based, so there are no
The MRI scan requires that the patient lay on a cushioned table inside the
MRI tube, which gives some people claustrophobia (a sedative can help with
this). Open MRI scanners were developed to solve the claustrophobia problem,
but it's not an option for heart procedures, says Steiner.
"We can't use open MRI with the heart, because there is motion. If
patients are claustrophobic, they can have the other tests - echocardiography,
nuclear stress tests, or CTA," Steiner says.
PET/CT Heart Scans
Positron emission tomography (PET) scanning -- combined with CTA -- "is
the future," Steiner tells WebMD. "We will have the combined advantages
of PET and CTA, either in one composite image or side-by-side images."
PET scans are a form of nuclear medicine -- "nuclear" being the
small dose of radioactive material you are injected with before the test (the
radiation exposure is similar to that of a standard X-ray). As with CTA, PET
involves a doughnut-like scanning device that takes the images.
With PET, the cardiologist and radiologist can examine biological functions,
like blood flow or glucose metabolism of the heart, Steiner explains.
"However, PET does not show the heart's shape or volume," he adds.
"CTA and MRI show us that."
There is a debate among cardiologists whether PET/CTA is appropriate for
heart diagnosis, Garcia says. "PET has been very useful in cancer
diagnosis. PET tells whether the tumor is active or not, whether it is
consuming a lot of blood. CTA tells where the tumor is. But we don't deal with
cancers in the heart that often."
In cardiology, Garcia believes that PET/CTA may help "in very specific
circumstances, like when we know there is a blockage but are uncertain how
severe it is. But in the majority of cases, the other tests can tell us
Garcia is also concerned about safety. "There are arguments that we're
giving too much radiation when we're doing both [tests] at the same time,"
PET/CTA "is in evolution," Levine tells WebMD. "It has the
potential to assess both heart anatomy and function, and can be a diagnostic
tool when the two are combined. But right now, only a minority of hospitals has
the capability to use it."
Medicare is now paying for PET/CTA, Steiner adds. "Each of these tools
has advantages and disadvantages. We want to do the right thing for each
patient decide the best approach."
Garcia remarks that older tests may in time be used less, or in different
ways. "We're still learning about the potential of this new
technology," he says.