Imaging the Heart: The New Frontier

From the WebMD Archives

Chest pains, heart flutters, heart attack -- they are the signposts of heart troubles. In the past, such symptoms might mean a treadmill stress test or a cardiac catheterization to diagnose the problem.

That's changing with the advent of new imaging technology: CT scans, MRI, 3-dimensional echocardiography (3-D echo), and PET/CT.

"It's a new era we're at the tipping point right now," says Robert M. Steiner, MD, FACC, director of cardiac and pulmonary imaging at Temple University Health System in Philadelphia.

The traditional stress test shows the heart's function and how it performs under exertion such as walking on a treadmill or pedaling a stationary bike. In cardiac catheterization (cardiac cath), the cardiologist can examine the valves, arteries, and chambers via the use of contrast dye and a catheter inserted into the groin or arm.

But with the new imaging technology, "we can now get much the same information as we could with the [older] tests -- and do it much less invasively," Steiner tells WebMD.

"All these new tests examine function and anatomy beautifully. They are easier to perform, and often less expensive," Steiner says. "And because they are less invasive, they are easier on the patient."

Computed Tomography Angiography (CTA)

As a diagnostic tool for early heart disease, CTA is a major advance. "CTA is a better technique for finding small blockages in coronary arteries," says Mario Garcia, MD, director of cardiovascular imaging at the Cleveland Clinic Foundation. "If you have a blockage in the arteries, CTA is the best way to find it."

The CT scanner -- which looks like a large donut -- is an X-ray machine. A contrast dye is injected into the patient's arm and, as the patient lies on a table, the CT scanner rotates taking multiple images -- yielding highly detailed images of blood vessels and the heart.

Just a few years ago, the diagnosis would have involved a cardiac cath procedure, which can take an hour or more, compared to the CT scanner's five minutes.

Cardiac cath is still the better test for determining treatment for patients with serious heart disease, says Glenn N. Levine, MD, a cardiology professor at Baylor College of Medicine and director of the Houston VA's Cardiac Catheterization Laboratory.

"But with CTA, we can rule in or rule out significant heart disease and artery disease, or congenital abnormalities -- and we can see it in just a few minutes," Levine tells WebMD. "With CTA, we can view the structures of the heart and coronary arteries in any dimension, including a three-dimensional view. It's a very good test." For patients, there's much less anxiety compared to a cardiac cath, says Steiner. "There is minimal risk with CTA. And the results are over 95% accurate."

Continued

Echocardiography

An echo test involves ultrasound -- high-frequency sound waves -- to evaluate the function of heart muscle and valves, the same technology used to ensure a developing baby is healthy. In a cardiac echo test, a wand-like device is used to transmit ultrasound waves against the chest, to produce moving images of the heart.

Advances in echocardiography have improved this already excellent medium, Garcia tells WebMD. "Echo is biologically very safe. It uses no contrast medium, no radiation -- so it can be repeated often. And echo can evaluate the function of the heart muscle and valves better than any modality."

  • Portable Echo: Laptop-sized echo machines are making the technology more portable than ever before, Garcia tells WebMD. "If you're a paramedic, you can take it in a helicopter or ambulance, and get much information before the patient gets to the hospital. We cannot do that with other devices. In fact, [we] can do echo in space with the astronauts."

    Portable echo devices are being used in high school and college sports programs, he says. "There is always a small percentage of student athletes that experience sudden cardiac death, who are too young to have developed heart disease," Garcia says. "We can screen athletes before they get into competitive sports. It is very inexpensive."

  • Three-Dimensional Echo: With 3-D echo, the cardiologist can obtain multiple ultrasound images of the heart's interior -- then assemble them into a complete image of the heart in motion, Steiner explains. "It allows us to view the heart anatomy in a different way -- to get all sorts of special images we couldn't get before."

    3-D echo provides more accurate measurements of heart muscle function and a better view of heart valves than possible before, Garcia tells WebMD. "It also provides automatic measurement of heart muscle function. Rather than eyeball it, we can use computer analysis of how strong the heart muscle is contracting -- how strong blood is pumping."

    The procedure is used to evaluate complex valve or congenital heart disease, he adds. "Because it is an emerging technology, we are still trying to define its clinical applications."

  • Intracardiac Echo: Echo is being used during cardiac cath procedures, Garcia says. "A small transducer is threaded through the catheter," he tells WebMD. "It's a way of taking echo into the heart, so we can use it as a guide during an interventional procedure - such as closing holes in the heart, ablating arrhythmias, or ballooning open a narrow valve. This ultrasound provides a more accurate image to monitor the procedure while it is being performed."

Continued

MRI Heart Scans

Cardiac MRI "provides the gold standard of cardiac function and anatomy unsurpassed image quality in evaluating heart structure and function in 3-D-quality moving images," Levine tells WebMD.

And cardiac MRI "shows us more than echocardiography or an exercise stress test," Steiner adds. "Those tests have benefits, but MRI shows more in terms of the heart's shape, size, volume, function. We can see if there is valve disease, heart abnormalities, heart tumors, clots in the heart -- anything to do with anatomy and function. All the other tests can show parts of that, but MRI potentially shows it all."

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 allergy problems.

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."

Continued

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 this."

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," he says.

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.

WebMD Feature Reviewed by Brunilda Nazario, MD

Sources

SOURCES: Robert M. Steiner, MD, FACC, director of cardiac and pulmonary imaging, Temple University Health System, Philadelphia. Mario Garcia, MD, director of cardiovascular imaging, Cleveland Clinic Foundation. Glenn N. Levine, MD, cardiology professor, Baylor College of Medicine; director, Houston VA's Cardiac Catheterization Laboratory. WebMD Medical Reference with The Cleveland Clinic: "Diagnosing Heart Disease: Cardiac Catheterization." WebMD Medical Reference with The Cleveland Clinic: "Heart Attacks." RadiologyInfo: Computed Tomography Angiography (CTA). WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Diagnosing Heart Disease: Echocardiogram." WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Diagnosing Heart Disease: MRI." RadiologyInfo web site: "Positron Emission Tomography (PET Imaging)." Medline Plus web site: "Isotope Study."

© 2006 WebMD, Inc. All rights reserved.

Pagination