At the Heart of Echocardiography

Technologies such as 3D, contrast agents, Doppler imaging and hand-held echocardiography systems are blazing new paths to better cardiac care - and research into intuitive ways to annotate digital echo studies to allow instant access to specific images hopes to speed diagnosis and image sharing in the not-too-distant future.

The only thing small about echocardiography is the footprint of the ultrasound units - in comparison to their CT, MR and nuclear medicine cousins. This robust component of any hospital's cardiology department is expanding annually due to the rising number of patients requiring cardiac care. And today, it is being driven by a number of innovative technologies, such as three-dimensional imaging, contrast agents, Doppler imaging and hand-held echo. These technologies also are opening the door to new applications in the future.

THE NUMBERS

Ultrasound has proven itself as a dependable, largely non-invasive and fairly inexpensive modality to diagnose and monitor conditions of the heart. Of these conditions, cardiovascular disease (CVD) is currently the No. 1 cause of death in the United States, claiming the lives of nearly 950,000 Americans each year. CVD includes high blood pressure, coronary heart disease, congestive heart failure, stroke and congenital heart defects.

In a recent report published by the American Heart Association (AHA) titled "Heart Disease and Stroke Statistics," the organization reveals a number of alarming statistics: coronary heart disease (the single largest killer of Americans) accounts for one in five women's deaths; an estimated 700,000 Americans will suffer a coronary attack this year; cardiovascular disease is the No. 3 cause of death for children under the age 15; and at age 40, the lifetime risk of developing congestive heart failure (CHF) for both men and women is one in five.

As these numbers increase, so has the use of echo in cardiology departments and heart centers. From 1992 to 2001, ultrasound use among U.S. cardiologists increased by 87 percent, according to a group of researchers from Thomas Jefferson University in Philadelphia. Led by David Levin, MD, former chairman of radiology at the institution, the study specifically concluded that echocardiography utilization among U.S. cardiologists surged 88 percent.

"The cardiology ultrasound imaging equipment market is the second largest clinical segment of the U.S. ultrasound market with more than $383 million in revenue in 2003," says Luke Liem, medical imaging research analyst for Frost & Sullivan. "The market will continue to experience healthy growth in both revenue and unit shipments going forward as a result of an increase in the U.S. population age 55 and older, an increase in the cumulative patient population who have undergone open-heart surgeries and cardiac catheterizations, and a strong pipeline of technological innovations."

3D IMAGING ON THE MOVE

One promising innovation in echocardiography is three-dimensional (3D) imaging. In November 2002, Philips Medical Systems debuted real-time 3D imaging, Live 3D Echo, on its Sonos 7500 high-end cardiovascular ultrasound unit. An installed base of about 700 hospitals, private practices and academic institutions are now using Live 3D Echo.

"It comes close to the resolution that you get in two-dimensional imaging, except its spread in 3D space in real time," says David Sahn, MD, professor of pediatric cardiology at the Oregon Health and Science University in Portland. The facility uses live 3D for both adult and pediatric echocardiography in clinical and research settings.

"The pediatric exams are for strange ventricles or strange valves, septal defects, and prenatal imaging at 16 to 17 weeks," explains Sahn. "We are doing intra-operative imaging in 3D to help the surgeon look at anatomy before and after bypass. We are looking at mostly valvular disease, although we are looking at some contrast implications of live 3D that may give us an approach to perfusion."

Capturing real-time 3D echo images requires a transducer technology that can put together the 3D volume in less than a 15th or 20th of a second, says Sahn. The speed of sound and the need to acquire the image one line at a time was the biggest limitation previously hindering 3D's use in live echo imaging. Most ultrasound machines create high-resolution images by transmitting and receiving single beams. One frame of a 2D ultrasound image is typically composed of 96,160 lines; for 3D, an image frame is composed of nearly 10,000 lines.

"It's not a question of how has 3D changed echocardiography, but how will this technology change echocardiography," says Miquel Quiñones, MD, medical director at the Baylor Heart Clinic. "It is still a technique that is being integrated and therefore finding the areas where it is going to have the biggest impact."

A helpful tool in pre-surgical planning and congenital heart disease for pediatric cardiologists, Quiñones explains that an area of focus (not yet ready for prime time) is coronary heart disease. "We are very optimistic that 3D echo will improve our ability to evaluate the movement and function of the segments of the heart, improving our diagnosis of coronary artery disease and looking at the effect of the severity of the problem," says Quiñones.

Researchers at Duke University's Department of Biomedical Engineering are currently working on combining contrast agents with 3D imaging technology to see if coronary artery flow can be assessed non-invasively with ultrasound. "If we can image coronary arteries with just a peripheral injection without having to do a catheter or MRI, it would be beneficial and inexpensive for the patient, performed sequentially on a follow-up basis and also quick to perform," explains Olaf T. Von Ramm, PhD, professor of biomedical engineering and director for the center of emerging cardiovascular technologies at Duke University.

CONTRAST AGENTS AT WORK

There is nothing comparatively new about contrast agents; they actually are a 15-year-old endeavor. But in the past several years, the use of contrast agents in echocardiography has gained regulatory approval, more popularity and further acceptance.

Research indicates that nearly 20 percent of the 80 million echocardiograms performed annually in the United States cannot provide clear images due to a patient's body structure or other heart conditions. Suboptimal echocardiograms are a key factor in the emerging use of ultrasound contrast agents in cardiovascular imaging.

The intravenous agents, which are composed of a solution of microbubbles or occasionally air-filled microspheres, provide clinicians with a "second opinion." In the United States and Europe, contrast agents are approved for left ventricular opacification and enhanced endocardial border delineation.

"There have been a multitude of instances where we thought we had a diagnosis and when we added a contrast agent, we discovered a whole different ball game," says Baylor Heart Clinic's Quiñones. While the technique has developed into an every-day imaging technique, Quiñones adds there is a certain culture change that happens as a result of its use.

"For many years, the ultrasound lab [in cardiology] did not put needles in anybody," explains Quiñones. "People now must realize that the world will not collapse if you have to put an intravenous in somebody's arm. It means that people have to be trained to think this way and people in the lab have to be trained on how to do it correctly. It does add a little bit of complexity to echocardiography."

In 2000, researchers from the American Society of Echocardiography reported that contrast agents are especially useful components in stress echo, imaging obese patients and imaging those with lung disease. "For us, in anywhere from 10 percent of transthoracic echo studies to upwards to 30 percent of stress echo studies, we cannot see all the [heart] walls well enough for final diagnosis," explains Vincent Sorrell, MD, chair of cardiovascular imaging and associate professor of medicine at the Sarver Heart Center at the University of Arizona Medical Center. "The contrast agents allow us to see the [heart] function and the heart wall motion a lot better."

Clinically, explains Sorrell, contrast agents can be used for poor quality images, poor quality left-sided Doppler tracing, possible left ventricular thrombus, vascular studies to enhance Doppler data or vessel wall imaging, and transesophageal echo studies for wall motion.

"I think right now across the country there are centers using quite a bit of contrast and plenty of centers that unfortunately have not yet evolved into using it," opines Sorrell. Up until now, contrast agents were hindered by high cost and a slim market that only included FDA approved agents from Bristol-Meyers Squibb Medical Imaging and GE Amersham. The prices of agents are expected to decrease as more companies join the market place and the agents become more affordable.

DIGGING DOWN ON DOPPLER

Techniques in echocardiography have improved so much over the years and installations became so abundant that almost any patient with suspected cardiac disease will get an echocardiogram. Sandeep Khosla, MD, chief of cardiology at Mount Sinai Hospital in Chicago, says that the hospital's echo volume has increased at least 300 percent in the last five years. "It would be fair to say that echocardiography today for a cardiologist is an extension of the physical exam," says Khosla. One reason for the steady incline in echo dependency is due to Doppler technology.

"As echo has evolved, we have discovered that the best way to learn heart physiology is with Doppler because it is non-invasive and gives you real-time cardiac flow," explains Khosla. "Now based on the newer and more sophisticated Doppler techniques, we can assess the way the chambers contract, the way the chambers relax, the relaxing properties of the heart, the contractility of the heart, and the segmental dysfunction of the heart associated with various heart diseases. Valvular disease is clearly getting to the point where some people would consider operating on the patient without doing the invasive test."

Color Doppler is most commonly used to evaluate the severity of a leaky valve - revealing the velocity of blood flow, not the volume. Baylor Heart Clinic's Quiñones says that integrating 3D technology with color Doppler will change this. "We are extremely optimistic that with the development of three-dimensional color flow, we will be able to be a lot more precise in stopping the severity of leaks to valves in a way that will be more accurate than what we already have."

Tissue Doppler imaging is a tried-and-true technique that has been around for more than a decade, particularly because spectral tissue Doppler is a dominant imaging technology used in echocardiography for diastolic evaluation. "Today, if you don't have spectral tissue Doppler, you cannot really say that you are doing a state-of-the-art evaluation of diastolic function," opines Quiñones. "We do 50 echo exams a day and at least 40 fall in a category where we would use spectral tissue Doppler."

Right now, tissue Doppler imaging and strain and strain rate are an exciting component of academic echocardiography labs but are not yet used clinically on a daily basis because of limited access, says Quiñones. GE Healthcare is currently the only company that offers the application for use on its high-end Vivid 7 cardiovascular ultrasound unit. The technology is useful in cardiac resynchronization therapy (CRT), used to make all the segments of the heart resynchronize. "This is a development we are very excited about," Quiñones says. "The technology will explode when other vendors also come out with this technology."

THE IMPACT OF PORTABLES

Robert Siegel, MD, director of cardiac non-invasive lab at Cedars-Sinai Medical Center and professor of medicine at UCLA School of Medicine, occasionally travels to Mexico with a portable echo device to screen and examine members of underserved communities, looking for harmful heart conditions. "I may find that they have Marfan syndrome [a disorder of connective tissue that can effect the heart] and need to be referred for surgery, or I may detect a congenital heart lesion and they need to be referred for closure of an atrial septal defect or I may discover that they have staple ventricular function," speculates Siegel. "They don't have to travel 150 miles for a diagnosis or wait for two weeks to hear back from a referring physician. The main point is that it is done at the point of patient care."

Since introduced in the spectrum of cardiac imaging, handheld echo units have proven to be helpful screening tools in the evaluation of heart conditions - wherever the patient and physician may be. Hospitals utilize the devices because they are relatively inexpensive - priced about $15,000 - reduce imaging time, free up the larger echo units for more in-depth exams and provide better patient triage.

Sarver Heart Center's Sorrell says that he looks at what he does with the portable echo device as an extension of the physical exam. "I think that [cardiologists] have a little bit of license here not to open the door and allow [other medical professionals] to make full cardiovascular evaluations with these handhelds," starts Sorrell. "But if you are examining a patient, it is such a powerful marker to know the contractility of the heart that we could just teach [students] nothing more than how to evaluate the systolic function. The patient is going to be managed with this information better than without it. This tool is just too powerful and too important to hold onto ourselves."

But extending the units beyond the cardiology world may be a dim reality. Ramon Castello, director of the echocardiography lab at the Mayo Clinic in Jacksonville, Fla., says that while portable echo units are useful, they also pose a lot of risk. "It could be in the hands of people who are not properly trained," says Castello. "This is a very serious concern for the American Society of Echocardiography. It is now pushing the concept of credentialing and competence in echocardiography labs."

The American College of Cardiology and the American Heart Association recently revealed new guidelines for establishing and maintaining competence in echocardiography, particularly in the performance and interpretation of newer modalities, including miniaturized hand-carried ultrasound. Stricter rules may limit the amount of access non-cardiologists have to these handheld devices.

RESEARCH CONTINUES

Hospitals and echocardiography labs have archived tons of studies on videotape in the past decade. A typical echocardiography lab accumulates more than 10,000 new echo videos each year. For research purposes, patient purposes and even medical diagnosis purposes, physicians typically want to go back and search these large, existing archives to find similar studies for comparison.

While analog video makes this scenario nearly impossible, digital echocardiograms offer possible solutions. At the same time, there need to be tools and systems that automatically annotate and index the contents of digital echocardiography archives, according to researchers at the School of Engineering and Applied Science and Presbyterian Hospital at Columbia University.

Funded by a grant from the National Science Foundation in 1999, Columbia researchers from groups such as Computer Science, Electrical Engineering, Medical Informatics and Echocardiography work extensively on a project called PERSIVAL - personalized retrieval and summarization of image, video and language resource. The development of the Digital Echocardiogram Video Library (DEVL), led by principal investigator Professor Shih-Fu Chang of Electrical Engineering, is part of the five-year PERSIVAL project.

The researchers developed a technology that analyzes and indexes the content of video echocardiography studies automatically to provide users with efficient tools for browsing and querying the archive of digital echocardiograms. The technology is applicable to digital videos converted from analog formats or directly captured by digital devices. "The goal of the project is to automatically analyze the content of the echo videos to identify the different views, modes, cycles and cardiac objects," says Shahram Ebadollahi, lead researcher of the project DEVL. "Without human intervention, we want to analyze the content automatically and actually provide those annotations based on the models of the content."

What happens can be described as a computer-assisted methodology that organizes large contents of echo videos, making them easier to retrieve and essentially transmit over a digital network. Instead of uploading a 20-minute digital study, users of the echocardiogram video can identify what they want to look at using specified frames of reference. "For example, if you are suspicious the patient has mitral valve regurgitation, then you don't want to look at the entire video because there are only certain views that one could use to detect that abnormality," explains Ebadollahi.

Ebadollahi says leading manufacturers in the field have shown interest in the concept and the technology, as have members of the American College of Cardiology and EuroPACS. "The main benefit is for the cardiologist because it indexes the content of the echocardiogram and gives random access to the different points, saving time in the process of review," says Ebadollahi. Companies are interested in the promising technology because it eliminates the need for sonographers to type in information and also has potential for adding echocardiography to the every day image management applications of the hospitals. Stay tuned.