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Mr. Sebastian Webel
Mr. Sebastian Webel

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Pictures of the Future
The Magazine for Research and Innovation
 

Medical Imaging

Personalized Assessment of Cardiac Valves

Researcher Tommaso Mansi, who participated in the development of the algorithm that drives eSie Valves (image on monitor), with a model of the human heart.

Siemens scientists have developed a new software algorithm, which, in combination with a new ultrasound probe, analyzes and visualizes a patient’s aortic and mitral valves in 3D and provides automated measurements in seconds. This information allows cardiologists to quickly evaluate valvular anatomy and physiology with previously unknown precision, thus making therapeutic decisions more objective.

From deep in the chest, somewhere just below the breastbone, a shortness of breath begins to develop and tighten like a vice. Known as dyspnea, this condition may be triggered by mild exertion such as climbing stairs, excitement, surprise, or stress. While dyspnea may be caused by a multitude of underlying diseases and conditions, the challenge is to identify its causes quickly and develop an accurate diagnosis – a prerequisite for optimal and timely therapy.

To accomplish this, Siemens has developed two paired elements: a unique new transesophageal echocardiography (TEE) probe that generates seamless, real-time images of anatomy and blood flow in 4D (three dimensions plus time), and an equally unique new algorithm known as “eSie Valves,” that uses the data generated by the probe to analyze and visualize the acquired image data and derive personalized models of the aortic and mitral valves. Based on machine learning, the algorithm incorporates key data from thousands of annotated images.

In the context of interventional valve therapies such as transcatheter aortic valve replacement (TAVR) and clipping of the mitral valve’s leaflets, this combination of technologies is being focused like a spotlight on key causes of death and quality-of-life impairment. The two most important valvular diseases addressed by these technologies are aortic valve stenosis (narrowing of the aortic valve which is located between the left ventricle and the aorta) and mitral valve regurgitation (a backflow of blood from the left ventricle into the left atrium due to incomplete closure of the mitral valve’s leaflets.)

Valvular heart disease, which also includes diseases of the pulmonary valve and tricuspid valve, affects 2.5 percent of the global population. Each year in the United States and Europe roughly 200,000 open heart surgeries are performed in order to repair or replace diseased valves. According to the American Heart Association, in the U.S. valve surgeries are among the most expensive and riskiest cardiac procedures, with an average cost of $164,238 and an in-hospital death rate of 3.63 percent.  Advanced imaging may help to improve the diagnostic assessment of diseased patients and thus help to optimize patient management by helping to identify those patients who really need a surgical/interventional therapy and will have a chance to benefit from it.

Precision Procedures

As it delivers a comprehensive assessment, echocardiography is the basic imaging method for assessing cardiac status. If significant valvular disease is detected, surgical valve repair or replacement may be indicated. But because both therapies are open heart procedures, many patients cannot benefit from them due to age-related contraindications. In view of this, over the last five years interventional therapies have become a valid therapeutic option. Such therapies are much more patient friendly compared to open heart surgery. For instance, TAVR in severe aortic valve stenosis and mitral clip therapy in severe functional mitral regurgitation may benefit from Siemens’ new TEE probe, while eSie Valves may help to improve diagnostic assessment, analyze intraprocedural results, and monitor valve prosthesis functions during follow-up.

To visualize a valve’s anatomy and function, a cardiologist would inch the new transesophageal echo probe down the patient’s esophagus until it was located close to the left atrium. Once satisfied with the images, he / she would record them, and then use eSie Valves, an advanced analysis semi-automated software package, to detect the valve by identifying the target object’s position and orientation, as well as landmarks such as key anatomical features. It would then completely segment (separate) the aortic valve (or mitral valve) from its neighboring structures.

“At that point,” explains Tommaso Mansi, PhD, a Senior Key Expert with Siemens Corporate Technology who participated in the development of the algorithm that drives eSie Valves, “the software fits a model of an average valve over the image of the real valve and warps it to follow the borders of the patient’s actual valve.” The result, he says, is a personalized model of the valve. Finally, the cardiologist clicks “analysis” and eSie Valves automatically provides key data, such as the annulus diameter, perimeters, areas, etc., which supports interventional planning.

Based on the resulting information, the physician can choose to go to the software’s dynamic mode, which allows for the visualization of an entire cardiac cycle. “This helps clinicians to model and measure the valves over time, making it possible, for instance, to see how the diameter of the mitral valve annulus varies throughout a cardiac cycle,” says Mansi, who explains that competing commercial systems are, for instance, capable of showing the mitral valve as a  static model in only a single position. “We show both valves dynamically,” he says.

And all of this happens at great speed. “While standard quantification software takes several minutes to provide measurements of one heart valve, in one single position,” says Mansi, who worked with Mihai Scutaru and Ingmar Voigt, both from Siemens Corporate Technology, as well as Dr. Razvan Ionasec of Siemens Healthcare, “eSie Valves provides automated objective and reproducible measurements of the aortic and mitral valves in seconds. This quantitative information allows physicians to quickly and easily evaluate valvular anatomy and physiology, which increases diagnostic accuracy and confidence. Furthermore, in patients scheduled to undergo surgical or interventional therapies, it helps in planning the procedure.”

A model of the mitral valve as calculated by eSie Valves (green-blue mesh with yellow contour) is overlaid on a 3D TEE, full volume ultrasound acquisition. Brown areas show heart tissue, while the red-blue cloud is a color Doppler image showing the direction of the blood. In this case, we see that some blood (red) abnormally crosses the valve.

Seamless Images

This is particularly important when it comes to the mitral valve. Unlike the aortic valve, the mitral valve’s leaflets, which control the flow of blood from the left atrium to the left ventricle, are held in place by muscles that make minimally-invasive treatments with current technology difficult. As surgical mitral valve therapy always needs an open heart approach, comprehensive cardiac and especially valvular assessment is crucial for optimal planning, performance and outcome. Unfortunately, however, this has not always been the case with previous 2D TEE systems. “Until now,” says Mansi, “cardiac surgeons have had to make many of their mitral valve treatment decisions when the heart was open. But eSie Valves, which is based on real-time 3D TEE data, is now enabling highly accurate diagnostic assessment, so that cardiac surgeons will hopefully no longer be surprised by the real anatomy. In short, eSie Valves is bringing valvular assessment to a new level of objectivity.”

In addition to the advantages offered by eSie Valves software, its associated ultrasound probe is breaking ground thanks to unique seamless imaging technology. “This is important,” says Helene Houle from Siemens Ultrasound, who has been the key clinical expert driving the development of eSie Valves, “because the aortic and mitral valve leaflets move very fast and you do not want to see stitching artifacts in your images, which is something that can happen if the patient is suffering from irregular heartbeats or an arrhythmia.” She points out that, to get sufficient temporal resolution, competing systems stitch images from consecutive heart cycles together to produce continuous ultrasound volumes, which have the shape of a pyramid. “Our technology acquires this information in continuous imaging. It simultaneously acquires anatomy and blood flow. The combination of capabilities provided by the new probe – high volume rate, true volume imaging with no stitching in real time and with color Doppler – is unique to Siemens.”

Personalized Picture

While Siemens’ new eSie Valves technology in conjunction with the recently-introduced real-time 3D TEE probe represents an important milestone toward personalized cardiac care, it is just the first step down the road to a much more ambitious vision. What researchers eventually hope to achieve is to model a patient’s entire heart, including hemodynamics – the movement, volume and pressure of blood – and to be able to perform therapies on that personalized model with a view to optimizing therapeutic procedures and minimizing collateral effects. Clinicians would thus be able to see what the effects of a therapy would be before performing therapy. “The learning technology behind eSie Valves is generic,” says Mansi. “This is not just a one-shot application. And that is its key differentiating factor: It offers the potential of opening up a world of new applications. It just depends on what you want to apply it to.“

Arthur F. Pease