SIEMENS

For tens of thousands of people each year it is the end of the line. If they are too frail to survive open heart surgery, many patients with aortic valve disease only have about two to three years to live. An ongoing stenosis of the valve resulting from calcification of the leaflets that allow oxygen-rich blood to flow from the left ventricle of the heart into the circulatory system, aortic valve disease affects about four percent of people 65 and older. Indeed, some 60,000 open heart aortic valve replacement operations are performed each year in Europe and even more in the United States, where the procedure costs approximately $140,000.

Now, however, there's hope not only for those deemed healthy enough to survive major surgery, but also for the roughly one third of prospective aortic valve replacement candidates who are not. Thanks to clinical cooperation between Siemens Healthcare, the Leipzig Heart Center, and the German Heart Center in Munich, as well as Siemens Corporate Research (SCR) in Princeton, New Jersey, a new, smart visualization and guidance technology facilitates implantation of a replacement valve by means of a catheter, thus sparing patients the trauma of surgery and cutting total per-patient costs. Already clinically introduced on a prototype-procedure basis in Europe, the technology may also become available in the U.S. in the near future.

The new procedure is based on the use of Siemens' DynaCT 3D cardiac angiographic imaging system. Normally used for so-called “interventional” procedures, such as inserting a stent in a clogged artery, X-ray based DynaCT provides exquisitely detailed images of the thorax. But during aortic valve implantation, what the surgeon wants to see in particular is the aortic root. With this in mind, Siemens researchers have developed a technology “that automatically identifies the aortic valve area in a DynaCT data set and segments it — that is, eliminates everything that is not important, such as the rib cage, from the picture,” explains Dr. Jan Boese, who heads innovations and prototyping at Siemens Healthcare's Angiography Business Unit.

As the replacement valve approaches the area of interest wrapped in the tip of a catheter, unique software makes it possible to identify the optimum angulation of the new valve. “This is the key to the new procedure,” says Dr. Rui Liao, who, with Dr. Yefeng Zheng, co-developed the software at SCR. “It automatically detects anatomical landmarks in the aortic valve area and provides visual confirmation of the exact angle of the prosthesis. This information is crucial in terms of correctly placing the device so that it covers the old valve without permitting leakage or covering the end points of the coronary arteries, which would cause an immediate heart attack.” When the prosthesis is in precisely the right position, a balloon inside the catheter (see illustration above) unfurls, thus opening the prosthesis and pressing it firmly against the aortic wall.

To date, the procedure has been performed on over 150 patients in Europe with an average age of 78. One of the few cardiac surgeons who has extensive experience with it is Prof. Dr. Rüdiger Lange, Director of the German Heart Institute of the Technical University of Munich. “The great advantage of the new software,” he says, “is that it allows you to clearly see the angle of the prosthesis. This is terribly important because the aortic valve is sometimes twisted, making it very risky to guess what is right. With this procedure, accuracy makes all the difference, and this software is very accurate.”

Operating in the Imaging Space. It is one of the quintessential diseases of old age. Like the nicks and scratches that accumulate over the years on the once shiny surfaces of our cars, our hearts, for reasons that are still not fully understood, often build up fibrous scar tissues. Such tissues can cause electrical anomalies known as arrhythmias; and 60 percent of all arrhythmias develop on the thin inner walls of the left atrium, causing an often asymptomatic condition called atrial fibrillation (AF) that is a leading cause of stroke and heart failure among people 65 and older.

With more and more people living longer lives, the number of people with atrial fibrillation is expected to double over the next ten years. In view of this alarming trend, Siemens has teamed with SurgiVision, a Memphis, Tennessee-based medical device company, and with the University of Utah's School of Medicine (for more see interview) to develop a new, minimally-invasive procedure that will allow a cardiologist to see fibrous tissues and ablate them with extreme precision using a specialized catheter that enters the heart from a tiny incision and is guided using real-time magnetic resonance imaging.

Still under development, the procedure is expected to offer significant advantages over existing ablation treatment, which also relies on catheters, but is X-ray-based, takes over four hours with significant radiation exposure to the patient and the clinician, and is characterized by difficult visualization, poor precision, and a success rate of only 50 to 75 percent. “By comparison, with the new MR-based guidance procedure, we expect to see a significant improvement in quality and a marked reduction in procedure time,” says Walter Märzendorfer, CEO, Magnetic Resonance, at Siemens Healthcare.

Associated research under the direction of Dr. Nassir F. Marrouche, Executive Director of the Comprehensive Arrhythmia Research & Management Center at the University of Utah in Salt Lake City, has already resulted in an MR-based pre-treatment evaluation system (see image below) that groups AF patients into one of four categories, with stage 1 having an excellent prognosis and stage 4 representing such an advanced condition that ablation would not help. “This methodology gives the attending cardiologist a better decision tool in determining whether it makes sense to treat a particular patient. The result is that for the first time cardiologists can more confidently exclude patients that would have no benefit from such a procedure,” says Märzendorfer.

Although the new MR-based AF ablation procedure has made significant progress in animal studies, more work remains to be completed before it can head for clinical trials. “Together with the University of Utah team and SurgiVision, we are fine tuning the pulse sequences on our MR scanners for continuous real-time acquisition of MR images and catheter tracking,” says Christine H. Lorenz, PhD, Director, Center for Applied Medical Imaging, a collaboration between Siemens Healthcare and Siemens Corporate Research based in Baltimore, Maryland. Siemens is also developing navigation software that makes it possible to visualize catheters and the heart in 3D space — the key technology in allowing cardiologists to position their catheters for precise ablation of tissue.

Essential to all of this is the development of ablation and mapping catheters that are compatible with the powerful magnetic fields typical of MRI and can interact with a scanner's signals and software in order to be tracked and visualized in real time. With this in mind, SurgiVision has developed a family of catheters outfitted with tiny MR micro transmitter coils. “With our minimally invasive catheters in the body and the patient resting in the scanner, the signals produced by the catheter's coils are picked up by the scanner's pulse sequences, giving us the real-time position and orientation of each catheter in three dimensions,” explains SurgiVision CEO Kimble Jenkins. “At that point, the cardiologist will see the exact position of the catheters along with high resolution images of the patient's cardiac anatomy in the same 3D space. In short, the imaging space will become the surgical space.”

Aneurysms: Shedding Light on Risk. It is used for designing everything from coffee makers to oil and gas pipelines. A well-established tool in industry, computational fluid dynamics (CFD) is now being investigated by Siemens researchers to determine its applicability to a range of medical questions. Take aneurysms, for instance, which are potentially life-threatening balloon-like structures that form on arterial walls. If an aneurysm bursts in your brain, it can leave you disabled or dead. Indeed, only about one third of those who experience an aneurysm rupture recover completely. Experts estimate that between one and five percent of the population — with the proportion growing steadily with age—have an aneurysm. On the other hand, the vast majority of aneurysms never rupture. Thus, according to Dr. Thomas Redel, an expert on angiographic imaging systems at Siemens Healthcare, “The key question is, if an aneurysm is discovered in the course of a routine angiographic or magnetic resonance imaging test, how does the attending physician determine its level of threat?” The answer could have significant economic consequences, since the worldwide price tag for aneurysm treatments is estimated to be around $1.8 billion.

Aneurysms come in all shapes and sizes. The most commonly affected areas are the brain, the abdomen and the aorta. And with the growing sensitivity of angiographic imaging systems — the newest of which can resolve structures down to 150 µm — more and more are being discovered. But you can't necessarily tell whether an aneurysm is dangerous by just looking at it, which is where CFD comes in. Using high-resolution images as a starting point, Princeton, New Jersey-based Siemens researchers Bogdan Georgescu, Viorel Mihalef, and Puneet Sharma have produced exact 3D models of aneurysms and subjected them to algorithms that simulate blood flow. “Preliminary research indicates that the probability of rupture is based on factors that include blood flow and pressure changes as they relate to vessel wall characteristics,” says Georgescu. Adds Redel: “This is an important step toward the eventual personalization of aneurysm treatment.”

As Siemens researchers simulate different combinations of parameters in an effort to understand what can trigger an aneurysm to rupture — and what can keep it from doing so — they are testing the effects of so-called “flow diverters.” Unlike conventional therapy, which is designed to clip an aneurysm at its neck, but can result in a life-threatening perforation, flow diverters merely redirect some blood toward other vessels. “We believe that CFD can play an important role here,” says Dr. Jan Boese, who heads innovations and prototyping at Siemens Healthcare's Angiography Business Unit. “Before introducing a diverter, doctors could perform simulations to optimize its placement.” With this in mind, Siemens researchers in Germany and the U.S. are now developing a software platform that clinicians will be able to use to validate simulated results against actual patient measurements.

Further down the road, researchers hope that, by identifying potential hemodynamic risks, CFD will help to predict a patient's risk of heart attack, and will support optimized therapies, such as selection and placement of prosthetic aortic and mitral valves and the localized delivery of therapeutic substances, not to mention helping to train the next generation of physicians.