Siemens adds flat-panel system to cardiac cath offering

Plans integrate digital unit with surgical guidance

Siemens Medical Solutions has quietly launched the flat-panel version of its Axiom Artis cardiac cath lab. The product appeared for the first time July 1 in the company's price book of products. The Artis dFD (dynamic flat detector) carries a 12% premium compared with a similarly equipped system outfitted with an image intensifier. Three systems are now in clinical operation, and another 50 could be installed by year's end, according to Siemens.

The Artis dFD was preceded in the cardiac marketplace by the digitally based GE Innova (SCAN 3/15/00) and Philips Integris Allura 9 (SCAN 3/20/02). The Siemens product shares the same 20 x 20-cm detector used by Philips. The flat detector is supplied by Trixell, a joint venture among Philips, Siemens, and Thales Electron Devices. Its increased dynamic range promises better spatial resolution and clinical advantages when doing coronary angiography. Early results with the Artis dFD obtained by cardiologists at the University of Erlangen in Germany support this expectation.

"We have seen an improvement in resolution and in the contrast of the image," said Prof. Dr. Werner Daniel, chief of cardiology at the Hospital of the University of Erlangen-Nürnberg. "In the end, we use less contrast material. We also have faster diagnostic and interventional procedures, because we need fewer different projections of the coronary tree. This improves comfort for the patient."

Siemens plans to go beyond typical angiographic applications. The company is exploring two related applications for the Artis dFD. One is to serve as a major part of an interventional system that employs magnetic waves to steer catheters through blood vessels and into the heart and possibly other organs. The other is an elaboration of this interventional system that would integrate optical coherence tomography (OCT) to help characterize disease and tailor treatment.

On the floor of the AX (angiography and x-ray) manufacturing plant in Forchheim, Germany, an engineering bay is home to engineers testing an advanced model of the interventional system, called Niobe. Semispherical, floor-mounted devices housing permanent magnets sandwich the Artis dFD. The two physically separate technologies complement each other in purpose and method of operation.

The Artis dFD provides a real-time view of the object in the field-of-view using digital fluoroscopy. The flat-panel detector is unaffected by the magnetic waves generated by Niobe, an interventional device being developed by St. Louis-based Stereotaxis. By shifting these permanent magnets, physicians can direct the distal end of catheters inside the body with extraordinary accuracy.

"I compare this to driving a car. The steering wheel doesn't do anything to the motor, but it takes you where you are going," said Klaus Hambüchen, president of Siemens AX division. "With the magnetic field, you steer and the (forward movement) is done with an advancer."

In the past, computer-integrated surgery has taken the form of either robotic assistants that improve dexterity by precisely holding or manipulating instruments, or image guidance software systems that enhance the surgeon's view of a manually controlled instrument. Niobe integrates both approaches.

Siemens is working under a 30-month exclusive partnership with Stereotaxis to help develop and market the device. The challenge is to fuse 3D models created using preoperative MR and CT scans with real-time fluoro images obtained using the Artis dFD.

"When we match the 3D model with the 2D real-time data, then the patient is registered," Hambüchen said. "This sounds very simple but it is not."

The concept has been proven, but the methodology is cumbersome and slow, he said. The companies are now working with luminaries at clinical sites to develop techniques for speeding up the registration process.

If Siemens and Stereotaxis succeed, physicians using Niobe and the Artis dFD will be able to exactly guide catheters to locations in the heart and possibly other organs using the body's vasculature as a roadway. At the very least, the integrated system could dramatically reduce physician exposure to radiation, as the catheter is steered remotely from an x-ray-shielded control room. The increased precision in catheter guidance could reduce procedure time, minimizing patient exposure to x-rays and cutting costs associated with staff and OR time.

Niobe is the latest iteration of a prototype, called Telstar, which was installed at Barnes-Jewish Hospital in St. Louis in 1995 and later at the University of Oklahoma (SCAN 2/14/01). The Niobe preproduction model of the technology is scheduled for installation at two other sites this year. If FDA clearance is granted soon, Niobe could be in place at 10 institutions by the end of this year, Hambüchen said. The goal is to place 25 more systems in 2003.

Clinical benefits are more speculative than proven. Only about 30 patients have been treated with the prototypes. Data from 20 of these procedures have been submitted to the FDA as part of the company's 510(k) submission, according to Hambüchen, who expects the agency to sign off on the technology.

"If you think about the clinical advantage, I would think the FDA would be in favor of this," he said. "It reduces x-ray exposure, reduces time, and reduces risk."

Patients with atrial fibrillation will be the first to benefit if the product is commercialized. These patients typically are treated by ablating tissue in the heart associated with errant electrical currents that cause the heart to beat abnormally. Niobe, in combination with the Artis dFD, promises to make this process very precise as a means for mapping the electrical current inside the heart chamber and then guiding the ablation tool exactly to the tissue that should be destroyed.

Niobe would be continually under the control of an operator, Hambüchen said. Ultimately, however, Stereotaxis would like to automate the system so that the clinician has only to select a site on the heart wall, for example. The computer would then automatically navigate the catheter to that site, according to Stereotaxis. Niobe is also being developed to estimate the force with which the catheter contacts the tissue and to modify this force to achieve the optimal contact, an essential part of the ablation process.

Further in the future, the Artis dFD and Niobe might be combined with OCT to characterize tissues inside the body. The idea is to channel infrared light to locations inside the body using optical fiber. The fiber would be threaded inside a catheter containing a lens assembly from which data are gathered. If this concept can be implemented clinically, OCT may be useful in identifying unstable arterial plaque, which can suddenly rupture and cause myocardial infarction. It may also help visualize vessels and nerves that need surgical repair, as well as identify the margins of low-grade invasive neurological tumors, according to LightLab, which is developing OCT technology compatible with catheter-based systems.

The company, based in Westford, MA, was founded in 1998. It evolved from staff and resources contributed by MIT, Harvard, Lincoln Laboratory, and the international optics firm Carl Zeiss. No formal agreement has yet been struck between Siemens and LightLab, but some preliminary collaboration has taken place.

Under consideration is the development of a system that can effectively and accurately deliver the OCT-integrated catheter to specific locations in the body. Niobe, outfitted with the Artis dFD, could be that system. Before such an OCT system is available, however, Hambüchen expects the Siemens flat-panel technology to have already made a substantial clinical impact, possibly in electrophysiology as a complement to Niobe, and certainly in cardiac cath labs, where its images provide advantages to physicians and patients alike. To get there may take some adjustment on the part of physicians, however.

"Cardiologists have been trained to use IIs (image intensifiers), which deliver high spatial resolution and the highest contrast," Hambüchen said. "The flat panel has high spatial resolution but also shows lower contrast objects, so the character of the image has changed. The challenge is really to make the customer appreciate that he is seeing more."