Cardiac Mariners prepares digital x-ray device for market

The cardiology community may soon encounter an innovative imaging device, one that literally reverses the way cardiac cath images are made. The technology, being developed by Cardiac Mariners of Los Gatos, CA, uses a detector less than an inch in diameter and an x-ray source about the size of a television picture tube. The company expects to start selling the device in 1998. The Food and Drug Administration approved the use of the technology in basic fluoroscopic applications last year, but Cardiac Mariners decided to aim higher.

"We wanted a machine capable not only of fluoro but also of cine levels of performance, which is why we chose not to enter the market at that time," said Ron Rankin, president and CEO of Cardiac Mariners.

Fluoro levels in cardiac labs are associated with low-intensity exposures used when floating catheters are positioned in the patient. Cardiologists then administer the contrast agent and pump up the x-ray dose to cine levels. The seven to 10 times increase in x-ray photons on conventional systems provides the kind of diagnostic images needed for a coronary angiogram. Rankin expects the device, now in its final stages of development, to reach that level of image quality, but with the x-ray delivery dose below the fluoro level.

"We will be able to turn our x-rays on and run them all day," he said.

The company has built two prototype systems, conducting both animal and human tests with the devices. The University of Wisconsin in Madison and the Stanford Research Institute are participating in the research. As engineers work on the final version of the product, Rankin and his colleagues are assembling a sales force for a device that could be shipping by the fourth quarter of 1998, if FDA clearance is obtained.

"In the U.S., we will have direct sales, with sales and distribution partners overseas," Rankin said.

Every part of the device-from imaging concept to components-is novel. The tiny detector is composed of cadmium zinc telluride (CZT), the same material being groomed by various companies for use in gamma cameras. CZT is widely recognized as having properties ideal for the registration of
x-rays, as the material transforms each x-ray into a discrete electrical signal. The problem in its use has been cost. Because CZT is very expensive, fashioning even a 9-inch detector to do fluoroscopy would be prohibitively expensive. CZT does not present a cost-barrier in this case because so little of the material is needed.

"We don't need to be as large as an image intensifier because we're using a reverse geometry system and reconstructing the image using a computer," Rankin said. "So we don't have all the problems that go into making large-area, solid-state detectors that are uniform, noise free, and reasonably inexpensive."

Scanning-beam digital x-ray. Reverse geometry refers to the concept of having a small detector and a large x-ray source. One of the keys to making this concept work is the use of a cathode-ray tube (CRT) to generate x-rays. The CRT collimates electrons into a thin beam that scans across the face of the tube, just as a television picture tube does. But instead of emitting visible light, which occurs when an electron beam hits the phosphor screen of a television, the electrons strike a target that produces a pencil-thin beam of x-rays that angles through the patient and to the detector array. The electron beam scans the face of the target so rapidly that the patient area is covered instantaneously and continuously, leading to real-time images comparable with those generated by cardiac cath labs, Rankin said.

"This is real-time fluoroscopy-30 frames per second, multiple image-plane reconstruction," he said. "It's fast stuff."

One of the major benefits of this technology, called scanning-beam digital x-ray, is its potential to markedly reduce radiation exposure to patients and staff. Preliminary tests indicate that the technology can reduce radiation exposure to a patient's skin 10-fold and reduce by more than four times the total exposure during a procedure. That achievement takes on added importance considering the rise in fluoroscopically guided interventional procedures.

Cardiologists perform more than 1.6 million diagnostic and therapeutic procedures annually under x-ray guidance, according to the American College of Cardiology. They have reason to be concerned about radiation scatter, which is caused when x-rays pass through the patient and strike the detector used in conventional systems. Engineers at Cardiac Mariners believe they have solved the problem of scatter by reducing the size of the detector to about 1/20th the size of conventional ones.

The company has protected its fledgling position in the market with patents covering the core technologies, including the grid that allows multiple x-ray sources to be focused on the detector, the interface between the x-ray beam and detector, and an x-ray sensor that can be used to determine the 3-D position of probes traveling in the field-of-view. This aid to localization promises to improve navigation of instruments in the body, a particularly important concern during interventional procedures.

Although the company anticipates the first applications of its product to be for cardiac cath labs, the technology could be tailored for other fluoroscopic uses. Angiography is a likely second market for the system. Conventional R/F will probably not be developed in the near term, because the company believes access to the market may be difficult.

The company has focused its initial efforts on cardiac cath because that area offers the greatest financial potential. Cardiac cath labs sell from $800,000 to well over $1 million, depending largely on whether imaging is single plane or bi-plane. Rankin expects to construct products that fall within that price range.

"Our price will be comparable to that of conventional systems," he said.will operate under the Marmer name as a subsidiary of HCP.