Sectra adds low-dose digital mammography to product offerings

Responding in part to concerns that screening mammography exposes women to unnecessary radiation, Sweden-based Sectra has developed a work-in-progress digital system that it claims can reduce x-ray exposure by up to 80%.

The system, which has not been named, will be introduced at the 2000 RSNA meeting. Clinical trials using the technology are expected to begin in 2001, and several participating sites in the U.S. may be announced during the meeting, the company said.

In addition to considerably reducing radiation exposure, Sectra touts the system as being capable of producing breast images that are equal to or better than those captured using traditional film-based systems. In fact, image quality would be far superior to that of film-based systems if comparable radiation dosages were used, a spokesman for the company said.

"The detector's main feature is unprecedented dose efficiency," said Torbjorn Kronander, president of Sectra Imtec AB. "It might be possible to extend its usage to other modalities, but for the foreseeable future (the detector) will be used for mammography only."

The underlying technology emerged from research in particle physics conducted at the European Laboratory for Particle Physics (CERN) in Geneva and was refined by a research group at the Royal Institute of Technology in Stockholm. The technology facilitates the detection and signal processing of each individual x-ray photon directly on silicon.

The result is improved collection efficiency and signal-to-noise ratio relative to competing detector systems. According to the company, the system is the first true digital photon counter.

Bypassing the need for a scintillator, Sectra's system detects x-rays directly substantially increasing resolution and accuracy. Nearly every photon that passes through the breast is used in the diagnostic process. Photons are detected and processed individually. Each incoming photon results in approximately 5000 electron holes that can be amplified to yield a detectable signal.

The higher detection efficiency should enable clinicians to examine women with dense breast tissue without exposing them to unacceptable radiation levels, Kronander said.

"Our system is the first true digital photon counter in the world," he said. "This is a perfect match for the digital nature of x-rays, and it yields advantages in optimizing the transfer of information from detected x-rays into the image, and thus a dose reduction."

By contrast, current digital x-ray imaging systems integrate signals from a large number of photons into an analog value, Kronander said. Amorphous selenium and amorphous silicon detectors do not count individual photons, but instead amalgamate the impact of a stream of photons over a given time interval. About half the photons in those systems pass through screen/sensor units and are lost to detection.

"That means an increase in noise and a loss of information," he said.

In Sectra's detector more than 95% of photons are used for image creation.

Sectra's effort to reduce radiation exposure is not unique. As interest in medical imaging has grown, so have concerns over radiation dosage, particularly among women. That concern has been heightened in recent years as medical organizations in the U.S. have urged all women over 40 to undergo yearly mammography.

In July, direct digital x-ray innovator Swissray made an announcement similar to Sectra's, although it did not involve dedicated mammography equipment. Swissray introduced enhancements that it claims substantially improve the performance of its direct digital radiography detector while cutting the radiation dose in half.

The Sectra system is expected to become commercially available in Europe in 2002. Clearance by the FDA could take longer, Kronander said.

In large part due to low federal reimbursement rates, digital mammography is not yet cost-efficient in the U.S. Kronander was unsympathetic.

"What is the cost-efficiency to avoid inducing cancer in healthy human beings, even if those cancers are few compared to the number of women screened?" he said.

If its claims prove accurate, the improved image quality could have added benefits for Sectra. The company is one of Sweden's largest PACS vendors.