Because modern digital detectors can be tuned to be more efficient than screen-film systems, they automatically lower the radiation dose to the patient while maintaining the image quality radiologists crave.

Photon-counting, the method used in Sectra's detector, for example, minimizes patient exposure to radiation. In a 2006 analysis, the British National Health Service Breast Screening Programme reported that the Sectra MicroDose Mammography system achieved significant dose savings over screen-film mammography. The average mean glandular dose of the MicroDose System in this analysis was 0.57 mGy, 75% lower than average dose levels in film imaging systems.

A Swedish study confirms that clinical performance in terms of cancer detections rate and recall rate can be improved, while decreasing the radiation dose.1

"The secret to the dose reduction possible with Sectra MicroDose Mammography is a high detective quantum efficiency (DQE) and contrast transfer, which basically translates to very low noise in the system and absorption and use of all incident x-rays with high efficiency," said Prof. Mats Danielsson, a professor of physics at the Royal Institute of Technology in Stockholm and cofounder of Sectra Mamea. "The photon-counting system, in fact, rejects all electronic noise that would otherwise blur the image."

OTHER MEANS

Manufacturers of digital mammography systems are seeking to reduce radiation dose to patients by other means as well. One approach involves changing the way in which x-rays are generated. Going to a higher kV makes the average x-ray energy higher, which means it will penetrate the breast and hit the detector more efficiently, said Dr. Andrew Smith, principal scientist for Hologic of Bedford, MA.

"For the same amount of signal hitting the detector, there is less signal being absorbed in the breast," Smith said. "That is something that could not be done with screen-film imaging because screen-film systems must operate in a very limited kiloelectron volt range to provide a high-quality image. But digital detectors are capable of imaging over a wide range of exposures and incident kV energies. So changing x-ray generation is the strategy by which people are further reducing dose."

The focus of change is on composition of the x-ray tube and x-ray filters. The gold standard for analog imaging has been a molybdenum x-ray tube and a molybdenum x-ray filter. However, the x-rays emitted from a tungsten tube have higher energy.