Full Field Digital Mammography: A New Breast Cancer Screening Tool

A new type of mammography equipment called full-field digital mammography has generated a good deal of press during its first year of availability in the United States. Mammography remains the best method of early breast cancer detection. However, traditional film-screen mammography is limited in its ability to detect some cancers, especially those occurring in women with radiographically "dense" breasts. For this reason, extensive research efforts to improve mammography have occurred. Digital mammography offers theoretical advantages compared to film-screen mammography for cancer detection. I will discuss this new technology, its current use, and future applications.

What is digital mammography?

Conventional film screen mammography uses low energy x-rays that pass through a compressed breast during a mammographic examination. The exiting x-rays are absorbed by film (x-ray film) which is then developed into a mammographic image that can be held and looked at by the radiologist. This traditional process is analogous to personal photographic cameras and photographic film where light is focused on the film and developed to produce a negative which can be printed as a picture.

With digital mammography, low energy x-rays pass through the breast exactly like conventional mammograms but are recorded by means of an electronic digital detector instead of the film. This electronic image can be displayed on a video monitor like a TV or printed onto film. Again, this is similar to digital cameras that produce a digital picture that can be displayed on a computer screen or printed on paper. The radiologist can manipulate the digital mammogram electronically to magnify an area, change contrast, or alter the brightness.

Most radiographic imaging is currently done by digital means including CT scans, ultrasound, MRI, nuclear scans, and the some standard radiographs such as bone or chest examinations. Mammography was the last area of radiologic imaging to use digital technology due to the unique needs of mammography. The high resolution and contrast needed to produce excellent quality mammographic imaging exceeds all other areas of digital imaging. For this reason, the technology to produce digital mammography is very complex, expensive, and time consuming to develop reliable systems. Patients undergoing digital mammographic examinations will see few differences during the examination itself. There is more equipment in the room which includes a small TV monitor which allows the mammographic technologist to view the mammogram in several seconds instead of developing films and waiting ten minutes to see an image. Breast compression, unfortunately, is still required to produce optimal images at the lowest possible radiation dose.

Digital mammography offers potential and practical advantages over film screen mammography by improving contrast and signal to noise ratios. These may allow better cancer detection. Near instantaneous image acquisition and the ability to transmit images electronically around the world are also significant advantages. One can have a mammogram at a remote site with the images sent, displayed, and interpreted at a medical center. However, the most important scientific application is the potential to use advanced computer and electronic technologies to manipulate the image in order to better "see" certain breast tumors that are currently difficult to visualize on film screen mammography systems. These applications include direct computer-aided diagnosis (computer reading of mammograms), 3-D imaging, dual energy mammography, and the contrast-enhanced mammography. Most of these processes remain in the development stage.