Stereoscopic digital mammography (SDM) uses a pair of digital mammograms, taken from slightly different angles, to create a three-dimensional image of the internal structure of each breast. The resulting stereo image reveals more detail within the breast tissue than a standard two-dimensional mammogram -- so much so that this method may reduce false positives by half.
Good, Better, and Stereo Mammograms
Traditional film mammography is slowly giving way to digital mammography, a technology that uses less time and less radiation to make the image of your breast's internal tissue. Digital mammograms can be stored in a computer, enlarged to see more detail, adjusted for image brightness, or increased in contrast, making all areas of the breast easier to see. Stereoscopic mammograms build upon the advantages of digital mammograms by revealing more depth of detail in three dimensions, allowing your radiologist to see past layers of tissue that can hide breast masses.
Stereoscopy - An Old Idea Used With Imagery
Our eyes are similar to cameras, taking pictures from two slightly different positions. Our brains resolve these pairs of images into one picture that shows us the three-dimensional world, a concept explained in 1840 by Sir Charles Wheatstone. He invented, among many other things, the stereoscope a device that uses two photos of the same object, taken from different angles, and a pair of lenses that shows a different picture to each eye. The brain interprets these combined two-dimensional images in a three-dimensional way. A person in the Victorian era could look through a stereoscope at stereoscopic image pairs, such as the gunboat USS Monocracy at left, and feel as if they were seeing the real thing (although in black and white).
Stereo Digital Mammograms Gives More Accurate ResultsStereoscopy has been put to use mainly for looking at the outer surfaces of objects or scenes. Stereo digital mammograms allow radiologists to look at the inner terrain of your breast by using a pair of digital two-dimensional images, and a stereo display workstation loaded with image-analysis software. Dr. David Getty, a scientist at BBN Technologies, has done a clinical trial of SDM at Emory University in Atlanta, with 1,458 women that are at high risk for breast cancer. Each patient was evaluated with standard mammograms and stereo mammograms. Near the end of the clinical trial, Dr Getty reported that SDM reduced false positives by 39%,and false negatives by 46%. Stereo mammography finds cancer earlier than standard mammography.
Stereo Mammography May Someday Be Used for Breast Cancer Screening
The SDM technology is still in development, so you won't see this at your local radiology clinic soon. Dr Getty and his colleague at Emory University, Dr. Carl D'Orsi, say that it would take minor adjustments to current digital mammography systems to make stereo mammography possible. However, the computer workstation used to view the stereo digital images requires more processor power than was used in the trial, The SDM workstation, developed by Planar, uses a stereo mirror system. One horizontal and one vertical image of the breast is displayed with a sheet of half-silvered glass between them. The radiologist wears passively polarized glasses, in order to see the combined two-dimensional images appear as a three-dimensional x-ray.
RSNA 2007. Improved Accuracy of Lesion Detection in Breast Cancer Screening with Stereoscopic Digital Mammography. David Getty, Carl D'Orsi, Ronald Pickett, et al.
Stereoscopic Image: USS Monocacy (1866-1903), dressed with flags, in the Pei-Ho River, Tientsin, China, in about 1902. U.S. Naval Historical Center Photograph.