There are two main types of mammography: film-screen mammography and digital mammography, also called full-field digital mammography or FFDM. The technique for performing them is the same. What differs is whether the images take the form of photographic films or of digital files recorded directly onto a computer.
When you have a mammogram, a skilled technologist positions and compresses your breast between two clear plates. The plates are attached to a highly specialized camera, which takes two pictures of the breast from two directions. Then the technologist repeats the technique on the opposite breast. For some women, more than two pictures may be needed to include as much tissue as possible.
Mammography can be painful for some women, but for most it is mildly uncomfortable, and the sensation lasts for just a few seconds. Compressing the breast is necessary to flatten and reduce the thickness of the breast. The X-ray beam should penetrate as few layers of overlapping tissues as possible. From start to finish, the entire procedure takes about 20 minutes. A diagnostic mammogram generally takes more time than a screening mammogram because it takes more pictures from more angles.
Mammography involves minimal radiation exposure. In fact, the amount of radiation exposure from modern-day mammography machines is much lower than it was in past decades. The American Cancer Society notes that the dose of radiation received during a screening mammogram is about the same amount of radiation a person gets from their natural surroundings (background radiation) in an average 3-month period.
If you’ve had breast surgery for another reason, such as a benign biopsy or surgery to reduce the size of your breasts, the radiologist will want to know where those scars are in case the scar tissue has to be distinguished from another kind of breast abnormality. If you've had breast cancer surgery, small metal balls will be taped on your skin to mark your scar. Your scar defines the site with the highest risk of recurrence.
At least one radiologist reads the mammogram. A radiologist is a doctor who specializes in analyzing imaging studies of the body to diagnose disease or other problems. Having two radiologists read your mammogram reduces the chance of missing a problem by about 10-15%. Some centers routinely have your mammogram read twice, but this is expensive, and most insurance companies won’t pay for it. You can also get a “second opinion” on your mammogram by having the images analyzed by a computer. This is called computer-aided detection (CAD). Special computer software reviews the images and marks any areas of suspicion. The radiologist then examines each area and decides if it needs further evaluation.
Types of mammography: Film-screen vs. digital
If you’ve had a film-screen mammogram, the images will be in black and white on large sheets of film. With digital mammography, the images are recorded directly into a computer. The image can then be viewed on a computer screen and specific areas can be enlarged or highlighted. If there is a suspicious area, your doctors can use the computer to take a closer look. The images also can be transmitted electronically from one location to another.
Many studies have shown that film-screen and digital mammography are equally accurate in screening for breast cancer. One 2005 study of nearly 50,000 women, the Digital Mammographic Imaging Screening Trial (DMIST), found that digital mammography was a better screening tool than film-screen mammography only for women who either:
- are under age 50
- have very dense or extremely dense breast tissue
- are still menstruating or are perimenopausal (starting menopause), but have had a period within the previous 12 months
If you fall into any one of these three categories, talk to your doctor about having digital mammography. If you’re not sure whether or not you have dense breast tissue, your doctor can help — usually by looking at previous mammograms you may have had.
The other advantages of digital mammography versus film-screen are that (1) digital images can be manipulated for better views and they can be stored more easily, and (2) digital mammograms deliver about three-fourths of the radiation that film-screen mammograms do (although film-screen mammograms deliver a safe and very small amount of radiation). The disadvantages of digital mammography are that it is more expensive and not as widely available as film-screen mammography.
In the future, it’s expected that digital mammography will become more common. In the meantime, you can speak with your doctor about which type of mammography is best for your individual situation. If your doctor recommends digital mammography, or you want to have it, you can work together to determine where it is available in your area. You also may need to confirm that your insurance plan will cover this type of screening.
Many imaging centers are now in the process of switching over from traditional film mammography to digital mammography. According to an April 2008 article in the New York Times, this is causing a temporary increase in the number of women who are getting called back for additional testing. As radiologists get used to reading the digital images — especially for a woman who has always had films done — they may be more likely to call a woman back to take more views of potentially suspicious areas. Be aware of this if you make the switch from film mammography to digital mammography, and try not to worry prematurely if you get called back.
If you do not have access to digital mammography, you should still have film-screen mammography as you normally would.