by Dr. Gary Farr on 22 April 2002
What is Mammography?
Mammography is a specific type of imaging that uses a low-dose x-ray system and high-contrast, high-resolution film for examination of the breasts. Successful treatment of breast cancer depends on early diagnosis. Mammography plays a central part in early detection of breast cancers. Mammography can show changes in the breast up to two years before a patient or physician can feel them. The Food and Drug Administration (FDA) says that mammography can detect 85 to 90 percent of breast cancers in women over 50. Current guidelines from the American Medical Association (AMA) and the American College of Radiology (ACR) recommend that beginning at age 40 women get annual mammograms.
Mammography is used to diagnose breast diseases in women. The use of screening mammography can assist in the detection of disease even if you have no complaints or symptoms.
While the AMA and ACR recommend that women aged 40 and older get annual mammograms, the National Cancer Institute (NCI) says women who are at increased risk due to a genetic history of breast cancer, or who have had breast cancer, may need to get mammograms at an earlier age.
The initial two mammography images themselves are not always enough to determine the existence of a benign or malignant disease with certainty. If a suspicious finding or spot is seen, the radiologist may recommend further diagnostic studies.
Before scheduling a mammogram, the American Cancer Society (ACS) recommends that you discuss any new findings or problems in your breasts with your doctor. In addition, inform your doctor of any prior surgeries, hormone use, and family or personal history of breast cancer.
Do not schedule your mammogram for the week before your period if your breasts are usually tender during this time. The best time is one week following your period. Always inform your doctor or x-ray technologist if there is any possibility that you are pregnant.
The American Cancer Society also has these recommendations:
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Do not wear deodorant, talcum powder, or lotion under your arms on the day of the exam. These can appear on the x-ray film as calcium spots.
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Describe any breast symptoms or problems to the technologist performing the exam.
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If possible, obtain prior mammograms and make them available to the radiologist at the time of the current exam.
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Ask when your results will be available; do not assume the results are normal if you do not hear from your doctor or the mammography facility.
In addition, before the examination, you will be asked to remove all jewelry and clothing above the waist and you will be given a gown or loose-fitting material that opens in the front.
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A mammography unit looks similar to any radiographic equipment that produces x-rays to obtain an image of some part of the human body; such as chest organs or bones. The main part of a mammography unit looks like a rectangular box that houses the tube in which x-rays are produced. A mammography unit is "dedicated equipment," because it is used exclusively for x-ray exam of the breast. The unit has special accessories that allow only the breast to be exposed to the x-rays. Attached to the unit is a device that holds and compresses the breast and positions it so images can be obtained at different angles.
Below are examples of the mammography equipment that may be used.
The breast is exposed to a small dose of radiation to produce an image of internal breast tissue. The image of the breast is produced as a result of some of the x-rays being absorbed (attenuation) while others pass through the breast to expose the film. The exposed film is either placed in a developing machine, producing images much like the negatives from a 35-mm camera, or images are digitally stored on computer.
During mammography, a specially-qualified radiologic technologist will position the patient and image the breast. The breast is first placed on a special cassette and compressed with a paddle (often made of clear Plexiglas or other soft plastic).
Breast compression is necessary in order to:
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Even out the breast thickness so that all of the tissue can be visualized
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Spread out the tissue so that small abnormalities won’t be obscured by overlying breast tissue
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Allow the use of a lower x-ray dose since a thinner amount of breast tissue is being imaged
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Hold the breast still in order to eliminate blurring of the image caused by motion
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Reduce x-ray scatter which also leads to poor image quality
The technologist will go to behind a glass shield while making the x-ray exposure, which will send a beam of x-rays through the breast to the film behind the plate, thus exposing the film.
You will be asked to change positions slightly between images. The routine views are a top-to-bottom view and a side view. The process is repeated for the other breast.
The examination process should take about half an hour. When the mammography is completed you will be asked to wait until the technologist examines the images to determine if more are needed.
Generally, this is a painless procedure. You will feel pressure on the breast as it is squeezed by the compressor. Some women with sensitive breasts may experience discomfort. If this is the case, schedule the procedure when your breasts are least tender. The technologist will apply compression in gradations. Be sure to inform the technologist if pain occurs as compression is increased. If discomfort is significant, less compression will be used.
Benefits
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Imaging of the breast improves a physician's ability to detect small tumors. When tumors are small, effective treatment and cure are more likely.
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The use of screening mammography (imaging examination of the breast by means of x-rays, of individuals usually without symptoms to detect those with a high probability of having breast disease) increases the detection of small abnormal tissue growths confined to the milk ducts in the breast, called ductal carcinoma in situ (DCIS). These early tumors cannot harm patients if they are removed at this stage and mammography is the only proven method to reliably detect these tumors.
Risks
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Radiation exposure. Mammography is an x-ray imaging procedure. Federal mammography guidelines limit the radiation used for each exposure of the breast to 0.3 rad. The exposure to radiation received from two mammographic views is equivalent to six months of natural background exposure. This amount of exposure is believed to be safe.
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Special care is taken during x-ray examinations to ensure maximum safety for the patient by shielding the abdomen and pelvis with a lead apron, with the exception of those examinations in which the abdomen and pelvis are being imaged. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
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False Positive Mammograms. Between 5 and 10 percent of mammogram results are abnormal and require more testing (more mammograms, fine needle aspiration, ultrasound, or biopsy), and most of the follow-up tests confirm that no cancer was present. It is estimated that a woman who has yearly mammograms between ages 40 and 49 would have about a 30 percent chance of having a false-positive mammogram at some point in that decade, and about a 7 to 8 percent chance of having a breast biopsy within the 10-year period. The estimate for false-positive mammograms is about 25 percent for women ages 50 or older.
Interpretations of mammograms can be difficult because a normal breast can appear differently for each woman. Also, the appearance of an image may be compromised if there is powder or salve on the breasts or if you have undergone breast surgery. Because some breast cancers are hard to visualize, a radiologist may want to compare the image to views from previous examinations. Not all cancers of the breast can be seen on mammography.
Breast implants can also impede accurate mammogram readings because silicone implants are not transparent on x-rays and can block a clear view of the tissues behind them, especially if the implant has been placed in front of, rather than beneath, the chest muscles. But the NCI says that experienced technologists and radiologists know how to carefully compress the breasts to improve the view without rupturing the implant. When making an appointment for a mammogram, women with implants should ask if the facility uses special techniques designed to accommodate them. And before the mammogram is taken, they should make sure the technologist is experienced in performing mammography on patients with breast implants.
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