Mammography
Mammography is the process of using low-dose amplitude-X-rays (usually around 0.7 mSv) to examine the human breast. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses and/or microcalcifications. Mammography is believed to reduce mortality from breast cancer. No other imaging technique has been shown to reduce risk, but breast self-examination (BSE) and physician examination are considered essential parts of regular breast care.
In many countries routine mammography of older women is encouraged as a screening method to diagnose early breast cancer. The United States Preventive Services Task Force recommends screening mammography, with or without clinical breast examination, every 1-2 years for women aged 40 and older.[1]
Like all x-rays, mammograms use doses of ionizing radiation to create images. Radiologists then analyze the image for any abnormal findings. It is normal to use longer wavelength X-rays (typically Mo-K) than those used for radiography of bones.
At this time, mammography along with physical breast examination is the modality of choice for screening for early breast cancer. Ultrasound, ductography, positron emission mammography (PEM), and magnetic resonance imaging are adjuncts to mammography. Ultrasound is typically used for further evaluation of masses found on mammography or palpable masses not seen on mammograms. Ductograms are still used in some institutions for evaluation of bloody nipple discharge when the mammogram is non-diagnostic. MRI can be useful for further evaluation of questionable findings as well as for screening pre-surgical evaluation in patients with known breast cancer to detect any additional lesions that might change the surgical approach, for instance from breast-conserving lumpectomy to mastectomy. New procedures, not yet approved for use in the general public, including breast tomosynthesis may offer benefits in years to come.
Mammography has a false-negative (missed cancer) rate of at least 10 percent. This is partly due to dense tissues obscuring the cancer and the fact that the appearance of cancer on mammograms has a large overlap with the appearance of normal tissues.
Often women are quite distressed to be called back for a diagnostic mammogram. Most of these recalls will be false positive results.
A mammogram is a quick and easy X-ray of the breast done in complete privacy by a specially trained female technologist.
Who interprets the results and how do I get them?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will discuss the results with you. You will also be notified of the results by the mammography facility.
What are the benefits vs. risks?
Benefits
- Imaging of the breast improves a physician's ability to detect small tumors. When cancers are small, the woman has more treatment options and a cure is more likely.
- The use of screening mammography 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.
- It is also useful for detecting all types of breast cancer, including invasive ductal and invasive lobular cancer.
- No radiation remains in a patient's body after an x-ray examination.
- X-rays usually have no side effects in the diagnostic range.
Risks
- There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
- The effective radiation dose from a mammogram is about 0.7 mSv, which is about the same as the average person receives from background radiation in three months. Federal mammography guidelines require that each unit be checked by a medical physicist every year to ensure that the unit operates correctly.
- Five percent to 15 percent of screening mammograms require more testing such as additional mammograms or ultrasound. Most of these tests turn out to be normal. If there is an abnormal finding, a follow-up or biopsy may have to be performed.
- Most of the biopsies confirm that no cancer was present. It is estimated that a woman who has yearly mammograms between ages 40 and 49 has about a 30 percent chance of having a false-positive mammogram at some point in that decade and about a 7 percent to 8 percent chance of having a breast biopsy within the 10-year period.
- Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. See the Safety page for more information about pregnancy and x-rays.
Personal Quote"I wasn't looking for surprises. I just wanted to keep watch over my health with a routine mammogram. Something worried somebody, because I had to have more pictures. Then a biopsy. I thought it would be just a needle stick—but it was a real operation. I can't complain. It was benign. I'm okay."
—Marcia
Mammograms are probably the most important tool doctors have not only to screen for breast cancer, but also to diagnose, evaluate, and follow people who’ve had breast cancer. Safe and reasonably accurate, a mammogram is an x-ray photograph of the breast. The technique has been in use for about 40 years.
The Procedure
What will I experience during and after the procedure?
You will feel pressure on your breast as it is squeezed by the compression paddle. Some women with sensitive breasts may experience discomfort. If this is the case, schedule the procedure when your breasts are least tender. Be sure to inform the technologist if pain occurs as compression is increased. If discomfort is significant, less compression will be used.
Alternatives to mammography
While the cost of mammography is relatively low, its sensitivity is not ideal, with reports listing the range from 45% to about 90% depending on factors such as the density of the breast. Neither is the X-ray based technology completely benign, as noted above. Therefore there is considerable ongoing research into the use of alternative technologies.
One approach, contrast enhanced magnetic resonance imaging (MRI), has shown substantial progress. In this method, the breast is scanned in an MRI device before and after the intravascular injection of a contrast agent (Gadolinium DTPA). The pre-contrast images are "subtracted" from the post-contrast images, and any areas that have increased blood flow are seen as bright spots on a dark background. Since breast cancers generally have an increased blood supply, the contrast agent causes these lesions to "light up" on the images. The available literature suggests that the sensitivity of contrast-enhanced breast MRI is considerably higher than that of either radiographic mammography or ultrasound and is generally reported to be in excess of 95% (though not all reported studies have been as encouraging). The specificity (the confidence that a lesion is cancerous and not a false positive) is only fair, thus a positive finding by MRI should not be interpreted as a definitive diagnosis. The reports of 4,271 breast MRIs from eight large scale clinical trials were reviewed recently by CD Lehman. Overall the sensitivity ranged from 71% to 100% in these reports, however the call-back rates were low at 10% and the risk of having a benign biopsy was reported at 5%, a significant improvement over mammography.
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