Introduction
Mammography is a type of imaging that uses a low-dose
x-ray system for examination of the breasts. The images of the
breasts can be viewed on film at a view box or as soft copy on
a digital mammography work station. Most medical experts agree
that successful treatment of breast cancer often is linked to
early diagnosis. Mammography plays a central part in early detection
of breast cancers because it can show changes in the breast up
to two years before a patient or physician can feel them. Current
guidelines from the U.S. Department of Health and Human Services
(HHS), the American Cancer Society (ACS), the American Medical
Association (AMA) and the American College of Radiology (ACR)
recommend screening mammography every year for women, beginning
at age 40.
The National Cancer Institute (NCI) adds that women who have
had breast cancer and those who are at increased risk due to
a genetic history of breast cancer should seek expert medical
advice about whether they should begin screening before age 40
and about the frequency of screening.
Uses of the Procedure
Mammography is used to aid in the diagnosis of breast
diseases in women. Screening mammography can assist your physician
in the detection of disease even if you have no complaints or
symptoms.
Initial mammographic images themselves are not always enough
to determine the existence of a benign or malignant disease with
certainty. If a finding or spot seems suspicious, your radiologist
may recommend further diagnostic studies, such as an MRI.
Diagnostic mammography is used to evaluate a
patient with abnormal clinical findings, such as a breast lump
or lumps that have been found by the woman or her doctor. Diagnostic
mammography may also be done after an abnormal screening mammography
in order to determine the cause of the area of concern on the
screening exam.
Prepare for a Mammogram
Before scheduling a mammogram, the ACS and other specialty
organizations recommend 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 ACS also recommends you do not wear deodorant,
talcum powder, or lotion under your arms or on your breasts on
the day of the exam. These can appear on the x-ray film as calcium
spots. Describe any breast symptoms or problems to the technologist
performing the exam.
If possible, obtain prior mammograms and make them available to
the radiologist at the time of the current exam. 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.
Mammography Equipment
A mammography unit is a rectangular box that houses the
tube in which x-rays are produced. The unit is dedicated equipment
because it is used exclusively for x-ray exam of the breast, with
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.
The Procedure
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 either a film (conventional
mammography) or digital image receptor (digital mammography).
The exposed film is either placed in a developing machine or images
are digitally stored on computer.
During mammography, a specially qualified radiologic
technologist will position you to image your breast. The breast
is first placed on a special platform and compressed with a paddle
(often made of clear plexiglas or other plastic).
Breast compression is necessary in order to:
- Even out the breast thickness so that all of the tissue can
be visualized;
- Spread out the tissue so that small abnormalities won't be obscured
by overlying breast tissue;
- Allow the use of a lower x-ray dose since a thinner amount
of breast tissue is being imaged;
- Hold the breast still in order to eliminate blurring of the
image caused by motion; and
- Reduce x-ray scatter to increase sharpness of picture.
The
technologist will go 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 may be asked to wait until the
technologist examines the images to determine if more are needed.
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 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.
Risks:
The effective radiation dose from a mammogram is about the same
as the average person receives from background radiation in three
months. The Federal mammography guidelines require that each
unit be checked by a medical physicist each year to insure that
the unit operates correctly.
Women should always inform their doctor or x-ray
technologist if there is any possibility that they are pregnant.
Five to 10 percent of screening 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 seven to eight 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.
Limitations of Mammography
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 both silicone and saline 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.
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