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Magnetic resonance breast imaging (MRI, MR) has been
approved by the U.S. Food and Drug Administration (FDA) since 1991 for use as a
supplemental tool, in addition to mammography, to help
diagnose breast cancer. Breast MRI is an excellent problem-solving technology. It is often
used to investigate breast concerns first detected with mammography, physical exam, or
other imaging exams. MRI is also excellent at imaging the augmented
breast, including both the breast implant itself and the breast tissue surrounding the
implant (abnormalities or signs of breast cancer can sometimes be obscured by the implant
on a mammogram). MRI is also useful for staging breast cancer,
determining the most appropriate treatment, and for patient follow-up after breast cancer
treatment.
In addition to its role as a diagnostic tool, researchers have been investigating whether
breast MRI may be useful in screening younger women at high risk of breast cancer. Most
women under 40 years of age do not require any breast imaging. However, the American Cancer
Society recently recommended that women at very high risk of developing breast cancer have annual
breast MRI exams in addition to annual mammograms to increase the likelihood that breast cancer
will be detected early, when the chances of survival are greatest. Because MRI is more sensitive
than mammography, it can help detect cancer that may be missed by mammography. However, because
this increased sensitivity can also lead to false positive results, which requires breast
biopsy procedures, the American Cancer Society does not recommend MRI for all women.
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MRI image of the breast,
showing a lesion. Image
courtesy of Siemens Medical.
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Main Menu:
How Breast MRI is Performed
Unlike mammography which uses low dose x-rays to image the breast, MRI uses
powerful magnetic fields and radio waves to create images of the breast. The MRI system is
able to switch magnetic fields and radio waves to achieve views in any plane and from any
orientation while x-ray mammography requires re-orientation of the breast and mammography
system for each view desired.
The main component of most MRI systems is a large tube-shaped or cylindrical magnet. To
begin the MRI exam, the patient is positioned on a special table inside the MRI system
opening where a magnetic field is created by the magnet. Each total MRI exam is typically
comprised of a series of 2 to 6 sequences, with each sequence lasting between 2 and 15
minutes. An "MRI sequence" is an acquisition of data that yields a specific
image orientation and a specific type of image appearance or "contrast."
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A recent advance in MRI breast imaging is the CP Breast Array Coil, which
allows for bilateral breast imaging and improved differentiation between various breast
tissue. The patient is placed directly on the table and the technologist has visual
control of breast position through a transparent window. Images courtesy of Siemens
Medical. |
During the examination, a radio signal is turned on and off, and subsequently, the
energy which is absorbed by different atoms in the body is echoed or reflected back out of
the body. These echoes are continuously measured by the MRI scanner. A digital computer
reconstructs these echoes into images of the breast. The tapping heard during the MRI exam
is created when "gradient coils" are switched on and off to measure the MRI
signal reflecting back out of the patient's body. A benefit of MRI is that it can easily
acquire direct views of the breast in almost any orientation while mammography requires
re-orientation of the breast and mammography system for each view desired. An MRI exam of
the breasts typically takes between 30 and 60 minutes.
The most useful MRI technique for breast imaging uses a contrast material called
Gadolinium DTPA, which is injected into a vein in the arm before or during the exam to
improve the quality of the images. This contrast agent helps produce stronger and clearer
images and "highlight" any abnormalities.
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Transverse high-resolution MRI scan of breast and implants. Note the implant
twisting on the upper (left) image and the implant valve on the lower (left) image.
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