is an Assistant Clinical Professor and
is a Professor in the Department of Radiology, University of
North Carolina School of Medicine, Chapel Hill, NC.
Magnetic resonance imaging (MRI) of the breast has been in use
since the mid-1980s. Primarily, it has been used for evaluating
implant rupture and for searching for a primary breast cancer in
cases in which the mammogram and physical examination were negative
in patients with metastatic disease to axillary lymph nodes. Since
MRI allows for improved soft-tissue contrast, enhancement of a
lesion, and multiplanar imaging, investigations continue to
evaluate its usefulness and role in breast cancer detection.
Breast cancer is often similar in density to the surrounding
normal dense breast tissue; therefore, 10% to 20% of cancers are
not visualized by conventional film-screen mammography.
Mammography is the only imaging study that has been shown to reduce
breast cancer mortality.
However, mammography has limited sensitivity and specificity in
dense breasts, postsurgical/postradiation breasts, and augmented
breasts. Recent studies have demonstrated that the sensitivity of
breast MRI in lesion detection is as high as 100%; however, breast
MRI has a low specificity, ranging from 37% to 86%.
To detect malignant breast lesions, an intravenous contrast
agent, gadolinium-DTPA, must be administered to the patient. Lesion
enhancement is based on the phenomenon of angiogenesis (increased
tumor vascularity that is disorganized and has increased
permeability). The contrast agent also causes T-1 shortening, which
allows for increased conspicuity of the lesion. Therefore, lesions
would be expected to enhance rapidly and strongly. Benign lesions
such as fibroadenomas, fibrocystic changes, and inflammation can
also be vascular and can demonstrate rapid and strong enhancement.
Consequently, if a lesion or region demonstrates these findings,
malignancy cannot be excluded, which produces a high false-positive
False negatives have also been reported in the literature, but
appear to be less common. False negatives have been reported with
ductal carcinoma in situ (DCIS), and slowly enhancing lesions, such
as invasive lobular and mucinous carcinomas.
Prior to imaging the patient, there are several imaging
variables that need to be considered. First, since there is no
universally accepted breast MRI technique, what type of magnetic
field strength is your institution going to use? When using a lower
field strength, such as 0.5 Tesla, the radiologist needs to be
aware that low-field protocols create several issues, including a
lower signal-to-noise ratio (SNR), possible problems with chemical
shift dispersion, and less T1 tissue variability, which offers less
enhancement. Most of the MRI breast literature is based on a 1.5
Tesla field strength.
Second, since there is no consensus on which imaging sequences
to use, the radiologist must decide how to determine a balance
between spatial and temporal resolution. Also, the slice thickness
and interslice gap/no gap between the slices must be chosen, since
not all breast cancers are >1 cm in size or have a focal growth
pattern. Currently, fat-suppressed T1-weighted, three-dimensional
(3D) volumetric images seem to be sensitive to contrast and to
allow rapid acquisition so that enhancing lesions can be identified
before the enhancement of normal breast tissue.
Third, to increase lesion detection against a fatty background,
image subtraction or fat saturation is required. One method for
accomplishing this is to subtract the precontrast images from the
postcontrast images. This makes it imperative that there is no
patient motion between the precontrast and postcontrast images.
Alternatively, the fat signal can be eliminated by a variety of
In order to report enhancement relative to the rest of the tissue
(minimal, mild, etc.) and for biopsy guidance, the radiologist
should be comfortable with viewing fat saturation images.
For breast MR imaging, a dedicated breast coil is required to
improve the signal-to-noise ratio. Unilateral and bilateral coils
are available. To decrease imaging time, several institutions use a
compression plate to decrease the thickness of the breast and
reduce respiratory motion. The patient is imaged in a prone
The study can be optimized further if the patient has minimal
hormone stimulation that can be obtained by imaging the patient in
the second week of the menstrual cycle or by stopping hormone
replacement therapy for several weeks.
It is also very important to know the patient's clinical history,
including past surgeries, and to have reviewed the patient's recent
mammogram and/or ultrasound before viewing the MR images.
Use of contrast media
Breast cancers enhance after intravenous contrast administration
(Figures 1 and 2). Numerous authors have evaluated the kinetics or
dynamic measurements of contrast medium uptake in breast masses. By
doing so, they are attempting to differentiate malignant from
benign lesions based on how rapid the initial uptake and washout of
the contrast, which is plotted as a kinetic curve. Breast cancers
tend to have rapid enhancement and washout while benign lesions
tend to have slow progressive enhancement.
Heywang-Kobrunner et al
have seen rapid enhancement with slow washout, as well as less
rapid enhancement in breast cancers. Both of these types of
enhancement have also been seen at our institution. In addition,
benign lesions can also have these types of kinetic curves.
Since there is such an overlap with kinetic analysis of
malignant and benign lesions, Heywang-Kobrunner et al
and Nunes et al
have been evaluating the morphologic features of a breast mass
after contrast administration. Currently, these researchers have
demonstrated higher positive predictive values for malignancy for a
spiculated enhancing mass and for an irregular mass with peripheral
enhancement. The same appears to be true with ductal enhancement.
Also, a mass that was smooth or gently lobulated in contour and had
no enhancement or minimal enhancement was most likely found to be
Indications for breast MRI
Currently, there is not enough data available to justify routine
performance of MRI on all patients due to its high cost and lack of
well-established accuracy. Research into its utility continues in
multicenter studies such as the one led by Sylvia
Heywang-Kobrunner, MD at the University of Halle, Germany, and
Mitchell Schnall, MD at the University of Pennsylvania,
Philadelphia, PA, with the latter results not yet published. MRI of
the breast may find its niche in evaluating patients who are
recommended for biopsy to evaluate for multicentric or multifocal
disease. It may change the patient's staging and the type of
surgical procedure selected, such as mastectomy instead of breast
conservation surgery. In the literature, it has been reported that
up to one-third of patients have other foci of disease than
Others who may benefit from breast MRI are those who have
undergone breast conservation surgery. Sometimes it is difficult
with mammography to determine if the patient has a breast cancer
recurrence versus postsurgical changes at the lumpectomy site. With
the increased sensitivity of MRI and the use of contrast
administration, a malignant lesion would enhance while scar tissue
should not. However, scar tissue that is <18 months of age may
enhance and create a false-positive result.
In addition, to evaluate for recurrence, MRI can be helpful in the
immediate postoperative period to assess for residual disease.
MRI may be useful in women who are at high risk of developing
breast cancer and have dense breasts. Recent reports from Germany
assessing this population are promising so far.
However, there may be more false-positive results in this
subpopulation due to the increased sensitivity of MRI compared with
conventional mammography. This patient subgroup tends to be
younger. Brown et al
have shown that in a younger population group with increased breast
density there are usually more incidental enhancing lesions, and
management of these incidental lesions is problematic. At our
institution, we have evaluated incidental enhancing lesions with
additional mammography and ultrasound, and we have been able to
find a lesion(s) retrospectively using these modalities. An
appropriate work-up of the lesion(s) is then performed, including
biopsy if necessary. Additionally, some institutions do a
short-term follow-up MRI for incidental enhancing lesions.
If a suspicious lesion is detected only with MRI, then the
lesion can be biopsied or localized for surgical excision only with
MRI guidance. It is essential that an institution that provides
breast MRI to its patients have the capability to perform the
appropriate procedure for the area(s) of concern. MRI-guided
procedures are performed with the patient in the prone position and
with the patient's breast in a compression system with an open or
perforated lateral side plate. All of these procedures must be
performed with the introduction of the needle from a lateral
approach. After preoperative needle localization, one cannot give
the specimen contrast or image it with MRI to look for the original
abnormality. At our institution, a specimen radiograph confirms
that the localization wire has been removed and determines if an
abnormality can be visualized to mark for the pathology
Compared with mammography, breast MRI has the advantage of
improved tissue contrast and information about vascularity and
enhancement of a lesion. However, it has the limitations of greater
expense, lack of universal imaging parameters, the low risk
associated with the administration of intravenous contrast, and the
need for MRI-compatible biopsy or localization systems. Despite
these disadvantages, preliminary research demonstrates that MRI of
the breast is a promising imaging tool. It appears to be most
promising for the detection and staging of breast cancer in
patients with a known suspicious lesion, identifying a
mammographically occult lesion in patients with axillary lymph
nodes positive for adenocarcinoma, distinguishing scar tissue from
cancer recurrence, and for the evaluation of residual disease.
Further research is still needed to determine if MRI technology can
provide valuable clinical information that cannot be obtained with
conventional breast imaging methods.