Breast MRI

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What are the indications for breast magnetic resonance imaging (MRI)?

General indications for breast MRI include:

• Establish the extent of disease in the setting of a newly diagnosed breast cancer.

• Further evaluate an imaging finding that is incompletely characterized by diagnostic mammography and/or breast ultrasonography (US).

• Evaluate for residual disease in the setting of positive margins after lumpectomy or other operative procedure.

• Evaluate a patient with metastatic adenocarcinoma to the axilla of unknown primary.

• Evaluate for silicone breast implant rupture.

• Presence of a hereditary gene or syndrome known to predispose to breast cancer (BRCA1/2 carrier, Li-Fraumeni syndrome, Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome) or a first-degree relative affected by one of these.

• An estimated lifetime risk of breast cancer greater than 20% to 25%.

• History of prior thoracic radiation therapy between the ages of 10 and 30.

• Monitor the response of a known breast cancer to neoadjuvant chemotherapy.

2

What are the contraindications for breast MRI?

Pregnancy is a contraindication for breast MRI because it is not known if the contrast agent used is safe during pregnancy. Other contraindications are those that apply to any MRI examination, such as presence of a pacemaker; a metallic foreign body in the eye, brain, or near other vital structures; a cochlear implant; or a drug infusion device, to name a few. A patient completes a detailed questionnaire about possible contraindications and is checked with a metal detector before being brought into the MRI suite.

3

What are the risks of breast MRI?

The main risks are a reaction to the contrast agent used during the examination and false-positive results, resulting in unnecessary medical tests and procedures.

4

How sensitive is breast MRI at finding breast cancer?

A large meta-analysis of fourteen studies in high-risk women between 2000 and 2011 found that breast MRI had a sensitivity of 84.6% for detecting cancer versus 38.6% for mammography and 39.6% for US. MRI can detect cancer that is occult on mammography, US, and physical examination [ ].

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If a biopsy is performed based on an abnormal MRI finding, how likely will this be cancer?

One analysis evaluating 10 studies using breast MRI for screening women at high risk for breast cancer found that the positive predictive value (PPV) for malignancy among patients who had a biopsy varied from 17% to 89% (mean of 45%) [ ]. Approximate benchmarks in the current BI-RADS atlas for biopsies performed as a result of screening breast MRI are that 20%-50% of biopsies for high risk women should be positive for cancer [ ].

6

What are the typical sequences used in a breast MRI?

Breast MRI is usually performed in the axial or sagittal plane on a 1.5- or 3-Tesla (T) magnet. We perform breast MRI in the sagittal plane on a 1.5-T magnet and use T1-weighted spin echo, fat-suppressed T2-weighted fast spin echo, and fat-suppressed three-dimensional T1-weighted spoiled gradient-recalled echo sequences. After intravenous contrast administration, the breast is usually scanned three times approximately 90 seconds apart to obtain dynamic postcontrast images. These sequential images provide information for kinetic analysis that can help to characterize lesions as benign or malignant. Delayed phase axial T1-weighted fat-suppressed images are then obtained to visualize the axillae and chest wall, and to allow for multiplanar correlation. Subtraction images are created by subtracting the precontrast images from the postcontrast images to aid with identification of areas of abnormal enhancement. These images are easily degraded by patient motion between sequences and so it is important to assess for motion before using these images for diagnostic interpretation. Both spatial (morphology) and temporal (kinetic) information is acquired in every case unless the examination is performed without contrast material to evaluate the integrity of silicone implants.

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Which is more helpful to characterize a lesion as malignant, morphology on postcontrast images or kinetic analysis features?

Lesion morphology is a more accurate predictor of malignancy and should be given priority over lesion kinetic analysis.

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