Before using a contrast agent, a MRI scan of the breast can show the following:
Malignant breast tumors begin to grow their own blood supply network once they reach a certain size; this is the only way the cancer can continue to grow. In a breast MRI scan, a contrast agent injected into the bloodstream can provide information about blood supply to the breast tissues: The agent "lights up" a tumor by highlighting its blood vessel network. The contrast agent also highlights normal vessels in the breast. After a few minutes the contrast agent diffuses (or spreads) into the rest of the breast. High blood vessel density is a characteristic of cancer. It is the use of the contrast agent that makes breast MRI more sensitive than mammography or ultrasound when detecting breast cancer.
After the contrast agent is injected, abnormalities show up bright on the images; this is called enhancement. (See the Pictures pages for examples). After having a breast MRI exam to evaluate a suspicious lump or mammogram, the first question that the radiologist asks is, is there enhancement or not? If there is enhancement, does it show a lesion (mass or tumor)? If there is an enhancing lesion, the radiologist must then look at other features to determine if the lesion is benign or malignant, such as the amount of enhancement, the pattern of enhancement (such as slow or fast) and the characteristics of the lesion (such as the border or dark lines within the lesion).
When there is no enhancement, the radiologist can exclude the possibility of a lesion (either benign or malignant) with about 95% confidence. This means that if nothing lights up, (most likely) there is nothing abnormal in the breast.
When surgery (excisional biopsy or lumpectomy) shows cancer at the margins (also known as "positive margins"), a subsequent breast MRI exam might assess extent of disease away from the surgical site. The actual surgery site cannot be evaluated since, right after surgery (for a period of 6-12 months), it is hard to tell the difference between residual disease and inflammation from post-surgical changes at the site. However, further surgery should not wait for this delay. Future research may try to get around this problem.
Patients with large tumors (or tumors extending to the skin or chest wall) may have chemotherapy before their surgery. This is also known as "neoadjuvant chemotherapy." One possibility of breast MRI is to have exams before and after the chemotherapy in order to see if the treatment is working and if so, how much the tumor has shrunk.
The MRI might show something in addition to why you were first asked to have the exam, something not felt or seen on mammography. If this happens, you and your doctor will have to decide how to use the additional information. However, researchers are currently developing MRI-guided breast biopsy to determine what a suspicious lesion is when it is only seen on a breast MRI exam. Not all institutions currently have MRI-guided biopsy capabilities.
To sum up, by looking at all of the images (before and after contrast agent injection), the radiologist uses breast MRI to answer the following questions:
With mammography, a certain type of very small calcifications can be an early indication of cancer. However, breast MRI cannot detect calcifications. Instead, different markers for cancer are used, including the blood flow of the tumor, as well as the size and appearance of the tumor.
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Breast MRI cannot replace mammography or the physical breast exam. Information from the MRI exam is used in addition to all of the other information your doctor has available to make treatment decisions (mammography, physical exam, biopsy). |
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