What is it?
Contrast-enhanced magnetic resonance imaging (MRI) is a noninvasive medical test that uses very strong magnets and pulses of radio waves to manipulate natural magnetic properties in the body to create images of the part of the body being evaluated. Breast MRI requires intravenous injection of gadolinium-based contrast to evaluate the breast tissue (Fig. 13), looking at both anatomy and blood flow patterns. Normal tissue, cancers, and benign (noncancerous) findings can enhance (light up) on MRI. MRI is recommended for breast screening for high-risk women. MRI can be used in “diagnostic” cases to help answer questions that may have been raised by other tests or physical exam. MRI is also commonly used to assess the local extent of disease in women with newly diagnosed breast cancer. It is not possible to scan other parts of the body with MRI at the same time as the dedicated breast MRI examination, as the “listening” devices need to be close to the body part in question.
How it works
For breast MRI, a patient lies face down on a special table and the breasts are positioned into the two openings of a “coil” (the imaging device) (Figs. 14, 15). The exam takes place in the “tunnel” of the MRI scanner. The MRI scanner makes loud “tapping” noises for several minutes at a time while the exam is taking place. After an initial set of images has been obtained, the contrast agent is injected into a vein in the arm. MRI can be performed any time during the menstrual cycle, but to reduce possible confusion caused by normal hormonal changes in the breast in premenopausal women, screening MRI is ideally performed from day 7-10 of the menstrual cycle. It is important for the patient to lie very still during the exam as any motion will make the study hard to interpret. The usual breast MRI examination takes about 20 to 40 minutes. A shorter technique, called “abbreviated” or “fast” MRI can be performed for screening in some centers which uses fewer sequences and takes only about 10 minutes.
Breast MRI reveals an average of 10 additional cancers per thousand women screened after mammography/tomosynthesis, even when both mammography and ultrasound have been performed. The cancer-detection benefit is seen across all breast density categories and similar results have been seen with MRI even in average-risk women . MRI is very sensitive and is recommended every year for women who are at high risk for breast cancer, including women with a personal history of breast cancer and dense breasts or diagnosis by age 50 . Modeling studies suggest a slight improvement in cancer detection when MRI is performed on an alternating six-month basis with mammography (e.g. mammogram in January and MRI in July) . There is no benefit to screening US in women having screening MRI [4, 5].
In the Netherlands, MRI was studied in average-risk women with negative mammograms and extremely dense breasts. A total of 4,783 women had screening MRI and 79 cancers were detected by MRI (cancer detection rate of 16.5 per 1000). Among women who underwent MRI, there were only 4 cancers presenting as interval cancers (detected as lumps) in the 2-year interval between screens (rate of 0.8/1000), compared to 16 in women having only mammography (rate of 4.9 to 5.1 per 1000) .
Breast MRI is a sensitive test and will find more areas of concern than either a mammogram or ultrasound. Some of those “finds” will be cancer, but more than half will not (known as a “false positive”). It is important to have the examination performed at a facility where the radiologist correlates the MRI with the patient’s mammogram and any other breast imaging and prior biopsy results. The facility should also be able to perform an MRI-guided biopsy or formally refer to another facility that can; all facilities accredited in breast MRI by the American College of Radiology should meet these requirements.
MRI cannot be performed in women who have certain metal implants such as pacemakers or spinal fixation rods, and is not recommended if the patient is pregnant. Not all patients can tolerate a contrast agent and it may pose a small risk for women with kidney disease. Some women find claustrophobia an issue. The positioning can be difficult for some patients with neck problems, obesity or breathing issues. There can be accumulation of gadolinium in parts of the brain in patients who have multiple contrast-enhanced MRI studies ; the importance of this finding is unknown, and this appears to be an issue only with certain types of contrast agents .*
A last consideration for MRI currently is its high cost, which is not always covered by insurance. The lower cost “fast” MRI is performed on standard MRI equipment after gadolinium-based contrast injection but with fewer sequences; its availability is still quite limited [9-11]. The pivotal multicenter 2020 ECOG-ACRIN 1141 study  of fast or “abbreviated” MRI in patients with dense breasts found an overall 3D mammography cancer detection rate of 6.2/1000 women screened vs. an overall abbreviated MRI cancer detection rate of 15.2/1000, a difference of 9/1000.
* “Linear” contrast agents “leak” more gadolinium and therefore show greater accumulation of gadolinium in the brain than “caged” or “macrocyclic” agents. Linear agents include gadopentetate dimeglumine [Magnevist], gadodiamide [Omniscan], and gadoversetamide [OptiMARK]. Macrocyclic agents include gadoterate meglumine [Dotarem], gadobutrol [Gadavist], and gadoteridol [ProHance].
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