Every year the staggering statistics regarding breast cancer continue to grow. In 2018, it is estimated that over 250,000 new cases of invasive breast cancer will be diagnosed in women in the United States, along with 63,000 new cases of non-invasive breast cancer. In fact, approximately one in eight U.S women will develop invasive breast cancer in the course of her life. This data calls attention to the need for advanced early detection techniques and better treatment options. However, studies also show that since 1989, the death rates from breast cancer have steadily decreased, as a result of treatment advances, earlier detection through screening, and increased awareness.1
Medical Exams for Early Detection of Breast Cancer
For many years, mammography and ultrasound have been the standard for evaluating the breast and detecting abnormal tissues. Indeed, mammography is an invaluable tool in the fight against breast cancer, helping to reduce the mortality rate from 8-65%. This is largely due to the fact that mammography is a relatively inexpensive imaging modality, it is widely available, and the screening process is quick.2 However, mammography is limited in its ability to assess the extent of abnormal tissue borders, due to overlying dense breast tissue.
Ultrasound is also a useful imaging tool, because it allows radiologists to examine the breasts without an harmful ionizing radiation. However, this modality is not the most accurate and consistent when evaluating dense breasts and is less reliable as it depends on the skill of the technologist performing the scan.2
With the rise of technological advancements, many physicians have considered whether magnetic resonance imaging (MRI) can play a significant role in helping to screen and detect breast cancer. An MRI is a diagnostic imaging exam that uses a strong magnetic field, radio wave pulses, and a computer to produce detailed, high-resolution images of soft tissues within the body. MRI is not density-dependent and does not emit harmful radiation, making this modality well-suited for imaging the breast. MRI’s impressive imaging capabilities allow the scanner to locate small breast lesions that are sometimes missed by mammography and can help detect cancer in women with breast implants and in women who have dense breast tissue.3
However, studies have concluded that while MRI is a powerful diagnostic tool, it is not recommended as a routine breast cancer screening tool for all women, but rather as a supplemental tool that offers many important uses. For women who are at a high risk for breast cancer, undergoing a breast MRI with an annual mammogram is the physician recommended approach.
How does an MRI work?
An MRI machine is a large cylindrical machine, with a hollow center. When the system is active it creates a strong magnetic field around the patient. When radio wave pulses are added to the magnetic field, it energizes the hydrogen atoms within the patient’s body, forcing them to spin out of their normal alignment. When the hydrogen atoms return to their original position, they emit an energy signal, which is received and interpreted by a computer, and converts them into an image of the body.
For a breast MRI, the patient generally lies face down with her breasts positioned through openings in the table. This helps to ensure the breast positioning and limit movement artifacts in the images, which can be caused by breathing. Furthermore, most breast MRIs are performed with the aid of a gadolinium-based contrast agent. This dye is injected into the body during or before the exam and enhances and provides more clarity to images. A contrast dye helps radiologists view tissue abnormalities and have more diagnostic confidence.
In addition, these contrast-enhanced images also allow the radiologist to analyze the rate of peak enhancement and “wash-out”. This means, the radiologist is examining how fast a tissue mass takes in the contrast, and how fast it releases it. These characteristics are significant, because they help distinguish benign tumors from malignant ones. Malignant breast tumors take in and absorb a great deal of contrast very quickly, but they also release it very fast. Benign masses have the opposite affect; they take in the contrast gradually and consistently over several minutes.2
Who Should Have a Breast MRI?
Recent guidelines detailing who should screen for MRI with mammography have been determined by the American Cancer Society. This kind of screening should be considered by the following people:
- Women with BRCA1 or BRCA2 gene mutation
- Women with a first-degree relative (mother, sister, and/or daughter) with a BRCA1 or BRCA2 mutation
- Women with a 20-25% or greater lifetime risk of breast cancer, based on one of several accepted risk assessment tools that look at family history and other factors
- Women who have had radiation treatment to the chest between the ages of ten and thirty, for treatment such as Hodgkin disease
- Women with certain genetic disorders, such as Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome 3
Benefits and Limitations of MRI when Imaging Breast Tissue
While MRI alone does not provide enough information to diagnose breast cancer, it still provides valuable diagnostic and prognostic information. For example, in some cases MRI can find early breast cancer that was not detected by other tests, especially in women who are at high risk or who have dense breast tissue. In addition, MRI is more accurate when scanning women who have implant-augmented breasts or scar tissue that can produce an inaccurate result on a mammogram.
Moreover, MRI is known for detecting small tissue abnormalities that were not discovered with mammography or ultrasound, such as breast cancer cells present in an underarm lymph node. Once detected, an MRI can analyze and evaluate the exact size and precise location of breast cancer lesions. This provides useful information regarding the stage of the cancer and can signify whether it is spreading.3
Furthermore, sometimes an MRI can distinguish between benign and malignant tissue abnormalities. The features of a malignant breast condition often have irregular outer borders, while the features of a benign mass typically include smooth and rounded borders.4 The ability do determine whether a tumor is malignant or benign can save patients from having to undergo additional unnecessary exams or biopsies. However, MRI does not always offer clear enough data to determine if a mass is malignant or benign, which may lead to an unnecessary breast biopsy. This is referred to as a “false positive” test result. Advancements in MRI software are working to enhance breast MRI scans, in order to reduce the number of false positive results with malignant tumors, therefore decreasing the need for biopsies.
Accuracy of 3.0T versus 1.5T Breast MRI
In the past decade the use of 3.0T MRI has increased, however there is still little data comparing it to 1.5T when assessing cancerous tissues in the breast. In a study by Habib Rahbar et al., an institutional review board examined 20 patients with ductal carcinoma in situ (DCIS) diagnosed by core needle biopsy. DCIS is the presence of abnormal cells inside the milk ducts of the breast, considered to be the earliest form of breast cancer. These patients agreed to undergo pre-operative breast MRI at both 3.0T and 1.5T, to compare lesion sizes and imaging characteristics of the different MR field strengths.
Of the initial 20 cohort of patients with diagnosed DCIS, 19 underwent definitive surgery. The median DCIS sizes of these 19 patients were 6mm on 3.0T, and 13mm on 1.5T. When the pathology was surgically examined, the median DCIS sizes were confirmed at 6mm. Therefore, size correlation between MRI and pathology was higher for 3.0T than 1.5, and it may be more accurate when assessing disease extent prior to surgery. 5
Ultimately, the role of MRI in breast imaging in an important one, and it continues to expand as technology advances. In several recent studies regarding high risk women, the sensitivity of breast MR of invasive cancer has actually approached 100%, demonstrating it to be an extremely valuable tool. Furthermore, even though clinicians have apprehension surrounding MRI’s false-positive rates, studies have also shown that as criteria is refined, and experience is gained, the specificity of breast MRI has increased over the past several years. In fact, today it ranges from 75-90%.2 As medical imaging technology continues to improve, the role of MRI in breast cancer screening is likely to grow as well.
1. "U.S. Breast Cancer Statistics." Breastcancer.org. 9 January 2018. Web. 15 August 2018. <https://www.breastcancer.org/symptoms/understand_bc/statistics?gclid=EAIaIQobChMI0OfM49vv3AIVD8ZkCh3GHALKEAAYAyAAEgK9gPD_BwE>.
2. "Breast Cancer: The Sobering Statistics." 3T Imaging. Web. 15 August 2018. <http://www.3timaging.com/breast-mri-center-morton-grove-burbank-chicago-illinois.htm>.
3. "Breast Magnetic Resonance Imaging (MRI)." Johns Hopkins Medicine. Web. 15 August 2018. <https://www.hopkinsmedicine.org/healthlibrary/test_procedures/gynecology/breast_mri_92,P09110>.
4. Halls, Steven. "Magnetic Resonance Imaging (MRI) and malignancy detection." Moose & Doc Breast Cancer. 14 August 2018. Web. 15 August 2018. <https://breast-cancer.ca/mri-malnancy/>.
5. Rahbar, Habib, et al. "Accuracy of 3T versus 1.5T breast MRI for pre-operative assessment of extent of disease in newly diagnosed DCIS." PMC. NCBI. 8 January 2015. Web. 15 August 2018. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4348176/>.