Several large-scale studies have demonstrated a clear benefit to mammographic screening for breast cancer, particularly in women older than 50 years. Despite its success, mammography is recognized as a less-than-perfect screening method.
The limitations of mammography are particularly evident in women with dense breasts, where the sensitivity of mammography can be less than 50%. Increased breast density is a serious risk factor for breast cancer and is a major factor that greatly diminishes the value of mammography in the screening of younger women who have a high familial risk of breast cancer.
Results from several recent studies comparing mammography, ultrasonography, and magnetic resonance imaging (MRI) have consistently shown that both mammography and ultrasonography had a low sensitivity in women at increased risk, while MRI in the same patients had an increased sensitivity of between 75% and 100%. MRI, however, has variable specificity and high cost (10 to 15 times that of mammography).
Over the past 6 years, a new breast imaging technique called molecular breast imaging (MBI), which uses small, ultra-high-resolution gamma cameras, has been under development at Mayo Clinic.
MBI uses small, ultra-high-resolution gamma cameras configured in a dual-head design to overcome limitations of older technologies. The 2 main technical problems associated with scintimammography that prevented the detection of small cancers were:
The compact design of the MBI system allows the breast to be positioned directly between 2 gamma cameras in positions analogous to those used in mammography. Each gamma camera is also made up of small elements of a semiconductor called cadmium zinc telluride, which gives superior spatial and energy resolution compared with conventional technology and greatly improves image quality and the ability to detect small cancers.
MBI has a high sensitivity of more than 93% for the detection of lesions measuring 5 to 10 mm. A recent large screening study at Mayo Clinic found that in women at increased risk of breast cancer, MBI was 3 times more sensitive at early detection of breast cancer than screening mammography, while demonstrating better specificity.
The Mayo Clinic Nuclear Cardiology Laboratory offers a combined heart-breast scan to any woman coming to the laboratory for a clinically indicated myocardial perfusion scan (such as a technetium-sestamibi SPECT study). Interest in screening for breast cancer in women undergoing evaluation for coronary artery disease (CAD) has increased because there is a definite association between these 2 diseases. They share common risk factors, and some breast cancer treatments increase a woman's risk of developing CAD. Combined, CAD and breast cancer represent a woman's greatest health risk over her lifetime. MPI can be combined with myocardial perfusion imaging to accurately assess a woman's risk of both conditions.
The MBI scan is painless (only light breast compression is required) and can be performed during the waiting period between the stress study and cardiac imaging. As part of an ongoing research protocol, the MBI procedure is available at no additional charge to all female patients undergoing myocardial perfusion imaging in the Nuclear Cardiology Laboratory. Patients undergoing MBI must not have had breast biopsies, surgery, or radiation within the past year and must have a mammogram on record at Mayo within the past year, so that any findings on the MBI study can be correlated with a prior mammogram.
Patients are required to indicate on the study consent form their preference for communicating any unexpected findings on the MBI study. If the patient elects to proceed with follow-up at Mayo, she will be seen at the Mayo Clinic Breast Center and will likely follow the standard of care that is already established at Mayo for the MBI screening program.
MBI was developed at Mayo Clinic. Currently no other medical institution offers this combined heart-breast procedure. This test has the potential to enhance the clinical value of myocardial perfusion imaging for female patients by providing additional information on breast function that could only otherwise be obtained with expensive procedures such as contrast-enhanced MRI. In the future, this technique may also prove to have application in selected groups of women as a tool for initial breast cancer screening.