MBI is designed to see beyond dense breast tissue. Instead of using low-energy X-ray, as in mammography, MBI relies on gamma radiation. This type of radiation has the advantage of being unaffected by breast tissue density.
Before the MBI images are made, a short-lived radioactive agent (radioisotope) is injected into an arm vein. The patient is then seated in front of the gamma camera, and the breast is positioned between two plates with light compression — only about one-third the pressure used in a mammogram. Two 10-minute images are taken of each breast. If breast tumor cells are present, they absorb this substance like a sponge and show up as hot spots on the resulting image.
Recent advances in the MBI gamma camera have made it possible to significantly reduce the radiation dose, making the reduced MBI radiation levels comparable to the dose that’s delivered during one to two digital screening mammograms.
Images generated from MBI provide physiological information about the breast similar to that of magnetic resonance imaging (MRI). And while MRI is radiation-free, can provide detailed images of the breast and is highly sensitive in detecting small breast cancers, the cost for this test can exceed thousands of dollars. MBI generally runs about $600. Although the MBI unit was approved by the Food and Drug Administration in 2010, most insurance companies don’t currently cover the cost of MBI as a screening test.
While not a substitute for mammography, MBI may aid in breast cancer detection in women with dense breasts. Although the tool isn’t yet widely available, it’s anticipated that this will change over the next few years. — Deborah Rhodes, M.D., Breast Diagnostic Clinic, and Amy Conners, M.D., Radiology, Mayo Clinic, Rochester, Minn.