BSGI is an emerging molecular imaging technology that uses a high-resolution gamma camera to discover very early-stage cancers. To perform the procedure, the patient is given a radioactive tracing agent and the gamma-ray emission from this radiotracer is used to form a digital image showing the metabolic activity of the breast tissue.
While mammography findings are characterized by the difference in appearance between normal and suspicious breast tissue, BSGI is based on how cancerous cells function. Due to their higher metabolic rate, cancerous cells absorb more tracer than healthy cells and thus appear as "hot spots" on a BSGI image.
"BSGI can identify the most difficult to detect breast cancer - invasive lobular carcinoma," explained lead author Rachel Brem, professor of radiology and director of the Breast Imaging and Interventional Center at the George Washington University Medical Center (Washington, DC). "It also can help us detect additional lesions of all types of breast cancer in women whose mammograms show only one suspicious lesion."
Brem and colleagues reviewed the records of all patients who had BSGI examinations between January 2004 and June 4, 2007. Among these, 159 women had at least one suspicious or cancerous breast lesion found by mammography and/or physical exam, and had undergone BSGI to determine whether additional lesions were present.
BSGI examinations were classified as normal or abnormal based on the presence of focal radiotracer uptake. The team examined the BSGI findings and medical records to see how often additional sites of abnormal uptake were detected, and to determine the frequency of detecting clinically and mammographically occult cancerous sites.
The BSGI results showed an additional suspicious lesion, which was missed by mammography and physical exam, in 46 (29%) of the women. In 14 (36%) of the 39 women who underwent biopsy, the newly discovered lesions were cancerous.
Brem points out that BSGI is designed as an adjunct to mammography. "The data suggest that BSGI allows for the diagnosis of more and earlier breast cancers. It is an excellent tool for locating difficult-to-detect cancers and for screening high-risk women who have normal mammograms and physical examination," she said.