Breast-specific gamma imaging or BSGI (Dilon) complements mammography and ultrasound. After intravenous injection of 99m Technetium sestamibi, images of both breasts are obtained using a gamma camera with a small field of view device which is able to detect cancers greater than 3 mm. Positron emission mammography or PEM (Naviscan) involves intravenously injecting a glucose-containing radiopharmaceutical fluordexoyglucose (FDG) and imaging with a high-resolution, organ- specific PET scanner. Since both sestamibi and glucose uptake is greater in cancerous cells, BSGI and PEM demonstrate many of the same advantages as MRI including for presurgical planning and in differentiating a scar from a recurrent cancer. Image acquisition is made with the patient in a seated position so that claustrophobia is not an issue and being able to obtain the standard mammographic views makes it easy to compare modalities. Interpretation of the BSGI and PEM is much faster than with MRI since the number of images obtained is significantly less. Both modalities achieve high sensitivity for the detection of breast cancer and higher specificity than mammography with no difference noted between the detection of cancer in the fatty and dense breast. False positives such as fibroadenomas, fibrocystic changes and fat necrosis are seen on BSGI and PEM but less frequently than with MRI. PEM can be followed with whole body PET imaging to evaluate for metastatic disease. It should be noted that, the radiotracer and procedure cost is higher for PEM than BSGI. PEM also requires patient to fast for imaging to begin one hour after the injection, and with the patient needing to maintain a distance from others for 45 minutes after the procedure. In addition, PEM studies are only reimbursed in those patients with known cancer while with BSGI reimbursement is for both pre and post diagnosis of breast cancer. Similar to MRI, these techniques require image specific biopsy capabilities, so that when a suspicious lesion is visualized it can be sampled using that modality. The BSGI guided biopsy device is currently not FDA approved.
The indications for BSGI include;
-Complements mammography and ultrasound for patients who are difficult to image such as those with dense breast tissue, breast implants, in the post surgical breast and for those women who have had silicone and paraffin injections.
-In patients with known cancer to determine the extent of the disease, evaluate for multifocal, multicentric and bilateral disease.
-In those patients with questionable areas seen on mammography or breast ultrasound to reassure probably benign lesions or BI-RADS 3.
-Palpable abnormality or nipple discharge with a normal mammogram and breast ultrasound.
-To differentiate a scar from a recurrent cancer.
-Evaluating the axillary regions for lymph node status in breast cancer patients.
-Predicting chemotherapeutic response,
-Monitoring primary tumor response to neoadjuvant therapy.
-Evaluation of multiple lesions or clusters or microcalcifications to aid in the biopsy targeted selection.
-Evaluation in women with indeterminate or malignant type cluster of microcalcifications prior to stereotactic core biopsy.
-Patients in which an MRI of the breast is indicated and in those where MRI is not technically possible due to the presence of ferromagnetic implants, body habitus, obesity or patient claustrophobia.
-In high risk patients similar to the MRI screening criteria; personal history, parent, child or sibling with BRCA1 or BRCA 2 mutations, established lifetime risk of 20-25% or history of chest radiation between the ages of 10-30 years of age.
In our practice, we found that BSGI is helpful in evaluating those patients who have a palpable mass but with a negative mammogram and ultrasound. Traditionally, these patients would have been sent to a breast surgeon for management.
Our results show that if the BSGI is normal in this group of patients, the negative predictive value is 95%. That is to say we can reassure these patients that there is less than 5% chance she does has an invasive cancer.
In those patients with a positive BSGI, the abnormality was usually identified on a second look targeted ultrasound and subsequent biopsies were positive in 27% of the cases.
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