Breast-Specific Gamma Imaging Has Higher Specificity Than MRI

Armen Hareyan's picture
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Breast-Specific Gamma Imaging

Breast-Specific Gamma Imaging (BSGI) may be more specific than MRI for evaluating patients with equivocal mammographic findings. The study, compiled by Dr. Rachel Brem and colleagues at The George Washington University Medical Center, compared the use of BSGI and MRI for women with an indeterminate mammogram. Standard procedure requires women with an indeterminate mammogram to have additional clinical work-ups.

According to Dr. Brem, Breast Specific Gamma Imaging (BSGI) -- nuclear medicine imaging of the breast -- is a physiologic approach to breast imaging. BSGI uses a high-resolution gamma camera and Tc-Sestamibi. Previous patient examinations demonstrated high-resolution cameras to be superior to conventional gamma imaging for both detecting breast cancer and screening high-risk patients.

"With the advent of high-resolution gamma cameras, further studies of BSGI versus MRI is warranted as both are physiologically-based adjunct imaging modalities for the diagnosis of breast cancer," said Dr. Brem.

Study Methods & Materials

The retrospective study included twenty-three women with an indeterminate breast finding. In these cases, the interpreting radiologist or referring physician had determined BSGI and MRI examinations were necessary. Subsequently, these patients proceeded to biopsy. If a patient's lesion, for which MRI guided biopsy was recommended, was not seen at the time the patient presented for biopsy, then the patient had a short interval follow-up with MRI.

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Patients had BSGI with the Dilon 6800 -- a high-resolution, small-field-of-view gamma camera in craniocaudal and mediolateral oblique projections. MRI was performed with a GE 1.5-T system using a dedicated breast coil. The sensitivity, specificity, positive and negative predictive values were calculated for both BSGI and MRI. Statistical significance was determined by comparing the confidence interval of each parameter for BSGI and MRI. All imaging findings were correlated with pathologic diagnosis.

BSGI versus MRI

In the study, thirty-three indeterminate lesions were evaluated. There were a total of 9 pathologically confirmed cancers in 8 patients. Breast MRI resulted in 18 false positive cases while BSGI demonstrated only 7. There was no statistically significant difference in sensitivity of cancer detection between BSGI and MRI. BSGI demonstrated a greater specificity than MRI, 71 percent and 25 percent, respectively.

The study authors concluded, BSGI has comparable sensitivity and greater specificity than MRI for the detection of breast cancer in patients with equivocal mammograms. The smallest cancer detected by BSGI was 3 mm.

Details about BSGI with the Dilon 6800 Gamma Camera

Breast-Specific Gamma Imaging (BSGI), performed with the Dilon 6800, is a molecular breast imaging technique that can see lesions independent of tissue density and thereby discover very early stage cancers. For difficult-to-diagnose patients, BSGI serves as a complementary diagnostic adjunctive procedure to mammography and ultrasound. With BSGI, the patient receives a radioactive tracing agent that is absorbed by all the cells in the body. Cancerous cells in the breast, due to their increased rate of metabolic activity, absorb a greater amount of the tracing agent than normal, healthy cells and generally appear as "hot spots" on BSGI images.

BSGI is ideal for patients with mammograms that are difficult to interpret. The interpretation challenges include dense breast tissue; suspicious areas on a mammogram; lumps that can be felt but not seen with mammography or ultrasound; implants and breast augmentation; scarring from previous surgeries and for women with notable family history of breast cancer.

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