Breast-Specific Gamma Imaging Has Higher Specificity Than MRI in Patients With Equivocal Mammograms

Recently published study results in The Breast Journal indicate that breast-specific gamma imaging (BSGI) may be more specific than magnetic resonance imaging (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, 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 vs MRI is warranted as both are physiologically based adjunct imaging modalities for the diagnosis of breast cancer," said Dr. Brem.

Study Methods and Materials

The retrospective study included 23 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.

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.

In the study, 33 indeterminate lesions were evaluated. There were a total of nine pathologically confirmed cancers in eight patients. Breast MRI resulted in 18 false-positive cases, whereas 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% and 25%, respectively.

The study authors concluded that 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.