Quantification of Radio-tracer Uptake in Axillary Lymph Nodes using Breast Specific Gamma Imaging (BSGI): Benign Radio-tracer Extravasation versus Uptake Secondary to Breast Cancer

Abstract:  To develop a means of quantifying axillary radio-tracer uptake in patients undergoing breast specific gamma imaging. This may help differentiate uptake secondary to extravasation of the radio-tracer at the injection from increased uptake as a result of breast cancer metastatic to lymph nodes. A retrospective analysis of patients who had undergone breast specific gamma imaging was performed. Scans from 26 patients showing increased axillary uptake of radio-tracer were identified from 939 patients reviewed. Eighteen of these patients had increased axillary uptake ipsilateral to the side of tracer injection in the absence of breast cancer on that side. Of these 18 cases, eight patients had pathologic proven axillary metastatic disease with increased axillary uptake contralateral to the side of tracer injection. The maximum signal intensity for each region of increased radio-tracer uptake was measured using the net maximum uptake per region of interest and the two groups of patients were compared. Statistical significance was determined using a two-tailed p-value and 95% confidence intervals were considered statistically significant. The calculated means of the "net maximum uptake per region of interest" in the subjects with increased radio-tracer uptake secondary to radio-tracer extravasation and metastatic breast cancer were 177.89 and 117.25, respectively. Comparison of the means yielded a two-tailed p-value of 0.0498, which is statistically significant. There is a statistically significant greater intensity of axillary radio-tracer uptake when the uptake occurs secondary to extravasation when compared with metastases to axillary lymph nodes.