Evaluation of the effect of fasting and exercise on uptake of Tc-99m sestamibi in breast tissue

Objectives To determine if changes in a subject’s prandial status (fasting versus fed) and metabolic status (rest vs.light exercise) at the time of injection of Tc-99m sestamibi alter its uptake in breast tissue.

Methods Evaluation of Prandial Status - After an overnight fast, 24 women underwent 2 consecutive molecular breast imaging (MBI) studies before and 30 minutes after consuming a standard meal. Evaluation of Metabolic Status - 22 women underwent 2 consecutive MBI studies before and after performing upright exercise at 70%-80% of maximum predicted heart rate. Medio-lateral oblique (MLO) views of both breasts were obtained using a dual head CZT gamma camera system. ROI analysis was performed on the left MLO views and breast activity was normalized to units of counts/pixel/mCi. As appropriate, corrections were applied for residual activity from the first MBI study. Changes in breast activity with intervention were computed to determine influence of fasting or exercise on breast activity.

Results In 24 subjects who completed the prandial study, the average count density (cts/pixel/mCi) in the breast was 6.3+2.2 in fed state and 8.0+2.4 in fasting state (p < 0.001). The fasting / fed ratio was 1.29+0.17 and there was a strong correlation between uptake measured pre and post-prandial, (R=0.9). A total of 22 subjects completed the resting / exercise study. The average count density (cts/pixel/mCi) in the breast was 9.5+2.8 in fasting pre-exercise state and decreased to 5.4+1.4 after exercise (p < 0.001). The resting / exercise ratio was 1.81+0.52 and no correlation was found between uptake measured pre-and post-exercise.

Conclusions Uptake of Tc-99m sestamibi in breast tissue is influenced by prandial state and exercise. Maintaining the subject in a fasting / resting state can result in ~25% increased uptake of Tc-99m sestamibi in breast tissue. This has important implications for strategies aimed at reducing patient dose or procedure time in MBI.