Abstract
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Objectives: Molecular breast imaging (MBI) is a valuable supplemental screening tool in detecting mammographically-occult breast cancers in women with dense breast tissue [1,2]. At our institution, MBI is performed with 300 MBq Tc-99m sestamibi for all patients. For some nuclear medicine procedures, administered activity or imaging time is increased for patients of larger size in order to obtain adequate counts. Our objective was to assess whether uptake of Tc-99m sestamibi in the breast is influenced by patient size.
Methods: Records from patients who underwent a clinical MBI examination between July - November 2016 were reviewed. Those in whom our standard injection and preparation techniques were followed were included in the analysis [3,4]. Prior to injection, patients fasted (minimum 4 hours) and a warm blanket was placed around the patient’s shoulders and chest to facilitate peripheral blood flow and increase uptake of Tc-99m sestamibi in the breast tissue. Patients were injected with 300 MBq Tc-99m sestamibi using a syringe known to provide low adhesion of sestamibi. Residual activity was measured to allow calculation of exact administered activity for each patient. Bilateral cradiocaudal (CC) and mediolateral oblique (MLO) views were acquired at 10 min/view using a dual-head CZT-based gamma camera optimized for low-dose imaging [5]. Breast thickness was measured as the distance between the two detectors while the breast was lightly compressed. Patient height, weight, body surface area and body mass index were obtained from records. Lean body mass with the James equation (LBMJames) and Janmahasatian correction (LBMJanma) was calculated as described in [6]. Count density in the breast tissue was measured by drawing a region of interest around the central breast tissue of the right breast MLO view of the lower detector excluding the pectoral muscle, lesions and edges of the detector. Count density was expressed as cts/cm2/MBq administered activity. Spearman’s correlation coefficient (rs) was calculated to assess correlation between count density and patient body size factors.
Results: A total of 200 patients were analyzed. No dose infiltration was suspected at any injection. Average administered activity was 292 MBq (s.d.= 13.8 MBq; range 247 - 326 MBq). Average count density was 7.2 cts/cm2/MBq (s.d. = 2.7 cts/cm2/MBq; range 3.1 - 17.8 cts/cm2/MBq). MBI count density was weakly negatively correlated with height (rs = -0.18; p=0.01), weight (rs = -0.23; p=<0.001), body mass index (rs = -0.16; p=0.02), body surface area (rs = -0.22; p=0.002), LBMJames (rs = -0.23; p=0.001), and LBMJanma (rs = -0.23; p= 0.001). No correlation was observed between count density and breast thickness (rs=0.06; p=0.37).
Conclusion: Our results suggest a lack of relationship between uptake of Tc-99m sestamibi in breast tissue and body size or compressed breast thickness. Altering from the standard 300 MBq administered activity for larger patients is likely unnecessary. $$graphic_C383444B-97FB-4C60-AEA6-AB094CA7D951$$