Abstract
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Objectives: Molecular Breast Imaging (MBI), performed with 300 MBq Tc-99m sestamibi and a dedicated gamma camera, has shown utility in detecting breast cancer occult on mammography due to dense breast tissue (Rhodes et al., AJR 2015; Shermis et al., AJR 2016). Strategies to improve uptake of sestamibi in breast tissue and allow for further reduction in the administered activity have been explored. Patient preparation including fasting prior to the exam and warming of the breasts were shown to increase breast uptake of Tc-99m sestamibi in a controlled research setting (O’Connor et al., JNMT 2015). Pre-examination instructions including a 3- hour fast and warming of the upper torso via a warm blanket prior to injection have been implemented at our institution, but validation in the clinical setting is lacking. Our objective was to assess patient compliance with pre-examination instructions and to evaluate whether image count density, a surrogate measure of breast uptake, was improved with fasting and warming in the clinical environment.
Methods: Under an IRB-approved and HIPAA compliant protocol, we performed a retrospective review of patients who had an MBI examination at Mayo Clinic Rochester between July 2016 and October 2017 (N=1428). Patients were excluded from analysis if dose infiltration was suspected (N=13), if residual activity was not recorded (N=7), if fasting or warming status was not known (N=10), or if the prescribed activity was higher than 300 MBq (N=1), leaving 1397 available for analysis. A subset of 100 subjects was randomly selected for count density analysis, including four groups of 25 subjects with the following preparation statuses: fasting and warmed, fasting and not warmed, not fasting and warmed, not fasting and not warmed. Count density of the breast tissue was measured by drawing regions of interest within an area of normal (non-lesion) breast parenchyma on the right mediolateral oblique view of the lower detector, avoiding the pectoral muscle and edges of the breast. Patients with breast implants were excluded from count density analysis (N=2). Count density was expressed as cts/cm2/MBq of administered activity. Characteristics between groups were compared by either chi-squared test or Fisher’s exact test and by one-way ANOVA or Kruskal-Wallis test.
Results: Of 1397 patients, the number and proportion of patients with each status was 1133 (81%) fasting and warmed, 54 (3.9%) fasting and not warmed, 185 (13%) not fasting and warmed, 25 (1.8%) not fasting and not warmed. Overall, 1187 of 1397 (85%) subjects reported compliance with fasting instructions and 1318 of 1397 (94%) used a warm blanket prior to injection. No significant differences were observed between groups in regard to age, menopausal status, and exogenous hormone use (all p>0.36). There was no significant difference (p=0.75) in count density between patients who fasted (average = 7.5 counts/cm2/MBq) vs. those who did not fast (average = 7.3 counts/cm2/MBq). There was also no difference in count density between the non-warmed (7.1 counts/cm2/MBq) and warmed (7.7 counts/cm2/MBq) patients (p=0.26).
Conclusions: Our results showed a high compliance rate with fasting and warming instructions, however, findings suggest that a 3-hour fast and warming of the upper torso, does not result in significant improvements in image count density in the clinical environment. These findings are in contrast to count density improvements observed in a controlled research study as a function of fasting or warming, where serial examinations were assessed within the same patient. A limitation of the current analysis conducted in clinical practice is that fasting status is patient-reported and time spent warming is patient-directed, which may result in higher variability in fasting and warming protocol. Additional research using a larger sample size is needed to confirm these findings and determine if count density from fasting and warming can be replicated in the clinical setting.