Ambient Temperature and Cardiac Accumulation of 18F-FDG

Abstract

Warming patients by changing the ambient environment (rather than core temperature) has been reported to reduce brown adipose tissue activity, thereby reducing artifacts in 18 F-FDG PET. Nonetheless, a reduction in cardiac uptake of 18 F-FDG has been incidentally noted during ambient warming. This study examined the impact of seasonal variations in ambient temperatures on cardiac uptake of 18 F-FDG. Methods: Consecutive 18 F-FDG PET patients were recruited into summer and winter cohorts. The protocol was highly standardized; however, data were excluded when scanning took place other than 60 min after injection. Mean and maximum counts per pixel in the cardiac region and cardiac standardized uptake value were determined and correlated with the daily minimum, maximum, and mean temperature (day of scan), mean temperature on the scan day and preceding 2 d (3-d window), and mean temperature 1, 2, 3, and 4 wk before scanning. Results: No statistically significant differences were noted between cohorts (summer and winter) for age, sex, weight, height, or dose. As expected, the summer cohort was associated with statistically higher minimum, maximum, and mean temperatures, longer days, and greater sunlight hours (all P , 0.001). The mean and maximum heart counts were statistically higher in winter than summer (P 5 0.031 and P 5 0.024, respectively). The cardiac standardized uptake value was statistically higher for winter than summer (P 5 0.026). The key factors in cardiac accumulation of 18 F-FDG were the minimum temperature on the day of the scan and the 3-d mean temperature. Conclusion: Cardiac accumulation of 18 F-FDG is influenced by the ambient temperature, in particular the minimum temperature on the day of the scan and the 3-d average temperature before the scan. Further investigation is warranted to examine the impact of this observation on clinical protocols and cardiac 18 F-FDG PET study results. PET with the glucose analog tracer 18 F-FDG evaluates cellular metabolism and is commonly used for the detection and staging of disease in oncology patients (1-3). 18 F-FDG PET is also widely used to assess myocardial viability (4,5). 18 F-FDG PET in oncology has been reported to confront issues with artifactual accumulation of 18 F-FDG in brown adipose tissue (BAT) (6). Warming patients by changing the ambient environment (rather than core temperature) has been reported to successfully reduce BAT activity; however, one recent report noted that warming patients also reduced cardiac uptake of 18 F-FDG (Fig. 1) (6). Although this observation may relate to seasonal variations in cardiac event rates, there may also be important implications for cardiac 18 F-FDG PET diagnostic integrity. Cardiac glucose metabolism depends on numerous factors including substrate availability, cardiac workload, myocardial perfusion, and medication (7). Increased sympathetic activity drives increased metabolic demand for glucose (8,9), and although the connection has yet to be reported in the literature, this investigation hypothesized that t...

Pediatric Brown Adipose Tissue on 18F-FDG PET: Diazepam Intervention

“…For personal use only. tech.snmjournals.org Downloaded from increased metabolic demand for glucose (10) and cooler ambient conditions may be associated with increased cardiac sympathetic activity.…”

“…O'Loughlin et al (10) showed that the sympathetic activation associated with ambient thermal conditions reflects a 3 day window rather than the period immediately adjacent 18F FDG injection. Thus, warming a patient for 90 minutes may not be effective if that patient was exposed to cooler ambient temperatures with no warming strategy in the preceding days.…”