Calibrated image-derived input functions for the determination of the metabolic uptake rate of glucose with [18F]-FDG PET

PURPOSE: We investigated the use of a simple calibration method to remove bias in previously proposed approaches to image-derived input functions (IDIFs) when used to calculate the metabolic uptake rate of glucose (K(m)) from dynamic [(18)F]-FDG PET scans of the thigh. Our objective was to obtain nonbiased, low-variance K(m) values without blood sampling. MATERIALS AND METHODS: We evaluated eight previously proposed IDIF methods. K(m) values derived from these IDIFs were compared with K(m) values calculated from the arterial blood samples (gold standard). We used linear regression to extract calibration parameters to remove bias. Following calibration, cross-validation and bootstrapping were used to estimate the mean square error and variance. RESULTS: Three of the previously proposed methods failed mainly because of zero-crossings of the IDIF. The remaining five methods were improved by calibration, yielding unbiased K(m) values. The method with the lowest SD yielded an SD of 0.0017/min – that is, below 10% of the muscle K(m) value in this study. CONCLUSION: Previously proposed IDIF methods can be improved by using a simple calibration procedure. The calibration procedure may be used in other studies, thus obviating the need for arterial blood sampling, once the calibration parameters have been established in a subgroup of participants. The method has potential for use in other parts of the body as it is robust with regard to partial volume effects

Effect of Different Doses of Exercise on Sleep Duration, Sleep Efficiency and Sleep Quality in Sedentary, Overweight Men

Objective: To evaluate the dose-response effect of aerobic exercise on sleep duration, sleep efficiency and sleep quality in previously sedentary, moderately overweight men. Methods: In a randomized, controlled trial, 53 sedentary Caucasian men aged between 20 and 40 years (VO2- max<45 mL O2 kg-1 min-1, BMI: 25-30 kg/m2, body fat>25%) completed a 13-week aerobic exercise intervention consisting of either a physical activity energy deficit of 600 kcal day-1 (HIGH: n=18), 300 kcal day-1 (MOD: n=18), or being sedentary (CON: n=17). The endpoints were sleep duration (objectively measured by actigraphy over 3 days), sleep efficiency (3-day actigraphy), and subjectively rated sleep quality (Pittsburgh Sleep Quality Index). Results: Because of missing sleep data, a total of 32 subjects were included in the present analysis (CON: n=12, MOD: n=12, HIGH: n=8). A significant increase in sleep duration was observed in HIGH (80 ± 30 min, p=0.03). However, the change was not significantly different from the change in CON. Sleep efficiency tended to decrease in HIGH (p=0.05), and there was a tendency towards an improved sleep quality within MOD and HIGH (p=0.08 in both). Conclusion: Our study suggests that a high daily dose of aerobic exercise for 13 weeks increases sleep duration, tends to decrease sleep efficiency, and tends to improve subjective sleep quality in sedentary, moderately overweight men. Because our sample included relatively young and sleep-efficient individuals, future studies should examine the dose-response effects of aerobic exercise on sleep parameters in older adults with sleeping problems