Influence of B₁-Inhomogeneity on Pharmacokinetic Modeling of Dynamic Contrast-Enhanced MRI: A Simulation Study

OBJECTIVE: To simulate the B₁-inhomogeneity-induced variation of pharmacokinetic parameters on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). MATERIALS AND METHODS: B₁-inhomogeneity-induced flip angle (FA) variation was estimated in a phantom study. Monte Carlo simulation was performed to assess the FA-deviation-induced measurement error of the pre-contrast R₁, contrast-enhancement ratio, Gd-concentration, and two-compartment pharmacokinetic parameters (K(trans), v(e), and v(p)). RESULTS: B₁-inhomogeneity resulted in −23–5% fluctuations (95% confidence interval [CI] of % error) of FA. The 95% CIs of FA-dependent % errors in the gray matter and blood were as follows: −16.7–61.8% and −16.7–61.8% for the pre-contrast R₁, −1.0–0.3% and −5.2–1.3% for the contrast-enhancement ratio, and −14.2–58.1% and −14.1–57.8% for the Gd-concentration, respectively. These resulted in −43.1–48.4% error for K(trans), −32.3–48.6% error for the v(e), and −43.2–48.6% error for v(p). The pre-contrast R₁ was more vulnerable to FA error than the contrast-enhancement ratio, and was therefore a significant cause of the Gd-concentration error. For example, a −10% FA error led to a 23.6% deviation in the pre-contrast R₁, −0.4% in the contrast-enhancement ratio, and 23.6% in the Gd-concentration. In a simulated condition with a 3% FA error in a target lesion and a −10% FA error in a feeding vessel, the % errors of the pharmacokinetic parameters were −23.7% for K(trans), −23.7% for v(e), and −23.7% for v(p). CONCLUSION: Even a small degree of B₁-inhomogeneity can cause a significant error in the measurement of pharmacokinetic parameters on DCE-MRI, while the vulnerability of the pre-contrast R₁ calculations to FA deviations is a significant cause of the miscalculation.

Health Behavior and Nutrient Intake in Metabolically Abnormal Overweight and Metabolically Abnormal Obesity

BACKGROUND: The purpose of this study was to investigate the differences in health behaviors and dietary habits between the metabolically healthy group and the metabolically abnormal group in overweight and obese subjects based on the data of National Health and Nutrition Survey (NHANES). METHODS: Using the NHANES data (2007–2010), a total of 18,188 subjects were grouped into the metabolically healthy group and the abnormal group using the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) definition. Then we compared their health behaviors, dietary behaviors and nutrient intakes after adjustment for variables in overweight and obese groups. RESULTS: The proportion of metabolic abnormalities tended to increase with increasing age in both overweight and obesity groups.(P for trend <0.001) After adjusting various confounding variables, the odds ratio (95% confidence interval) of skipping any meal and breakfast for metabolically abnormality were 1.318 (1.066–1.631) and 1.354 (1.076–1.705) in male obese group and those of skipping breakfast and carbonated drink intake were 1.578 (1.168–2.133) and 1.540 (1.188–2.492) in female obese group. Daily potassium intake (P=0.032) and daily vitamin C intake (P=0.048) in the male overweight group and daily water intake (P=0.046) and daily carbohydrate intake (P=0.038) in the female overweight group were associated with metabolically abnormality. CONCLUSIONS: There were differences in health behaviors and nutrient intake according to metabolically abnormality in overweight and obese groups.