Effect of microscopic susceptibility gradients on chemical-shift-based fat fraction quantification in supraclavicular fat.

Background: Susceptibility differences between fat and water can cause changes in the water-fat frequency separation that can negatively affect the accuracy of fat fraction techniques. This may be especially relevant for brown adipose tissue, as MRI fat fraction techniques have been proposed for its detection.

Purpose: To assess the effect of microscopic magnetic susceptibility gradients on the water-fat frequency separation and its impact on chemical-shift-based fat fraction quantification techniques in the supraclavicular fat, where brown adipose tissue is commonly found in humans.

Effects of superparamagnetic iron oxide nanoparticles on the longitudinal and transverse relaxation of hyperpolarized xenon gas.

SuperParamagnetic Iron Oxide Nanoparticles (SPIONs) are often used in magnetic resonance imaging experiments to enhance Magnetic Resonance (MR) sensitivity and specificity. While the effect of SPIONs on the longitudinal and transverse relaxation time of H spins has been well characterized, their effect on highly diffusive spins, like those of hyperpolarized gases, has not. For spins diffusing in linear magnetic field gradients, the behavior of the magnetization is characterized by the relative size of three length scales: the diffusion length, the structural length, and the dephasing length.

Simple and robust referencing system enables identification of dissolved-phase xenon spectral frequencies.

Purpose: To assess the effect of macroscopic susceptibility gradients on the gas-phase referenced dissolved-phase Xe (DPXe) chemical shift (CS) and to establish the robustness of a water-based referencing system for in vivo DPXe spectra.

Methods: Frequency shifts induced by spatially varying magnetic susceptibility are calculated by finite-element analysis for the human head and chest. Their effect on traditional gas-phase referenced DPXe CS is then assessed theoretically and experimentally.

Incidental finding of low brown adipose tissue activity in endurance-trained individuals: Methodological considerations for positron emission tomography.

Brown adipose tissue (BAT) in adults has been shown to have a meaningful impact on energy expenditure and cold-induced thermogenesis. Data from rodent research have suggested that exercise may be a promising method of increasing BAT activity, with potential applications to the treatment and prevention of obesity and diabetes. However, emerging human research using positron emission tomography (PET) with [18F] Fluorodeoxyglucose (FDG) has identified lower BAT activity in endurance-trained athletes compared to sedentary controls, despite similar metabolic rate responses to cold exposure.