Age-dependent brain temperature decline assessed by diffusion-weighted imaging thermometry.

Brain metabolism declines with age, but cerebral blood flow (CBF) is less age dependent. We therefore hypothesized that the brain temperature would decline with age, and measured the temperatures of the lateral ventricles in healthy volunteers. Diffusion-weighted imaging (DWI) data from 45 healthy volunteers [mean (± standard deviation) age, 30.6 ± 8.66 years; range, 19-56 years] were used for this study. The temperature of water molecules is directly related to the diffusion coefficient, so that the temperature of cerebrospinal fluid can be measured using DWI. Temperature was calculated using the equation, T ( °C) = 2256.74/ln(4.39221/D) - 273.15, where D is the diffusion coefficient. The lateral ventricles were manually extracted by an experienced neuroradiologist on b(0) images. The mean ventricular temperature was determined from the distribution function of the temperature of all selected voxels. The mean lateral ventricular temperature in healthy volunteers showed a linear decrease with age (correlation coefficient R(2)  = 0.8879; p < 0.01), presumably caused by an asynchronous decline in brain metabolism and CBF. DWI-based thermometry demonstrates that ventricular temperature declines with the normal aging process. Further study is warranted to define the relationships between temperature, metabolism and circulation.