Determination of pore size distributions using twofold diffusion-weighted magnetic resonance imaging

Pathological processes can modify the microscopic structure of biological tissue. A number of methods for detecting and investigating such changes is based on measuring diffusion of water molecules in the tissue. Thermal energy causes the molecules to move randomly in and around the cells. This diffusion motion is hindered or restricted by the cell membranes. The characteristics of water diffusion hence reflects the tissue structure. Magnetic resonance imaging can be used to measure the characteristics of water diffusion noninvasively. Here, the measured signal is diffusion weighted by magnetic fields that linearly depend on position. Double diffusion weighting is a relatively new approach to assessing the mean cell size and shape. The difference between signals acquired with parallel or antiparallel field gradients is a measure of pore or cell size. When the delay between the two weightings is increased, this difference decreases. In this project, the shape of the decrease is exploited to obtain the distribution function of pore sizes, instead of a mean pore size. In another part of the project it is investigated whether the effects exploited in the proposed method need to be considered in measurements of the cell membrane permeability. Such measurements also apply double diffusion weighting.