Assessing Exchange between Multiple Compartments Using Multi-Directional Double Wave Diffusion Sequences

Casper Snderby¹, Henrik Lundell¹, Tim B. Dyrby¹

The apparent exchange rate (AXR) has recently been proposed as a model free measure of water diffusional exchange processes. The dependency of AXR upon measurement directions is investigated. It is proposed that different compartmental exchange rates are measured when altering the measurement direction and hence AXR is not a rotational invariant measure. A novel double wave diffusion sequence is proposed and used for ex-vivo experiments in gray matter of a fixated monkey brain and the rotational dependency of AXR is demonstrated.