Perfusion tensor imaging.

Arterial spin labeling (ASL) provides a method by which to noninvasively measure the spatial and temporal characteristics of local tissue perfusion. Standard methods employ spatial tagging schemes, but recently methods based on velocity dependent tags, called Velocity Selective ASL (VSASL), have been introduced wherein the tagging depends upon the vascular velocity profile. In this article, we point out an interesting feature of VSASL: the velocity can be encoded in any direction, thereby allowing for the measurement of perfusion with a specified angular resolution. This then facilitates the reconstruction of the local perfusion field, characterized by a perfusion tensor P, from which can be derived quantities related to the structure of the local perfusion field, such as the mean perfusion, the perfusion anisotropy, and the principal directions of flow feeding each voxel. We demonstrate this new method, Perfusion Tensor Imaging (PTI), in both the brain and skeletal muscle of normal human volunteers and discuss possible applications. (c) 2008 Wiley-Liss, Inc.