ISOTROPIC DIFFUSION-WEIGHTED AND SPIRAL-NAVIGATED INTERLEAVED EPI FORROUTINE IMAGING OF ACUTE STROKE

An interleaved echo-planar imaging (EPI) technique is presented for th e rapid acquisition of isotropic diffusion-weighted images of stroke p atients. Sixteen isotropic diffusion-weighted images at three b values are acquired in less than 3 min. A spiral navigator echo is used to m easure the constant and linear phase shifts across the head in both th e x and y directions which result from motion during the isotropic dif fusion-sensitizing gradients. The measured k-space errors are correcte d during a gridding reconstruction. The gridding kernel has a constant width in k(x),and a variable width in k(y) which eliminates variable data-density ghosts. The resulting isotropic diffusion-weighted images have excellent lesion-to-normal brain contrast, very good spatial res olution, and little sensitivity to susceptibility effects in the base of the brain. Examples of diffusion-weighted images and ADC maps from several stroke patients are shown.