Navigated diffusion-weighted imaging with interpolated phase-correction for high-resolution imaging of stroke.

Abstract

Stroke imaging was revolutionised with the introduction of diffusion-weighted MRI (DWI). The commonly used echoplanar DWI suffers from geometrical distortion near the skull base and the frontal regions and from reduced spatial resolution and fat suppression. To allow a voxel-by-voxel comparison between high-resolution spin-echo images, we implemented spin-echo-based DWI. Motion artefacts were eliminated by phase correction in hybrid frequency-Fourier domain using navigator echoes. In a novel approach, distorted navigator echoes which did not eliminate motion artefacts were replaced with interpolated navigator echoes, leading to restored image information. Navigated DWI yielded high-resolution images in 21 of 24 patients with brain ischaemia, allowing diagnosis of even small or diffuse zones of ischaemia. We determined the spatial distribution and mean of T(2)- and DWI signal intensity and apparent diffusion coefficients (ADC), using a multidimensional histogram-based analysis. Mean ADC were decreased in ischaemic areas less than 9 days old. The technique may also be useful for high-resolution DWI of tissue other than the brain.