Analyse der Bildqualität einer diffusionsgewichteten (EPI DWI) Sequenz: Untersuchungen an einem 1,5 T MRT mit höherer Gradientenfeldstärke : Analysis of MR image quality of echo planar diffusion -weighted imaging: investigations at 1.5 Tesla with higher gradient field strength

Abstract

Purpose: Single – shot echo planar Diffusion – weighted – Imaging (EPI DWI) requires extended gradient facilities with strong, fast switching gradients. Up to now the image quality of EPI DWI is enormously influenced by some kinds of artifacts. Therefore we evaluated the image quality of EPI DWI in demonstrating anatomical structures using a 1.5 T MR scanner with a higher gradient field strength of 40 mt/m, a risetime of 200 μs and a slewrate of 200 T/m/s. Materials and methods: Using an evaluation scale with four categories two independent readers evaluated 12 different infra – and supratentorial anatomic regions of the brain on 50 DWI images and compared them with the corresponding T2 turbospin echo image. Results: No region was judged to be undistinguishable. On axial DWI images the assessment of the brain stem was poor. In the level of the putamen and thalamus the image quality of DWI was judged to be from adequate to excellent. The central sulcus and the boundary of the white and grey matter was assessed to be adequately visible. The interobserver variability showed a good agreement between the two readers. Conclusion: The image quality of EPI DWI improves from a higher gradient field strength. The shortening rise time of 200 μs and the slewrate of 200 T/m/s will lead to a faster gradient switching. Single shot EPI DWI is less influenced by image artefacts and the presentation of different anatomical structures profits when a MR scanner with higher gradient field strength is used.