COMPARISON OF ECHO-PLANAR SEQUENCES FOR PERFUSION-WEIGHTED MRI - WHICH IS BEST

We compared gradient-echo (GRE), spin-echo (SE) and stimulated-echo (S TE) echo-planar imaging sequences for perfusion-weighted imaging at di fferent field strengths. Focal cerebral ischaemia was induced by endov ascular occlusion of the middle cerebral artery in eight rats. MR was performed at 4.7 T or 2.35 T. With each sequence, we acquired data set s before, during and after bolus injection of Gd-DTPA with a time reso lution of 1.2 s per image. The perfusion-weighted images were assessed with regard to image quality, artefacts, signal-to-noise ratio (SNR), and signal-attenuation-to-noise ratio (Delta SNR) of the non-ischaemi c tissue. Visual assessment showed GRE-EPI images acquired at 4.7 T to suffer from distortion due to susceptibility artefacts. Artefacts wer e less marked with the SE and STE series. The GRE-EPI sequence gave th e highest SNR and Delta SNR. At 2.35 T, the SNR of the STE sequences w as less than 3 and therefore did not allow construction of reliable si gnal-time curves. SE-EPI was best suited for perfusion-weighted imagin g at high field strength thanks to its minimal distortion artefacts an d high SNR. Using lower field strengths (2.35 T and less), susceptibil ity artefacts are reduced; GRE-EPI sequences are then best suited, bec ause they have the highest SNR and T2 sensitivity.