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Calibration of echo-planar 2D-selective RF excitation pulses

✍ Scribed by Markus Oelhafen; Klaas P. Pruessmann; Sebastian Kozerke; Peter Boesiger

Publisher
John Wiley and Sons
Year
2004
Tongue
English
Weight
954 KB
Volume
52
Category
Article
ISSN
0740-3194

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✦ Synopsis

Abstract

Echo‐planar radiofrequency (RF) pulses (EPP) are increasingly being used for 2D‐selective excitation in MRI. Pulse schemes of this kind are susceptible to eddy‐current effects, timing imperfections, and anisotropy of the gradient system. As a consequence, practical EPP implementations have been restricted to robust fly‐back strategies that use only every other leg of the echo‐planar trajectory for RF transmission. The present work is dedicated to enabling forward‐backward EPP with RF transmission during each k‐space segment, hence doubling the pulses' time efficiency. This is accomplished by comprehensive pulse calibration based on preparatory measurements of the system imperfections, including potential gradient anisotropy. The effectiveness of the method is demonstrated in vitro and in vivo. By doubling the speed of k‐space coverage, the proposed method enhances the potential of EPP for numerous applications. For example, motion‐sensitive techniques benefit from shorter feasible echo times (TEs) and improved excitation profiles resulting from reduced in‐pulse motion. In sequences with fast repetition, shorter EPP help reduce the overall scan duration. Alternatively, the higher time efficiency of forward‐backward EPP can enhance their spatial selectivity. Magn Reson Med 52:1136–1145, 2004. © 2004 Wiley‐Liss, Inc.

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