Consequences of T2 relaxation during half-pulse slice selection for ultrashort TE imaging
✍ Scribed by Matthew D. Robson; Peter D. Gatehouse
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 324 KB
- Volume
- 64
- Category
- Article
- ISSN
- 0740-3194
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✦ Synopsis
Abstract
A “half‐pulse” slice selection approach is used in the ultrashort echo time pulse sequence and is required to give minimal transverse relaxation in a two‐dimensional acquisition. This method splits the normal excitation radiofrequency pulse in half and acquires a pair of images, each using one of these half‐pulses. These half‐pulses are used without a refocusing gradient since summing the pair of images yields images with accurate slice selection. When the radiofrequency pulse duration is similar to the sample T~2~, characteristics such as the effective echo time and choice of radiofrequency pulse require careful evaluation as some of the approximations in conventional slice selection do not apply. We derive a theory that includes relaxation during excitation using Pauly's excitation k‐space formalism. Further, this theory is tested on phantoms with a range of values of T~2~ demonstrating the effect on the slice profile. We conclude that relaxation during excitation is significant and should be included in our estimate of the T~2~ weighting of the sequence. In general, the T~2~ weighting should be measured from the time of the centroid of the excitation pulse. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.