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Optimizing pulsed-chemical exchange saturation transfer imaging sequences.

Zu Z, Li K, Janve VA, Does MD, Gochberg DF
Magn Reson Med. 2011 66 (4): 1100-8

PMID: 21432903 · PMCID: PMC3151337 · DOI:10.1002/mrm.22884

Chemical exchange saturation transfer (CEST) provides a new imaging contrast mechanism sensitive to labile proton exchange. Pulsed-CEST imaging is better suited to the hardware constraints on clinical imaging systems when compared with traditional continuous wave-CEST imaging methods. However, designing optimum pulsed-CEST imaging sequences entails complicated and time-consuming numerical integrations. In this work, a simplified and computationally efficient technique is provided to optimize the pulsed-CEST imaging sequence. An analysis was performed of the optimal average irradiation power and the optimal irradiation flip angle as a function of the acquisition parameters and sample properties in both a two-pool model and a three-pool model of endogenous amine exchange. Key simulated and experimental results based on a creatine/agar tissue phantom show that (1) the average irradiation power is a more meaningful sequence metric than is the average irradiation field amplitude, (2) the optimal average powers for continuous wave and pulsed-CEST imaging are approximately equal to each other for a relevant range of solute frequency offsets, exchange rates, and concentrations, (3) an irradiation flip angle of 180° is optimal or near optimal, independent of the other acquisition parameters and the sample properties, and (4) higher duty cycles yield higher CEST contrast.

Copyright © 2011 Wiley-Liss, Inc.

MeSH Terms (8)

Agar Algorithms Computer Simulation Creatine Image Enhancement Image Processing, Computer-Assisted Magnetic Resonance Imaging Phantoms, Imaging

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