Purpose: Chemical exchange saturation transfer (CEST) is a contrast mechanism enhancing low-concentration molecules through saturation transfer from their exchangeable protons to bulk water. Often many scans are acquired to form a Z-spectrum, making the CEST method time-consuming. Here, an ultrafast localized CEST-spectroscopy with PRESS (UCEPR) is proposed to obtain the entire Z-spectrum of a voxel using only two scans, significantly accelerating CEST.
Theory and methods: The approach combines ultrafast nonlocalized CEST spectroscopy with localization using PRESS. A field gradient is applied concurrently with the saturation pulse producing simultaneous saturation of all Z-spectrum frequencies that are also spatially encoded. A readout gradient during data acquisition resolves the spatial dependence of the CEST responses into frequency. UCEPR was tested on a 3T scanner both in phantoms and in vivo.
Results: In phantoms, a fast Z-spectroscopy acquisition of multiple pH-variant iopamidol samples was achieved with four- to seven-fold acceleration as compared to the conventional CEST methods. In vivo, amide proton transfer (APT) in white matter of healthy human brain was measured rapidly in 48 s and with high frequency resolution (≤ 0.2 ppm).
Conclusion: Compared with conventional CEST methods, UCEPR has the advantage of rapidly acquiring high-resolution Z-spectra. Potential in vivo applications include ultrafast localized Z-spectroscopy, quantitative, or dynamic CEST studies.
Keywords: APT; PRESS; broadband saturation; iopamidol; ultrafast localized CEST.
© 2015 Wiley Periodicals, Inc.