A new method for detecting exchanging amide protons using chemical exchange rotation transfer

Abstract

In this study, we introduce a new method for amide proton transfer imaging based on chemical exchange rotation transfer. It avoids several artifacts that plague conventional chemical exchange saturation transfer approaches by creating label and reference scans based on varying the irradiation pulse rotation angle (π and 2π radians) instead of the frequency offset (3.5 and −3.5 ppm). Specifically, conventional analysis is sensitive to confounding contributions from magnetic field (B0) inhomogeneities and, more problematically, inherently asymmetric macromolecular resonances. In addition, the lipid resonance at −3.5 ppm complicates the interpretation of the reference scan and decreases the resulting contrast. Finally, partial overlap of the amide signal by nearby amines and hydroxyls obscure the results. By avoiding these issues, our new method is a promising approach for imaging endogenous protein and peptide content and mapping pH.

Amide Proton Transfer (APT) MR imaging and Magnetization Transfer (MT) MR imaging of pediatric brain development

“…Finally, the standard APTW metric based on the MTR asymmetry analysis could be subject to contamination by the upfield nuclear Overhauser enhancement and other effects. To more accurately quantify the APT effect, a more complicated APT imaging acquisition [34, 35] or analysis [36-38] approach may be used in the future. However, it has been demonstrated recently that the MTR asymmetry at 3.5 ppm remains a valid metric for APT imaging at 3 T (clinical B 0 field strengths) and 4.7 T [38].…”

Fast simulation and optimization of pulse-train chemical exchange saturation transfer (CEST) imaging

“…Indeed, it has been shown that for dilute CEST agents undergoing slow chemical exchange, pulse-train CEST MRI provides similar CEST effect as the CW-CEST MRI. Because the typical CEST effect is only a few percent, it is important to optimize pulse-train CEST MRI for in vivo applications (Sun et al , 2011a; Wu et al , 2012; Tee et al , 2013; Yuan et al , 2013; Sun et al , 2013b; Sun et al , 2014a; Sun et al , 2014b; Zhu et al , 2010; Shah et al , 2011; Zu et al , 2013). However, because of the long computation time it takes to simulate pulse-train CEST MRI, it remains challenging to fit pulse-train CEST MRI measurements and solve the underlying CEST system.…”

Minimizing the effects of magnetization transfer asymmetry on inhomogeneous magnetization transfer (ihMT) at ultra-high magnetic field (11.75 T)

“…Such investigation would have required modeling of complex lineshapes to disentangle the contributions of ihMT to MT-asymmetry and vice versa, as well as a full treatment of MT-asymmetry in the proposed experimental set-up. In particular, factors complicating the CEST signal, such as water direct saturation at different offsets, effects of RF pulse bandwidths and flip angles [34], should have been precisely analyzed.…”