ABSTRACT
My early interest in chemical exchange saturation transfer (CEST)
imaging was a natural progression from work on exchange-based
nuclear magnetic resonance (NMR) during the 1990s, when Susumu
Mori, still a graduate student at the time, and I were developing
multi-dimensional 1H NMR spectroscopy methods to study amide
protons in proteins [1-6]. At that time, it was difficult to detect
rapidly exchanging amide protons using proton NMR, because the
water suppression that was essential to perform spectroscopy
Figure 3.1 1H MRS spectra of exchangeable protons in cat brain (a-c) and perfused breast cancer cells (d, e). When comparing spectra with CHESS
water suppression before the pulse sequence (a, d) to those without (b, e),
it can be seen that much of the signal is lost due to exchange of saturated
water protons to the protons of interest. In the postmortem case in the cat,
exchange is reduced due to lower pH and even less signal is lost (c), which
is especially clear at the composite amide resonance at 8.3 ppm. In (f) the
large gain in signal when using a water flip-back pulse is shown for the cells.
Reprinted with permission from Ref. [8], Copyright 2005, John Wiley and
Sons.
