Guanidinium and amide CEST mapping of human brain byhigh spectral resolution CEST at 3T.

Abstract

To extract guanidinium (Guan) and amide CEST on the human brain at 3T MRI with the high spectral resolution (HSR) CEST combined with the polynomial Lorentzian line-shape fitting (PLOF). Continuous wave (cw) turbo spin-echo (TSE) CEST was implemented to obtain the optimum saturation parameters. Both Guan and amide CEST peaks were extracted and quantified using the PLOF method. The NMR spectra on the egg white phantoms were acquired to reveal the fitting range and the contributions to the amide and GuanCEST. Two types of CEST approaches, including cw gradient- and spin-echo (cwGRASE) and steady state EPI (ssEPI), were implemented to acquire multi-slice HSR-CEST. GuanCEST can be extracted with the PLOF method at 3T, and the optimum was determined for GuanCEST in white matter (WM) and 1.0μT in gray matter (GM). The optimum B1 =0.8-1μT was found for amideCEST. AmideCEST is lower in both WM and GM collected with ssEPI compared to those by cwGRASE (ssEPI=[1.27-1.63]%; cwGRASE=[2.19-2.25]%). The coefficients of variation (COV) of the amide and Guan CEST in both WM and GM for ssEPI (COV: 28.6-33.4%) are significantly higher than those of cwGRASE (COV: 8.6-18.8%). Completely different WM/GM contrasts for Guan and amide CEST were observed between ssEPI and cwGRASE. The amideCEST was found to have originated from the unstructured amide protons as suggested by the NMR spectrum of the unfolded proteins in egg white. Guan and amide CEST mapping can be achieved by the HSR-CEST at 3T combing with the PLOF method.