Numerical solutions to the Bloch-McConnell equations with radio frequency irradiation scheme for CEST MRI

Abstract

Chemical exchange saturation transfer (CEST) is a new mechanism of contrast generation in magnetic resonance imaging (MRI) which differentiates molecule biomarkers via chemical shift. CEST MRI contrast mechanism is complex and depends on radio frequency (RF) pulses used in experimental conditions. To find the optimal RF pulse, numerical solutions of Bloch-McConnell equations may be used. The purpose of this work is to compare the effects of different RF pulses on the CEST phenomenon. First, a two-pool exchange model for CEST in MRI is used. Z-spectra and signal calculations for the two-pool model have been carried out for some RF pulses. Efficiency of both continuous and binomial RF pulses is investigated by calculating three parameters, namely: CEST image contrast, flip angle and specific absorption ratio (SAR). The contrast of CEST image is considered proportional to amount of saturation. As a binomial RF pulse, WALTZ-16* demonstrates a good efficiency, but generates some unwanted direct saturations. On the other hand, continuous RF pulses do not create any unwanted direct saturation, but have less efficiency.