Figure 1. General pipeline of a semisolid MT/CEST MRF experiment.

a. Initially, a pseudo-random imaging protocol is designed, where at least one acquisition parameter is being varied, to produce a set of N images. Importantly, a pre-saturation block needs to be implemented, where at least the saturation pulse power (B₁), duration (T_sat), or frequency offset (ω_rf) should vary, for sufficient encoding of the chemical exchange parameters. The protocol typically includes a rapid readout, e.g., using EPI or turbo spin echo, with either a fixed or varied flip angle (FA) and recovery time (T_rec). b. The designed protocol is then loaded into a computerized Bloch-McConnell equations-based signal simulator, which produces the signal trajectories expected for a large number of tissue parameter combinations. The same CEST-MRF acquisition protocol is fed as an instruction file to the MRI scanner, allowing the acquisition of N molecular information encoding images, where each pixel series comprises an experimentally acquired trajectory (e[1] – e[N]). c. Each trajectory (e[n]) is then compared to all dictionary entries (d[n]), via a pattern recognition algorithm (such as the dot-product metric) for the determination of the best match. Importantly, this step can be accelerated and improved using a deep neural-network. d. Finally, simultaneous pixel-wise quantification of the proton exchange rates (k), and volume fractions (f) for a single or several metabolite/protein/lipid pools of interest can be made, based on the neural network output, or the best-matched dictionary entry.