  Purpose: To understand the influence of various acquisition parameters on the
ability of CEST MR-Fingerprinting (MRF) to discriminate different chemical
exchange parameters and to provide tools for optimal acquisition schedule
design and parameter map reconstruction. Methods: Numerical simulations were
conducted using a parallel-computing implementation of the Bloch-McConnell
equations, examining the effect of TR, TE, flip-angle, water T$_{1}$ and
T$_{2}$, saturation-pulse duration, power, and frequency on the discrimination
ability of CEST-MRF. A modified Euclidean-distance matching metric was
evaluated and compared to traditional dot-product matching. L-Arginine phantoms
of various concentrations and pH were scanned at 4.7T and the results compared
to numerical findings. Results: Simulations for dot-product matching
demonstrated that the optimal flip-angle and saturation times are 30$^{\circ}$
and 1100 ms, respectively. The optimal maximal saturation power was 3.4 $\mu$T
for concentrated solutes with a slow exchange-rate, and 5.2 $\mu$T for dilute
solutes with medium-to-fast exchange-rates. Using the Euclidean-distance
matching metric, much lower maximum saturation powers were required (1.6 and
2.4 $\mu$T, respectively), with a slightly longer saturation time (1500 ms) and
90$^{\circ}$ flip-angle. For both matching metrics, the discrimination ability
increased with the repetition time. The experimental results were in agreement
with simulations, demonstrating that more than a 50% reduction in scan-time can
be achieved by Euclidean-distance-based matching. Conclusion: Optimization of
the CEST-MRF acquisition schedule is critical for obtaining the best exchange
parameter accuracy. The use of Euclidean-distance-based matching of signal
trajectories simultaneously improved the discrimination ability and reduced the
scan time and maximal saturation power required.
