Influences of experimental parameters on chemical exchange saturation transfer (CEST) metrics of brain tumors using animal models at 4.7T

Purpose To investigate the dependence of magnetization transfer ratio asymmetry at 3.5 ppm (MTRasym(3.5 ppm)), quantitative amide proton transfer (APT#), and nuclear Overhauser enhancement (NOE#) signals or contrasts on experimental imaging parameters. Methods Modified Bloch equation‐based simulations using 2‐pool and 5‐pool exchange models and in vivo rat brain tumor experiments at 4.7T were performed with varied RF saturation power levels, saturation lengths, and relaxation delays. The MTRasym(3.5 ppm), APT#, and NOE# contrasts between tumor and normal tissues were compared among different experimental parameters. Results The MTRasym(3.5 ppm) image contrasts between tumor and normal tissues initially increased with the RF saturation length, and the maxima occurred at 1.6−2 s under relatively high RF saturation powers (>2.1 μT) and at a longer saturation length under relatively low RF saturation powers (