PURPOSE: To optimize a 100 ms pulse for producing CEST MRI contrast and evaluate in mice. METHODS: A gradient ascent algorithm was employed to generate a family of 100 point, 100 ms pulses for use in CEST pulse trains (proton resonance enhancement for CEST imaging and shift exchange). Gradient ascent optimizations were performed for exchange rates = 500, 1500, 2500, 3500, and 4500 s RESULTS: The most promising pulse in terms of contrast performance across all three phantoms was the 9.6 ppm, 2500 s CONCLUSION: A new 100-ms pulse was developed based on gradient ascent optimizations, which produced better contrast compared to standard Gaussian and Fermi pulses in phantoms. This shape also showed a substantial improvement for CEST MRI pH mapping in live mice over the Gaussian shape and appears promising for a wide range of CEST applications.