Simulation and optimization of pulsed Chemical Exchange Saturation Transfer for clinical application at 3T

Abstract

Chemical Exchange Saturation Transfer (CEST) is often overlooked as a method for the investigation of metabolites in vivo due to the time required to obtain a full spectrum. We investigated the feasibility and optimization of a pulsed CEST technique that interleaves an echo planer imaging (EPI) readout with saturation in order to reduce time. In addition, we incorporated a multi-shot EPI sequence that reduces distortions. To achieve this, computer simulations based on the Bloch equations were used to optimize scan parameters while keeping scan time in the clinical timeframe. To analyze the data, a number of Lorentizian fitting algorithms were investigated to evaluate their ability to isolate CEST contrast. By using a 30 ms pulse at 2 μT, we were able to achieve CEST contrast on the order of 2% and could provide APT maps based on an adapted Lorentzian fitting method. In the process of this fitting, it was also discovered that MTR contrast could also be recovered from the CEST data, allowing for MT and CEST to be acquired at the same time.