title: Optimizing pulsed-chemical exchange saturation transfer imaging sequences.
abstract: Chemical exchange saturation transfer (CEST) provides a new imaging contrast mechanism sensitive to labile proton exchange. Pulsed-CEST imaging is better suited to the hardware constraints on clinical imaging systems when compared with traditional continuous wave-CEST imaging methods. However, designing optimum pulsed-CEST imaging sequences entails complicated and time-consuming numerical integrations. In this work, a simplified and computationally efficient technique is provided to optimize the pulsed-CEST imaging sequence. An analysis was performed of the optimal average irradiation power and the optimal irradiation flip angle as a function of the acquisition parameters and sample properties in both a two-pool model and a three-pool model of endogenous amine exchange. Key simulated and experimental results based on a creatine/agar tissue phantom show that (1) the average irradiation power is a more meaningful sequence metric than is the average irradiation field amplitude, (2) the optimal average powers for continuous wave and pulsed-CEST imaging are approximately equal to each other for a relevant range of solute frequency offsets, exchange rates, and concentrations, (3) an irradiation flip angle of 180° is optimal or near optimal, independent of the other acquisition parameters and the sample properties, and (4) higher duty cycles yield higher CEST contrast.
authors: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee 37232-2310, USA.
authors: Zhongliang
authors: Z
authors: Zu
authors: Ke
authors: K
authors: Li
authors: Vaibhav A
authors: VA
authors: Janve
authors: Mark D
authors: MD
authors: Does
authors: Daniel F
authors: DF
authors: Gochberg
mesh_terms: D000362:Agar / Q000737:chemistry; D000465:Algorithms; D003198:Computer Simulation; D003401:Creatine / Q000737:chemistry; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
chemical_list: D000362:Agar; D003401:Creatine