B(1) Power Optimization for Chemical Exchange Saturation Transfer Imaging: A Phantom Study Using Egg White for Amide Proton Transfer Imaging Applications in the Human Brain

The chemical exchange saturation transfer (CEST) effect on an egg white (EW) suspension was investigated for optimization of magnetization transfer (MT) power (B(1,rms)) and pH dependency with the addition of lactic acid. Applying a higher MT pulse, B(1,rms), Z-spectrum shows higher asymmetry and the magnetisation transfer ratio (MTR)(asym) signal increases to around 1–3.5 ppm, indicating a higher CEST effect. Amide proton transfer (APT) at 3.5 ppm shows a signal elevation in MTR(asym) with the application of higher B(1,rms) power and high pH. In addition, the hydroxyl proton signal in MTR(asym) increases as pH is reduced by lactic acid. In Z-spectrum of B(1,rms) at 1.0 μT and 2.0 μT, the dependence on CEST effect of amide proton and hydroxyl proton could be observed by using an EW suspension phantom. The CEST MT power was optimized on the EW suspension phantom with pH dependency and further confirmed on volunteers. In addition, APT imaging at 3.5 ppm using B(1,rms) at 1.0 μT performed on two human brains with different pathophysiological conditions indicated appropriate ATP effect.