SNR-boosted whole-brain chemical exchange saturation transfer imaging by optimized variable flip angles

It is well-known that the refocusing flip angles (FAs) of the SPACE sequence can be optimized to generate different image contrasts, such as T1-weighted or T2-weighted. However, the existing SPACE variable FA scheme is unsuitable for CEST imaging whose utmost aim is to increase the SNR during signal readout instead of enforcing contrast. Here, we derived a model to describe the signal-to-noise ratio (SNR) of the SPACE sequence, and maximized SNR by varying refocusing flip angles. Compared to the original constant FA protocol, the optimized variable flip angles yielded both SNR and resolution improvement.