Variable Flip Angle SPIR for Fat Suppression in APT-weighted Imaging

Motivation: Fat signal remains a major impediment to the translation of amide proton transfer (APT)-weighted imaging to applications in the body. Goal(s): The present work aims at improving the extent and uniformity of fat suppression in this domain. Approach: A spectral presaturation with inversion recovery (SPIR) with variable flip angle is devised for this purpose and explored in proof-of-concept experiments. Results: The proposed approach is demonstrated to equalize the residual fat signal in measurements with corresponding positive and negative saturation frequency offsets. In the subsequent subtraction, performed as part of the magnetization transfer ratio (MTR) asymmetry analysis, the residual fat signal then cancels out. Impact: Variable flip angle SPIR may alleviate persisting artifacts from fat signal in APT-weighted imaging without prolonging the acquisition or requiring elaborate postprocessing.