Chemical Shift Separated and Compensated Ultra-Short Echo-Time Imaging

To develop a modified binomial excitation scheme for ultra-short echo-time (UTE) imaging that allows for the separation of water and fat signals and the correction of chemical shift artifacts.

Theoretical derivation and numerical Bloch simulations were performed for a modified water-excitation binomial pulse scheme to calculate fat and water signals as well as a chemical shift corrected UTE image from two acquisitions with these configurations. Chemical shift correction was applied at the readout level by multiplying the fat signal with a corresponding linear phase term. Measurements with the proposed binomial pulse scheme were performed at 3 T and 7 T.

Imaging results at 7 T and 3 T showed robust fat and water separation and images free of chemical shift-induced blurring after applying the proposed method. Compared to standard UTE, the corrected UTE images exhibited improved tissue boundary delineation and improved visibility of fine details. Bloch simulations demonstrated that deviations of the phase differences between water and fat from the analytical solution were below 1% for typical UTE acquisition parameters.

The proposed binomial excitation scheme and post-processing effectively separate water and fat signals and correct for chemical shift artifacts in UTE imaging, providing improved image quality, especially at high field strengths.