Hahnsung Kim^{1,2}, Lisa C. Krishnamurthy ^{3,4}, Kimberly B Hoang^{5}, Ranliang Hu^{2}, and Phillip Zhe Sun^{1,2}

^{1}Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States, ^{2}Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, United States, ^{3}Center for Visual and Neurocognitive Rehabilitation, Atlanta VA, Decatur, GA, United States, ^{4}Department of Physics & Astronomy, Georgia State University, atlanta, GA, United States, ^{5}Department of Neurosurgery, Emory University School of Medicine, Atlanta, GA, United States

The multi-slice CEST signal evolution was
described by the spin-lock relaxation during saturation duration (T_{s}) and longitudinal relaxation
during the
relaxation delay time (T_{d}) and post-label
delay (PLD), from which the QUASS
CEST was generalized to fast multi-slice acquisition. In addition, normal human subjects and tumor patients scans were performed to compare the conventional
apparent and QUASS CEST measurements with different T_{s}, T_{d},
and PLD. Bland-Altman analysis bias of the proposed QUASS
CEST effects was much smaller than the PLD-corrected apparent
CEST effects (0.03% vs. -0.54%),
indicating the proposed fast multi-slice CEST imaging is robust and
accurate.

$$\frac{I'_{sat}\left(\Delta\omega\right)}{I'_{0}}=\frac{\left(1-e^{-R_{1w}T_{d}}\right)e^{-R_{1\rho}\cdot T_{s}}+\frac{R_{1w}}{R_{1\rho}}\cos^{2}\theta\left(1-e^{-R_{1\rho}\cdot T_{s}}\right)}{1-e^{-R_{1w}\cdot \left(T_{s}+T_{d}+pld\right)}}e^{-R_{1w}\cdot pld}+\frac{1-e^{-R_{1w}\cdot pld}}{1-e^{-R_{1w}\cdot \left(T_{s}+T_{d}+pld\right)}}\qquad\qquad\left[1\right]$$

where $$$R_{1w}$$$ is the bulk water longitudinal relaxation rate, $$$I_{0}$$$ is the equilibrium magnetization, $$$R_{1\rho}$$$ is the spin-lock relaxation rate and $$$\theta=\arctan\left(\frac{\gamma B_{1}}{\Delta \omega}\right)$$$, in which $$$\gamma$$$ is the gyromagnetic ratio and B

$$\frac{I'^{pldcor}_{sat}\left(\Delta \omega\right)}{I'^{pldcor}_{0}}\cdot \left\{\frac{1-e^{-R_{1w}\left(T_{s}+T_{d}\right)}}{1-e^{-R_{1w}\cdot T_{d}}}\right\}=e^{-R_{1\rho}\cdot T_{s}}+\frac{R_{1w}\cdot \cos^2 \theta}{R_{1\rho}\cdot \left(1-e^{-R_{1w}\cdot T_{d}}\right)}\cdot \left(1-e^{-R_{1\rho}\cdot T_{s}}\right)\qquad\qquad\left[2\right]$$

in which the superscript

$$\left(\frac{I_{sat}\left(\Delta \omega\right)}{I_{0}}\right)^{QUASS}=\frac{R_{1w}}{R_{1\rho}}\cos^{2}\theta\qquad\qquad\left[3\right]$$

DOI: https://doi.org/10.58530/2022/4419