Approximated analytical characterization of the steady-state chemical exchange saturation transfer (CEST) signals.
PURPOSE
CEST MRI can indirectly detect low-concentrated molecules via their proton exchange with the bulk water and is widely measured by a sensitivity index, the asymmetry of magnetization transfer ratio (MTRasym ). Because CEST applications are often limited by their low sensitivity or specificity, it is important to characterize MTRasym analytically to optimize its sensitivity or specifity.


METHODS
Approximated analytical solutions of the MTRasym spectrum were derived based on a 2-pool chemical exchange model for slow-to-intermediate exchanges. The optimal saturation pulse power for maximizing the MTRasym or tuning MTRasym to a specific exchange rate and the peak position and linewidth of a MTRasym spectrum were also derived. These approximated analytical solutions were compared with the solutions from the Bloch-McConnell equations using computer simulations.


RESULTS
The approximated analytical solutions of the MTRasym spectra, the optimizing parameters, and the peak and linewidth of MTRasym matched well with the solutions of Bloch-McConnell equations in the slow or slow-to-intermediate exchange regimes.


CONCLUSION
These approximate analytical solutions can provide insights to the understanding of CEST signal property and help the optimization of saturation parameters and the interpretation of CEST data.
['Jin|Tao|T|0000-0003-2912-3517', 'Kim|Seong-Gi|SG|']
D007089:Image Enhancement D008279:Magnetic Resonance Imaging D011522:Protons D012680:Sensitivity and Specificity D014867:Water
chemical exchange CEST sensitivity specificity analytical solution