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Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
Published on: November 12, 2016
Water saturation shift referencing (WASSR) for chemical exchange saturation transfer (CEST) experiments
Mina Kim1, Joseph Gillen, Bennett A Landman
1Russell H. Morgan Department of Radiology and Radiological Sciences, Neurology Section, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Magnetic Resonance in Medicine
|April 10, 2009
Summary
Direct water saturation imaging precisely centers chemical exchange saturation transfer (CEST) spectra by measuring absolute water frequencies. This water saturation shift referencing (WASSR) method overcomes magnetic field variations for accurate CEST quantification.
Area of Science:
- Magnetic Resonance Imaging
- Biomedical Engineering
- Spectroscopy
Background:
- Chemical exchange saturation transfer (CEST) is a magnetic resonance imaging (MRI) contrast mechanism.
- CEST relies on magnetization transfer (MT) between solute and water protons.
- CEST quantification is challenged by direct water saturation, conventional MT, and magnetic field inhomogeneities.
Purpose of the Study:
- To develop a method for accurate voxel-by-voxel centering of Z-spectra in CEST MRI.
- To overcome sensitivity to magnetic field inhomogeneities in CEST spectral analysis.
- To enable reliable CEST quantification, particularly for metabolites with small chemical shift differences from water.
Main Methods:
- Introduced direct water saturation imaging for absolute water frequency measurement.
- Developed the "water saturation shift referencing" (WASSR) approach for Z-spectrum centering.
- Utilized Monte Carlo simulations and experimental validation to optimize WASSR acquisition parameters.
Main Results:
- Direct water saturation imaging allows precise voxel-wise centering of Z-spectra, independent of B(0) variations.
- Optimal WASSR parameters involve a sweep width to linewidth ratio of 3.3-4.0 and 16-32 sampling points.
- The WASSR method achieves frequency errors <1 Hz at SNR ≥ 40.
- Demonstrated WASSR's utility in studying glycogen, where small chemical shifts make standard CEST analysis inconclusive.
Conclusions:
- Water saturation shift referencing (WASSR) provides accurate, field-independent Z-spectrum referencing in CEST MRI.
- WASSR enables reliable quantification of CEST effects, even for challenging metabolites like glycogen.
- This method significantly improves the diagnostic potential of CEST imaging.
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