Development of Efficient and Robust NMR Techniques for Diffusion Measurements with Application to MRI Studies

Research Team/Collaborators

Gang Zheng, Tim Stait-Gardner, Allan M. Torres and Prof William S. Price 

Project Purpose

Since almost all chemical reactions result from reactants coming together by diffusion, and as diffusion is one of the most important sources of contrast in MRI (e.g., diffusion filters allow differentiation of ischaemic tissue), improvements in pulsed gradient spin-echo (PGSE) sequences are vitally important to both scientists and clinicians. Many important applications of PGSE (e.g., drug binding, clinical diffusion weighted MRI) involve the diffusion of low molecular weight species and yet accurate measurements of low molecular weight species is not always straightforward due to the presence of large solvent peaks and other complications such as background gradients.

This research group undertakes appropriate theoretical analysis and then designs new pulse sequences and data analysis techniques.

Methodology

Instrument used: 
Bruker 11.7 T Avance spectrometer

Analytical development is performed with the symbolic algebra program MAPLE.

Results

UWS Example Project - Figures 1 & 2 
Figure 1                                                                                      Figure 2
PGSTE-WATERGATE sequence with                             A 400 MHz 1H PGSTE-WATERGATE
        new binomial-like sequences.                                  spectrum of sample containing 2 mM
                                                                                                  sucrose, 0.5 mM DSS and 2 mM NaN3
                                                                                                   in water (10:90 D2O:H2O) at 298 K.
 UWS Example Project - Figure 3

Figure 3
A series of 500 MHz 1H PGSTE-WATERGATE spectra of a sample containing 2 mM lysozyme in water (10:90 D2O:H2O) at 298 K.

 

 UWS Example Project - Figure 4

Figure 4
Apparent diffusion coefficient (ADC) of residual HDO (DHDO = 1.90 × 10-9 m2 s-1 at 298 K) in a phantom containing packed glass beads filled with D2O.

 

UWS Example Project - Figures 5 & 6

 Figure 5                                                                 Figure 6
MRI images of a mouse brain                          MRI image of a calamansi

Discussion/Conclusions

  • PGSE-WATERGATE and PGSTE-WATERGATE sequences with new binomial-like soft pulses have been developed for high quality solvent suppression in NMR diffusion experiments and fat and/or water suppression in diffusion weighted MRI.
  • Magnetic inhomogeneity (i.e., background gradients, internal gradients) mainly induced by differences in magnetic susceptibilities inside and/or around the sample can significantly hamper accurate k-space encoding and diffusion weighting. In a typical magnetically inhomogeneous system such as human tissue, these background gradients are nonconstant both spatially and temporally, which makes the suppression of their deleterious effects more challenging. MAG-PGSTE sequence has been developed for the suppression of nonconstant background gradients in diffusion weighted MRI. As shown in Figure 4, the new sequence provides ADC's closer to the real diffusion coefficient.
  • The Bruker 11.7 T Avance spectrometer equipped with imaging probe provides us a perfect platform to develop new NMR and MRI techniques.

Selected Publications

  1. G. Zheng, T. Stait-Gardner, P. G. Anil Kumar, A. M. Torres, and W. S. Price, PGSTE-WATERGATE: A stimulated-echo-based PGSE NMR sequence with excellent solvent suppression, J. Magn. Reson. 191, 159-163 (2008).
  2. G. Zheng and W. S. Price, Suppression of Background Gradients in (B0 Gradient-Based) NMR Diffusion Experiments, Concepts Magn. Reson. 30A, 261-277 (2007).

Acknowledgements

The NSW State Government is acknowledged for financial support through a BioFirst award to WSP.

Project Contact

Prof William S. Price 
Phone +61 2 4620 3336 , Email: w.price@uws.edu.au

 

 

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