MAGNETIC RESONANCE SPECIMEN EVALUATION USING MULTIPLE PULSED FIELD GRADIENT SEQUENCES

• US 20100033182A1
• Filed: 08/11/2009
• Published: 02/11/2010
• Est. Priority Date: 08/11/2008
• Status: Active Grant

• Current Assignee: United States Department Of Health And Human Services
• Original Assignee: US Department of Health and Human Services (Government of the United States of America)
• Inventors: Ozarslan, Evren, Basser, Peter J.
• Granted Patent: US 8,704,515 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: G01N 24/081 Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
• CPC Class Codes: G01R 33/44 using nuclear magnetic resonance [NMR] G01R33/24, G01R33/62 take precedence
• CPC Class Codes: G01R 33/56341 Diffusion imaging

Abstract

Using pulsed-field-gradient (PFG) sequences, the sizes of the pores in ordered porous media can be estimated from the “diffraction” pattern that the signal attenuation curves exhibit. A different diffraction pattern is observed when the experiment is extended to a larger number (N) of diffusion gradient pulse pairs. Differences in the characteristics of attenuation curves also permit distinguishing different pore shapes and distributions using the N-PFG technique. Using an even number of PFG pairs, an approximation to the average pore size can be obtained even when the sample contains pores with a broad distribution of sizes. Multi-PFG sequences can also be used to differentiate free and multi-compartment diffusion, and to estimate compartment sizes and orientations, and to distinguish microscopic and ensemble anisotropy.

Claims

1. At least one computer readable medium having stored thereon computer-executable instructions for a method comprising:

obtaining a recorded magnetic resonance signal as a function of magnetic resonance wavevector in response to a multi-PFG sequence that includes at least two PFG sequences;

generating an estimate of a distribution of restricted compartments of a sample based on the magnetic resonance signal; and

communicating the generated estimate of the distribution.

2. The at least one computer readable medium of claim 1, wherein the method comprises providing an estimate of a mean value of a restricted compartment size distribution.

3. The at least one computer readable medium of claim 2, wherein the estimate of the mean value is provided based on determination of a magnetic resonance wavenumber value associated with a local minimum value of the recorded magnetic resonance signal.

4. The at least one computer readable medium of claim 2, wherein the multi-PFG sequence includes an odd number of PFG sequences:

5. The at least one computer readable medium of claim 2, wherein the estimate of the mean value is provided based on determination of a magnetic resonance wavenumber value associated with sign change in the recorded magnetic resonance signal.

6. The at least one computer readable medium of claim 5, wherein the multi-PFG sequence includes an even number of PFG sequences.

7. The at least one computer readable medium of claim 5, wherein the mean value is associated with a radius of cylindrical or spherical restricted compartments or a separation of planar compartments.

8. The at least one computer readable medium of claim 1, wherein the PFG sequences of the multi-PFG sequence have common effective gradient magnitudes.

10. The method of claim 1, wherein the estimate is associated with a mean value of a size distribution and is based on a magnetic resonance wavenumber associated with a local minimum or a sign change of the recorded magnetic resonance signal.

9. A method, comprising:

receiving a recorded magnetic resonance signal responsive to a multi-PFG sequence; and

based on the recorded magnetic resonance signal, providing an estimate of at least one size characteristic of a distribution of restricted compartments in a specimen.

11. A method, comprising:

applying at least a first PFG sequence and a second PFG sequence to a specimen, wherein the first and second sequences are applied with a plurality of angles between field gradients of the first and second sequences;

recording a magnetic resonance signal as a function of the plurality of angles; and

based on the recorded signal, providing an estimate of a dimension associated with a restricted compartment of the specimen.

12. The method of claim 11, wherein the dimension is associated with a distribution of restricted compartments of the specimen.

13. The method of claim 11, wherein the dimension is associated with a diffusion distance that is a function of a diffusion constant in the restricted compartment.

14. The method of claim 11, further comprising providing an estimate of a restricted compartment distribution.

15. The method of claim 11, further comprising providing an estimate of a restricted compartment orientation based on the recorded magnetic resonance signal.

16. The method of claim 15, further comprising providing estimates of restricted compartment orientations for at least first and second restricted compartment distributions.

17. The method of claim 16, further comprising displaying an image based on restricted compartment properties as a function of specimen location.

18. The method of claim 11, wherein the dimension is associated with a radius of a spherical or cylindrical restricted compartment.

19. The method of claim 11, wherein the applied field gradients are selected so that product of a magnetic resonance wavenumbers and the estimated dimension are less than about 0.5.

20. The method of claim 11, further comprising obtaining a plurality of recorded magnetic resonance signals as a function of angle, wherein the recorded signals are associated with a plurality of mixing times, diffusion times, or magnetic resonance wavenumbers.

21. The method of claim 11, further comprising obtaining a distribution associated with orientations of a plurality of restricted compartments.