Magnetic field gradient structure characteristic assessment using one dimensional (1D) spatial-frequency distribution analysis
The disclosed innovation is a method for acquiring spatial frequency spectra from specific locations in a 3D sample using modifications of the current MRI techniques for localized NMR spectroscopy. The innovation in its simplest abstraction is to add the use of a read out gradient to the current NMR spectroscopy pulse sequences and record the resultant echo. These techniques generate spectra from a selected region or generate an image of the results over a region of the sample. These methods can be applied to analyzing the structure of trabecular bone as well as for analyzing or diagnosing disease in cases where there is a difference in the spatial frequency power spectrum due to physiologic or disease processes. Various embodiments are disclosed.
1. A method of assessing a spatial frequency distribution within a sample of a structure comprising:
a) subjecting the sample to a magnetic field;
b) subjecting the sample to magnetic resonance excitation;
c) receiving an echo signal from the sample while the sample is subjected to a magnetic field gradient;
d) taking an inverse transform of the received echo signal to obtain an echo signal intensity in one dimension;
e) identifying a region of interest in the echo signal intensity in one dimension;
f) windowing the region identified in e) to shape the echo signal intensity in the region of interest;
g) taking a transform of the windowed echo signal intensity in one dimension obtained in f); and,
h) analyzing the one dimensional spatial frequency content in the transform obtained in g) in order to access a one dimensional spatial frequency distribution within the sample of the structure without having to acquire all of the data required to create an image.
2. The method of claim 1 wherein the structure is a bone structure.
3. The method of claim 1 wherein the structure is petroleum dispersed in strata.
4. The method of claim 1 wherein the structure is a biologic structure.
5. The method of claim 1 wherein the transform obtained in g) is a Fourier transform.
6. The method of claim 1 wherein the transform obtained in g) is a wavelet transform.
7. The method of claim 1 wherein analyzing the spatial frequency content in the transform obtained in g) comprises comparing spatial frequency distribution in the transform obtained in g) with spatial frequency distributions of transforms of a same type of structure, but of differing characteristics.
8. The method of claim 1 wherein analyzing the spatial frequency content in the transform obtained in g) comprises comparing content of frequency bands in the transform obtained in g) with frequency bands of transforms of a same type of structure, but of differing characteristics.
9. The method of claim 1 wherein:
in b), subjecting the sample to magnetic resonance excitation comprises subjecting the sample to first and second excitations to excite a stick shaped region in the sample;
in c), receiving an echo signal from the sample while the sample is subjected to a magnetic field gradient comprises receiving an echo signal from the stick shaped region while the sample is subjected to a magnetic field gradient; and,
in f), windowing the region identified in e) to shape the echo signal intensity in the region of interest comprises windowing the region identified in e) along the stick shaped region to shape the echo signal intensity in the region of interest along the stick shaped region.
10. The method of claim 1 wherein in d), taking an inverse transform of the echo signal comprises taking an inverse Fourier transform of the echo signal.
11. A method of assessing at least one spatial frequency characteristic of a sample of a structure comprising:
a) subjecting the sample to a magnetic field;
b) subjecting the sample to first and second RF excitations to excite a stick shaped region in the sample;
c) receiving an echo signal from the stick shaped region while the sample is subjected to a magnetic field gradient;
d) taking an inverse transform of the received echo signal to obtain an echo signal intensity in one dimension;
e) identifying a region of interest in the echo signal intensity in one dimension;
f) windowing the region identified in e) along the stick shaped region to shape the echo signal intensity in the region of interest along the stick shaped region;
g) taking a transform of the windowed echo signal intensity in one dimension obtained in f); and,
h) analyzing the one dimensional spatial frequency content in the transform obtained in g) in order to access a one dimensional spatial frequency distribution within the sample of the structure without having to acquire all of the data required to create an image.
12. The method of claim 11 wherein the RF excitation includes a band of frequencies, and the magnetic field gradient is imposed before termination of the RF excitation.
13. The method of claim 11 wherein the transform in g) is a Fourier transform.
14. The method of claim 11 wherein the transform in g) is a wavelet transform.
15. The method of claim 11 wherein the structure is a bone structure.
16. The method of claim 11 wherein the structure is petroleum dispersed in strata.
17. The method of claim 11 wherein the structure is a biologic structure.
18. The method of claim 11 wherein in h), analyzing the one dimensional spatial frequency content in the transform obtained in g) comprises comparing spatial frequency distribution in the transform obtained in g) with spatial frequency distributions of transforms of a same type of structure, but of differing characteristics.
19. The method of claim 11 wherein analyzing the one dimensional spatial frequency content in the transform obtained in g) comprises comparing content of frequency bands in the transform obtained in g) with frequency bands of transforms of a same type of structure, but of differing characteristics.