Synthetic aperture MRI

• US 20040263169A1
• Filed: 06/25/2004
• Published: 12/30/2004
• Est. Priority Date: 06/27/2003
• Status: Active Grant

• Current Assignee: Resolutionmd Incorporated
• Original Assignee: Calgary Scientific Inc.
• Inventors: Lauzon, M. Louis, Mitchell, J. Ross, Zhu, Hongmei, Mayer, Gregory S.
• Granted Patent: US 7,005,854 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: G01R 33/56 Image enhancement or correction, e.g. subtraction or averaging techniques , e.g. improvement of signal-to-noise ratio and resolution
• CPC Class Codes: G01R 33/5604 Microscopy; Zooming
• CPC Class Codes: G01R 33/5608 Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels image data processing or generation, in general G06T

Abstract

The present invention relates to a method and system for enhancing resolution of a magnetic resonance image of an object. The method combines information from a plurality of low-resolution images with a Field Of View shifted by a distance less than a pixel width to create a synthesized image having substantially improved image quality. Information from the low-resolution images is merged and application of an aperture function enhances the SNR of the synthesized image resulting in synthesized images having a substantially higher spatial resolution as well as a substantially increased SNR. The method and system for enhancing resolution of a magnetic resonance image is highly beneficial for a MRI practitioner by substantially improving image quality, thus facilitating diagnostic methods such as texture analysis and disease specific tissue segmentation.

Claims

1. A method for enhancing resolution of a magnetic resonance image of an object comprising:

receiving a first analog Fourier domain signal indicative of a first magnetic resonance image of an area of the object;

receiving a second analog Fourier domain signal indicative of a second magnetic resonance image of the area of the object;

superposing a phase ramp on the first analog Fourier domain signal in frequency encode direction, the phase ramp corresponding to a shift of a field of view of the first image with respect to the field of view of the second image of less than a pixel width;

discretizing the first and the second analog Fourier domain signal producing a first and a second digital Fourier domain signal;

merging in Fourier domain the first and the second digital Fourier domain signal producing a merged digital Fourier domain signal;

deconvoluting the merged digital Fourier domain signal using an aperture function; and

,

determining image data indicative of a synthesized magnetic resonance image of the area of the object by inverse Fourier transforming the merged digital Fourier domain signal, the synthesized magnetic resonance image having substantially higher resolution than the first and the second magnetic resonance image.

2. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 1 comprising anti aliasing filtering the first and second analog Fourier domain signal.

3. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 2 wherein the first and the second digital Fourier domain signal are merged using an interleaving process, the interleaving process modeling interleaving of image pixels of the first and the second magnetic resonance image in the Fourier domain.

4. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 3 wherein the interleaving process is based on a Fourier model of zero interleaving of signals.

5. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 3 comprising splitting an analog Fourier domain signal into the first and the second analog Fourier domain signal.

6. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 3 comprising determining the aperture function in dependence upon magnitude and phase differences between the first and second analog Fourier domain signal.

7. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 6 comprising determining a total phase difference between the first and second analog Fourier domain signal in the Fourier domain.

8. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 6 wherein the aperture function is set to unity in a region corresponding to an extended spectral range created by interleaving.

9. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 8 comprising smoothing transition of the aperture function into the unity region.

10. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 8 comprising adding a positive non-zero constant to the aperture function.

11. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 10 wherein the constant is determined such that a signal-to-noise ratio of the merged digital Fourier domain signal is substantially maximized.

12. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 11 wherein the constant is determined through an optimization procedure initialized using predetermined values for the constant.

13. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 8 comprising adding a positive non-zero varying parameter to the aperture function.

14. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 6 comprising estimating high frequency content of the aperture function based on high frequency data collected during a pre-scan.

15. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 6 wherein the deconvolution is performed based on Fourier division.

16. A method for enhancing resolution of a magnetic resonance image of an object comprising:

receiving N analog Fourier domain signals indicative of N magnetic resonance images of an area of the object;

superposing a phase ramp on each of the first to N−

1^th analog Fourier domain signals in frequency encode direction, the phase ramp corresponding to a different shift of a field of view of each of the first to N−

1^th images with respect to the field of view of the N^th image of less than a pixel width;

discretizing the N analog Fourier domain signals producing N digital Fourier domain signals;

merging in the Fourier domain the N digital Fourier domain signals producing a merged digital Fourier domain signal;

deconvoluting the merged digital Fourier domain signal using an aperture function; and

,

determining image data indicative of a synthesized magnetic resonance image of the area of the object by inverse Fourier transforming the merged digital Fourier domain signal, the synthesized magnetic resonance image having substantially higher resolution than the N magnetic resonance images.

17. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 16 comprising anti aliasing filtering the N analog Fourier domain signals.

18. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 17 comprising estimating high frequency content of the aperture function based on high frequency data collected during a pre-scan.

19. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 18 comprising adding a positive non-zero constant to the aperture function.

20. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 19 wherein the constant is determined such that a signal-to-noise ratio of the merged digital Fourier domain signal is substantially maximized.

21. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 17 comprising;

repeating the steps for a second set of N analog Fourier domain signals, the second set of N analog Fourier domain signals acquired along different axes of the frequency domain with respect to the object providing second image data indicative of at least another portion of a synthesized magnetic resonance image of the area of the object; and

, combining the image data and the second image data producing combined image data.

22. A method for enhancing resolution of a magnetic resonance image of an object as defined in claim 20 wherein N is equal to 2.

23. A system for enhancing resolution of a magnetic resonance image of an object comprising:

a ramp circuitry for superposing a phase ramp on a first analog Fourier domain signal in frequency encode direction, the first analog Fourier domain signal being indicative of a first magnetic resonance image of an area of the object, the phase ramp corresponding to a shift of a field of view of the first magnetic resonance image with respect to the field of view of a second magnetic resonance image of less than a pixel width;

an A/D converter in communication with the ramp circuitry for discretizing the first analog Fourier domain signal and a second analog Fourier domain signal indicative of the second magnetic resonance image of the area of the object producing a first and a second digital Fourier domain signal; and

,

a processor in communication with the A/D converter, the processor for;

merging in the Fourier domain the first and the second digital Fourier domain signal producing a merged digital Fourier domain signal;

deconvoluting the merged digital Fourier domain signal using an aperture function; and

,

determining image data indicative of a synthesized magnetic resonance image of the area of the object by inverse Fourier transforming the merged digital Fourier domain signal, the synthesized magnetic resonance image having substantially higher resolution than the first and the second magnetic resonance image.

24. A system for enhancing resolution of a magnetic resonance image of an object as defined in claim 23 comprising an anti aliasing filter in communication with the ramp circuitry and the A/D converter for anti aliasing filtering the first and the second analog Fourier domain signal.

25. A system for enhancing resolution of a magnetic resonance image of an object as defined in claim 24 comprising a controller in communication with the ramp circuitry and the processor for controlling provision of the phase ramp in dependence upon a control signal received from the processor.

26. A system for enhancing resolution of a magnetic resonance image of an object as defined in claim 25 comprising an analog splitter in communication with the ramp circuitry for splitting an analog Fourier domain signal into the first and the second analog Fourier domain signal.

27. A storage medium having executable commands for execution on at least a processor stored therein, the at least a processor when executing the commands performing:

receiving a first digital Fourier domain signal indicative of a first magnetic resonance image of an area of an object;

receiving a second digital Fourier domain signal indicative of a second magnetic resonance image of the area of the object, the second digital Fourier domain signal having superposed a phase ramp corresponding to a shift of a field of view of the second magnetic resonance image with respect to the field of view of the first magnetic resonance image of less than a pixel width;

merging in the Fourier domain the first and the second digital Fourier domain signal producing a merged digital Fourier domain signal;

deconvoluting the merged digital Fourier domain signal using an aperture function; and

,

determining image data indicative of a synthesized magnetic resonance image of the area of the object by inverse Fourier transforming the merged digital Fourier domain signal, the synthesized magnetic resonance image having substantially higher resolution than the first and the second magnetic resonance image.