Wavelet depulsing of ultrasound echo sequences

• US 20040054281A1
• Filed: 01/29/2003
• Published: 03/18/2004
• Est. Priority Date: 05/11/2000
• Status: Active Grant

• Current Assignee: TECHNION RESEARCH AND DEVELOPMENT FOUNDATION, LTD.
• Original Assignee: TECHNION RESEARCH AND DEVELOPMENT FOUNDATION, LTD.
• Inventors: Adam, Dan, Michailovich, Oleg
• Granted Patent: US 7,025,724 B2
• Time in Patent Office: Days
• US Class Current: 600/437
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: A61B 8/587 Calibration phantoms models for medical purposes G09B23/28
• CPC Class Codes: G01S 15/8977 using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution
• CPC Class Codes: G01S 7/52077 with means for elimination of unwanted signals, e.g. noise or interference
• CPC Class Codes: G06F 2218/06 by applying a scale-space analysis, e.g. using wavelet analysis
• CPC Class Codes: G06T 2207/10132 Ultrasound image
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening

Abstract

Methods and associated apparatuses for imaging a target. An echo sequence image of the target is acquired and a log spectrum of at least a portion of the echo sequence image is computed. A point spread function is estimated by one of two methods. According to the first method, a low-resolution wavelet projection of the echo sequence log spectrum is used as an estimate of the log spectrum of the point spread function. According to the second method, an outlier-resistant wavelet transform of the echo sequence log spectrum is effected, followed by soft-thresholding and an inverse wavelet transform. Under both methods, a frequency domain phase of the point spread function also is estimated. the relevant portion of the echo sequence image is deconvolved using the estimated point spread function.

Claims

1. A method of imaging a target, comprising the steps of:

(a) acquiring an echo sequence image of the target;

(b) computing a log spectrum of at least a portion of said echo sequence image;

(c) computing a low-resolution wavelet projection of said log spectrum;

(d) estimating a point spread function from said low-resolution wavelet projection; and

(e) deconvolving said at least portion of said echo sequence image with said point spread function.

2. The method of claim 1, further comprising the step of:

(f) partitioning the echo sequence image into a plurality of segments;

said computing of said log spectrum, said computing of said wavelet projection, said estimating and said deconvolving then being effected separately for each said segment.

3. The method of claim 2, wherein said segments are disjoint.

4. The method of claim 2, wherein at least two of said segments at least partly overlap.

5. The method of claim 1, wherein said wavelet projection is based on a wavelet selected from the group consisting of Coiflet wavelets, minimum-phase Daubechies wavelets, symmetric Daubechies wavelets and biorthogonal wavelets.

6. The method of claim 1, wherein said computing of said wavelet projection includes effecting an outlier-resistant wavelet transform of said log spectrum.

7. The method of claim 1, wherein said estimating of said point spread function includes estimating a frequency domain phase of said point spread function.

8. The method of claim 7, wherein said phase estimating assumes that said point spread function is a minimum phase sequence.

9. The method of claim 1, wherein said deconvolving is effected using an approximate inverse.

10. A method of imaging a target, comprising the steps of:

(a) acquiring an echo sequence image of the target;

(b) computing a log spectrum of at least a portion of said echo sequence image;

(c) effecting an outlier-resistant wavelet transform of said log spectrum, thereby producing a plurality of wavelet coefficients;

(d) soft-thresholding said wavelet coefficients;

(e) applying an inverse wavelet transform to said soft-thresholded wavelet coefficients to obtain a point spread function log spectrum;

(f) estimating a point spread function from said point spread function log spectrum; and

(g) deconvolving said at least portion of said echo sequence image with said point spread function.

11. The method of claim 10, further comprising the step of:

(h) partitioning the echo sequence image into a plurality of segments;

said computing of said log spectrum, said effecting of said wavelet transform, said soft-thresholding, said applying, said estimating and said deconvolving then being effected separately for each said segment.

12. The method of claim 11, wherein said segments are disjoint.

13. The method of claim 11, wherein at least two of said segments at least partly overlap.

14. The method of claim 10, wherein said outlier-resistant wavelet transform is based on minimizing an L₁ norm.

15. The method of claim 10, wherein said outlier-resistant wavelet transform is a Smoother-Cleaner Wavelet Transform.

16. The method of claim 10, wherein said outlier-resistant wavelet transform includes a plurality of resolution levels, with robust residuals being removed in only a portion of said resolution levels.

17. The method of claim 16, wherein said robust residuals are removed only in a first said resolution level.

18. The method of claim 10, wherein said estimating of said point spread function includes estimating a frequency domain phase of said point spread function.

19. The method of claim 18, wherein said phase estimating assumes that said point spread function is a minimum phase sequence.

20. The method of claim 10, wherein said deconvolving is effected using an approximate inverse.

21. An apparatus for imaging a target, comprising:

(a) a transducer for acquiring an echo sequence image of the target; and

(b) a processor for;

(i) computing a log spectrum of at least a portion of said echo sequence image,

(ii) computing a low-resolution wavelet projection of said log spectrum,

(iii) estimating a point spread function from said low-resolution wavelet projection, and

(iv) deconvolving said at least portion of said echo sequence image with said point spread function.

22. An apparatus for imaging a target, comprising:

(a) a transducer for acquiring an echo sequence image of the target; and

(b) a processor for;

(i) computing a log spectrum of at least a portion of said echo sequence image,

(ii) effecting an outlier-resistant wavelet transform of said at least portion of said log spectrum, thereby producing a plurality of wavelet coefficients,

(iii) soft-thresholding said wavelet coefficients,

(iv) applying an inverse wavelet transform to said soft-thresholded wavelet coefficients to obtain a point spread function log spectrum,

(v) estimating a point spread function from said point spread function log spectrum, and

(vi) deconvolving said at least portion of said echo sequence image with said point spread function.