Adaptive persistence processing

• US 5,595,179 A
• Filed: 05/02/1995
• Issued: 01/21/1997
• Est. Priority Date: 05/02/1995
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Acuson Corporation (Siemens AG)
• Inventors: Guracar, Ismayil M., Wright, J. Nelson, Plugge, Jay S., Finger, David J., Fash, D. Grant III, Langdon, Donald R., Normand, Brian M.
• Primary Examiner(s): Jaworski, Francis
• Application Number:
  US08/433,217
• Time in Patent Office: 630 Days
• Field of Search: 128/660.01, 128/660.07, 128/661.01, 128/661.09, 348/447-448, 382/50, 382/59
• US Class Current: 600/443
• CPC Class Codes: G01S 7/52026 Extracting wanted echo signals Doppler systems G01S15/50; Doppler short range imaging systems G01S15/8979
• CPC Class Codes: G01S 7/52034 Data rate converters
• CPC Class Codes: G01S 7/52046 Techniques for image enhancement involving transmitter or receiver image enhancement by image data processing G06T5/00
• CPC Class Codes: H03H 2021/0079 using look-up tables
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

The invention provides a method and system for adaptive persistence processing in an ultrasound imaging system. Acoustic signals are temporally filtered using an adaptive persistence filter, having a recursive stage followed by a nonrecursive stage. A set of filtering coefficients for each stage are supplied by a look-up table in a memory, addressed or indexed in response to a plurality of input or output pixel values. The look-up table may therefore embody any selected function of its input variables. The input variables for the look-up table function are a current input pixel value X_n and a previous intermediate pixel value W_n-1, and the function embodied by the look-up table includes a relative first difference function for selecting a filter coefficient. A recursive filtering coefficient α is held constant over time, while a nonrecursive filtering coefficient γ is adjusted dynamically in response to the current input pixel value X_n and the previous intermediate pixel value W_n-1. The nonrecursive stage filter has a frequency response that attenuates higher frequency components without attenuating a broad range of lower frequency components, relative to the recursive stage frequency response. The step response or settling time of the nonrecursive stage filter always spans one frame interval, independent of the nonrecursive filtering coefficient, while the step response or settling time for the recursive stage filter is generally longer and is dependent on the recursive filtering coefficient.

Claims

1. An adaptive persistence filter in an ultrasound imaging system, comprising

a node disposed for coupling to an input pixel, said input pixel having an input pixel value X_n ;

a recursive stage filter coupled to said node, having an recursive stage output, and responsive to a first filtering coefficient α

, said recursive stage output having an intermediate pixel value W_n ;

a nonrecursive stage filter coupled to said recursive stage output, and responsive to a second filtering coefficient γ

; and

a function block coupled to said node and to said recursive stage output, and generating said second filtering coefficient γ

in response to said input pixel value X_n and a previous said intermediate pixel value W_n-1.

2. A filter as in claim 1, wherein a transfer function H(z) of said filter comprises a term k₁ k₂ (1+β

z^-1)/(1-α

z^-1), wherein k₁ =(1-α

);

k₂ =(1-γ

); and

β

=γ

/(1-γ

).

3. A filter as in claim 2, wherein -1≦

α

<

1, -1≦

γ

≦

1, and -0.5≦

β

<

∞

.

4. A filter as in claim 1, wherein

said first filtering coefficient α

is held constant over time; and

said second filtering coefficient γ

is adjusted dynamically in response to the current input pixel value X_n and the previous intermediate pixel value W_n-1.

5. A filter as in claim 1, wherein said function block comprises a memory having a look-up table stored therein, said memory comprising a first address input coupled to said node and a second address input responsive to said recursive stage output.

6. A filter as in claim 1, wherein said second filtering coefficient γ

is adjusted dynamically in response to a function of |X_n -W_n-1 |/W_n-1.

7. A filter as in claim 1, wherein said second filtering coefficient γ

is adjusted dynamically in response to a function of |X_n -W_n-1 |.

8. A filter as in claim 1, wherein said second filtering coefficient γ

is adjusted dynamically in response to a is function of |X_n -W_n-1 |/X_n.

9. A method of adaptive persistence filtering in an ultrasound imaging system, comprising the steps of

receiving an input pixel value X_n ;

filtering said input pixel value X_n with a recursive stage filter, responsive to a first filtering coefficient α

, and generating an intermediate pixel value W_n ;

filtering a current said intermediate pixel value W_n with a nonrecursive stage filter, responsive to a second filtering coefficient γ

; and

generating said second filtering coefficient γ

in response to said input pixel value X_n and said previous said intermediate pixel value W_n-1.

10. A method as in claim 9, wherein

said step of generating comprises holding said first filtering coefficient α

constant over time; and

said step of generating comprises adjusting said second filtering coefficient γ

dynamically in response to the current input pixel value X_n and the previous intermediate pixel value W_n-1.

11. A method as in claim 9, wherein said step of generating comprises retrieving said second filtering coefficient from a memory.

12. A method as in claim 9, wherein said step of generating said second filtering coefficient γ

is comprises a function of |X_n -W_n-1 |/W_n-1.

13. A method as in claim 9, wherein said step of generating said second filtering coefficient γ

comprises a function of |X_n -W_n-1 |.

14. A method as in claim 9, wherein said step of generating said second filtering coefficient γ

comprises a function of |X_n -W_n-1 |/X_n.

15. An adaptive persistence filter in an ultrasound imaging system, comprising

a node disposed for coupling to an input pixel, said input pixel having an input pixel value X_n ;

a recursive stage filter coupled to said node, having an recursive stage output, and responsive to a first filtering coefficient α

, said recursive stage output having a current intermediate pixel value W_n and a previous intermediate pixel value W_n-1 ;

a nonrecursive stage filter coupled to said recursive stage output, and responsive to a second filtering coefficient γ

, wherein said second filtering coefficient γ

is responsive to said current intermediate pixel value input pixel value W_n and said previous intermediate pixel value W_n-1.

16. A filter as in claim 15, wherein

said first filtering coefficient α

is held constant over time; and

said second filtering coefficient γ

is adjusted dynamically in response to the current input pixel value W_n and the previous intermediate pixel value W_n-1.

17. A filter as in claim 15, wherein said nonrecursive stage comprises a memory having a look-up table stored therein, said memory comprising a first address input coupled to said current input pixel value W_n and a second address input coupled to said previous intermediate pixel value W_n-1.

18. A filter as in claim 15, wherein said second filtering coefficient γ

is adjusted dynamically in response to said current intermediate pixel value W_n and said previous intermediate pixel value W_n-1.

19. A filter as in claim 15, wherein said second filtering coefficient γ

is adjusted dynamically in response to a function of |W_n -W_n-1 |/W_n.

20. A filter as in claim 15, wherein said second filtering coefficient γ

is adjusted dynamically in response to a function of |W_n -W_n-1 |.

21. A filter as in claim 15, wherein said second filtering coefficient γ

is adjusted dynamically in response to a function of |W_n -W_n-1 |/W_n-1.

22. A method of adaptive persistence filtering in an ultrasound imaging system, comprising the steps of

receiving an input pixel value X_n ;

filtering said input pixel value X_n with a recursive stage filter, responsive to a first filtering coefficient α

, and generating a current intermediate pixel value W_n and a previous intermediate pixel value W_n-1 ;

filtering a current said intermediate pixel value W_n with a nonrecursive stage filter, responsive to a second filtering coefficient γ

; and

generating said second filtering coefficient γ

in response to said current intermediate pixel value input pixel value W_n and said previous intermediate pixel value W_n-1.

23. A method as in claim 22, wherein

said step of generating comprises holding said first filtering coefficient α

constant over time; and

said step of generating comprises adjusting said second filtering coefficient γ

dynamically in response to said current intermediate pixel value W_n and said previous intermediate pixel value W_n-1.

24. A method as in claim 22, wherein said step of generating said second filtering coefficient γ

is comprises a function of |W_n -W_n-1 |/W_n-1.

25. A method as in claim 22, wherein said step of generating said second filtering coefficient γ

comprises a function of |W_n -W_n-1 |.

26. A method as in claim 22, wherein said step of generating said second filtering coefficient γ

comprises a function of |W_n -W_n-1 |/W_n.