Apparatus and method for generating echographic images

• US 5,111,823 A
• Filed: 04/16/1990
• Issued: 05/12/1992
• Est. Priority Date: 04/20/1989
• Status: Expired due to Fees

• Current Assignee: National Fertility Institute
• Original Assignee: National Fertility Institute
• Inventors: Cohen, Nathan
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/508,131
• Time in Patent Office: 757 Days
• Field of Search: 128/660.01, 128/661.01, 128/660.06, 73/602, 73/625, 73/626, 367/7, 367/100, 367/103
• US Class Current: 600/443
• CPC Class Codes: G01S 7/52028 using digital techniques
• CPC Class Codes: G01S 7/52047 for elimination of side lobes or of grating lobes; for increasing resolving power
• CPC Class Codes: G01S 7/52049 using correction of medium-induced phase aberration
• CPC Class Codes: G01S 7/52077 with means for elimination of unwanted signals, e.g. noise or interference

Abstract

An apparatus and method to generate low power ultrasonic, echograph images of selected stationary and moving target objects having high resolution. The apparatus and method include: an apparatus for transmitting a plurality of ultrasonic signals into a selected area of tissue, and apparatus for receiving the corresponding ultrasonic echo signals for each of the transmitted signals. A correlator autocorrelates and cross-correlates the transmitted and received ultrasonic signals. The correlated signals are summed, combined in ratios and partitioned into visibility amplitude data, visibility phase data, differential phase data, closure amplitude data and closure phase data for mapping. The preferred apparatus and method thereafter perform a non-linear image processing, either by an iterative side lobe subtraction signal processing procedure to remove signal noise and/or by an interative hybrid mapping signal processing procedure. The resulting data map yields a high resolution image of the selected target with more data and less noise. Signal processing to show motion or target object changes after noise reduction is also disclosed. In a preferred embodiment, the apparatus and method is employed as a clinical diagnostic tool for generating non-traumatic, high resolution imaging of bodily tissue.

Claims

1. In a method of generating an echographic image of a target object including the steps of transmitting a plurality of ultrasonic signals toward said target object, receiving a corresponding plurality of echo signals from said target object, correlating said ultrasonic signals and said echo signals to produce correlated data including amplitude data sufficient to map an image of said target object and phase data, mapping said amplitude data, the improvement comprising the steps of:

partitioning said correlated data into a plurality of data sets including a visibility amplitude data set and a visibility phase data set;

reducing noise present in said correlated data by at least one of;

(i) a side lobe subtraction process, (ii) a hybrid mapping process, (iii) a vectorial summing of possible combinations of three visibility phase data values to produce a closure phase data set, and (iv) forming ratios of possible combinations of four visibility amplitude data values to produce a closure amplitude data set; and

during said mapping step, mapping said amplitude data and said phase data after said step of reducing noise.

2. The method as defined in claim 1 wherein,

said reducing step is accomplished by a vectorial summing of all possible combinations of three visibility phase data values to produce a closure phase data set free of phase aberration, and

during said mapping step, mapping said closure phase data set.

3. The method as defined in claim 2 wherein,

said reducing step additionally includes the step of forming ratios of all possible combinations of four visibility amplitude data values to produce a closure amplitude data set, and

during said mapping step, mapping said closure phase data set and said closure amplitude data set.

4. The method as defined in claim 3, and the step of:

prior to said mapping step, generating a differential phase data set, and

during said mapping step, mapping said differential phase data.

5. The method as defined in claim 4, and

after said steps of vectorial summing, forming ratios and generating, reducing noise by a side lobe subtraction process using said closure phase data set, said closure amplitude data set, said differential phase data set, said visibility amplitude data set and said visibility phase data set.

6. The method as defined in claim 4, and

after said steps of vectorial summing, forming ratios and generating a differential phase data set, reducing noise by a hybrid mapping process using said visibility amplitude data set, said closure amplitude data set, said closure phase data set.

7. The method as defined in claim 6, and

during said hybrid mapping process, using said visibility phase data set and said differential phase data set.

8. The method as defined in claim 2, and

after said vectorial summing step, reducing noise by a side lobe subtraction process using said closure phase data set.

9. The method as defined in claim 8, and the steps of:

during said reducing step, employing a side lobe subtraction process including the steps of;

(i) mapping said visibility amplitude data set and visibility phase data set and said closure phase data set into a first map having noise in the time domain;

(ii) identifying one bright data point on said first map;

(iii) synthesizing a beam side lobe pattern from frequency data for said visibility amplitude data set, said visibility phase data set, and said closure phase data set;

(iv) transforming said first map into the frequency domain;

(v) subtracting said beam side lobe pattern from data around said bright data point in said first map in said frequency domain to produce noise-reduced frequency data;

(vi) transforming said noise-reduced frequency data to time domain to produce a second map;

(vii) identifying a second bright data point on said second map;

(viii) transforming said second map into the frequency domain;

(ix) subtracting said beam side lobe pattern from data around said bright data point in said second map in said frequency domain to produce further noise-reduced frequency data; and

(x) transforming said further noise-reduced frequency data into the time domain.

10. The method as defined in claim 9, and the step of:

after said step of transforming said further noise-reduced data, displaying a time domain map.

11. The method as defined in claim 2, and

after said vectorial summing step, reducing noise by a hybrid mapping process using said closure phase data set.

12. The method as defined in claim 1 wherein,

said transmitting step is accomplished by transmitting ultrasonic signals from an array of ultrasonic transducers to enable synthesis of an aperture for imaging of said target object;

and

said reducing step is accomplished by a side lobe subtraction process in which side lobe response inherent in said aperture synthesized from said array of ultrasonic transducers is subtracted from selected data in said data sets.

13. The method as defined in claim 12 wherein,

said side lobe subtraction process includes the steps of:

(i) mapping the amplitude and phase data in said plurality of data sets into a dirty map in the time domain;

(ii) identifying a bright point in said dirty map;

(iii) generating a side lobe response pattern for said aperture in the frequency domain;

(iv) transforming said dirty map into the frequency domain;

(v) subtracting said side lobe response pattern from data points around the identified bright point in the frequency domain to produce cleaned frequency data;

(vi) transforming said cleaned frequency data to a cleaned map in the time domain; and

after said side lobe subtraction process, displaying said cleaned map.

14. The method as defined in claim 13 and the steps of:

comparing said cleaned map to said dirty map for reduction of noise, and

iterating said side lobe subtraction process for other bright points in said dirty map.

15. The method as defined in claim 13 wherein,

said ultrasonic signals are transmitted in sets of a plurality of signals at a plurality of sequential time intervals;

each set of signals and corresponding set of echo signals is processed by said partitioning and reducing steps; and

wherein,

said displaying step is accomplished by the steps of;

(i) mapping all said data sets;

(ii) identifying a plurality of bright features on each of said maps and storing feature data as to the position and brightness of each of said bright features;

(iii) cross-correlating said feature data of each feature data set with said feature data of the sequentially next set of feature data;

(iv) identifying changes in data between feature data sets to indicate motion;

(v) revising data to remove jitter from each feature data set;

(vi) cross-correlating the sequentially adjacent revised data sets to identify sequential motion; and

(vii) sequentially displaying the revised cross-correlated data set.

16. The method as defined in claim 1 wherein,

said reducing step is accomplished by a hybrid mapping process in which model data for a given data point is substituted for actual data in the partitioned data sets.

17. The method as defined in claim 16 wherein,

said hybrid mapping process is accomplished by the steps of:

(i) mapping amplitude data in the time domain to create a first amplitude map;

(ii) identifying a bright data point in said first amplitude map;

(iii) inverse transforming said bright data point into the frequency domain using a brightness distribution algorithm to generate model amplitude and phase data for said bright data point;

(iv) substituting said model amplitude and phase data for corresponding actual amplitude and phase data in said partitioned data sets; and

thereafter mapping said partitioned data sets.

18. The method as defined in claim 17, and the step of:

(i) after said substituting step, mapping a second amplitude map from the amplitude data sets;

(ii) identifying a second bright data point in said second amplitude map different from said first bright data point;

(iii) inverse transforming said second bright data point into the frequency domain using a brightness distribution algorithm to generate model amplitude and phase data for said second bright data point; and

(iv) substituting said model amplitude and phase data for corresponding actual amplitude and phase data in said partitioned data sets.

19. The method as defined in claim 18, and the steps of:

during said partitioning step, generating data sets for visibility amplitude, visibility phase, during said reducing step, generating data sets for closure amplitude and closure phase.

20. The method as defined in claim 19 wherein,

said step of mapping amplitude data is accomplished by mapping visibility amplitude data and closure amplitude data.

21. The method as defined in claim 19 wherein,

during said partitioning step, generating a data set for differential phases.

22. The method as defined in claim 18, and the step of:

comparing model amplitude data to actual amplitude data by a goodness-of-fit comparison;

iterating the amplitude mapping, bright data point identification, inversion of the bright data point and substitution of model data steps until said comparing step produces a specified fit; and

mapping all data sets when said comparing step finds said amplitude data matches a specified fit.

23. The method as defined in claim 22, and the step of:

displaying the map of all data sets.

24. The method as defined in claim 23 wherein,

said ultrasonic signals are transmitted in sets of a plurality of signals at a plurality of sequential time intervals;

each set of signals and corresponding set of echo signals is processed by said partitioning and reducing steps; and

wherein,

said displaying step is accomplished by the steps of;

(i) mapping all said data sets;

(ii) identifying a plurality of bright features on each of said maps and storing feature data as to the position and brightness of each of said bright features;

(iii) cross-correlating said feature data of each feature data set with said feature data of the sequentially next set of feature data;

(iv) identifying changes in data between feature data sets to indicate motion;

(v) revising data to remove jitter from each feature data set;

(vi) cross-correlating the sequentially adjacent revised data sets to identify sequential motion; and

(vii) sequentially displaying the revised cross-correlated data set.

25. The method as defined in claim 1, and the steps of:

said ultrasonic signals being transmitted in sets of a plurality of signals at a plurality of sequential time intervals;

each set of signals and corresponding set of echo signals being processed by said partitioning and reducing steps;

displaying the mapped amplitude data and phase data; and

wherein,

said displaying step is accomplished by the steps of;

(i) mapping all said data steps;

(ii) identifying a plurality of bright features on each of said maps and storing feature data as to the position and brightness of each of said bright features;

(iii) cross-correlating said feature data of each feature data set with said feature data of the sequentially next set of feature data;

(iv) identifying changes in data between feature data sets to indicate motion;

(v) revising data to remove jitter from each feature data set;

(vi) cross-correlating the sequentially adjacent revised data sets to identify sequential motion; and

(vii) sequentially displaying the revised cross-correlated data set.

26. The method as defined in claim 25, and the step of:

separating unchanged data resulting from the first cross-correlating step.

27. The method as defined in claim 26, and the step of:

displaying said unchanged data.

28. The method as defined in claim 26, and the step of:

using said unchanged data to filter said remaining data.

29. The method as defined in claim 1 wherein,

said reducing step includes both said side lobe subtraction process and said hybrid mapping process.

30. The method as defined in claim 29 wherein,

said side lobe subtraction process is performed first and an output of said side lobe subtraction process is subsequently processed by said hybrid mapping process.

31. The method as defined in claim 30 wherein,

said ultrasonic signals are transmitted in sets of a plurality of signals at a plurality of sequential time intervals;

each set of signals and corresponding set of echo signals is processed by said partitioning step and by said side lobe subtraction process and said hybrid mapping process; and

the steps of;

(i) mapping all said data sets;

(ii) identifying a plurality of bright features on each of said maps and storing feature data as to the position and brightness of each of said bright features;

(iii) cross-correlating said feature data of each feature data set with said feature data of the sequentially next set of feature data;

(iv) identifying changes in data between feature data sets to indicate motion;

(v) revising data to remove jitter from each feature data set;

(vi) cross-correlating the sequentially adjacent revised data sets to identify sequential motion; and

(vii) sequentially displaying the revised cross-correlated data set.

34. The apparatus as defined in claim 3 wherein,

said means for subtracting hybrid data is positioned to receive an output from said means for subtracting side lobe noise.

32. In an apparatus for generating an echographic image including an ultrasonic transducer, generator means coupled to drive said transducer, signal processing means coupled to said transducer to receive echo signal data therefrom and coupled to receive transmitted ultrasonic signal data, said signal processing means correlating and mapping amplitude data from said ultrasonic signal data and said echo signal data, and display means coupled to said signal processing means to receive mapped data from said signal processing means and to display said mapped data as an image, the improvement comprising:

said apparatus including a plurality of ultrasonic transducers mounted in an array and coupled to said generator means and said signal processing means; and

said signal processing means including means for processing phase data, said means for processing phase data including means for reducing noise in said phase data, said means for reducing noise being provided by one of;

(i) means for subtracting side lobe noise from said phase data, and (ii) means for substituting hybrid map data for actual phase and amplitude data; and

said processing means further mapping substantially all of said amplitude data and said phase data after the reduction of noise therefrom.

33. The apparatus as defined in claim 32 wherein,

said signal process apparatus includes means for subtracting side lobe noise and means for substituting hybrid map data.

35. The apparatus as defined in claim 32 wherein,

said signal processing means includes means for processing a plurality of sequential sets of ultrasonic signals with each set being processed to reduce noise, and

said signal processing means includes means to sequentially cross-correlate feature data from each set of signals and to sequentially display said cross-correlated feature data to show target object motion.

36. In an apparatus for generating an echographic image including a plurality of ultrasonic transducers mounted in an array, signal generator means coupled to drive said transducers, signal processing means coupled to receive echo signals from said transducers and coupled to receive echo signals, said signal processing means being response to correlate said echo signals relative to said transmitted signals to produce amplitude signals suitable for image mapping, and display means coupled to said signal processing means to receive said amplitude signals and response thereto to produce an image, the improvement in said apparatus comprising:

said signal processing means being responsive to said transmitted signals and said echo signals to correlate said echo signals relative to said transmitted signals to produce both amplitude signals and phase signals;

said signal processing means further including noise reduction means responsive to said phase signals and said amplitude signals to reduce noise in said phase signals and said amplitude signals;

said noise reduction means including at least one of;

(i) means for subtracting side lobe noise from said amplitude signals and said phase signals, (ii) means for substituting hybrid map signals for said amplitude signals and said phase signals, (iii) means for vectorially summing sets of three phase signals to produce closure phase signals, and (iv) means for forming ratios of sets of four amplitude signals to produce closure amplitude signals;

said display means coupled to said signal processing means to receive signals therefrom at a position after noise reduction has been effected.

37. The apparatus as defined in claim 36 wherein,

said noise reduction means includes means responsive to phase signals and said amplitude signals to communicate to said display means having reduced side lobe noise.

38. The apparatus as defined in claim 36 wherein,

said noise reduction means includes means for subtracting side lobe noise from said amplitude and said phase signals.

39. The apparatus as defined in claim 36 wherein,

said noise reduction means includes means for substituting hybrid map signals for said amplitude and said phase signals.

40. The apparatus as defined in claim 36 wherein,

said noise reduction means includes means for forming ratios of sets of four amplitude signals to produce closure amplitude signals.

41. The apparatus as defined in claim 36 wherein,

said noise reduction means includes means for vectorially summing sets of three phase signals to produce closure phase signals.

42. The apparatus as defined in claim 41 wherein,

said signal processing means includes means for partitioning said amplitude signals, said phase signals and said closure phase signals into separate signal sets, and

said signal processing means is formed for mapping of said image in response to said separate signal sets.

43. The apparatus as defined in claim 42 wherein,

said noise reduction means also includes means for forming ratios of sets of four amplitude signals to produce closure amplitude signals, and

said means for partitioning partitions said amplitude signals from the remaining signals.

44. The apparatus as defined in claim 43 wherein,

said signal processing means is formed to respond to said phase signals to produce a set of differential phase signals, and

said means for partitioning partitions said differential phase signals from the remaining signals.

45. The apparatus as defined in claim 44 wherein,

said noise reduction means includes means for substituting hybrid map signals coupled to said partitioning means to receive signals therefrom and response thereto for substitution of hybrid mapping signals for signals in said separate signal sets.

46. The apparatus as defined in claim 44 wherein,

said noise reduction means includes means for subtracting side lobe noise coupled to said partitioning means to receive signals therefrom and responsive thereto for reduction of side lobe noise from signals in said separate signal sets.