Ultrasonic transmission imaging apparatus and method

• US 5,460,178 A
• Filed: 01/31/1995
• Issued: 10/24/1995
• Est. Priority Date: 01/31/1995
• Status: Expired due to Fees

• Current Assignee: Centre de recherche industrielle du Québec
• Original Assignee: Centre de recherche industrielle du Québec
• Inventors: Isabelle, Pierre, Archambault, Real, Ross, Alain, Gauthier, Pierre, Hudon, Romeo
• Primary Examiner(s): MANUEL, GEORGE C
• Application Number:
  US08/381,651
• Time in Patent Office: 266 Days
• Field of Search: 128/660.01, 128/660.06, 128/660.07, 128/660.08, 128/661.01, 128/661.02, 128/663.01, 73/602, 73/606, 73/607, 73/626, 73/620
• US Class Current: 600/443
• CPC Class Codes: A61B 8/15 Transmission-tomography

Abstract

A new ultrasonic transmission imaging apparatus is disclosed, which uses a new imaging method providing image focusing capability. The apparatus comprises an ultrasonic emitter producing substantially continuous coherent ultrasonic waves toward an object to be inspected. The apparatus further comprises an ultrasonic detectors array comprising a plurality of ultrasonic detectors receiving the object traversing ultrasonic waves to produce a plurality of series of electrical signals coming from the ultrasonic detectors, the electrical signals characterizing transmission of the ultrasonic waves through the object and being associated with series of image elements. The apparatus further comprises a signal vector components detector detecting signal vector components for each of the electrical signals. The apparatus further comprises a computer for controlling the apparatus and for receiving pairs of first and second signal vector component digital signals coming from the signal vector components detector. The computer has a memory for storing the pairs of first and second signal vector component digital signals and for storing focusing function data, which is used by the computer to produce corresponding pairs of first and second resulting signal vector component digital signals forming a focused digital image representation of the object traversing ultrasonic waves.

Claims

1. An ultrasonic transmission imaging apparatus comprising:

ultrasonic emitter means for producing substantially continuous coherent ultrasonic waves toward an object to be inspected positioned in a detecting zone;

ultrasonic coupling means in contact with said object on opposed sides thereof, for providing transmission of said ultrasonic waves thereto, transfer of said ultrasonic waves therethrough, and transmission of object traversing ultrasonic waves out of said object;

scanning ultrasonic detectors array means comprising a plurality of ultrasonic detectors adapted to receive said object traversing ultrasonic waves for producing a plurality of successive series of electrical signals coming from said ultrasonic detectors, said electrical signals characterizing transmission of said ultrasonic waves through said object;

means for creating a scanning relative movement between said object to be inspected and said ultrasonic emitter means and scanning ultrasonic detectors array means, whereby said series of electrical signals respectively characterizes transmission of said ultrasonic waves through said object in a plurality of transmission planes substantially defined by said scanning ultrasonic detectors array means and a direction perpendicular thereto and to said emitter means as said object to be inspected is being displaced relative to said ultrasonic emitter means and scanning ultrasonic detectors array means, said series of electrical signals being respectively associated with a series of image elements;

dynamic focusing means for producing focused image element data from said series of electrical signals and associated with each one of said ultrasonic detectors, said focusing means phase shifting each one of said series of electrical signals in accordance with each location within said object to be imaged in focus for producing a composite image element.

2. An ultrasonic transmission imaging apparatus as claimed in claim 1, wherein said dynamic focusing means comprise:

signal vector components detector means adapted to receive said electrical signals, said signal vector components detector means detecting signal vector components for each of said electrical signals, to produce pairs of first and second signal vector component signals corresponding to said electrical signals;

computer means for controlling said apparatus and adapted to receive said pairs of first and second signal vector component signals, said computer having memory means for storing said pairs of first and second signal vector component signals and for storing focusing function data establishing, for each image element comprised in a focusing aperture comprising a plurality of juxtaposed image elements of said series of image elements, a phase displacement value relative to a reference phase value associated with a focal line passing through a focus point and a center of said aperture, said computer means using said focusing function data to produce corresponding pairs of first and second resulting signal vector component signals forming a focused image representation of said object traversing ultrasonic waves.

3. An ultrasonic transmission imaging apparatus as claimed in claim 2, wherein said signal vector component detector means include analog-to-digital converter means adapted to receive said pairs of first and second signal vector component signals for producing corresponding pairs of first and second signal vector component digital signals.

4. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said computer means resulting amplitude signals corresponding to said pairs of first and second resulting signal vector component digital signals, said apparatus further comprising display means adapted to receive said resulting amplitude signals to produce a visual display of said focused digital image representation of said object traversing ultrasonic waves.

5. An ultrasonic transmission imaging apparatus as claimed in claim 3, further comprising multiplexer means coupling said ultrasonic detector means with said signal vector components detector means, said computer means being connected to said multiplexer means for control thereof, said multiplexer means having a plurality of inputs respectively fed by each one of said electrical signals, said multiplexer means further having output through which each one of said electrical signals is sequentially transferred to said signal vector components detector means.

6. An ultrasonic transmission imaging apparatus as claimed in claim 5, wherein said multiplexer means is provided with preamplifier means for amplifying each one of said electrical signals prior transferring thereof to said signal vector components detector means.

7. An ultrasonic transmission imaging apparatus as claimed in claim 5, wherein said signal vector components detector means is a synchronous detector circuit comprising first and second multipliers having respective signal inputs coupled to said multiplexer means output and having respective reference inputs means, said synchronous detector circuit further comprising a reference signals generator means having first and second outputs means respectively connected to said respective reference inputs means provided on said first and second multipliers to respectively sent thereto a first reference signal and a second reference signal in phase quadrature with said first reference signal at a common operating frequency, said computer means being connected to said reference signals generator for control thereof, said first and second multiplier means further having respective outputs for respectively producing a first signal comprising a primary signal vector component and a second signal comprising a secondary quadrature phased signal vector component, said synchronous detector circuit further comprising first and second lowpass filters respectively coupled to said multiplier outputs and in series with respective first and second output amplifiers for producing at first and second outputs thereof said pairs of first and second signal vector component signals corresponding to said electrical signals, said computer means being connected to said output amplifiers for control thereof, said apparatus further comprising amplifier means coupled to a third output means provided on said reference signals generator means for receiving a driving reference signal to produce at an output thereof an amplified driving reference signal at said common operating frequency, said computer means being connected to said amplifier means for control thereof, said ultrasonic emitter means receiving said amplified driving reference signal at an input thereof for producing said continuous coherent ultrasonic waves.

8. An ultrasonic transmission imaging apparatus as claimed in claim 7, wherein said synchronous detector circuit further comprises an input amplifier coupling said first and second multipliers signal inputs with said multiplexer means output, said computer means being connected to said input amplifier means for control thereof, said input amplifier amplifying each one of said electrical signals prior sending thereof to said first and second multipliers signal inputs, said synchronous detector circuit further comprising first and second intermediate amplifier means for coupling said first and second lowpass filters respectively to said multiplier outputs.

9. An ultrasonic transmission imaging apparatus as claimed in claim 7, wherein said first and second reference signals are square wave reference signals, said apparatus further comprising a preamplifier in series with a bandpass filter for coupling said amplifier means to said third output means provided on said reference signals generator means.

10. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said computer means detects the presence of said object to be inspected apparently moving in said detecting zone prior producing said corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves.

11. An ultrasonic transmission imaging apparatus as claimed in claim 10, wherein said computer means detects the presence of said apparently moving object to be inspected in said detecting zone by deriving a mean intensity value for consecutive ones of said pairs of first and second signal vector component digital signals corresponding with at least one of said series of electrical signals coming from said ultrasonic detectors and by comparing said mean intensity value with a predetermined presence threshold value.

12. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said first and second signal vector component digital signals are respectively associated with a real component value and an imaginary component value, said computer means multiplying said component values of said first and second signal vector component digital signals with respective real component value and imaginary component value of a correction parameter prior using said focusing function data to produce a corrected signal vector, said correction parameter and said corrected signal vector being defined according to the following mathematical expressions:

##EQU11## wherein k and l are primary coordinates according to first and second axis X and Y of a cartesian reference system for the ultrasonic detector array and associated image elements, with k=0,K-1 and l=0,L-1;

A_k is the correction parameter associated with one of the image elements having coordinate k, this correction parameter compensating for detector sensibility variation among corresponding ones of the ultrasonic detectors;

AI_k is the real component value of the correction parameter associated with one of the image elements having coordinate k;

AQ_k is the imaginary component value of the correction parameter associated with one of the image elements having coordinate k;

T is a target parameter being characterized by a target uniform amplitude and phase values corresponding to a reference target image;

M_k is a mean value of sample pairs of first and second signal vector component signals associated with one of the image elements having coordinate k, prior detecting the presence of an object apparently moving in the detecting zone;

J is a predetermined number of said sample pairs of first and second signal vector component signals;

S_j,k is the signal vector of a sample j associated with one of said image elements having coordinate k;

SI_j,k is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector of a sample j associated with one of said image elements having coordinate k;

SQ_j,k is an imaginary component associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector of a sample j associated with one of said image elements having coordinate k;

C_k,l is a corrected signal vector associated with one of said image elements having coordinates k and l;

CI_k,l is a real component value associated with said first corrected signal vector component digital signals and corresponds to a real component value of said corrected signal vector associated with one of said image elements having coordinates k and l;

CQ_k,l is an imaginary component value associated with said second corrected signal vector component digital signals and corresponds to an imaginary component value of said corrected signal vector associated with one of the image elements having coordinates k and l;

B_k,l is the signal vector associated with one of said image elements having coordinates k and l;

BI_k,l is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k and l;

BQ_k,l is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k and l.

13. An ultrasonic transmission imaging apparatus as claimed in claim 12, wherein said computer means compares values of said correction parameter with a predetermined threshold value to detect corresponding unusable ones of said ultrasonic detectors, said computer means substitute for corresponding ones of said pairs of first and second signal vector component signals respective first and second signal vector component signals corresponding to proximate usable ones of said ultrasonic detectors.

14. An ultrasonic transmission imaging apparatus as claimed in claim 12, wherein said computer means applies a convolution technique to produce corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expressions:

##EQU12## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

D_k,l is the resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary component value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

C_k-m,l-n is the corrected signal vector associated with one of said image elements having coordinates k-m and l-n;

A_k-m is the correction parameter associated with one of said image elements having coordinate k-m;

B_k-m,l-n is the signal vector associated with one of said image elements having coordinates k-m and l-n;

BI_k-m,l-n is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

BQ_k-m,l-n is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n, is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n.

15. An ultrasonic transmission imaging apparatus as claimed in claim 14, wherein said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU13##

16. An ultrasonic transmission imaging apparatus as claimed in claim 14, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU14## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(wλ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.

17. An ultrasonic transmission imaging apparatus as claimed in claim 12, wherein said computer means derives a normalized focusing function data according to the following mathematical expressions:

##EQU15## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

said computer further applies a first Fourier transform operation on said normalized focusing function data L_m,n according to said coordinates k or l to produce transformed focusing function data in a spatial frequency domain, a second Fourier transform operation to values of said pairs of first and second corrected signal vector component digital signals according to said coordinates k or l to produce transformed signal vector component values in the spatial frequency domain, a multiplication of corresponding values of said transformed focusing function data and said transformed signal vector component values followed by an inverse Fourier Transform operation on the result thereof to produce said corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expression;

space="preserve" listing-type="equation">D.sub.k,l =DI.sub.k,l +iDQ.sub.k,l (

     16)

wherein;

D_k,l is a resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l.

18. An ultrasonic transmission imaging apparatus as claimed in claim 17, wherein said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU16##

19. An ultrasonic transmission imaging apparatus as claimed in claim 17, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU17## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(w,λ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.

20. An ultrasonic transmission imaging apparatus as claimed in claim 3, further comprising a plurality of multiplexers coupling said ultrasonic detector means output with said signal vector components detector means, said computer means being connected to said multiplexers for control thereof, each of said multiplexers having a plurality of inputs respectively fed by a plurality of said electrical signals, each of said multiplexers further having respective output through which each one of said plurality of said electrical signals is sequentially transferred to said signal vector components detector means.

21. An ultrasonic transmission imaging apparatus as claimed in claim 20, wherein each of said multiplexers is provided with preamplifier means for amplifying each one of said plurality of said electrical signals prior transferring thereof to said signal vector components detector means.

22. An ultrasonic transmission imaging apparatus as claimed in claim 20, wherein said signal vector components detector means comprises a plurality of synchronous detector circuits comprising first and second multipliers having respective signal inputs coupled to respective ones of said multiplexer outputs and having respective reference inputs means, said signal vector components detector means further comprising a reference signals generator means having first and second outputs means respectively connected to said reference inputs means provided on said first and second multipliers to respectively sent thereto an first reference signal and a second reference signal in phase quadrature with said first reference signal and at a common operating frequency, said computer means being connected to said reference signals generator means for control thereof, said first and second multiplier means further having respective outputs for respectively producing a first signal comprising a primary signal vector component and a second signal comprising a secondary quadrature phased signal vector component, each of said synchronous detector circuits further comprising first and second lowpass filters respectively coupled to said multiplier outputs and in series with first and second output amplifiers for producing at first and second outputs thereof said pairs of first and second signal vector component signals associated with a corresponding one of said plurality of said electrical signals, said computer means being connected to said output amplifiers for control thereof, said apparatus further comprising amplifier means coupled to a third output means provided on said reference signals generator means for receiving a driving reference signal to produce at an output thereof an amplified driving reference signal at said common operating frequency, said computer means being connected to said amplifier means for control thereof, said ultrasonic emitter means receiving said reference signal at an input thereof for producing said continuous coherent ultrasonic waves.

23. An ultrasonic transmission imaging apparatus as claimed in claim 20, wherein each of said synchronous detector circuits further comprises an input amplifier coupling said first and second multipliers signal inputs with a corresponding one of said multiplexer outputs, said computer means being connected to said input amplifier means for control thereof, said input amplifier means amplifying each one of said plurality of said electrical signals prior sending thereof to said first and second multipliers signal inputs, each of said synchronous detector circuits further comprising first and second intermediate amplifier means for coupling said first and second lowpass filters respectively to said multiplier outputs.

24. An ultrasonic transmission imaging apparatus as claimed in claim 20, wherein said first and second reference signals are square wave reference signals, said apparatus further comprising a preamplifier in series with a bandpass filter for coupling said amplifier means to either of said first or second reference generator outputs.

25. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said scanning ultrasonic detectors array means is a scanning ultrasonic detectors linear array.

26. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said scanning ultrasonic detectors array means is comprised of a plurality of scanning ultrasonic detectors arrays covering respective complementary portions of said detection zone.

27. An ultrasonic transmission imaging apparatus as claimed in claim 3, wherein said apparatus is used as a fish fillet imaging apparatus, said object being a fish fillet, said coupling means is a mass of water traversing said detecting zone and surrounding said fish fillet to be inspected, said means for creating a scanning relative movement between said object to be inspected and said ultrasonic emitter means and scanning ultrasonic detectors array means is a fish fillet transport unit for immersing said fish fillet to be inspected in said water mass and in said detecting zone and for bringing an inspected fish fillet out of said water mass toward an output provided on said transport unit, and wherein said apparatus further comprises:

a frame on which are mounted said ultrasonic emitter means, said scanning ultrasonic detectors array means and said fish fillet transport unit;

a main tank mounted on said frame containing said detecting zone and filled with said water mass, said ultrasonic emitter means and said scanning ultrasonic detectors array means being immersed in said water mass and being adjustably secured to said frame so as to be maintained in a stationary positioned within said main tank.

28. An ultrasonic imaging apparatus as claimed in claim 27, wherein said fish fillet transport unit comprises:

first conveyer means mounted at a first end of said fish fillet transport unit, said first conveyer means having an input end for receiving said fish fillet to be inspected, said first conveyer means immersing said fish fillet in said water mass and carrying said fish fillet toward an output end provided on said first conveyer means;

second conveyer means mounted in said main tank and totally immersed in said water mass, said second conveyer means having a first end extending over said first conveyer means output end and an output end, said main tank being provided with a plurality of first water feeding means tranversely extending therethrough and disposed from said first conveyer means output end and under said second conveyer means, said first water feeding means having first nozzle means projecting series of water jets toward said fish fillet to be inspected to move thereof from the vicinity of said first conveyer means output end to an underside surface of said second conveyer means, said main tank being provided with at least one second water feeding means tranversely extending therethrough under said second conveyer means output end, said second water feeding means having at least one second nozzle for projecting series of water jets toward said fish fillet to be inspected to propel thereof from the vicinity of said second conveyer means output end toward said detecting zone;

third conveyer means mounted at a second end of said fish fillet transport unit, said third conveyer means having an input end for receiving an inspected fish fillet as it comes out of said detecting zone, to bring said inspected fish fillet out of said water mass toward said transport unit output;

conveyer driving motor means coupled to said first, second and third conveyer means for driving thereof;

water supply means coupled to said first and second water feeding means for supplying under pressure said water thereto.

29. An ultrasonic imaging apparatus as claimed in claim 28, wherein said second conveyer means is a chain conveyer having an upper portion and a lower portion, said main tank is further provided with at least one third water feeding means tranversely extending therethrough between said upper portion and said lower portion in the vicinity of said second conveyer means output, said third water feeding means having at least one third nozzle means projecting series of water jets toward said fish fillet to be inspected to remove thereof from the underside surface of said second conveyer means at the vicinity of said output end thereof, said water supply means being coupled to said at least one third water feeding means for supplying under pressure said water thereto.

30. An ultrasonic imaging apparatus as claimed in claim 29, wherein said second water feeding means is further provided with respective valve means to control flow of said water therethrough.

31. An ultrasonic imaging apparatus as claimed in claim 28, wherein said fish fillet transport unit further comprises:

a filtration tank positioned at said fish fillet transport unit second end and under said third conveyer means output end, said filtration tank being in fluid communication with an outlet provided on said main tank to receive said water flowing out of said main tank, said filtration tank being provided with filter means to filter said water received from said main tank, said filtration tank having an outlet through which filtered water is flowing;

wherein said water supply means is a pump having an inlet coupled to said filtration tank outlet and an outlet coupled to said first, second and third water feeding means for supplying thereof with said filtered water.

32. An ultrasonic imaging apparatus as claimed in claim 28, wherein said first conveyer means comprises:

a feeding conveyer adapted to receive said fish fillet to be inspected at said first conveyer means input end for carrying said fish fillet to an output end provided on said feeding conveyer over said main tank and toward said water mass;

an immersing conveyer mounted in said main tank for receiving said fish fillet from said feeding conveyer, said immersing conveyer being totally immersed in said water mass to immerse said fish fillet therein and carrying said fish fillet toward an output end provided on said first conveyer means.

33. An ultrasonic imaging apparatus as claimed in claim 28, wherein said first water feeding means is further provided with respective valve means to control flow of said water therethrough.

34. An ultrasonic transmission imaging apparatus comprising:

ultrasonic emitter means for producing substantially continuous coherent ultrasonic waves toward an object to be inspected positioned in a detecting zone;

ultrasonic coupling means in contact with said object on opposed sides thereof, for providing transmission of said ultrasonic waves thereto, transfer of said ultrasonic waves therethrough, and transmission of object traversing ultrasonic waves out of said object;

a two-dimensional ultrasonic detectors array means comprising a plurality of rows of ultrasonic detectors disposed in a parallel relationship and adapted to receive said object traversing ultrasonic waves for producing a plurality of corresponding series of electrical signals coming from said ultrasonic detectors, said series of electrical signals respectively characterizing transmission of said ultrasonic waves through said object in a plurality of transmission planes substantially defined by said plurality of rows of ultrasonic detectors and a direction perpendicular thereto and to said emitter means, said series of electrical signals being respectively associated with series of image elements;

dynamic focusing means for producing focused image element data from said series of electrical signals and associated with each one of said ultrasonic detectors, said focusing means phase shifting each one of said series of electrical signals in accordance with each location within said object to be imaged in focus for producing a composite image.

35. An ultrasonic transmission imaging apparatus as claimed in claim 34, wherein said dynamic focusing means comprise:

signal vector components detector means adapted to receive said electrical signals, said signal vector components detector means detecting signal vector components for each of said electrical signals, to produce pairs of first and second signal vector component signals corresponding to said electrical signals;

computer means for controlling said apparatus and adapted to receive said pairs of first and second signal vector component signals, said computer having memory means for storing said pairs of first and second signal vector component signals and for storing focusing function data establishing, for each image element comprised in a focusing aperture comprising a plurality of juxtaposed image elements of said series of image elements, a phase displacement value relative to a reference phase value associated with a focal line passing through a focus point and a center of said aperture, said computer means using said focusing function data to produce corresponding pairs of first and second resulting signal vector component signals forming a focused image representation of said object traversing ultrasonic waves.

36. An ultrasonic transmission imaging apparatus as claimed in claim 35, wherein said signal vector component detector means include analog-to-digital converter means adapted to receive said pairs of first and second signal vector component signals for producing corresponding pairs of first and second signal vector component digital signals.

37. An ultrasonic transmission imaging apparatus as claimed in claim 36, wherein said computer means resulting amplitude signals corresponding to said pairs of first and second resulting signal vector component digital signals, said apparatus further comprising display means adapted to receive said resulting amplitude signals and to produce a visual display of said digital image representation of said object traversing ultrasonic waves.

38. An ultrasonic transmission imaging apparatus as claimed in claim 36, further comprising multiplexer means coupling said ultrasonic detector means output with said signal vector components detector means, said computer means being connected to said multiplexer means for control thereof, said multiplexer means having a plurality of inputs respectively fed by each one of said electrical signals, said multiplexer means further having output through which each one of said electrical signals is sequentially transferred to said signal vector components detector means.

39. An ultrasonic transmission imaging apparatus as claimed in claim 38, wherein said multiplexer means is provided with preamplifier means for amplifying each one of said electrical signals prior transferring thereof to said signal vector components detector means.

40. An ultrasonic transmission imaging apparatus as claimed in claim 38, wherein said signal vector component detector means is a synchronous detector circuit comprising first and second multipliers having respective signal inputs coupled to said multiplexer means output and respective reference inputs means, said synchronous detector circuit further comprising a reference signals generator means having first and second output means respectively connected to said reference input means provided on said first and second multipliers to respectively sent thereto a first reference signal and a second reference signal in phase quadrature with said first reference signal at a common operating frequency, said computer means being connected to said reference signals generator for control thereof, said first and second multiplier means further having respective outputs for respectively producing a first signal comprising an primary signal vector component and a second signal comprising a secondary quadrature phased signal vector component, said synchronous detector circuit further comprises first and second lowpass filters respectively coupled to said multiplier outputs and in series with respective first and second output amplifiers for producing at first and second outputs thereof said pairs of first and second signal vector component signals corresponding to said electrical signals, said computer means being connected to said output amplifiers for control thereof, said apparatus further comprising amplifier means coupled to a third output means provided on said reference signals generator means for receiving a driving reference signal to produce at an output thereof an amplified driving reference signal at said common operating frequency, said computer means being connected to said amplifier means for control thereof, said ultrasonic emitter means receiving said amplified driving reference signal at an input thereof for producing said continuous coherent ultrasonic waves.

41. An ultrasonic transmission imaging apparatus as claimed in claim 40, wherein said synchronous detector circuit further comprises an input amplifier coupling said first and second multipliers signal inputs with said multiplexer means output, said computer means being connected to said input amplifier means for control thereof, said input amplifier means amplifying each one of said electrical signals prior sending thereof to said first and second multipliers signal inputs, said synchronous detector circuit further comprising first and second intermediate amplifier means for coupling said first and second lowpass filters respectively to said multiplier outputs.

42. An ultrasonic transmission imaging apparatus as claimed in claim 40, wherein said first and second reference signals are square wave reference signals, said apparatus further comprising a preamplifier in series with a bandpass filter for coupling said amplifier means to said third output means provided on said reference signals generator means.

43. An ultrasonic transmission imaging apparatus as claimed in claim 36, wherein said computer means detects the presence of said object to be inspected in said detecting zone prior producing said corresponding pairs of first and second resulting signal vector component digital signals forming said digital image representation of said object traversing ultrasonic waves.

44. An ultrasonic transmission imaging apparatus as claimed in claim 43, wherein said computer means detect the presence of an object to be inspected in said detecting zone by deriving a mean intensity value for a plurality of said pairs of first and second signal vector component digital signals corresponding with a plurality of said electrical signals coming from said ultrasonic detectors and by comparing said mean intensity value with a predetermined presence threshold value.

45. An ultrasonic transmission imaging apparatus as claimed in claim 36, wherein said first and second signal vector component digital signals are respectively associated with a real component value and an imaginary component value, said computer means multiplying said components values of said first and second signal vector component digital signals with respective real component value and imaginary component value of a correction parameter prior using said focusing function data to produce a corrected signal vector, said correction parameter and said corrected signal vector being defined according to the following mathematical expressions:

##EQU18## wherein k and l are primary coordinates according to first and second axis X and Y of a cartesian reference system for the ultrasonic detector array and associated image elements, with k=0,K-1 and l=0,L-1;

A_k,l is the correction parameter associated with one of the image elements having coordinates k and l, this correction parameter compensating for detector sensibility variation among corresponding ones of the ultrasonic detectors;

AI_k,l is the real component value of the correction parameter associated with one of the image elements having coordinate k;

AQ_k is the imaginary component value of the correction parameter associated with one of the image elements having coordinates k and l;

T is a target parameter being characterized by a target uniform amplitude and phase values corresponding to a reference target image;

M_k,l is a mean value of sample pairs of first and second signal vector component signals associated with one of the image elements having coordinates k and l, prior detecting the presence of an object apparently moving in the detecting zone;

J is a predetermined number of said sample pairs of first and second signal vector component signals;

S_j,k,l is the signal vector of a sample j associated with one of said image elements having coordinates k and l;

SI_j,k,l is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector of a sample j associated with one of said image elements having coordinates k and l;

SQ_j,k,l is an imaginary component associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector of a sample j associated with one of said image elements having coordinates k and l;

C_k,l is a corrected signal vector associated with one of said image elements having coordinates k and l;

CI_k,l is a real component value associated with said first corrected signal vector component digital signals and corresponds to a real component value of said corrected signal vector associated with one of said image elements having coordinates k and l;

CQ_k,l is an imaginary component value associated with said second corrected signal vector component digital signals and corresponds to an imaginary component value of said corrected signal vector associated with one of the image elements having coordinates k and l;

B_k,l is the signal vector associated with one of said image elements having coordinates k and l;

BI_k,l is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k and l;

BQ_k,l is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k and l.

46. An ultrasonic transmission imaging apparatus as claimed in claim 45, wherein said computer means compares values of said correction parameter with a predetermined correction threshold value to detect corresponding unusable ones of said ultrasonic detectors, said computer means substitute for corresponding ones of said pairs of first and second signal vector component signals respective first and second signal vector component signals corresponding to proximate usable ones of said ultrasonic detectors.

47. An ultrasonic transmission imaging apparatus as claimed in claim 46, wherein said computer means applies a convolution technique to produce corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expressions:

##EQU19## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

D_k,l is a resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary component value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

C_k-m,l-n is the corrected signal vector associated with one of said image elements having coordinates k-m and l-n;

A_k-m is the correction parameter associated with one of said image elements having coordinate k-m;

B_k-m,l-n is the signal vector associated with one of said image elements having coordinates k-m and l-n;

BI_k-m,l-n is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

BQ_k-m,l-n is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

48. An ultrasonic transmission imaging apparatus as claimed in claim 47, wherein said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU20##

49. An ultrasonic transmission imaging apparatus as claimed in claim 47, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU21## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(w,λ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.

50. An ultrasonic transmission imaging apparatus as claimed in claim 45, wherein said computer means derives a normalized focusing function data according to the following mathematical expressions:

##EQU22## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

said computer further applies a first Fourier transform operation on said normalized focusing function data L_m,n according to said coordinates k or l to produce transformed focusing function data in a spatial frequency domain, a second Fourier transform operation to values of said pairs of first and second corrected signal vector component digital signals according to said coordinates k or l to produce transformed signal vector component values in the spatial frequency domain, a multiplication of corresponding values of said transformed focusing function data and said transformed signal vector component values followed by an inverse Fourier Transform operation on the result thereof to produce said corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expression;

space="preserve" listing-type="equation">D.sub.k,l =DI.sub.k,l +iDQ.sub.k,l (

     16)

wherein;

D_k,l is a resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l.

51. An ultrasonic transmission imaging apparatus as claimed in claim 50, when said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU23##

52. An ultrasonic transmission imaging apparatus as claimed in claim 50, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU24## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(w,λ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.

53. An ultrasonic transmission imaging apparatus as claimed in claim 36, further comprising a plurality of multiplexers coupling said ultrasonic detector means output with said signal vector components detector means, said computer means being connected to said multiplexers for control thereof, each of said multiplexers having a plurality of inputs respectively fed by a plurality of said electrical signals, each of said multiplexers further having respective output through which each one of said plurality of said electrical signals is sequentially transferred to said signal vector components detector means.

54. An ultrasonic transmission imaging apparatus as claimed in claim 53, wherein each of said multiplexers is provided with preamplifier means for amplifying each one of said plurality of said electrical signals prior transferring thereof to said signal vector components detector means.

55. An ultrasonic transmission imaging apparatus as claimed in claim 53, wherein said signal vector components detector means comprises a plurality of synchronous detector circuits comprising first and second multipliers having respective signal inputs coupled to respective ones of said multiplexer outputs and having respective reference inputs means, said signal vector components detector means further comprising a reference signals generator means having first and second output means respectively connected to said reference inputs provided on said first and second multipliers to respectively sent thereto a first reference signal and a second reference signal in phase quadrature with said first reference signal at a common operating frequency, said computer means being connected to said reference signals generator means for control thereof, said first and second multiplier means further having respective outputs for respectively producing a first signal comprising a primary signal vector component and a second signal comprising a secondary quadrature phased signal vector component, each of said synchronous detector circuits further comprising first and second lowpass filters respectively coupled to said multiplier outputs and in series with first and second output amplifiers for producing at first and second outputs thereof said pairs of first and second signal vector component signals associated with a corresponding one of said plurality of said electrical signals, said computer means being connected to said output amplifiers for control thereof, said apparatus further comprising amplifier means coupled to a third output means provided on said reference signals generator means for receiving a driving reference signal to produce at an output thereof an amplified driving reference signal at said common operating frequency, said ultrasonic emitter means receiving said amplified driving reference signal at an input thereof for producing said continuous coherent ultrasonic waves.

56. An ultrasonic transmission imaging apparatus as claimed in claim 55, wherein each of said synchronous detector circuits further comprises an input amplifier coupling said first and second multipliers signal inputs with a corresponding one of said multiplexer outputs, said computer means being connected to said input amplifier means for control thereof, said input amplifier means amplifying each one of said plurality of said electrical signals prior sending thereof to said first and second multipliers signal inputs, each of said synchronous detector circuits further comprising first and second intermediate amplifier means for coupling said first and second lowpass filters respectively to said multiplier outputs.

57. An ultrasonic transmission imaging apparatus as claimed in claim 55, wherein said first and second reference signals are square wave reference signals, said apparatus further comprising a preamplifier in series with a bandpass filter for coupling said amplifier means to either of said first or second reference generator outputs.

58. An ultrasonic transmission imaging apparatus as claimed in claim 36, wherein said two-dimensional ultrasonic detectors array means is comprised of a plurality of two-dimensional ultrasonic detectors arrays covering respective complementary portions of said detection zone.

59. An ultrasonic transmission imaging method comprising steps of:

(i) producing substantially continuous coherent ultrasonic waves toward an object to be inspected positioned in a detecting zone;

(ii) providing transmission of said ultrasonic waves to said object to be inspected, transfer of said ultrasonic waves therethrough, and transmission of object traversing ultrasonic waves out of said object;

(iii) receiving said object traversing ultrasonic waves and producing a plurality of series of electrical signals characterizing transmission of said ultrasonic waves through said object in a plurality of transmission planes, said series of electrical signals being respectively associated with series of image elements;

(iv) detecting signal vector components for each of said electrical signals and producing pairs of first and second signal vector component signals corresponding to said electrical signals;

(v) digitally converting said pairs of first and second signal vector component signals and producing corresponding pairs of first and second signal vector component digital signals;

(vi) providing focusing function data establishing, for each image element comprised in a focusing aperture comprising a plurality of juxtaposed image elements of said series of image elements, a phase displacement value relative to a reference phase value associated with a focal line passing through a focus point and a center of said aperture; and

(vii) using said focusing function data to produce corresponding pairs of first and second resulting signal vector component digital signals forming focused digital image elements representative of said object.

60. An ultrasonic transmission imaging method as claimed in claim 59, wherein after said step (vii) there are provided steps of:

(a) producing resulting amplitude signals corresponding to said pairs of first and second resulting signal vector component digital signals; and

(b) producing a visual display of said digital image representation of said object traversing ultrasonic waves.

61. An ultrasonic transmission imaging method as claimed in claim 59, wherein after said step (v) there is provided a step of:

(a) detecting the presence of said object to be inspected apparently moving in said detecting zone.

62. An ultrasonic transmission imaging method as claimed in claim 61 wherein said step (a) is carried out by deriving a mean intensity value for consecutive ones of said pairs of first and second signal vector component digital signals corresponding with said electrical signals and by comparing said mean intensity value with a predetermined presence threshold value.

63. An ultrasonic transmission method as claimed in claim 61, wherein said first and second signal vector component digital signals are respectively associated with a real component value and an imaginary component value and wherein after said step (a) there is provided steps of:

(b) providing a correction parameter defined according to the following mathematical expressions;

##EQU25## wherein k and l are primary coordinates according to first and second axis X and Y of a cartesian reference system for the ultrasonic detector array and associated image elements, with k=0,K-1 and l=0,L-1;

A_k,l is the correction parameter associated with one of the image elements having coordinates k and l, this correction parameter compensating for detector sensibility variation among corresponding ones of the ultrasonic detectors;

AI_k,l is the real component value of the correction parameter associated with one of the image elements having coordinates k and l;

AQ_k,l is the imaginary component value of the correction parameter associated with one of the image elements having coordinates k and l;

T is a target parameter being characterized by a target uniform amplitude and phase values corresponding to a reference target image;

M_k,l is a mean value of sample pairs of first and second signal vector component signals associated with one of the image elements having coordinates k and l, prior detecting the presence of an object apparently moving in the detecting zone;

J is a predetermined number of said sample pairs of first and second signal vector component signals;

S_j,k,l is the signal vector of a sample j associated with one of said image elements having coordinates k and l;

SI_j,k,l is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector of a sample j associated with one of said image elements having coordinates k and l;

SQ_j,k,l is an imaginary component associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector of a sample j associated with one of said image elements having coordinates k and l; and

(c) multiplying said component values of said first and second signal vector component digital signals with respective real component value and imaginary component value of said correction parameter to produce a corrected signal vector according to the following mathematical expressions;

space="preserve" listing-type="equation">C.sub.k,l =A.sub.k,l B.sub.k,l =CI.sub.k,l +iCQ.sub.CQ.sub.k,l(

     7)

space="preserve" listing-type="equation">B.sub.k,l =BI.sub.k,l +iBQ.sub.k,l (

     8)

wherein

C_k,l is the corrected signal vector associated with one of said image elements having coordinates k and l;

CI_k,l is a real component value associated with said first corrected signal vector component digital signals and corresponds to a real component value of said corrected signal vector associated with one of said image elements having coordinates k and l;

CQ_k,l is an imaginary component value associated with said second corrected signal vector component digital signals and corresponds to an imaginary component value of said corrected signal vector associated with one of the image elements having coordinates k and l;

B_k,l is the signal vector associated with one of said image elements having coordinates k and l;

BI_k,l is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k and l; and

BQ_k,l is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k and l.

64. An ultrasonic transmission imaging method as claimed in claim 63, wherein after said step (b) there is provided the step of:

(d) comparing values of said correction parameter with a predetermined correction threshold value to detect corresponding unusable ones of said electrical signals; and

(e) substituting for corresponding ones of said pairs of first and second signal vector component signals respective first and second signal vector component signals corresponding to proximate usable ones of said ultrasonic detectors.

65. An ultrasonic transmission imaging method as claimed in claim 63, wherein said step (vii) is carried out by applying a convolution technique to produce corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expressions:

##EQU26## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

D_k,l is the resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary component value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

C_k-m,l-n is the corrected signal vector associated with one of said image elements having coordinates k-m and l-n;

A_k-m,l-n is the correction parameter associated with one of said image elements having coordinates k-m and l-n;

B_k-m,l-n is the signal vector associated with one of said image elements having coordinates k-m and l-n;

BI_k-m,l-n is a real component value associated with said first signal vector component digital signals and corresponds to the real component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

BQ_k-m,l-n is an imaginary component value associated with said second signal vector component digital signals and corresponds to the imaginary component value of said signal vector associated with one of said image elements having coordinates k-m and l-n;

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n.

66. An ultrasonic transmission imaging method as claimed in claim 65, wherein said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU27##

67. An ultrasonic transmission imaging method as claimed in claim 65, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU28## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(w,λ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.

68. An ultrasonic transmission imaging method as claimed in claim 63, wherein after said step (vi) there are provided the steps of:

(c) providing a normalized focusing function data according to the following mathematical expressions;

##EQU29## wherein;

m and n are secondary coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detector array and associated image elements, with m=-M,M and n=-N,N, the size of said focusing function data being equal to (2M+1)(2N+1);

L_m,n is a normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LI_m,n is a real component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

LQ_m,n is an imaginary component value of said normalized focusing function data corresponding to one of said image elements having coordinates m and n;

L_norm is a focusing function normalization parameter;

LI_norm is a real component value of said focusing function normalization parameter;

LQ_norm is an imaginary component value of said focusing function normalization parameter;

F_m,n is the focusing function data corresponding to one of said image elements having coordinates m and n;

FI_m,n is a real component value of said focusing function data corresponding to one of said image elements having coordinates m and n;

FQ_m,n is an imaginary component value of said focusing function data corresponding to one of said image elements having coordinates m and n; and

wherein said step (vii) is carried out by steps of;

(d) applying a first Fourier transform operation on said normalized focusing function data L_m,n according to said coordinates k or l to produce transformed focusing function data in a spatial frequency domain;

(e) applying a second Fourier transform operation to values of said pairs of first and second corrected signal vector component digital signals according to said coordinates k or l to produce transformed signal vector component values in the spatial frequency domain;

(f) multiplying corresponding values of said transformed focusing function data by said transformed signal vector component values;

(g) applying an inverse Fourier Transform operation on the result of said multiplication step (f) to produce said corresponding pairs of first and second resulting signal vector component digital signals forming said focused digital image representation of said object traversing ultrasonic waves according to the following mathematical expression;

space="preserve" listing-type="equation">D.sub.k,l =DI.sub.k,l +iDQ.sub.k,l (

     16)

wherein;

D_k,l is a resulting signal vector associated with one of said image elements having coordinates k and l;

DI_k,l is a real component value of said first resulting signal vector component digital signals and corresponds to a real component value of said resulting signal vector associated with one of said image elements having coordinates k and l;

DQ_k,l is an imaginary value of said second resulting signal vector component digital signals and corresponds to an imaginary component value of said resulting signal vector associated with one of said image elements having coordinates k and l.

69. An ultrasonic transmission imaging method as claimed in claim 68, wherein said normalization parameter L_norm can be derived according to the following mathematical expression:

##EQU30##

70. An ultrasonic transmission imaging method as claimed in claim 68, wherein said focusing function data further establishes, for each image element comprised in said focusing aperture, an amplitude displacement value relative to a reference amplitude value associated with said focal line, said focusing function data F_m,n being derived according to the following mathematical expressions:

##EQU31## wherein;

x_m and y_n are physical position coordinates according to first and second axis X and Y of the cartesian reference system for said ultrasonic detectors array and associated image elements, and associated with one of said image elements having coordinates m and n;

K(w,λ

,z) is a wave propagation damping factor;

dx is physical dimension along X axis of said image elements

dy is physical dimension along Y axis of said image elements

w is a desired image resolution;

λ

is the wavelength of the ultrasonic waves;

z is the distance between said focus point and a nearest one of said ultrasonic detectors.