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WO1998055882A1 - Systeme d'imagerie presentant une mise au point residuelle numerique - Google Patents

Systeme d'imagerie presentant une mise au point residuelle numerique Download PDF

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Publication number
WO1998055882A1
WO1998055882A1 PCT/NL1998/000330 NL9800330W WO9855882A1 WO 1998055882 A1 WO1998055882 A1 WO 1998055882A1 NL 9800330 W NL9800330 W NL 9800330W WO 9855882 A1 WO9855882 A1 WO 9855882A1
Authority
WO
WIPO (PCT)
Prior art keywords
image
fourier
processor
designed
medium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/NL1998/000330
Other languages
English (en)
Dutch (nl)
Inventor
Augustinus Johannes Berkhout
Maurits Sebastiaan Van Der Heiden
Leo Ongkiehong
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Stichting voor de Technische Wetenschappen STW
Original Assignee
Stichting voor de Technische Wetenschappen STW
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Stichting voor de Technische Wetenschappen STW filed Critical Stichting voor de Technische Wetenschappen STW
Priority to AU80402/98A priority Critical patent/AU8040298A/en
Publication of WO1998055882A1 publication Critical patent/WO1998055882A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
    • G01S15/8977—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging

Definitions

  • the present invention relates to a device for forming an image of an object, comprising: - transmitting means for generating and transmitting a transmitted beam having a certain transmitted-beam property to a medium; receiving means for receiving echo signals caused by the medium within a received beam having a certain received-beam property; conversion means for converting the echo signals into incoming electrical signals; a processor which is connected to the conversion means and is designed to receive the incoming electrical signals and to transform the transmitted beam and the received beam, respectively, into a virtual transmitted beam of a predetermined desired shape and a virtual received beam of a predetermined shape, respectively, for the formation of an image.
  • Ultrasonic imaging systems use transducers for generating and registering acoustic waves.
  • imaging systems have separate transmitting transducers and receiving transducers.
  • the transmitting transducers generate a high- frequency acoustic wave which irradiates the medium, which, in medical applications, may be tissue.
  • the acoustic wave is reflected by acoustic inhomogeneities.
  • the receiving transducer detects the reflected signal and converts it into electrical signals, which can be made visible.
  • the transmitting transducer and receiving transducer form one unit and reference is made to "single-transducer pulse echo measurements".
  • the medium is irradiated differently during each measurement and an image is obtained by combining and visualizing all the measured signals.
  • Imaging with a high resolution means the formation of an image with a high separation power, both radially and axially.
  • High axial resolution means that, viewed from the transducer, inhomogeneities just behind one another can be distinguished.
  • High radial resolution means that, viewed from the transducer, inhomogeneities just next to one another can be imaged separately.
  • a high axial resolution is generally achieved by irradiating the medium with a short acoustic pulse. Spectrally, this means that the transmitting transducer has to generate a broad-band acoustic pulse.
  • a high radial resolution is generally achieved by keeping the width of the generated beams of the transmitting and receiving transducers as small as possible in a focal zone.
  • a focusing beam having one fixed focus has the shape of an "hourglass" which is narrowest in the focal zone.
  • the focus does not have infinitely small dimensions.
  • punctiform particles at the focus undergo a widening. Particles outside the focal zone are spread out still more severely.
  • the above applies not only to ultrasonic imaging systems, but to all types of imaging systems in which use is made either of sound or of electromagnetic radiation.
  • the present invention therefore relates to all such imaging systems.
  • the present invention proposes a device for forming an image of an object as defined above, which device is characterized in that the processor is designed to apply at least one spatial phase adjustment during the transformation for the formation of the image.
  • the invention therefore applies at least one spatial phase matching.
  • the beam shape in the entire space can be adjusted more satisfactorily in calculating the image. As a result, a more accurate image can be obtained.
  • the application of spatial phase adjustment proves to be faster in the sense that a mathematically desired shape of the beams can be obtained more quickly.
  • the invention relates to a device as defined above and which is characterized in that the spatial phase adjustment takes place as a component of a residual focusing process according to:
  • P is the Fourier transform of an unprocessed image
  • r m is the residual Fourier-transformed focusing result for a time value t m
  • F m is a Fourier-transformed focusing operator which is given by
  • Am amplitude factor
  • k x wave number
  • ⁇ angular frequency
  • c wave velocity
  • z r z 0 distance between focus and transmitting means.
  • a device avoids dynamic focusing during the measuring process and focusing takes place virtually both in transmission and reception after the measuring process, namely during the processing of the incoming electrical signals by the processor.
  • the physical imaging system can remain robust and simple.
  • use is made of the high power and flexibility of modern processors.
  • an image can be obtained which has high resolution at all levels of depth.
  • the virtual transmitted beam and/or the virtual received beam have a constant cross-section.
  • the cross-section of the beams may be circular or ellipsoidal, or have any other desired shape.
  • the cross-section of the said virtual beams is preferably chosen to be as small as possible, the minimum size depending on the transducer(s) used and the frequency content of the transmitted signal.
  • the shape of the beam(s) must be known to the processor.
  • the shape of the beam(s) may be derived, for example, analytically by the processor on the basis of data relating to the type of transducer(s) used.
  • the shape of the beam(s) can be measured in one plane in the medium. With the aid of wave theory, the entire three-dimensional shape of the beam(s) can then be determined unambiguously.
  • the measurement of the shape of the beam(s) has the advantage that deviations of the transducer(s) are automatically allowed for in the measurement process.
  • the processor is designed to perform a lateral deconvolution process on the image, which deconvolution process depends on the distance in the medium from the imaging system and which deconvolution process yields a filtered image.
  • the operations performed by the processor preferably take place in the Fourier domain.
  • the lateral deconvolution process can be replaced by a simple multiplication process.
  • the processor is therefore designed to perform the following processing steps on the image: a. calculation of the Fourier transform of the image; b. performance of lateral deconvolution on the Fourier-transformed image as a multiplication process in the Fourier domain; c. performance of an inverse Fourier transformation on the result of step b.
  • the transmitted beam will have too long a pulse shape.
  • the processor is also designed to perform a temporal deconvolution step so that the pulse shape in the filtered image is shortened in time. This results in a higher axial resolution.
  • the present invention is not restricted to a device.
  • the invention also relates to a method for forming an image of an object, comprising:
  • Figure 1 shows a beam generated by a focusing transducer in an arrangement known per se
  • Figure 2 shows a diagrammatic image of six fully reflecting point diffractors, such as are produced by an imaging system having one fixed focus, such as is also known per se;
  • FIG. 3 shows a diagram for the more detailed illustration of the invention.
  • Ultrasonic imaging systems use transmitting and receiving transducers for generating and registering acoustic waves.
  • the essence of the invention will be explained below by reference to an acoustic pulse-echo imaging system in which use is made of a transmitted/received beam having an "hourglass shape" with one focus.
  • the shape of the beam may be any one, provided it is known to the processor 4 (see Figure 3) of the system.
  • Figure 1 shows a transmitting transducer 1 which generates a beam B + in an axis system in which the lateral positions are indicated by r and the axial positions are indicated by z.
  • the origin of the beam B 1 emitted by the transducer 1 is situated at the position (r k ,z 0 ).
  • the transmitting transducer 1 shown generates a focusing beam B', whose focus is situated at position (r k ,z f ).
  • a focusing beam B + having a fixed focus has the shape of an "hourglass" which is narrowest in the focus zone at a distance z r z 0 from the transmitting transducer 1, as shown in Figure 1.
  • electromechanical or electrical measures are taken in order to displace the position of the focus of the beam during the measurement process.
  • the process the mathematical formulation
  • the effective beam of the transmission/reception combination is given by the product of the two beams.
  • Any image P at position (r, ⁇ 0 ) can be represented as the summation of images P m (r,z 0 ) due to all the point diffractions in all the planes z m :
  • R + (r k ,z m ,co) represents the reflectivity distribution for depth level z m .
  • Formula 2a represents a lateral convolution process
  • the function G m has the smallest width and this depends on the dimensions, the shape and the frequency range of the transducer(s). Outside the focal zone, G m becomes wider as a consequence of a wave-propagation-dependent spreading. Said spreading is not transducer-dependent and can be calculated from wave theory if G m is known at only one z-plane.
  • Filter process (3) means the application of a depth-dependent lateral deconvolution process to the measured image:
  • G ⁇ (r, ⁇ ) represents a narrow depth-independent beam which can be termed a "pencil beam”.
  • the filter F m could also shorten the time pulse (temporal deconvolution) and/or alter the shape of the beam at the focus, for example virtually reduce the intensity of side lobes and narrow the width of the main lobe:
  • S 0 ( ⁇ ) represents the resulting pulse after the optional temporal "pulse shaping” process and GO(r, ⁇ ) represents the resulting beam after the optional lateral "beam shaping” process.
  • Result (4b) represents the result of an integrated hybrid imaging process which simulates a virtual imaging system having a narrow depth-independent beam ("pencil beam”), a variable focus being simulated, as it were, during transmission and reception with the aid of numerical methods.
  • pencil beam narrow depth-independent beam
  • the invention is now explained further by reference to an example with reference to Figure 3.
  • an analog electrical signal is generated which is fed to an A/D converter 3.
  • the digitized output signal of the A/D converter 3 is fed to a digital processor 4.
  • the physical imaging system 2 may be any known imaging system.
  • the A/D converter 3 and the digital processor 4 can also be commercially obtainable instruments.
  • Figure 3 indicates, with the aid of an ellipsoidal line 5 that the physical imaging system 3 gives a "rough" image.
  • Said image is an image which can be obtained using systems according to the prior art.
  • Another ellipsoidal line 6 indicates diagrammatically that the digital processor 4 is programmed so that an image having high resolution is obtained.
  • the digital processor is provided with a program which uses the theory given above.
  • the digital processor 4 comprises residual focusing operators which are associated with the filter process F m (r,z 0 , ⁇ ).
  • the rough image is treated with said operators (lateral deconvolution) to obtain a result having an unprecedentedly high separation capability which results in a completely variable focus during transmission and reception.
  • F m is the Fourier-transformed focusing operator which is given by
  • both the amplitude and the phase of the "rough" image can be adjusted mathematically.
  • the phase itself can be adjusted in a depth-dependent manner, which promotes the accuracy and speed.
  • ⁇ angular frequency
  • B + (r,z;r k ,z 0 ; ⁇ ) transmitted beam at position (r,z) due to transmitting transducer at position (r k ,z 0 ) having angular frequency ⁇
  • B " (r.,z 0 ,r,z; ⁇ ) received beam at position (r,z) due to receiving transducer at position (r.,z 0 ) having angular frequency ⁇ ;
  • P 0 (r,z 0 , ⁇ ) image after depth-dependent lateral deconvolution of P(r,z 0 , ⁇ );
  • G ⁇ (r, ⁇ ) narrow depth-independent beam (pencil beam) as a function of r and ⁇ ;
  • F m (r,z 0 , ⁇ ) filter process to make the depth-dependent beam G_(,(r,z 0 , ⁇ ) into a depth-independent beam G ⁇ (r, ⁇ ).

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Acoustics & Sound (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

Procédé et dispositif servant à créer l'image d'un objet, ce qui consiste à: générer et transmettre un faisceau d'émission (B+) à un milieu; recevoir des signaux d'écho provoqués par le milieu à l'intérieur d'un faisceau de réception (B-); convertir les signaux d'écho en signaux électriques d'arrivée; traiter ces signaux électriques d'arrivée afin d'obtenir une image (P(r,z¿0?,φ); p(x,t), P(kxφ)); le faisceau d'émission et le faisceau de réception étant respectivement transformés en un faisceau virtuel d'émission présentant une forme prédéterminée et en un faisceau virtuel de réception présentant une forme prédéterminée, afin de créer l'image (P(r,z0,φ); p(x,t), P(kx,φ)) et au moins un réglage spatial de phase étant appliqué pendant la transformation.
PCT/NL1998/000330 1997-06-04 1998-06-04 Systeme d'imagerie presentant une mise au point residuelle numerique Ceased WO1998055882A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU80402/98A AU8040298A (en) 1997-06-04 1998-06-04 Imaging system having numerical residual focusing

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1006229 1997-06-04
NL1006229A NL1006229C2 (nl) 1997-06-04 1997-06-04 Afbeeldsysteem met numerieke residuele focussering.

Publications (1)

Publication Number Publication Date
WO1998055882A1 true WO1998055882A1 (fr) 1998-12-10

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AU (1) AU8040298A (fr)
NL (1) NL1006229C2 (fr)
WO (1) WO1998055882A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6679847B1 (en) 2002-04-30 2004-01-20 Koninklijke Philips Electronics N.V. Synthetically focused ultrasonic diagnostic imaging system for tissue and flow imaging
JP2012071090A (ja) * 2009-11-17 2012-04-12 Canon Inc 画像形成装置及び画像形成方法

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4063549A (en) * 1975-12-22 1977-12-20 Technicon Instruments Corporation Ultrasonic method and apparatus for imaging and characterization of bodies

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4063549A (en) * 1975-12-22 1977-12-20 Technicon Instruments Corporation Ultrasonic method and apparatus for imaging and characterization of bodies

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
LIU C N ET AL: "Digital processing for improvement of ultrasonic abdominal images", IEEE TRANSACTIONS ON MEDICAL IMAGING, JUNE 1983, USA, vol. MI-2, no. 2, ISSN 0278-0062, pages 66 - 75, XP002054887 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6679847B1 (en) 2002-04-30 2004-01-20 Koninklijke Philips Electronics N.V. Synthetically focused ultrasonic diagnostic imaging system for tissue and flow imaging
US7448998B2 (en) 2002-04-30 2008-11-11 Koninklijke Philips Electronics, N.V. Synthetically focused ultrasonic diagnostic imaging system for tissue and flow imaging
CN100528089C (zh) * 2002-04-30 2009-08-19 皇家飞利浦电子股份有限公司 用于组织和血流成像的合成聚焦的超声诊断成像系统
JP2012071090A (ja) * 2009-11-17 2012-04-12 Canon Inc 画像形成装置及び画像形成方法

Also Published As

Publication number Publication date
NL1006229C2 (nl) 1998-12-07
AU8040298A (en) 1998-12-21

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