Apparatus and method for the imaging of the internal structure of a three-dimensional solid and/or liquid object

• US 4,077,253 A
• Filed: 04/30/1975
• Issued: 03/07/1978
• Est. Priority Date: 06/01/1973
• Status: Expired due to Term

• Current Assignee: Ronald D. Grisell
• Original Assignee: Ronald D. Grisell
• Inventors: Grisell, Ronald D.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Beauchamp, John P.
• Application Number:
  US05/573,044
• Time in Patent Office: 1,042 Days
• Field of Search: 73/67.5 H, 73/67.5 R, 73/67.8 R, 350/3.5, 340/5 MP
• US Class Current: 73/606
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: A61B 8/0816 using echo-encephalography
• CPC Class Codes: G01H 3/125 for representing acoustic field distribution using optical means G01H9/002; sonar systems for imaging G01S7/56, G01S15/89; acoustic holography G03H3/00
• CPC Class Codes: G01N 29/06 Visualisation of the interior, e.g. acoustic microscopy medical or veterinary diagnosis using sonic waves A61B8/00; representation of acoustic wave distribution G01H3/125, G01H9/002; short-range imaging systems using reflection of acoustic waves G01S15/8906
• CPC Class Codes: G01V 1/282 Application of seismic models, synthetic seismograms

Abstract

A system employing ultrasound for the reconstruction of the absorptivity and refractivity properties of ultrasonic radiation internal to a solid, liquid or partly solid and liquid object, air vacuoles being excluded, in the vase that this radiation is highly scattered (reflected or refracted). The reconstruction consists of a three-dimensional simulation of these acoustic properties in a powder mixture which allows access to absorptivity and refractivity information without disturbance either to itself or to the object which it simulates. The reconstruction method is a multi-stage process in which the absorptivity and refractivity of the object are sampled layer-by-layer and recorded in mirror-image layers in the reconstruction. At each stage of the process, the previously constructed image layers are used as "corrective optics" to decode the highly distorted information from the object into the exact wave front geometry and wave form at the given layer that this wave had in the corresponding, mirror-image layer in the object, except for being inverted with respect to one spatial dimension as a mirror image. The necessary sonic data processing is done with a powder mixture, each particle of which is a microscopic mechanism capable of amplifying, recording, erasing and recalling the acoustic impedance information by means of mechanical flexions and other movements.

Claims

1. A process for the multiple-layer, layer-by-layer reconstruction of the internal structure of a solid, liquid or solid-liquid object comprising:

exciting said object with

ultrasonic waves during a time interval where Δ

T determines thickness of an i-th object layer (L_i) as the time taken for said waves to pass through said layer, at an i-th step of said process, depending recursively on identical steps numbered 1, 2, . . . i-1 having been performed previously, such that a coherent, monochromatic wave-pulse pair (P_i, P_i '"'"') generated in standard ultrasonic generating means outside said object pass simultaneously through and define said i-th object layer during said time interval and generate two additional pulses in said i-th layer;

one (R_i) transmitting information about absorptivity in said i-th layer, and the second (T_i) transmitting information about propagation velocity or refractivity in said i-th layer,

said wave and pulse (P_i P_i '"'"') arriving at said i-th object layer after the pulse (P_i) has been conjugated in a conjugator operated as a reversal medium which returns the conjugate of an incident wave,

and in which said additional two pulses activate an image medium by having particles responsive to the activation and further responsive to the additional two pulses to constitute a recording means in the image medium wherein said absorptivity and refractivity information are used to reconstruct the acoustic impedance three dimensional analog of the object,

said image medium, reversal medium, generating means and object being sonically coupled to transmit and transfer said ultrasonic waves and pulses between said media, generating means and object, said image media being coupled to a magnet coil and a microwave source with means for energizing said coil and source to activate said media for recording.

2. Process according to claim 1, wherein said image medium is used to reconstruct the acoustic impedance properties, absorptivity and refractivity, in image layers contained in said image medium (I₁, I₂, . . . ) which are the mirror-images, geometrically and acoustically, of corresponding said object layers (L₁, L₂, . . . ) with respect to the plane in which said generator (G) lies;

said correspondence being one-to-one between said image and object layers such that the i-th image layer (I_i) reconstructed using absorptivity and refractivity information transmitted by said two additional pulses of said i-th step, is the geometrical and acoustic mirror-image of the said i-th (L_i) object layer with respect to the plane in which said generator lies.

3. Process further according to claim 1 wherein said i-th step depends on preceding and identically defined steps numbered 1, 2, . . . i-1 having been performed previously recursively, and is defined as follows:

firstly, generating said wave pulse outside said object in said generator, and passing through said object to the beginning of said i-th layer;

secondly, activating said object during said time interval |iΔ

T, (i+1) Δ

T | that said wave-pulse pair generates said two additional pulses (R_i, T_i);

thirdly, processing first said additional pulse (R_i) on passing through image layers number 1, 2, . . . and i-1 which have been properly prepared previously so that its said information transmitted about absorptivity at each point in said i-th object layer is then recorded as an amplification capacity at the corresponding mirror-image point in the i-th image layer;

fourthly, processing second said additional pulse (T_i) on passing through image layers number 1, 2, . . . and i-1 which have been properly prepared previously so that its said information transmitted about refractivity at each point in said i-th object layer is then recorded as velocity of propagation intrinsic at that point and equal to velocity of propagation at the corresponding mirror-image point in the i-th image layer.

4. Process according to claim 3 wherein said recorded amplification capacity at each point of said image layers is made equal to the attenuation coefficient, at the corresponding mirror-image point of said object;

and that said recorded velocity of propagation at each point of said image medium being equal to that at mirror-image object points, in combination with said equality of amplification factor and attenuation coefficient, such that the time-course of a wave arising in said object can be nearly exactly reconstructed in said image medium;

said time-course reconstruction including mirror-image wave-front geometry, and wave amplitude.

5. Process further according to claim 1 wherein said object activation and method of processing said additional two pulses (R_i, T_i) are defined and related as follows:

said wave (P_i '"'"') is generated as said outside object at an instant of time chosen so that said pulse (P_i) has already passed once through the entire said object into said conjugator, where its direction of propagation has been reversed, and thus it retraces exactly its path back through said object up to said i-th object layer (L_i);

wherein said wave and said pulse can then interact non-linearly to generate said additional two pulses (R_i, T_i);

said non-linear interaction comprising said activation method.

6. Process according to claim 1 utilizing said image medium, hereafter termed I, with the following image layer activation means and recording and recall properties:

firstly activating said I by an externally applied, alternating electromagnetic field of microwave frequency such that I alters said amplification capacity at each of its points proportionally to the intensity of an ultrasonic wave which is passing through I at the time of application of said field according to the formula (J_i-1 -J_i)/(J_i-1 Δ

T) wherein J_i-1 is the intensity of said wave (R_i-1) in the preceding step i-1 as it reaches the beginning of the i-1-st object layer, and wherein J_i is the intensity of said wave R_i in step i as it reaches the beginning of the i-th object layer;

further differently activating said I by said electromagnetic field in combination with an externally applied, constant magnetic field (e), for the duration of said activation, such that I alters its velocity of propagation of said ultrasonic waves in proportion to the frequency difference between the fundamental frequency of said ultrasonic wave, f_i, and the frequency of ultrasound as originally generated in said generator according to the formula C(f_i - f_o) / (Af_o) wherein C is approximately constant depending on dimensions or units and wherein A is the amplitude of said pulse as it reaches the beginning of the i-th object layer;

said information transmitted about absorptivity which is recorded after passage of said first of additional pulses of just preceding said step i-1 (R_i-1) and at the arrival of said second of additional pulses (T_i) of said step i at said i-th image layer will be destroyed by subsequent passage of another ultrasonic pulse or wave, but can be recalled by a momentary increase of ambient medium pressure, called reactivation, followed by application externally of a microwave electromagnetic alternating field of somewhat lesser intensity than said electromagnetic field, in combination with a second magnetic field as distinguished from the said constant magnetic field;

the former said electromagnetic field being hereafter called higher intensity RF-field and the latter electromagnetic field of lesser intensity being hereafter called lower intensity RF-field;

activating said I by the application externally of an electromagnetic field of greater or equal intensity to said higher intensity RF-field, following said alteration of intrinsic amplification capacity, such that at points which have been so activated and prepared, I has intrinsic absorptivity at each of its points in proportion to the intensity of said ultrasonic wave passing through said points at the time of activation;

said electromagnetic field of greater or equal intensity, as well as said lower intensity RF-field, being adjusted in their intensities relative to said higher intensity RF-field empirically as need for a particular image medium.

7. Process as in claim 1 wherein said conjugator (R) operates at the precise instant of time at which said conjugator is activated by the application of an alternating electromagnetic field of microwave frequency the direction of propagation of any ultrasonic wave or pulse which happens to be passing through the conjugator will be nearly exactly reversed, so that said wave or pulse retraces its path in reverse.

8. The process further as in claim 6 wherein said additional two pulses (R_i, T_i) are processed, is comprised of a repetition of the following step depending recursively on identical steps 1,2, . . . , i-1 preceding:

said pulse (P_i) is generated in said generator (G) and passes through said object (O) into said conjugator (R), wherein its direction of propagation is reversed;

next, said pulse collides in the said i-th object layer (L_i) similarly generated in said generator, such that by non-linear interaction of pulse and wave, said two additional pulses (R_i, T_i) are generated;

next, second of said additional two pulses (T_i) then passes on through said object into said conjugator, wherein it is reversed and passes back through said object and generator, and the first i-1 image layers, I₁, I₂, . . . , I_i-1, up to said i-th image layer, I_i ;

next, said i image layers I₁, . . . , I_i being under activation by said RF-field of lower intensity, together with said second magnetic field,

said second of two additional pulses (T_i) arrives at the (i+1)-st image layer (I_i+1), 19 with a wavefront geometry which is the mirror-image of that which said pulse had when it was at the corresponding (i+1)-st object layer (L_i+1), and with mirror image amplitude (A);

at which moment (19), said (i+1)-st image layer is then activated by said higher intensity RF-field of higher intensity, together with said constant magnetic field, so that said frequency difference (f_i + f_o) is recorded in said (i+1)-st image layer as an intrinsic velocity of propagation equal at each point to that of the corresponding mirror-image point in the (i+1)-st object layer, said frequency being recorded permanently under combination of fields applied externally by subsequent steps of said process;

next, said i-1 image layers I₁, . . . , I_i-1 having been prepared for activation previously by passage of first said additional pulse (R_i) and according to steps 1,2, . . . , i-1 in such a manner that said absorptivity of each of said i-1 image layers is proportional to the ratio of intensities of first pulse (R_j) in step number j over preceding first pulse (R_j-1) of step j-1, for j equal to 1, 2, . . . and i-1,

said first pulse (R_i+1) of said step i+1, reaches said (i+1)-st image layer, with intensity proportional at each point to its intensity at corresponding mirror-image points divided by the intensity of preceding said first pulse (R_i);

at which moment (18), said (i+1)-st image layer is put under said higher electromagnetic field, but not under said magnetic field (e);

and said newly arrived first pulse (R_i+1) has its absorptivity-information recorded by means of said higher intensity electromagnetic field, to be recalled in subsequent iteration 15 of said recursion by means of said reactivation, as an amplification capacity equal to absorptivity at corresponding mirror-image points of said object to points of said (i+1)-st image layer, completing said recursive step as i-th iteration;

said above recursive process starting at the zero-th iteration with said image medium having the same acoustical impedance, namely homogeneous, as the liquid bath in which said object is contained and coupled to said generator and said coupling apparatus (R), and said first pulse (R_o) as generated externally to said object in said liquid bath (L_o) by interaction of said pulse (P_o) and said wave (P_o '"'"') is discarded, whereas said second pulse (T_o), passing on through said object to said conjugator, where it is reversed, and passing back through said object and generator, and into said image medium (I) to a position which is the mirror-image with respect to said generator of its position when just touching said object, is recorded by activation of said higher intensity electromagnetic field and said magnetic field (e) during time Δ

T as first image layer (I₁).

9. Process as in claim 6 wherein the reconstruction medium, otherwise called image medium, I, consists of a uniform mixture, that is, homogeneous mixture of two types, aI and nf, of microscopic mechanisms in a liquid vehicle wherein

said type aI is prepared for operation by a temporary pressure greater than that equilibrium pressure under which the mechanisms perform their functions, which pressure conveyed to said mechanism by said liquid vehicle, while at the same time an electromagnetic field of sufficient, intensity and frequency is applied to said mechanism, by means (9) external to said I, to heat an adhesive coating (4) on the inner surface of said mechanism'"'"'s shell (3) above the melting point of said adhesive, while said greater-than-equilibrium pressure compresses said mechanism into a compressed state (3b) in which opposite sides of its said shell are lightly touching;

said shell having less volume in said compressed state than in its original, uncompressed state (3a);

said type aI is further prepared for operation by reduction of said electromagnetic field until such a time as adhesive temperature drops below said melting point, and then reduction of said pressure to said equilibrium value, said electromagnetic field being of such an intensity as to hold said adhesive temperature just below said melting point, all the while said reduction of electromagnetic field is taking place a constant magnetic field being applied to orient magnetic, electrically conducting particles in said adhesive and to keep them in electrical contact, and said equilibrium pressure being such that said shell remains in said compressed state;

said type aI is activated for the function of expanding in a stimulating ultrasonic wave within a time not greater than one-quarter period from pressure maximum, otherwise called over-pressure, of said ultrasonic wave by the application of a reduced electromagnetic field (b), otherwise called RF-field, which heats said adhesive in said prepared compressed mechanism to a temperature just below said melting point;

under said RF-field, said micromechanism has its said shell slightly compressed by said over-pressure of said stimulating ultrasonic wave so that said conducting particles are pressed into better electrical contact, that is, reducing the resistivity of the said adhesive and thus increasing its temperature in said RF-field above said melting point, allowing said shell to expand to its expanded, spherical, state (3d), with a probability closely proportional to intensity of said stimulating ultrasound within the dynamic range of normal, operating sound intensities for said type aI mechanisms, said expansion being called recording;

whereas under a magnetic field of strength lower than that of said constant magnetic field and under an electromagnetic field of same frequency but intensity equal to or somewhat lower than said electromagnetic field, being called lower intensity electromagnetic field,

said mechanism having its shell slightly compressed by said overpressure will expand to its spherical state (3d) with a probability closely proportional to stimulating sound intensity, within said dynamic range,

said expansion being called amplifying if said mechanism is in said medium I or conjugating if said mechanism is in said coupling apparatus (R);

said type aI mechanism is returned to its compressed state by recompression with said greater-than-equilibrium pressure, tacking broken bonds of said adhesive back together, and then reactivated by temporary application of said higher intensity electromagnetic field so that shells previously expanded will again expand (e);

said recording and amplifying expansions in said I being distinguished subsequently in the manner in which respective shells re-expand after said recompression and reactivation, as follows;

said adhesive will not have its electrical resistivity decreased by said amplifying expansion, so that unrecorded shells, if amplifying in said I, can be recompressed and reactivated without difference from their original, unexpanded and unrecorded state, whereas said recording expansions decrease said adhesive resistivity by disorienting said magnetic particles, or otherwise separating said magnetic particles, due to adhesive deformation and without the orienting and aggregating effect of said magnetic field, so that after said recompression and reactivation, said recorded shells re-expand;

said type aI mechanisms in said liquid vehicle are able to amplify, i.e. conjugate, a stimulating ultrasonic wave by increasing local pressure in their containing medium upon stimulation by smaller increase of said over-pressure due to said increase of volume in expansion.

10. Process as in claim 9 wherein:

said nf structure is a shell, coated on its inner side with said adhesive, the same as said type aI with the addition of a coating of magnetic particles on the outer side of said shell, held to the shell and held together by the same elastic material of which said shell is composed;

same said preparation as said type aI mechanisms, before activation;

under said activation, in addition to said RF-field as for said type aI,

with said constant magnetic field, said coating of magnetic particles increases the ability of said shell to resonate (Q) under the small compressions and rarefactions of a stimulating ultrasonic wave,

and said shell under said activation has a resonant frequency equal to the generation-frequency f_o of said generator (G), so that the probability that said type nf will expand from its said activated state in the presence of said ultrasonic wave is very much decreased by a slight increase in frequency of said ultrasound over f_o ;

once so expanded to its spherical state, otherwise called expanded state, said type nf cannot be returned to its unexpanded state except by said preparation, called permanent erasure.

11. Process as in claim 9 wherein the liquid vehicle has the following properties:

said liquid vehicle has the same acoustical impedance as both type aI and type nf mechanisms in their respective said compressed states, that is, mixtures of said mechanisms with said liquid vehicle in said prepared but unrecorded states are acoustically transparent and homogeneous with respect to acoustical properties;

said type aI mechanisms have lower density in said expanded state than the density of said liquid vehicle, hence said type aI mechanisms are able to scatter, or otherwise termed absorb, or otherwise termed attenuate, said ultrasonic waves;

said type nf mechanisms have bulk modulus of elasticity in said liquid vehicle when under said lower magnetic field or said constant magnetic field lower when expanded than bulk modulus of elasticity when compressed;

said liquid vehicle, when mixed with said powders of type aI mechanisms and nf mechanisms as in said image medium, and when said mechanisms are all compressed to said compressed states, has acoustical impedance equal to that of said liquid bath;

and said liquid vehicle, when all mechanisms are in said compressed states, has intrinsic velocity of propagation for said untrasound just greater than the maximum velocity of propagation of said untrasound in any object which it is desired to image, otherwise termed, reconstruct the image thereof.