GB2039671A

GB2039671A - Acoustic imaging

Info

Publication number: GB2039671A
Application number: GB7939733A
Authority: GB
Original assignee: Kretztechnik AG
Current assignee: GE Medical Systems Kretztechnik GmbH and Co oHG
Priority date: 1979-01-19
Filing date: 1979-11-16
Publication date: 1980-08-13
Also published as: GB2039671B; AT356793B; DE2919182A1; ATA38879A

Abstract

A mechanism scans a beam projected by a sound transducer head 2 in a preselected sectional plane. A fluorescent screen displays a section image derived from the echo signals. Additional means are provided for a simultaneous display of certain signals in a different mode, particularly in a time- motion or A display. An additional sound transducer head 1 is used for the display in said different mode and projects a sound beam in the plane which is scanned by the first sound beam. The pulse frequency of the second sound beam is a multiple of the picture frequency of the section image. The sound beams 3,4 of the two sound transducer heads 1,2, intersect at right angles and are incident on a semi-transparent reflector 5 at the intersection region. <IMAGE>

Description

SPECIFICATION Ultrasonic examination and display equipment This invention relates to ultrasonic examination and display equipment comprising a scanning mechanism for moving a sound beam in a preselectable section surface, display means for tracing a section image corresponding to said section surface on a fluorescent screen, and means for causing certain signals to be displayed on said screen in a different mode, particularly as a time-motion or A display.

The display of results of examinations in different modes of display affords certain advatnages, e.g., in diagnostics, because specific details or relationships which are not directly apparent from the display in one mode can be shown in another mode of display.

For instance, the section image furnishes a general view and a moving section image art a high picture frequency can be used to represent movements in their entirety. A display corresponding to a certain region of the section image may be used to indicate distances from reflecting surfaces to the surface of the object being examined and from each other by the known pip display and also to indicate the areas of the reflecting surfaces. Time motion displays may be used to trace lines which represent movement parameters on a time base. Reference is made here by way of example to examinations of the heart, which can be represented by a section image whereas the motion of the valve of the heart can be represented as a result of a time-motion scan by a curve, which is described as UCG (ultrasonic cardiogram).The use of the time-motion scan perexamination during a plurality of cardiac movements so that irregularities of motion can easily be detected and may be compared with records based on a ECG (electrocardiogram).

In known equipment, change-over means are simply provided which permit the displays in the different modes to be effected in succession. To that end, a scanning unit may comprise a sound transducer head which can be arrested and A displays or time-motion displays may be derived from the echo signals when the sound transducer head has been arrested. In such equipment, a major part of the switching and other means comprised in the ultrasonic examination and display equipment can be used for successive displays in different modes.

It has been recognized that a simultaneous display in different modes or a display in which different modes are changed rapidly furnishes more information than successive individual displays in different modes. U.S. Patent 4,010,634 discloses high-speed section image display equipment which permits a display of a moving section image and in which a target line which can be adjusted as desired is traced in the section display. In that equipment, switching means are provided which suppress the signals that would normally be displayed on said target line and cause said signals to be displayed in another mode.

For a simultaneous tracing of the section image and of the lines traced for the display in the other mode, signals for the display in said other mode are hics Hl Irinn neh r.nmnlpAe scannina of the section surface with the sound beam only during the tracing of the target line so that the signals for the display in the other mode are available twice for a short time during the tracing of each complete individual section picture. Owing to this disadvantage, the display in the other mode can be effected only 20 to 40 times per second if the usual picture frequency of 10 to 20 pictures per second is adopted.

Whereas steady-state conditions can be indicated by an A display, the number of individual signals is often inadequate for a satisfactory representation of movements because some hundred individual signals per second would be required for that purpose.

It has been contemplated to arrest the scanning mechanism or the sound transducer head in the position corresponding to the target line for such displays but this will decrease the contrast of the section image or render it invisible so that the section image and the time-motion image cannot.be observed continuously.

It is also known to provide a scanning mechanism which permits an entire volume rather than only a section surface of an object to be scanned and to select and process the signals required for displays in different modes from the echo signals, after their buffer storage, if desired. This practice gives also rise to the problem that a long time is required for the scanning of a volume and only a few signals from a certain address are available for a timemotion display.

In equipment of the kind described first hereinbefore, that object is accomplished according to the invention in that two different sound transducer heads are provided, one for the section image display and the other for display or displays in at least one different mode, the sound beam projected from the sound transducer head for the display in the different mode lies at least substantially in the section surface which is scanned by the sound beam moved by the section surface scanning mechanism, and the pulse frequency of the sound transducer head for generating the echo signals for the display in the different mode is preferably a multiple of the picture frequency of the section image.

Owing to the design according to the invention, simultaneous displays in at least two modes can be effected and the scanning frequency can be sufficiently high to permit even time-motion displays because a separate sound transducer head is available for the display in that mode. Each sound transducer head can be selected for the display in the mode for which the head is mainly intended, for instance, as regards the cross-sectional shape and area of the sound beam which is projected. It is obviously necessary to ensure that the sound beams projected by the two sound transducer heads do not interfere with each other. To that end, each sound transducer head must be disabled at least in those positions in which echoes generated by sound pulses projected from one sound transducer head could be received by the other sound transducer head.This can be accomplished in a simple manner in that the two sound-transducer heads are enabled in rapid-alternation so that a major part of the signal-processing means of the equipment may be used to process signals from both sound transducer heads and it is sufficient to ensure that the signals from each sound transducer head are properly processed and displayed on the fluorescent screen at the proper locations.

The two sound transducer heads may be applied to the object in juxtaposed positions to define sound paths which converge into the object so that the sound beams projected by both sound transducer heads are incident on the same section surface at somewhat different angles. In many cases, however, the signals for the display in the different mode should be derived from echoes from the middle portion of the section surface so that the sound beam used for the display in the different mode and the sound beam used to generate the section image must be coaxial in one position.

In equipment according to the invention, this requirement can be met in that the sound path of each sound beam has a portion of substantial length before entering the object, the two sound transducer heads are spaced apart and define intersecting or crossing sound paths, a semitransparent reflector is arranged adjacent to the intersection or crossing of the sound paths, said one sound transducer head projects a sound beam, e.g., parallel to the surface to the object, said other sound transducer head projects a sound beam toward the object the reflector reflects part of the sound from said one sound transducer head into said section surface and transmits part of the sound from said other sound transducer head on a substantially stationary part into said section surface, and the scanning mechanism is operable to cyclically move the sound beam which has been reflected into said scanning surface so that the sound beams which have been reflected and transmitted into the section surface have the same position therein at least once during each half-period of the movement of said reflected sound beam.

This embodiment may also be provided in various forms. In one form, the two sound transducer heads are stationary and define sound paths which intersect at right angles and the semitransparent reflector is adapted to be driven so as to move the reflected sound beam in the section surface and preferably performs an angular oscillation about the axis of the reflected sound beam.

Alternatively, a stationary reflector may be provided and said one sound transducer head may be driven to perform a periodic scanning motion, preferably an angular oscillation, whereas the other sound transducer head is stationary and defines a sound path that is at right angles to the plane of said oscillation and the reflector includes an angle of 45 with the sound path defined by the stationary sound transducer head and its plane of oscillation.

In both forms, the semitransparent reflector may consist, e.g., of a diaphragm which has a thickness that is much thinner than the wavelength of sound in the diaphragm, and at least one additional reflector may be provided, which is spaced from the semitransparent reflector and by which those sound beam parts which are kept from the object by the semitransparent reflector are reflected back to the associated sound transducer heads, if desired after multiple reflection, and the signals derived from said echoes generated at regular intervals of time are used for a display of time or distance marks.

Further details and advantages of the subject matter of the invention will become apparent from the following description of the accompanying drawings, in which the subject matter of the invention is shown by way of example.

Figure l is a diagrammatic perspective view showing the essential parts of a scanning unit which may be used in equipment according to the invention and Figure2 is a basic circuit diagram from which the changes of and additions to the circuitry of a simple section surface scanning and display equipment are apparent.

In Figure 1, a housing I shown only diagrammatically by its contours contains two sound transducer heads 1 and 2, which define sound paths 3,4 that intersect at right angles. A semitransparent reflector 5 for ultrasonic waves consists of a diaphragm, which is held in a carrying ring and is inclined 45" from the two sound paths 3,4 is disposed at the intersection of the two sound paths 3, 4. The reflector 5 is mounted at the suitably bevelled end of a tube 6, which is formed in its wall with an opening 7 for the entrance of the sound beam projected by the sound transducer head 1.

By means of a motor 8, the tube 6 can be oscillated about the sound path 4through the intermediary of a crank mechanism 9, which cooperates with a yoke 10 that is mounted on the tube. A sensor 11 is connected to the tube and generates signals which represent the instantaneous angular position of the tube 6 and the position of the sound beam as it is moved in the section surface.

It has already been mentioned that the mechanism is disposed in the housing I. The housing I is filled with a liquid which has a high conductivity for sound. The housing I is formed with an aperture, which is liquidtightly sealed by a thin plastic film which contains an elliptical or circular sound exit window 12, through which sound beams can enter the object. An absorber for sound waves or a reflector for sound waves, which is at right angles to the tube axis, may be disposed in the tube 6. The parts contained in the housing I have been indicated only by their contours. Their mounting means and connections have been omitted in the drawings.

Owing to its semitransparency, the reflector 5 reflects part of the sound beam projected from the sound transducer head 2 and transmits another part of said sound beam into the tube 6. As a result of the oscillating motion of the reflector 5, the reflected part of the sound beam scans the object in a section plane, which has been indicated in the drawing by an array 13 of spaced apart lines which extend from the window 12. That part of the sound beam projected from the sound transducer head 2 which is transmitted by the reflector 5 is either absorbed by an absorbing member which is provided or is reflected by a reflector which is provided inside the tube. In the latter case, the multiple reflection by said reflector and the sound transducer head 2 results in a sequence of echoes in regular intervals of time.

The absolute length of said intervals depends, inter alia, on the distance from the reflector in the tube to the sound transducer head 2 and can be selected within a certain range. These echoes are received by the sound transducer head 2 just as the "true" echoes from the object being examined and may be used for a display of time or distance marks on the fluorescent screen, e.g., in the section image.

Part of the sound beam projected by the sound transducer head 1 is also reflected into the tube 6 on the rear of the reflector 5. That reflected part of the sound beam can be used for the display of different time marks. As is indicated by dotted lines, that part of the sound beam projected from the sound transducer head 1 which is transmitted by the diaphragm 5 enters the object through the window 12. The position of this sound beam in the object is virtually not changed by the oscillating movement of the reflector 5. Theoretically, there is a parallel displacement of said beam part in dependence, inter alia, on the thickness of the reflector 5. The displacement will not be significant if the reflector is sufficiently thin.The section plane might also be scanned by an arrangement comprising a semitransparent reflector which is stationary if one of the two sound transducer heads 1 and 2 is moved at right angles to the sound path defined by it or subjected to an angular oscillation.

The equipment represented in Figure 2 by a block circuit diagram comprises simple means by which the information obtained by means of the two sound transducer heads 1 and 2 can be displayed in different modes virtually at the same time whereas an influence on each sound transducer head by the operation of the other sound transducer head is avoided.

The ultrasonic scanning and display equipment is controlled in conventional manner by a clock 14 which triggers a pulse generator 15 and a sweep generator 16 and actuates an electronic change-over switch 17. In the simplest case, the switch 17 moves from its present state to another state in response to each clock pulse. As a result, the control pulses are delivered to the scanning unit 20 via two different leads 18, so that only one of the two sound transducer head can be activated at time by the control pulses and echoes generated in response to the projected pulses can be received only by the sound transducer head which has projected the sound pulse that has generated the echo.It will be understood that each change-over of the switch 17 is delayed until the control pulse delivered by the switch 17 has initiated the projection of a corresponding sound beam and the echoes generated in response to said control pulse have been converted into echo signals. The echo signals generated by each of the sound transducer heads 1,2 are delivered via respective leads 25, 26 to the change-over switch and are delivered by the latter in alternation to an amplifier 21. The latter generates an output signal for controlling the brightness of the image, i.e., of the electron beam which traces the image on the fluorescent screen. The amplifier 21 is representative of the entire signal-processing circuitry, which includes a threshold selector, filtering means, demodulating means and depth-compensating means.

The output of the amplifier 21 is connected by a lead 27 to the brightness control means associated with the fluorescent screen 28.

Two units 22, 23 are provided for controlling the deflection of the electron beam on the fluorescent screens. The deflection control unit 22 is used for the time-motion display and derives vertical and horizontal deflecting voltages from the sawtooth voltage generated by the sweep generator 16 and from the sawtooth voltage generated by a second sweep generator 24, which has a sweep frequency that is much lower than that of the sweep generator 16. The vertical deflecting voltage delivered by the deflection control unit 22 includes a constant bias component which ensures that the display controlled by said unit 22 will appear on the screen in a region vertically spaced from the section image.

The deflection control unit 23 derives horizontal and vertical control voltages from the sawtooth voltage delivered by the sweep generator 16 and from the information delivered by the sensor 11 associated with the scanning mechanism 20 regarding the instantaneous position of the sound beam projected from the sound transducer head 2 in the section surface.

The vertical deflecting voltages generated by the units 22, 23 are delivered to one pair of input contacts of the change-over switch 17 via respective leads 29, 30 and from the associated output contact of the switch 17 via lead 32 to the vertical deflection electrodes of the fluorescent screen 28. The horizontal deflecting voltages generated by the units 22, 23 are delivered to another pair of input contacts (not shown) of the change-over switch 17 via respective leads (not shown) and from the associated output contact (not shown) of the change-over switch 17 are delivered via lead 31 to the horizontal deflection electrodes of the fluorescent screen 28. For the sake of simplicity, the lead 31 is shown in the drawing to be connected to the same output contact as the lead 32.

Because a change-over is effected after each clock pulse, the picture frequency of the time-motion display is the same as the line frequency of the section image. If such a high frequency is not required for the time-motion display, a counter (not shown) may be provided, which controls the change-over switch 17 and causes it to be in the position for the operation of the sound transducer head 2 for three consecutive clock pulses and subsequently in the position for the operation of the sound transducer head 1 for a single clock pulse.

Similar circuitry may be employed for an alternation between section displays and A displays if the deflection control unit 22 is designed for an A display.

The equipment may be designed for a simultaneous display in three modes, for instance, if the echo signals generated by the sound transducer head 1 are delivered via an additional change-over switch for alternating utilization for an A diplay and a time-motion display, which are visible at the same time.

Claims

1. Ultrasonic examination and display equipment comprising a scanning mechanism for moving a sound beam in a preselectable section surface, display means for tracing a section image corresponding to said section surface on a fluorescent screen, and means for causing certain signals to be displayed on said screen in a different mode, particularly as a time-motion or A display, characterized in that two different sound transducer heads are provided, one for the section image display and the other for display or displays in at least one different mode, the sound beam projected from the sound transducer head for the display in the different mode lies at least substantially in the section surface which is scanned by the sound beam moved by the section surface scanning mechanism, and the pulse frequency of the sound transducer head for generating the echo signals for the display in the different mode is preferably a multiple of the picture frequency of the section image.

2. Equipment according to claim 1, characterized in that the two sound transducer heads are spaced apart and define intersecting or crossing sound paths, a semitransparent reflector is arranged adjacent to the intersection or crossing of the sound paths, the reflector reflects part of the sound from said one sound transducer head into said section surface and transmits part of the sound from said other sound transducer head on a substantially stationary part into said section surface, and the scanning mechanism is operable to cyclically move the sound beam which has been reflected into said scanning surface so that the sound beams which have been reflected and transmitted into the section surface have the same position therein at least once during each half-period of the movement of saidreflected sound beam.

3. Equipment according to claim 2, characterized in that the two sound transducer heads are stationary and define sound paths which intersect at right angles and the semitransparent reflector is adapted to be driven so as to move the reflected sound beam in the section surface and preferably performs an angular oscillation about the axis of the reflected sound beam.

4. Equipment according to claim 1 or 2, characterized in that said one sound transducer head is driven to perform a periodic scanning motion, preferably an angular oscillation, whereas the other sound transducer head is stationary and defines a sound path that is at right angles to the plane on said oscillation and the reflector includes an angle of 45 with the sound path defined by the stationary sound transducer head and its plane of oscillation.

5. Equipment according to claim 1, characterized in that said one sound transducer head and said display means are operable to generate a moving section image, said display means comprise two deflection control units for generating deflecting voltages for said section image display and said display in said different mode and a selector switch means are provided, which are operable at a frequency which exceeds the picture frequency of said moving section image to connect said two sound transducer heads in alternation to control means for operating said sound transducer heads and to cause the echo signals derived by the sound transducer head thus connected to said control means to be processed by the deflection control unit associated with the respective mode of display.

6. Equipment according to claim 5, characterized in that the display means comprise additional signalprocessing means for processing echo signals derived by said second sound transducer head for a display in a third mode and said selector switch means are operable to cause the echo signals derived by said second sound transducer head to be processed in alternation by said delfection control unit for the display in said different mode and by said additional signal-processing means.

7. Equipment according to any of claims 2 to 6, characterized in that at least one additional reflector is provided, which is spaced from the semitransparent reflector and by which those sound beam parts which are kept from the object by the semitransparent reflector are reflected back to the associated sound transducer heads, if desired after multiple reflection, and the signals derived from said echoes generated at regular intervals of time are used for a display of time or distance marks.

8. Equipment constructed and adapted to operate substantially as hereinbefore described and as shown i r the figures of the accompanying drawings.