DE2443686A1 - Radiation converter for ultrasound - uses selector installation capable of adjusting distance of focus zone from radiation source - Google Patents

Abstract

Pre-focussed radiation converter for ultrasound is fitted with a number of radiation transmitting and receiving elements located next to each other connected to a signal generator and a signal decoder. There is a device to alter the distance of the focus zone from the radiation elements with a selector installation of photoelements (56 to 68) processing the adjustment and capable of connecting a number of radiation elements corresponding to the required focus distance simultaneously to the signal generator (71) and/or simultaneously to signal decoder (73). The ultrasonic elements (30 to 42) are connected to the photoelements (56 to 68), and there is a diaphragm (70) in front of these elements.

Description

Focused radiation converter, preferably for ultrasound on Folciissierter ultrasonic transducer according to the preamble of claim 1 is described in DT-OS 2 202 989. The known ultrasonic transducer has a the desired resolution - corresponding number of spatially next to each other lying transducer elements, which have controllable delay elements on the signal evaluator are connected. The transit time elements are connected to a control device, through which the electrical output signals of the transducer elements when receiving the ultrasound reflected by boundary layers in an examined body is so delayed that the focus zone of the ultrasonic transducer arrangement is always at a boundary layer arrives when the ultrasonic pulse reflected by this boundary layer hits the ultrasonic transducer achieved. In the known ultrasonic transducer there is therefore — because of the migration — the focus zone Achieved good sensitivity and resolution during reception.

The disadvantage of the known ultrasonic transducer is that the circuit-wise The effort for changing the focus distance from the ultrasonic transducer is large and that the focus zone is perpendicular to the direction of sound emission or reception for scanning of the transmission area of the examined body only mechanically displaced can be. After all, a focus zone is only effective during the reception phase0 The invention is based on the object of providing a focused radiation converter in accordance with to create the preamble of claim 1, in terms of the electrical The circuit structure is significantly simplified compared to the known ultrasonic transducer is and in which a shift of the radiation beam and thus also of the focus zone in a direction perpendicular to the radiation or

Receiving direction lying direction is electrically possible.

According to the invention, this object is achieved by the features of the label of claim 1, In the radiation converter according to the invention, all radiation elements can arranged in one plane and as a rectangular, zoB. square plates will. Their number can be chosen so that a scan of the irradiation area of the examined body in the direction of one or more lines is possible. the Changing the distance of the focus zone from the transducer can be done in a simple manner Change in the number of effective radiation elements.

Further advantages and details of the invention emerge from The following description of an exemplary embodiment for ultrasound with reference to FIG Drawing. 1 and 2 show representations to explain the invention, Fig. 3 shows a representation of the transducer elements of a focused ultrasonic transducer according to FIG of the invention, FIG. 4 shows an illustration to explain FIG. 3, and FIGS. 5 to 7 details of an ultrasonic transducer according to the invention.

Figure 1 shows a rectangular ultrasonic transducer element 1, which emits ultrasound in the direction of the z-axis of a coordinate system. Of the The course of the sound energy density, i.e. the sound lobe, is shown in FIG. The sound cone has a constriction at point 2 and in the area of this Place 2 thus a focus zone. When scanning a transmission area of a body, e.g. the human body, the resolution is all the better, the narrower the scanning sound cone is. The investigation of the transmission area can be done in a well-known manner by first emitting an ultrasonic pulse and then switched to reception and those at boundary layers, e.g. blood vessels or organ surfaces, reflected signals are received. Due to the running times the ultrasonic impulses from transmission to reception are then pictorial Representation of body areas in the direction of emission on the screen of a viewing device possible. The signals reflected from the respective body part are transmitted by a Receiving gate circuit detected.

The decisive factor for the lateral resolution is the The reciprocal of the sound cone width. The narrower the club scanning the field of view is, the better the resolution, i.e. the smaller the distance between neighboring ones can be Image points that should still be perceptible separately.

The main lobe width 5 of a rectangular sound emitter with the Edge length D is - in each case up to the first zero point of the energy distribution transversely to the z-axis in the near field S = D from the constriction 2 onwards in the far field S = 2z. # / D The constriction at the near-far field boundary is at a distance D²- # ² from the transducer and denotes a zone of increased energy.

4 # a is the wavelength of the ultrasonic radiation.

With a given transmission range of length ze in the z-direction and given sound frequency f - and thus known A = c / f - is the beam width 5 only depends on the radiator width D. In the following, under club width always the maximum width within the transmission range of interest Ze can be understood, which makes sense because at the location of the maximum width the resolution is worst.

The enlargement of D causes a broadening of the club in the near field9 the reduction of D means a broadening of the lobe in the far field. For D exists an optimum value which is characterized in that the maximum width S = Smax between z- = 0 and z = ze for D = Dopt becomes minimal.

This is the case when S (z = ze) = 2ze. # / D = D becomes. It then arises The value for the optimal lobe width Dopt can be read from the diagram in FIG. For the curve with the parameter ze - 100 mm and 5 z applies, for example

Dopt = 8 mm.

The achievable resolution is given with the reciprocal of Dopt.

Used to examine the transmission area for each pixel If a single, optimally dimensioned ultrasonic transducer element is used, the Sound cone width according to FIG. 1 over a large area in the direction of radiation D opt and only assumes values between Dopt / 2 and beyond the near-far field boundary Dopt on, that means that in the worst case e.g. two blood vessels with the wall distance of Dopt only appear as a single wide bar in the image.

The example shows that when using Eompakt radiators the resolution at a given wavelength and a given transmission range is determined by Dopt and therefore cannot be 1 better than. The invention Dopt therefore treads the toilet shown in FIG.

From FIG. 3 it can be seen that in each case several (k) partial oscillators 3 to 11 (ultrasonic elements) of the ultrasonic transducer simultaneously and in phase-g can be controlled. The number k is variable and is represented by the marginal rays in FIG of a cone, which is supposed to symbolically indicate their simultaneous excitation. The ultrasonic emitter consists of as many partial emitters as there are are within the variable opening angle.

The heater dimensions can be adjusted by switching on or off Increase or decrease partial vibrations step by step. Dauit changes the distance the zone of increased energy at the near-far field boundary from the beam surface according to the equation Zf (D) = D² D is the sum of the partial radiator widths.

So it is possible to focus the radiator - i.e. the constriction his club between near and far field - between z # # 0 and Z = ze by suitable Change of k to wander In Figure 3, for example, five are possible Locations 12 to 16 of the focus zone are shown.

The width of the focus zone is approximately D / 3 for a 6 dB drop in energy to the maximum value on the emitter axis. At a width of D / 2, the energy is dropped to about zero. In the following consideration, therefore, is used for the width D / 2 is always used at the narrowest point of the focus zone.

D is varied with P switching steps, whereby the focus is forced on the Z-axis goes through the entire sound reinforcement area. 5 MEIz impulses are used as sound energy emitted with a pulse frequency in the MIz range. A gate circuit in the receiving device ensures that reflected energy is only received from the area in which the focus is. This means that the effective lobe width is divided by the width the focus is determined.

Figure 4 shows on a scale of 2: 1 for three switching states, i.e. three Emitter diameter D - the expected location and Width of the focus zone. It can be seen that in the worst case - with z = ze = 100 mm - the effective lobe width Is 5.75 mm.

Compared to the arrangement consisting of compact radiators (with Dopt = 8 mm) already an improvement. The advantages of the Invention if one considers the resolution achievable in the most favorable case. These was determined for the compact radiator by Dopt / 2 = 4 mm. Both inventions on the other hand it depends on the smallest diameter Dmin äb, which is composed of the partial oscillators will. If this is 2 mm, then the optimum of the effective club is also 1 to 2 mm given. From Figure 4 it can be seen that the effective lobe width up to the point Ze / 4 = 25 mm first increased to 2.25 mm and up to point ze / 2 = 50 mm to 4 mm is. It therefore remains below 4 in the front half of the transmission area mm and in the rear half under 5.75 mm. In comparison to this (FIG. 1) the Beam width with the compact radiator with D = Dopt = 8 mm in the entire anterior half 8 mm and was between 4 and 8 mm in the rear half. FIG. 3 shows that at Appropriate choice of the total number of ultrasound elements also shifts the Focus zone in x-direction, i.e. perpendicular to the direction of sound radiation is possible. In this way, a line-by-line scan of the transmission area of the examined Body possible.

It should not be overlooked that when using compact radiators due to the center distance of the compact radiators of at least Dopt = 8 mm the divergent Clubs between the points z = ze / 2 and Z = z e do not adjoin one another, so that dead fronts arise that are between 0 and 4 mm wide and not with sound energy can be supplied. This disadvantage also does not arise with the subject matter of the invention on. The smallest increment by which the sound lobe moves along a scan line is given by the width of a partial radiator (ultrasonic element). However, it makes sense to adjust the increment equal to the smallest achievable The width of the club should be selected, since smaller increments no longer improve the image quality can.

With a step size of 2 mm, for example, the sound beam moves from left to right by turning off two elements, each 1 mm wide, on the left and on the right 2 elements can be switched on. This process continues until one Line is traversed * In Figure 3, the position of the beam axis after each sound step indicated by position numbers 20 to M 0 During the step change the radiator width D remains by combining up to P partial transducers the central axis at the location of the respective position number and only jumps to the next if the focus covers the entire transmission area between z - = 0 and z = ze once has passed through, the scan in the x-direction described above can analogously as well run in y-direction. Up to PxP partial oscillators become square one after the other Beams are summarized in the area DxD and step through a line Then it is switched by one partial step in the y-direction and the next one Line scanned until finally the entire image is built up That step by step Scanning in both coordinate directions is allerdirgs with considerably greater circuitry Effort connected It can also be subdivided into 1 mm wide partial oscillators in the y-direction be omitted and each element as a strip of z0B. 1 2 8 mm formed will. In the example according to FIGS. 1 and 2, the dimension 8 mm corresponded to Dopt for 5 MHz and 100 mm penetration ###. The 8 mm edge is then parallel to the y-axis and determines the worst resolution to be expected in the y-direction. The single ones Image lines then have - from the middle of the line to the middle of the line - one below the other, as well a distance of 8 mm. | In summary it can be stated be that the invention creates an ultrasonic transducer that allows the focus zone in the direction of emission, dohe in the direction of the central beam, while to allow the investigation of a transmission area to wander and thus to achieve that the focus zone is always in the area of the boundary layers from which pulses are received should be. The electrical circuit arrangement for this focus movement must be only the effective number of ultrasound elements continuously in the Change the sense of the desired focus movement and is therefore very much in its structure simple.

The invention also makes it possible to set the focus zone vertically Central beam of the ultrasonic radiation in the sense of a line-by-line image structure to move electrically. When the ultrasonic transducer according to the invention are only Signals from focus zones are evaluated, so that it is ensured that along the z-axis no dead zones due to minima within the near field of the sound cone the image shown. Since the signals come from the focus zone, is the intensity of these signals is relatively high. The signal-to-noise ratio of the received signals is therefore favorable. The focus is in the transmission phase and effective in the reception phase. The ultrasonic transducer according to the invention allows impulse sound and continuous operation, i.e. an operating procedure in which the transmission and the Evaluation of received ultrasonic pulses alternately one after the other, and one Operating procedure in which this occurs at the same time. Continuous wave operation is natural only makes sense if signals can only be expected from a certain depth zone and the focus is moved into this deep zone. This is the case, for example, when only -at a certain distance z1 blood vessels are located, which an ultrasonic Doppler signal deliver.

In the exemplary embodiment according to FIG. 5, only those are for one pixel provided ultrasound elements 30 to 42 of an image, line shown. According to FIG. 3, the row of ultrasonic elements can be displaced of the focus zone perpendicular to the central beam of the ultrasonic radiation and also in two mutually perpendicular directions (spanned plane) accordingly a line-by-line image structure. The ultrasonic elements 30 to 42 are photoelectric Coupling elements 56 to 68 connected by a point source 69 with light be irradiated. The number of each irradiated photo elements is by one mechanical aperture 70, which is adjustable, selectable. In the maximum position of the Aperture 70, all photo elements 56 to 68 are opened and all ultrasound elements 30 to 42 activated. In the minimum position of the diaphragm 70, only the Photo elements 61 to 63 are irradiated and thus only the ultrasonic elements 35 to 37 activated.

A signal generator is used to generate the Ultras'challin "pulse" 71 which can be coupled to the ultrasonic elements 30 to 42 via a coupler 43 and is controlled by a central clock 72. To evaluate the from Body layers reflected ultrasound signals from the ultrasound elements 30 to 42 are received, a signal evaluator 73 is used, which via a Kr, ppler 44 can be connected to the ultrasonic elements 30 to 42 during the door opening time is.

Wen, the illustrated ultrasonic transducer using the pulse reflection method works (pulsed sound operation), the clock generator 72 causes first that all effective Elements - in the illustrated position of the panel 70, the elements 35 to 37 - First, send out an ultrasonic transmission pulse at the same time. This ultrasonic transmission pulse passes through the body to be examined and becomes partial at each boundary layer After the end of the ultrasonic transmission pulse, the clock generator 72 effects the shutdown of the signal generator 71 by blocking the Coupler 43 and the switch to reception after exactly the time that a signal from the respective Focus zone needed to return to the ultrasonic elements 30-42. For this becomes the delay time of the delay element 45, its de s s en output pulses open the coupler 44, synchronously with the adjustment of the diaphragm 70, the focus migration causes, changed. The signal evaluator 73 now evaluates those from the effective ultrasonic elements (in Figure 5; 35 to 37) received ultrasonic pulses.

The best reception results are achieved when then when a Ultrasonic pulse reflected by a boundary layer on the ultrasonic elements arrives, the focus zone falls into the boundary layer that reflects this pulse Has. So when examining a body with several boundary layers lying one behind the other the greatest reception sensitivity and maximum resolution is achieved, if the focus corresponds to the arrival of the reflected ultrasonic pulses migrates, i.e.

the focus distance is changed accordingly by adjusting the diaphragm 70 will.

The point-shaped light emitter 69 can also be represented by the parallel light bundles 74 are replaced.

Instead of the mechanical screen 70, an arrangement according to FIG FIG. 6 occurs in which liquid crystals 75 are attached to translucent, electrically conductive ones Layers 76 lie. The arrangement is through translucent insulator layers 77 completed.

The electrically conductive layers 76, which for example consist of SnO2 can serve as ground electrodes and are electrically conductive transparent Layers 78, 79 and 80 opposite, which allow the insertion of n-light cones (in Example n = i) enable the photoelectric converters 56 to 68 (Fig 5) hit. If, for example, the layer 78 is connected to voltage via a switching device 46 placed and the arrangement according to Figure 6 of a punctiform If the light source shines through from the right, the crystal with the layer 78 becomes cloudy, so that the smallest aperture with the diameter D1 is set. At the When a voltage is applied to the layer 79, an average diameter is set and when a voltage is applied to layer 80, the largest diameter. A cloudiness of the liquid crystals 75 occurs only in those areas that are between two electrically conductive layers.

FIG. 7 shows an exemplary embodiment for a diaphragm device, in which between two translucent insulating layers 81, a transparent one connected to ground electrically conductive layer 82 and three transparent electrically conductive layers 83, 84 and 85, which are e.g. circular or as sections of a square can be formed. Between the layers 83 wld 84 as well as 84 and 85 lie non-transparent insulating layers 86 and 87. Further lies between the layer 82 on the one hand and the layers 83 to 85 on the other hand a liquid crystal 88. A Control voltage can be applied to layers 83 to 85 through three contacts 89 to 91 will. If the control voltage is applied to layer 83, the BristalSibis opaque to the insulating layer 86, i.e. that the largest aperture diameter is transparent to light is. If the contacts 89 and 90 are closed, the crystal 88 is up to Insulating layer 87 is cloudy and a medium aperture is selected. In the end the smallest aperture is selected when all three contacts 89 to 91 are closed will.

The diaphragm devices according to Figures 6 and 7 can, as mentioned, take the place of the diaphragm device 79 in Figure 5, i.e. between a point light source and the photoelectric coupling elements 56 to 68 lie or of a parallel one Light bundles are penetrated.

The ultrasonic transducer according to the invention is not only suitable for Examination of bodies using the pulse reflection method and pulse Doppler operation, but also for examining bodies using the Doppler effect in Continuous wave operation. In principle, the idea of the invention is not limited to ultrasonic emitters and receivers, but generally to an arrangement of radiating and receiving radiation Elements, e.g. in radar technology, can be used.

Claims (6)

Claims 1 Focused radiation converter, preferably for ultrasound, with a number of radiation transmitting and receiving elements that are spatially adjacent to one another, which are connected to a signal generator and a signal evaluator and with an arrangement for changing the distance of the focus zone (focus distance) from the radiation elements, d u r c h g e k e ii ii z e i c h n e t that to change the focal distance a selection device (56 to 68) is available5 the one dem desired focus distance corresponding number of radiation elements (30 to 4.2) simultaneously to the signal generator (71) and / or simultaneously to the signal evaluator (73) turns on. 2. Converter according to claim 1, wherein the radiation beam in at least is displaceable in a direction perpendicular to the central ray, thereby characterized in that a number corresponding to the desired amount of junction of radiating elements (3 to 11, 30 to 42) is present, and that by the selection device (56 to 68) alternately change the focus distance and shift the radiation beam takes place at a level perpendicular to the central ray. 3. Converter according to claim 2, characterized in that the displacement of the radiation beam in two coordinates in the sense of a line-by-line scan of the irradiation area of the examined body takes place. 4. Converter according to one of claims 1 to 3, characterized in that that each radiation element (3 to 11, 30 to 42) for coupling to the signal generator g71) and the Signal evaluators (73) each have a photoelectric coupling element (56 to 68) is assigned and that an exposure device (69, 70, Fig. 6, Fig. 7) is present, which the coupling elements (56 to 68) of the desired focus movement exposed accordingly. 5. Converter according to claim 4, characterized in that the exposure device (69, 70) a mechanically adjustable diaphragm (70) between a light source (69) and the ripple elements (56 to 68). 6. Converter according to claim 4, characterized in that the exposure device (Fig. 6, 7) at least one electrically controllable liquid crystal (75, 88) Ws Aperture device between a light source (69) and the coupling elements (56 to 68) contains.