GB2111207A

GB2111207A - Ultrasonic scanning unit

Info

Publication number: GB2111207A
Application number: GB08231344A
Authority: GB
Inventors: Christoph Theumer
Original assignee: Kretztechnik AG
Current assignee: GE Medical Systems Kretztechnik GmbH and Co oHG
Priority date: 1981-12-01
Filing date: 1982-11-02
Publication date: 1983-06-29
Also published as: DE3238541A1; GB2111207B; AT384545B; ATA515081A

Abstract

Ultrasonic examination equipment comprises a section plane- scanning unit, which includes at least two spaced apart sound transducer heads 7, and drive means 5,6 for rotating or angularly oscillating said heads in unison about an axis of rotation. Each of said heads is arranged to be activated only during its movement through a predetermined angular range, without need for mechanical contacts, by providing a commutator in the form of a transformer, which comprises a stationary coil 10, 11 about which rotate a plurality of movable coils 14, 15, 14a, 15a, associated with respective transducer heads. Said stationary coil is magnetically coupled to each of said movable coils by pole pieces 12,13 only when a said movable coil moves through said predetermined angular range, which is determined by the size and shape of at least one of said pole pieces. <IMAGE>

Description

SPECIFICATION Ultrasonic examination equipment This invention relates to ultrasonic examination equipment comprising a section-plane scanning unit and control and display means, which scanning unit comprises at least two sound transducer heads, which are adapted to be driven to rotate or oscillate on an axis of rotation and angularly spaced apart with respect to said axis and drive means for moving said sound transducer heads in unison about said axis, each of said sound transducer heads being adapted to be activated only during a predetermined range of its movement and when activated to project a sound beam into a specimen to be examined, so as to scan said specimen in a section plane, said equipment also comprising a transformer for connecting the control and display means to the sound transducer heads and comprises a stationary winding and a second winding which is movable with the sound transducer heads.

In section plane-scanning units of that kind, which are used particularly for so-called B displays, the sound beam emitted by each sound transducer head when it is activated is directed into the specimen to be examined, either directly, for instance, through a sound-transmitting window of a housing of the section-surface scanning unit, or via pre-entry paths, which may include reflectors. If reflectors are provided, each sound transducer head will be activated only when it faces the reflector which is associated with the section plane and is, e.g., parabolic. If the sound beam is directly projected into the specimen, the sound head will be activated as it moves past the sound-transmitting window.In this connection the term "activation" describes the connection of a sound transducer head to the in the control and display means for controlling the generation of ultrasonic sound by the sound transducer heads and for receiving the echo signals delivered by the sound transducer heads. There are special designs in which each sound transducer head is used only to transmit ultrasonic sound or to receive echoes.

The term "activation" covers both possibilities.

Whereas there are two or more sound transducer heads, the section plane-scanning unit comprise virtually only one transmitting unit and one receiving unit at any given time, and these units may be combined. A transmission or reception by a sound transducer head other than during its predetermined activation time must be prevented because the section image would otherwise be disturbed or falsified. In section plane-scanning units having reciprocable sound transducer heads, change-over switches may be provided in the control and display means and each sound transducer head may be connected by flexible leads to the switches and via the latter to the control and display means. In that case, the activation will depend on the switch position. But it is essential to use bounce-free switches because the image may otherwise be disturbed.

In scanning units having rotatable sound transducer heads, on the other hand, signals must be transmitted from a stationary part to a rotating part and vice versa. In this case too, care must be taken to activate the sound transducer heads only during predetermined times. These requirements can be met in that, as disclosed in U.S. Patent Specification 4,102,204, wiper contacts are provided, which are connected to the control and display means and which as in a collector slide on contacts which extend only around a portion of a rotating part and are connected to respective sound transducer heads and by their extent control the times for which the connected sound transducer heads are activated.In that case it is a disadvantage that the contact resistance between contacts having flat contacting surfaces cannot be kept constant in practice so that the signals are attenuated in varying degrees and this results in changes in sensitivity and in the brightness of a section image displayed on a fluorescent screen.

Sparking at the contacts will also result in disturbances and in changes of the contact resistance. In so-called "fast" section-plane scanning units having a picture repetition frequency above 10 Hz, which means that a sound transducer head must be activated to scan the section surface 10 or more times per second, it is virtually impossible to suppress the spurious signals which occur.

In view of the difficulties outlined above, designs of the kind mentioned first hereinbefore have been adopted for section plane-scanning units which comprise rotating sound transducer heads. Such designs have also been described in U.S. Patent Specification 4,102,204. A transformer is provided in such designs, which is known under the name "Dynamotor" and comprises a stationary inner winding and a concentric, coaxial annular outer winding, which rotates in unison with the sound transducer heads.

The inner winding contains a magnetic core. The two windings might also be concentrically arranged one beside the other around a coaxial core of suitable length. Alternatively, two shell-like cores facing each other with their open sides and accommodating respective windings may be provided in an arrangement in which one core is stationary and the other rotates with the sound transducer heads on a common axis of symmetry.

All these transformers do permit a virtually satisfactory transmission of signals from the stationary part to the rotating part and vice versa but in that arrangement the problem of the selective activation of each sound transducer head has not been solved. In order to solve that problem, special switching and control means are incorporated in the rotating part of the section plane-scanning unit or in a control unit rotating with said scanning unit and said switching and control means serve only to activate each sound transducer head at the proper time.It has been found in practice that such switching and control means must meet the following requirements: Each switching operation must be performed quickly because when the picture repetition frequency is high each sound transducer head will be activated only for a time which is somewhat shorter than the time which would correspond to the frequency and amounts to a fraction of a second (less than 0.1 second at 10 pictures per second), and the time which is available for activation must not be unduly shortened by excessively long switching times.

The switching means should have a very low resistance in a conducting state because any increase of the resistance will result in losses in sensitivity. The ratio between the resistances of the switching means in the conducting and nonconducting states, i.e., the switch-controlled attenuation, must be very high. In practice, a switch-controlled attenuation of at least 60 dB, preferably 80 dB, is required to ensure a satisfactory operation of the equipment. This requires a change in resistance of 1:1000 or 1:10000, respectively.

A bounce-free switching is required also for the switching means incorporated in the scanning unit. A switch is said to be bounce-free when the change from one state of the switch to the other takes place in a single step rather than in a rapid sequence of steps, which may be effected, e.g., when the operation of a mechanical switch involves a repeated resilient separation of the contact surfaces of the switch under the action of elastic forces before said surfaces remain finally in contact with each other.

Besides, the operation of the switching means must not depend on orientation because the section plane-scanning unit used in most cases or virtually exclusively for medical diagnosis must often be brought to different orientations during one examination.

A long life is essential in practice. Each switch or each activation control unit must perform several switching operations per second and nevertheless must not appreciably change its characteristics after a prolonged time of operation.

A uniform threshold sensitivity is essential too because the times at which the activation is initiated and terminated will determine the positions of the lateral boundaries of each picture which is generated by means of the sound transducer head and displayed by the control and display means and in case of irregularities these picture edges of consecutive pictures will be shifted so that the overall display will be inaccurate and blurred.

Mechanical switches which are actuated, e.g., by cam slots, would not be fast enough and would not be bounce-free and their operation would not be entirely independent of orientation. They have only a short life and have no uniform threshold sensitivity. Mechanical switches controlled by an external magnetic field are also not capable of a bounce-free switching in practice. They are not independent of position and have only a short life and no uniform threshold sensitivity. Besides, several switches have greatly varying characteristics so that it is necessary in practice to select switches having the same characteristics for each section plane-scanning unit. When one of these switches has failed in use, it is very difficult to find a new switch which has the same characteristics as the other switches of the scanning unit.

It has already been attempted to replace the mechanical switches by non-contacting switching means, for instance, by magnetic control means comprising chokes, magnetic circuit boards or Hall probes. Optical control means comprising photoelectric detectors, photocells and phototransistors may also be used. But such noncontacting electronic switching means can provide only a small switch-controlled attenuation and have a relatively high resistance also when they conduct. Whereas a resistance ratio of 1:1,000,000 between the conducting and nonconducting states can be achieved with mechanical switches, only a change in resistance of 1:100 can be effected by most non-contacting switches.The desired switch-controlled attenuation can be achieved by a proposal to connect at least one series switch and one parallel switch to each sound transducer head and to close the two switches in alternation but such an arrangement will result in higher losses and a complicated overall structure.

In section plane-scanning units of the kind with which the invention is concerned, each sound transducer head projects a large number of ultrasonic pulses during each activation period and the sound beam formed by said pulses is moved relative to the scanning unit and in the section plane of the specimen, which remains coupled to the sound-transmitting window of the scanning unit whereas the latter is not moved relative to the specimen to be examined or is only slowly moved relative thereto. In most cases, the same section plane is scanned with the sound beam from the next sound transducer head immediately thereafter and often during the time in which the sound transducer head which has just been inactivated leaves the region of the section plane.

U.S. Patent Specification 3,714,817 discloses ultrasonic equipment for testing materials and for displaying defects of materials in displays. In that equipment, which differs in kind from section plane-scanning equipment, the otherwise conventional sound transducer head which is moved by hand over the specimen to be inspected and in sliding contact therewith, is replaced by a sound transducer head wheel consisting basically of a polygonal disc-shaped prism having outside surfaces which are formed by rectangular sound transducer heads. As the wheel is rotated in contact with the specimen to be inspected, these outside surfaces successively contact the surface of said specimen. Only when a sound transducer head snugly contacts the specimen is the sound transducer head adequately coupled to the specimen. As the rotation of the wheel is continued so that the next following sound transducer head can be applied. the soundemitting surface of the sound transducer head will be lifted from the specimen so that the coupling will be eliminated. For this reason each sound transducer head can be effectively operated only in a single position relative to the scanning unit and to the specimen. By means of parallel sound beams generated by respective sound transducer heads, the specimen is scanned in spaced apart regions disposed on the path contacted by the rotating wheel. Each sound transducer head which is in a coupled position is activated by a transformer, which comprises a stationary coil having a ferrite core and movable coils which have also ferrite cores and are associated with respective sound transducer heads.The stationary coil is mounted in a stationary part of the wheel holder and is essentric with respect to the axis of the wheel. The movable coils associated with respective sound transducer heads are mounted on the wheel in a circular series and are spaced apart so that during a rotation of the wheel each movable coil which is associated with a given sound transducer head will be coaxial with the stationary coil and its core whenever the sound transducer head with which said movable coil is associated is in snug contact with the specimen so that the associated sound transducer head is coupled to the control and display means whenever said sound transducer head is in snug contact with the specimen. The coupling is less effective or interrupted in all intermediate positions of the wheel.

It is an object of the invention to provide examination equipment which is of the kind described first hereinbefore and in which each sound transducer head is activated and deactivated in such a manner that all requirements specified hereinbefore will be fulfilled even if adjacent sound transducer heads are activated almost without intervals of time.

This object is accomplished in that said movable winding part of the transformer comprises a plurality of movable coils, which have respective magnetic cores and are associated with respective sound transducer heads, the stationary winding part comprises a stationary coil having a magnetic core, the individual coils are parallel and eccentric to the axis of rotation, the stationary winding part is coaxial to the axis of rotation, two pole pieces are provided, which define a coupling range and are magnetically coupled to respective ends of said stationary coil and adapted to be magnetically coupled to respective ends of each of said movable coils when it is disposed in said coupling range and at least one of said pole pieces is non-rotatably connected to said stationary coil and adapted to define a narrow air gap with one end face of said core of each of said movable coils, and each of said movable coils is arranged to be magnetically coupled to said stationary coil only as long as said at least one pole piece defines said air gap with said end face of said core of said movable coil.

In this arrangement, each sound transducer head is activated and inactivated by noncontacting means comprising a transformer having specially designed elements. As the range in which each sound transducer head is coupled to said stationary coil will particularly depend on the size and shape of the at least one pole piece, the time in which a given sound transducer is activated head will be exactly controlled whereas the adjacent sound transducer head will be held inactive at that time. The provision of a concentric stationary transformer coil permits a symmetrical arrangement.

As has been mentioned, the beginning and termination of the time during which each sound transducer head is activated during the operation of the section plane-scanning unit depends on the configuration and size of the pole pieces and cores. Various structural variants are possible. In one embodiment, pole pieces having the shape of a sector of a circle and defining said coupling range are carried by the stationary coil at both ends of its core and the movable coils and their cores move between said pole pieces and define air gaps therewith which are as narrow as possible.

In another embodiment, the cores of the movable coils associated with respective sound transducer heads are carried by the arms of a common star-shaped pole piece, which is disposed at one end of the transformer and defines a narrow air gap with the adjacent end face of the core of the stationary coil, which at the other end of its core carries a sector-shaped pole piece, which defines said coupling range and is adapted to define a narrow air gap with the end face of the core of each of the movable coils.

In both embodiments mentioned above, the core of each movable coil which is coupled at a time together with the pole pieces and the core of the stationary coil constitute a magnetic circuit which has substantially no stray field so that there is a highly selective discrimination from the movable coils which are not coupled.

The transition between the uncoupled state of a movable coil and the state in which said movable coil is coupled to the stationary coil should be as abrupt as possible. That change of state can be favorably influenced by the selection of the geometric configuration of the pole pieces and cores and also by the provision of special shielding means.

In one embodiment, the pole pieces consist of inserts in coaxial discs of non-ferromagnetic material which has a high electrical conductivity and the movable coils are accommodated in openings of a concentric drum made of such material.

In practice, that design results in a sharper discrimination between the coupled and uncoupled states, in a higher efficiency of the transformer and in a decrease of the transmission losses. Eddy currents occur in the parts which are electrically conducting and non-ferromagnetic. A drum may be used which is formed adjacent to each movable coil with a longitudinal slot for suppressing the eddy currents so that the latter are directed in a predetermined direction to effect a concentration of the field lines of the transformer to the movable core which is in the coupling range.

Further detaiis and advantages of the subject matter of the invention will become apparent from the following detailed description of the drawings.

The subject matter of the invention is illustrated by way of example in the drawings, in which Figure 1 is a high schematic view showing a section plane-scanning unit with the housing that accommodates the sound transducer head, shown in section, whereas the associated control and display unit and the connecting lines are diagrammatically indicated, Figure 2 is a highly diagrammatic and simplified view showing the transformer used in the scanning unit, for an explanation of its overall structure and its function, Figure 3 is an elevation showing a transformer, Figure 4 shows as a detail of Figure 3 the drum of the transformer and the movable coil inserted in said drum, and Figure 5 is an exploded view showing the cores of a modified transformer.

The scanning plane-scanning unit shown in Figure 1 comprises a handle 1, which contains a drive motor and a gear unit and is provided with terminals V for the energization of the motor and for connection to lines L which lead to the pulse generator and the signal receiver of a control and display unit U for ultrasonic section plane examination. The unit U comprises a fluorescent screen S for displaying the section plane which has been scanned by the scanning unit.

The handle is connected to a housing 2, which has a shell 3 containing a sound-transmitting window in a portion which is adapted to be applied to a specimen to be examined. This window consists, e.g., of a sound-transmitting diaphragm 4 and extends over a peripheral portion corresponding to the sector-shaped area in which the section plane is to be scanned. The motor which is accommodated in the handle 1 drives by means of a shaft 5 a wheel 6, which is accommodated in the housing 2. A plurality of sound transducer heads 7 are carried by said wheel and flush with the periphery thereof. Each sound transducer head is in an activated state only during its movement past the window 4 and in an inactive state during the remainder of its revolution. The structure described thus far is basically known from U.S.Patent Specification 4,102,204, which describes also how the section image can be displayed on the fluorescent screen S. The same problems regarding the activation and inactivation of moving sound transducer heads will also arise if the sound transducer head must be in an activated state during its movement past a reflector and must be maintained in an inactive state during the remaining time. In section piane-scanning units having sound transducer heads which are angularly oscillated on an axis, the sound transducer heads must be activated and inactivated in a certain sequence and for a certain time in dependence on the position of each sound transducer head relative to the scanning unit.

In accordance with Figure 1 , the transmission of signals and the selective activation and inactivation of each sound transducer head will be effected by a transformer having a stationary part 9 and a movable part 8, which revolves with the wheel 6. In this embodiment, the transformer is accommodated in the wheel 6 but the transformer might alternatively be spaced from the wheel, provided that its movable part rotates in synchronism with the wheel 6.

The stationary part 9 of the transformer is connected by leads to the terminals which are provided in the handle and serve for the transmission of signals. To improve the coupling of sound, the housing 2 may be filled with liquid.

The wheel 6 may be eccentrically offset toward the sound-transmitting window 4 with respect to the housing 2.

Each of the two parts 8, 9 of the transformer comprises a winding part. In accordance with Figure 2, the stationary winding part may consist of a coil which is coaxial to the axis of rotation and comprises a winding 10, a magnetic core 11 and pole pieces 12. 13, which have the configuration of sectors of a circle and are rigid with the core 11 at opposite ends of the latter.

The movable part 8 of the transmitter comprises for each sound transducer head 7 a movable coil, which comprises a movable magnetic core 14 or 1 4a and a movable winding 1 5 or 1 spa, which is connected by leads 16 to the activating electrodes of the associated sound transducer head 7. The leads 1 7 by which the stationary winding 10 is connected to the control and display means have been mentioned hereinbefore.The movable coils 14, 15; 1 4a, 1 spa are parallel to the stationary coil 10, 11 and eccentric to the axis of rotation so that during a rotation of the wheel 6 only one of the movable coils 14, 15; 4a, 1 spa is disposed at a time between the pole pieces 12, 13 and is thus coupled to the stationary coil 10, 11 for the transmission of signals. The air gap between each end face of the core 1 4 or 1 4a of a movable coil and the adjacent pole piece 12, 13 should be as narrow as possible.The size and configuration of the pole pieces 12, 1 3 will determine the size of the sector through which a given movable coil 14, 1 5 etc. is movable while it is disposed between the pole pieces and coupled to the stationary coil 10, 1 When a given movable coil 1 4a, 1 spa etc. is disposed outside the pole pieces 12, 13, that coil will not be coupled to the stationary coil 10, 11 or will be so slightly coupled to it that the desired switch-controlled attenuation between the closely coupled coil and the uncoupled coil will be obtained so that there is no need for additional switching means for activating and inactivating each sound transducer head.

To ensure that the angle moved by the wheel 6 between the scanning of the specimen by a given sound transducer head 7 and the next following sound transducer head 7 is as small as possible, the angle subtended by each of the sector-shaped pole pieces 12, 1 3 is only slightly smaller, preferably by a few degrees, than the angular clearance between adjacent sound transducer heads included in the wheel 6, with respect to the axis of rotation of the wheel 6. In a preferred embodiment, the angle moved by the wheel 6 between the scanning of the specimen by a given sound transducer head and by the following sound transducer head should be only as large as is required to ensure that there will be no mutual disturbance of the displays generated by said sound transducer heads 7.

Figures 1, 3 and 4 show transformers which are used in practice and have improved switching and transmission characteristics when compared with a transformer as shown in Figure 2. This improvement is effected in that the ferromagnetic parts are incorporated in parts which consist of a material which is not ferromagnetic and has a high electrical conductivity, such as aluminum, The movable part 8 of that transformer comprises an aluminum drum, which has a center bore 1 8 and further comprises bores 19, 1 9a, 1 9b, 1 9c, which accommodate respective movable coils, each of which consists of a core 14, 1 4a; etc. and a winding, not shown. Each of the bores 1 9 to 1 9c communicates through an axially extending slot 20 with the bore 1 8.

The bore 1 8 accommodates the stationary coil 10, 1 The pole pieces 12, 13 are complemented by aluminum parts 21,22 to form complete discs.

Eddy currents can be generated in the parts 8, 21, 22 which are electrically conducting and not ferromagnetic. Owing to the slots 20, the eddy currents in the drum 8, particularly between the pole pieces 12, 13, are compelled to flow in a certain direction so that the concentration of the flux lines between each of the pole pieces 1 2 and 13 and the movable core, such as 14, which is coupled to said pole pieces.

Alternatively, the ferromagnetic parts may be designed as shown in Figure 5. In that embodiment, the movable cores 14, 1 4a, 1 4b, 1 4c are secured to the ends of the arms of a starshaped pole piece 23, which consists of ferromagnetic material and rotates with said movable cores. The stationary core 10 is coaxial to the star-shaped pole piece 23 and defines only a narrow air gap therewith. In the present case, only a single pole piece 12 having the shape of a sector of a circle is rigid with the stationary core 10 and defines a narrow air gap with the end face of the core, such as 14, of each movable coil when the latter is coupled. In that embodiment too, the cores 14, 1 4a, 1 4b, 1 4c and the pole piece 23 may be accommodated in a drum of aluminum and the pole piece 12 may be embedded in a disc, such as 21.

Claims

1. Ultrasonic examination equipment comprising a section plane-scanning unit and control and display means, which scanning unit comprises at least two sound transducer heads, which are adapted to be driven to rotate or oscillate on an axis of rotation and angularly spaced apart with respect to said axis and drive means for moving said sound transducer heads in unison about said axis, each of said sound transducer heads being adapted to be activated only during a predetermined range of its movement and when activated to project a sound beam into a specimen to be examined, so as to scan said specimen in a section plane, said equipment also comprising a transformer for connecting the control and display means to the sound transducer heads and comprises a stationary winding and a second winding which is movable with the sound transducer heads, characterized in that said movable winding part of the transformer comprises a plurality of movable coils, which have respective magnetic cores and are associated with respective sound transducer heads, the stationary winding part comprises a stationary coil having a magnetic core, the individual coils are parallel and eccentric to the axis of rotation, the stationary winding part is coaxial to the axis of rotation, two pole pieces are provided, which define a coupling range and are magnetically coupled to respective ends of said stationary coil and adapted to be magnetically coupled to respective ends of each of said movable coils when it is disposed in said coupling range and at least one of said pole pieces is nonrotatably connected to said stationary coil and adapted to define a narrow air gap with one end face of said core of each of said movable coils, and each of said movable coils is arranged to be magnetically coupled to said stationary coil only as long as said at least one pole piece defines said air gap with said end face of said core of said movable coil.

2. Ultrasonic examination equipment according to claim 1, characterized in that pole pieces having the shape of a sector of a circle and defining said coupling range are carried by the stationary coil at both ends of its core.

3. Ultrasonic examination equipment according to claim 1, characterized in that the cores of the movable coils associated with respective sound transducer heads are carried by the arms of a common star-shaped pole piece, which is disposed at one end of the transformer and defines a narrow air gap with the adjacent end face of the core of the stationary coil, which at the other end of its core carries a sector-shaped pole piece, which defines said coupling range and is adapted to define a narrow air gap with the end face of the core of each of the movable coils.

4. Ultrasonic examination equipment according to any of claims 1 to 3, characterized in that the pole piece consists of inserts in coaxial discs of non-ferromagnetic material which has a high electrical conductivity and the movable coils are accommodated in openings of a concentric drum made of such material.

5. Ultrasonic examination equipment according to claim 4, characterized in that the drum is formed adjacent to each movable coil with a longitudinal slot for suppressing or directing eddy currents.

6. Ultrasonic examination equipment according to any of claims 1 to 5, characterized in that said at least one pole piece has the configuration of a sector of a circle subtending an angle which is smaller than the angular clearance between adjacent ones of said movable coils with respect to said axis of rotation.

7. Ultrasonic examination equipment constructed and arranged substantially as hereinbefore described and as shown in the figures of the accompanying drawings.