CA1129564A - Computer tomography method and apparatus - Google Patents
Computer tomography method and apparatusInfo
- Publication number
- CA1129564A CA1129564A CA353,328A CA353328A CA1129564A CA 1129564 A CA1129564 A CA 1129564A CA 353328 A CA353328 A CA 353328A CA 1129564 A CA1129564 A CA 1129564A
- Authority
- CA
- Canada
- Prior art keywords
- assembly
- slip ring
- patient
- rotating
- electrical
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/56—Details of data transmission or power supply, e.g. use of slip rings
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/032—Transmission computed tomography [CT]
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R39/00—Rotary current collectors, distributors or interrupters
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/40—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis
- A61B6/4021—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis involving movement of the focal spot
- A61B6/4028—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis involving movement of the focal spot resulting in acquisition of views from substantially different positions, e.g. EBCT
Abstract
COMPUTER TOMOGRAPHY METHOD AND APPARATUS
ABSTRACT
Apparatus is disclosed for providing electrical energy to orbital components of a computed tomography (CT) scanning unit. The apparatus includes a number of high voltage slip rings immersed in an insulating dielectric material. Each slip ring contacts a sta-tionary brush biased to contact the slip ring to insure maintenance of a low resistance path between a stationary source of high potential and a cathode and anode pair of an orbital X-ray tube. A number of low voltage slip rings are further included to facilitate transmission of low voltages to other orbital components of the CT unit. The apparatus is of a compact light-weight design and is mounted for rotation of certain components about an axis which intersects a patient's torso to provide CT scan-ning flexibility.
ABSTRACT
Apparatus is disclosed for providing electrical energy to orbital components of a computed tomography (CT) scanning unit. The apparatus includes a number of high voltage slip rings immersed in an insulating dielectric material. Each slip ring contacts a sta-tionary brush biased to contact the slip ring to insure maintenance of a low resistance path between a stationary source of high potential and a cathode and anode pair of an orbital X-ray tube. A number of low voltage slip rings are further included to facilitate transmission of low voltages to other orbital components of the CT unit. The apparatus is of a compact light-weight design and is mounted for rotation of certain components about an axis which intersects a patient's torso to provide CT scan-ning flexibility.
Description
-Descr~tion 11~95~4 Technical Field . _ - Th~ invention relates to an improved apparatus for supplying electrical power to orbital elements of a computed tomography scanning unit.
sBackground Art The art of computed tomography (CT) scanning ; has greatly improved a physician's ability to acurately diagnose the internal structure of a patient. The process of CT scanning involves the sending of X
radiation through a patient from a variety oE different locations, and determining the intensity oE the transmitted radiation with one or more X-ray detectors.
Intensity data is sent to imaging electronics for image reconstruction. In many studies, the image viewed by the doctor presents greater detail than conventional X-ray techniques and therefore can be better used to diagnose the patient's condition.
; In a typical computed tomography scanning environ-; m~nt, an X-ray source is orbited about a patient 20while the patient is irradiated. The detector or d~tectors either orbit with tbe source or form a non orbiting array of detecting units. In either configuration a substantial amount of X-ray emitting and shaping apparatus rotates with the X-ray source.
25This apparatus as well as the X-ray source must be powered by electrical energy supplied from a source - exterior to the rotating CT apparatus.
One particular computed tomography scanning unit includes an orbiting source of X radiation which 30emits an X-ray beam in a spread configuration. The detector units are stationary relative to the X-ray source and form an annular ring of detectors about the patient. The X radiation source is positioned to transmit X-rays through the patient along a series 35Of beam paths as it is orbited. Since a variety of beam generating, shaping and transmitting functions - : - ~ : , .
1, ~ 9 ~ ri 4 must be performed on the orbiting apparatus as orbiting occurs, a num~er of electricaI signals must be supplied to tbis apparatus.
- To create X-~adiation, a large potential diEference 5 on the order of 150 kilovolts must be provided.
This voltage is used to accelerate electrons from an X-ray tube cathode to an anode for X radiation generation. Typically a filament voltage and an X-ray focusing cup control are required so that a 10 number of high voltage inputs are necessary. Providing these high voltage potential differences to the X radiation source creates design problems which have in the past required sophisticated cabling and input techniques.
A number of low voltage control and energization signals must also be transmitted to the orbiting apparatus. It is known that the X-ray tube tends to heat up due to the collisions of the accelerated electrons with the X-ray anode and to dissipate the 20 heat build up some CT units require tbat the X-ray anode be continuously rotated. A motor, which typically requires at least two and possibly three leads, provides this rotational cooling.
In order that the beam produced by the X radiation 25 tube occupies the proper dimensions, it is necessary that the X radiation be collimated. A collimator is therefore mounted to orbit with the x-ray tube.
The collimator includes an adjustment motor which is powered by an external source of energy.
Control solenoids and a laser source to aid in patient positioning also orbit the patient and receive power from a stationary power source. Actuation of the solenoids is achieved via command signals which are also transmitted to the orbiting apparatus.
35 Since these various functions must be coordinated to produce the proper X-ray transmission and shaping, a clocking signal must also be sent to the orbiting apparatus.
, ; ~
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t564 .
~ lt'hb~h most of the detectors on the descr,ibed CT
apparatus are stationary, one orbitinq de'cector is in-cIuded which is u~ed to calibrate the X radiation and provide a reference signal. This orbiting detector 5 requires ener~i~ation from a stationary source ~nd pro-vides an O~ltput signal which musc also pass through cabling ~hich leads from the orbiting appara-tus to non-rotating'elements, namely imaging elec-tronics.
Present state of the art CT scanning units provide , 10 the requisite ~abling inputs to the rotating portions i of the CT unit through rather sophisticated cable takeup mechanisms. Although such cable takeup mechanism have been used successfully they are limited in applicability by certain design disadvantages.
One such cable takeup mechanism includes a flex-ible cable of finite length which is woLlnd and unwouncl from a mandrel as the CT unit causes the X-ray tube to orbit. A CT unit employing such a mechanism can only be rotated a finite amount before its direction of rota-' 20 tion must be reversed. Such a reversal in direction introduces a complexity in controlling the rotation of the CT unit. Moreover, at leas~c one proposed diagnostic procedure has not been generally adopted by clinicians because of this limitation. That procedure would syn-
sBackground Art The art of computed tomography (CT) scanning ; has greatly improved a physician's ability to acurately diagnose the internal structure of a patient. The process of CT scanning involves the sending of X
radiation through a patient from a variety oE different locations, and determining the intensity oE the transmitted radiation with one or more X-ray detectors.
Intensity data is sent to imaging electronics for image reconstruction. In many studies, the image viewed by the doctor presents greater detail than conventional X-ray techniques and therefore can be better used to diagnose the patient's condition.
; In a typical computed tomography scanning environ-; m~nt, an X-ray source is orbited about a patient 20while the patient is irradiated. The detector or d~tectors either orbit with tbe source or form a non orbiting array of detecting units. In either configuration a substantial amount of X-ray emitting and shaping apparatus rotates with the X-ray source.
25This apparatus as well as the X-ray source must be powered by electrical energy supplied from a source - exterior to the rotating CT apparatus.
One particular computed tomography scanning unit includes an orbiting source of X radiation which 30emits an X-ray beam in a spread configuration. The detector units are stationary relative to the X-ray source and form an annular ring of detectors about the patient. The X radiation source is positioned to transmit X-rays through the patient along a series 35Of beam paths as it is orbited. Since a variety of beam generating, shaping and transmitting functions - : - ~ : , .
1, ~ 9 ~ ri 4 must be performed on the orbiting apparatus as orbiting occurs, a num~er of electricaI signals must be supplied to tbis apparatus.
- To create X-~adiation, a large potential diEference 5 on the order of 150 kilovolts must be provided.
This voltage is used to accelerate electrons from an X-ray tube cathode to an anode for X radiation generation. Typically a filament voltage and an X-ray focusing cup control are required so that a 10 number of high voltage inputs are necessary. Providing these high voltage potential differences to the X radiation source creates design problems which have in the past required sophisticated cabling and input techniques.
A number of low voltage control and energization signals must also be transmitted to the orbiting apparatus. It is known that the X-ray tube tends to heat up due to the collisions of the accelerated electrons with the X-ray anode and to dissipate the 20 heat build up some CT units require tbat the X-ray anode be continuously rotated. A motor, which typically requires at least two and possibly three leads, provides this rotational cooling.
In order that the beam produced by the X radiation 25 tube occupies the proper dimensions, it is necessary that the X radiation be collimated. A collimator is therefore mounted to orbit with the x-ray tube.
The collimator includes an adjustment motor which is powered by an external source of energy.
Control solenoids and a laser source to aid in patient positioning also orbit the patient and receive power from a stationary power source. Actuation of the solenoids is achieved via command signals which are also transmitted to the orbiting apparatus.
35 Since these various functions must be coordinated to produce the proper X-ray transmission and shaping, a clocking signal must also be sent to the orbiting apparatus.
, ; ~
.. . , ,~ . .
t564 .
~ lt'hb~h most of the detectors on the descr,ibed CT
apparatus are stationary, one orbitinq de'cector is in-cIuded which is u~ed to calibrate the X radiation and provide a reference signal. This orbiting detector 5 requires ener~i~ation from a stationary source ~nd pro-vides an O~ltput signal which musc also pass through cabling ~hich leads from the orbiting appara-tus to non-rotating'elements, namely imaging elec-tronics.
Present state of the art CT scanning units provide , 10 the requisite ~abling inputs to the rotating portions i of the CT unit through rather sophisticated cable takeup mechanisms. Although such cable takeup mechanism have been used successfully they are limited in applicability by certain design disadvantages.
One such cable takeup mechanism includes a flex-ible cable of finite length which is woLlnd and unwouncl from a mandrel as the CT unit causes the X-ray tube to orbit. A CT unit employing such a mechanism can only be rotated a finite amount before its direction of rota-' 20 tion must be reversed. Such a reversal in direction introduces a complexity in controlling the rotation of the CT unit. Moreover, at leas~c one proposed diagnostic procedure has not been generally adopted by clinicians because of this limitation. That procedure would syn-
2~ chronise CT X-ray tube energization during a heart study with heart movement through con-'crol signals generated ; by an EI~G machine. The problem has been the cyclical rever~al of orbital mo~tion is too apt to occur when the X-ray tube should be energized.
A certain amount of power is expended in moving the cable during CT unit rocation. This adcl-~d power expenditu-e limits scanning speed and may add a non-uniformi~y oE rotation dllring an X~ray exposure.
~laintenancA of the cables i5 perhaps the most 35 disadvant~geous feature of the cable takeup energiza-tion method. Constant f:lexing of the cable even ~ .
!~.~ " ' - . . ....
112 3 ~
with the tak~-up mechanism previously described may ~entu~lly cause it to crack or break so that it must perlo~icc~lly be replaced.
To overco~.e some disadvantages noted with regarcls 5 to the ca~le take~up mechanisms, a slip ring t~pe of power transferral has been suggested. The suggest~d s:lip ring arrangement, however, has not completely solved the problems inherent with prior mechanisms and may n~t ade~uately ins~late -the hiyh voltage 10 poten~ia~s required for CT scanning. The arrangement disclos.es only one slip ring for prov;ding power while from the above it is appar-ent that a number of high power inputs are necessary.
More CT sc2nning in~ormation is available if 1~ the plane in which the pa.ient lies can be tilte~
wi.h res~ect to the X-ray bea~ plane. Due to the siæe and configuration of prior art CT slip rings~
tlle e~amination oE the patient and the orbital axis could not be changed relatively. Thus, additional 2~ information was available only i~ the patient were shifted laterally with respect to the X-ray beam plane. It is there~ore apparent tha-t suggested slip ring power arrangements have inadequacely dealt with the power transmittal problems in prior art cable 25 take-up mechanisms Disclosure of Invention .. . . _ The present invention provides a unified, compact, slip-ring arrangement for transmitting electrical energ~ to orbiting components in a CT scanning unit.
30 The slip-ring arran~ement is completely immersed in an insulating fluid ade~uately to insulate the high X-ray generating voltages ~rom the est o~ the unit. A plurality of ~otll high and low voltage slip rings are provided to genera-te, calibrate and shape 35 the X radiation.
. ~
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9~6 4 5 One embodiment of the invention includes a station-ary gantry apparatus to which an orbiting assembly is mounted for orbital rotation about a scanning axis coincident with a patient axis. An X-ray source 5 powered by a high voltage input is attached to the : assembly and irradiates a patient for reconstruction imaging. The source generates X radiation which is collimated into beams beLore traversing the patient.
The radiation impinges upon an array of X-ray detectors 10 ~hich can either be non orbital or movable with the source.
Both high and low electrical potential is provided to the rotating assembly by the present design.
A high voltage input receptacle is mounted to the 15 gantry for receiving a high electrical input. The high ~lectrical input is transmitted to the orbitally rota~ing portion of the assembly by means of a connec-tion technique which includes spring loaded brushes i attached to the orbitally stationary gantry and a number of annularly shaped slip-rings attached to the rotating assembly. The brushes are maintained in contact with the slip rings to insure there exists a low resistance path from the input receptacle to the rotating assembly. Attached to the slip ring is a transmission line for coupling the hi~h input potential to the X-ray source. By means of this arrangement, a high electrical potential is transmitted to the orbiting ,Y-ray source without the use of a complex cable takeup arrangement.
In the preferred embodiment o~ the invention, a number o~ high voltage rotating slip rings are electrically coupled via brushes to stationary high voltage input receptacles. Multiple focus X-ray tubes with grid potential control require multiple high potential voltage inputs so that apparatus embodying the invention utilizes four orbitally , , , . " ::: . : . ..
:.i - .: : -~, ; :~. , ,. .. .. ;~ , .
" ,, , . : , , . . , -. ; : :
1~2~5t;~
"
rotating hig~ voltage slip rings. The apparatus further includes a plurality of low input 51ip rings for transmitting -low input voltages from the stationary gantry to the orhiting assembly. This configuration 5 provides the CT user significant design flexibilit~
in sending power and control signals to the orbiting assembly.
In this embodiment the orbiting and nonrotating portions of the CT scanning unit are configured to 10 define a cavity surrounding the high voltage input slip rings. This cavity is filled with an insulating dielectric fluid which completely surrounds the high volcage slip ring and brush arrangement to effectively insulate the high potential passing through the slip 15 ring from the rest of the CT unit. In this way arcing from the high poten-tial slip ring to electrical ground does not occur. Seals are provided to prevent - leakage o~ the dielectric fluid from the CT unit thereby maintaining the insulating fluid in contact 20 with the entire slip ring. Only the high potential slip ring arrangements are insulated since the low potential slip rings carry low power current and present no arcing danger.
The length along the axial dimension of the 25 CT unit embodying the improved high voltage slip-ring arrangement is short. This compact design allows the unit to be tilted about an axis transverse to the scanning axis by approximately 20 and allows the patient to be scanned in planes other than a 30 vertical cross section.
From the above, it is apparent that one feature and object of the present invention is to provide a simplified~ compact and safely insulated brush and slip-ring arrangement for providing both high 35 and low power to orbiting components of a CT scanning unit. A second advantage of the invention is to :.: : : , 11~95C,~ 7 provide a number of slip-rings thereby providing CT unit design flexibility. The compact nature of the apparatus allows the slip-ring arrangement to he tilted so the orbiting X-ray tube can transmit S radiation across non-vertical sross sections.
These and other features and advantages oE the invention will become more apparent as the invention - becomes better understood from the detailed description that follows, when considered in conjunction with 10 the accompanying drawings.
Brief_Description of the Drawings FIGURE 1 shows schematically the elements com-prising a CT scanning arrangement.
j FIGURE 2 schematically shows a source of X-rays 15 positioned to irradiate a patient cross section.
FI~URE 3A shows a front elevational view of elements of a CT scanner.
FIGURE 3B shows a partially sectioned view of the CT scanner shown in Figure 3A.
FIGURE 4 is an enlarged cross sectional view of a portion of the scanner shown in Figure 3B.
FIGURE 4A shows a further enlarged part of the cross sectional portion shown in Figure 4.
FIGURES 5A-5C sho~ wiring schematics for high 25 voltage energization of a CT X-ray tube.
Best Mode for Carrying Out the Invention Referring now to the drawings and Figure 1 in particular, a computed tomography system 10 designed for examining the internal structure of a patient 30 is shown. The system comprises a scanning unit 12, a couch 16, a signal processor ~0, and imager 22.
The scanning unit includes a housing 13 which covers the X-ray apparatus and provides an attractive appear-ance to the unit. Before a CT scan the couch 16 35 and a patient lying on the couch are moved into an aperture 14 in the housing 13. An X-ray tube within -;, ,. ... ~ .
. , ~. : .. . . .
the unit is energized and transmits X radiation, thereby irradiating the patien~.
The scanning unit 12 can be tilted about an axis 24 parallel to the floor. This movement provides 5 a flexibility in scanning without repositioning of the patient. Two support columns 23 mount the unit 12 for rotation about the axis 24. Rotational motion is applied by an AC motor 25, a right angle drive ;; 2~, and a pivot arm 27.
A series of X-ray detectors detect X-ray intensity af.er it passes through the patient and produce electrical signals in response to the radiation.
These electronic signals representing patient densities are sent from the scanning unit to the signal processor 15 20 by an electrical connection 15. The signal processor receives these signals and utlliæes known CT processing ; techniques to produce signals representing the varia-~ tions in patient density across a patient cross ; section. The signal processor then sends signals 20 to an imager 22 which provides an image o~ the patient.
Figure 2 schematically illustrates a CT X-ray source 30 and array of detectors 32 positioned about the patient aperture 14. The source 30 emits a spread of X radiation which passes through a collimator 25 34 which shapes the X radiation into a number of individual beams. One X-ray beam 33 is shown as it passes through the patient aperture and impinges upon a detector in the circular array 32 of X radiation detectors. The illustrated detectors are shown 30 positioned on the side of the patient aperture opposed from the source 30 and therefore certain of them detect radiation intensity a~ter that radiation has passed through the patient.
Although the Figure 2 -illustration shows a finite 35 num~er of detectors, so-called "stationary detector"
CT designs provide an array of detectors which com-pletely surround the patient aperture. Thus, it ~ J ~ ~_ is possible for the~X radiation detectors to remai stationary while the X radiation source 30 orbits about the patient~ aperture irradiating the patient from a number of different positions. The detec~ors 5 are of a known design and convert X radiation into an electrical signal whose outputs can be sen-t to the signal processor 20 ~or CT image formation.
All CT reconstruction algorithims require that the X radiation impinge upon the patient cross section 10 from a number of different positions so that intensity data from radiation originating ~rom various positions is obtained. By obtaining this multi-position intensity data it is possible to reconstruct a mapping or image of the density variations within the patient cross 15 section. To achieve this mul-ti~position irradiation the present invention includes a rotating assembly which supports the X-ray source 30 and is movable relative to the X-ray detector array 3~.
Movement of the X-ray source in a circular path 20 causes electrical energization problems which are compounded by the high voltage potential differences coupled to the X-ray tube.
Figures 3A and 3B illustrate a new and improved CT apparatus which facilitates the sending of potential 25 differences to the X-ray source for X-ray generation.
The CT apparatus shown includes a stationary gantry arrangement 40, a rotating assembly 42 and an X-ray tube housing 44. During operation a belt drive 48 causes the rotating assembly 42 to rotate within 30 the stationary gantry 40 thereby irradiating a patient cross section of interest from a number of different positions. The rotating assembly comprises a frame 50 attached to an annular portion of the assembly by eight connectors 43 (See Figure 3A) spaced evenly 35 about the patient aperture 14. The frame 50 carries the X-ray housing 44 Eor orbital rotation about the patient aperture 14.
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A certain amount of power is expended in moving the cable during CT unit rocation. This adcl-~d power expenditu-e limits scanning speed and may add a non-uniformi~y oE rotation dllring an X~ray exposure.
~laintenancA of the cables i5 perhaps the most 35 disadvant~geous feature of the cable takeup energiza-tion method. Constant f:lexing of the cable even ~ .
!~.~ " ' - . . ....
112 3 ~
with the tak~-up mechanism previously described may ~entu~lly cause it to crack or break so that it must perlo~icc~lly be replaced.
To overco~.e some disadvantages noted with regarcls 5 to the ca~le take~up mechanisms, a slip ring t~pe of power transferral has been suggested. The suggest~d s:lip ring arrangement, however, has not completely solved the problems inherent with prior mechanisms and may n~t ade~uately ins~late -the hiyh voltage 10 poten~ia~s required for CT scanning. The arrangement disclos.es only one slip ring for prov;ding power while from the above it is appar-ent that a number of high power inputs are necessary.
More CT sc2nning in~ormation is available if 1~ the plane in which the pa.ient lies can be tilte~
wi.h res~ect to the X-ray bea~ plane. Due to the siæe and configuration of prior art CT slip rings~
tlle e~amination oE the patient and the orbital axis could not be changed relatively. Thus, additional 2~ information was available only i~ the patient were shifted laterally with respect to the X-ray beam plane. It is there~ore apparent tha-t suggested slip ring power arrangements have inadequacely dealt with the power transmittal problems in prior art cable 25 take-up mechanisms Disclosure of Invention .. . . _ The present invention provides a unified, compact, slip-ring arrangement for transmitting electrical energ~ to orbiting components in a CT scanning unit.
30 The slip-ring arran~ement is completely immersed in an insulating fluid ade~uately to insulate the high X-ray generating voltages ~rom the est o~ the unit. A plurality of ~otll high and low voltage slip rings are provided to genera-te, calibrate and shape 35 the X radiation.
. ~
,. ~ ' , ' ' ,''; ~
9~6 4 5 One embodiment of the invention includes a station-ary gantry apparatus to which an orbiting assembly is mounted for orbital rotation about a scanning axis coincident with a patient axis. An X-ray source 5 powered by a high voltage input is attached to the : assembly and irradiates a patient for reconstruction imaging. The source generates X radiation which is collimated into beams beLore traversing the patient.
The radiation impinges upon an array of X-ray detectors 10 ~hich can either be non orbital or movable with the source.
Both high and low electrical potential is provided to the rotating assembly by the present design.
A high voltage input receptacle is mounted to the 15 gantry for receiving a high electrical input. The high ~lectrical input is transmitted to the orbitally rota~ing portion of the assembly by means of a connec-tion technique which includes spring loaded brushes i attached to the orbitally stationary gantry and a number of annularly shaped slip-rings attached to the rotating assembly. The brushes are maintained in contact with the slip rings to insure there exists a low resistance path from the input receptacle to the rotating assembly. Attached to the slip ring is a transmission line for coupling the hi~h input potential to the X-ray source. By means of this arrangement, a high electrical potential is transmitted to the orbiting ,Y-ray source without the use of a complex cable takeup arrangement.
In the preferred embodiment o~ the invention, a number o~ high voltage rotating slip rings are electrically coupled via brushes to stationary high voltage input receptacles. Multiple focus X-ray tubes with grid potential control require multiple high potential voltage inputs so that apparatus embodying the invention utilizes four orbitally , , , . " ::: . : . ..
:.i - .: : -~, ; :~. , ,. .. .. ;~ , .
" ,, , . : , , . . , -. ; : :
1~2~5t;~
"
rotating hig~ voltage slip rings. The apparatus further includes a plurality of low input 51ip rings for transmitting -low input voltages from the stationary gantry to the orhiting assembly. This configuration 5 provides the CT user significant design flexibilit~
in sending power and control signals to the orbiting assembly.
In this embodiment the orbiting and nonrotating portions of the CT scanning unit are configured to 10 define a cavity surrounding the high voltage input slip rings. This cavity is filled with an insulating dielectric fluid which completely surrounds the high volcage slip ring and brush arrangement to effectively insulate the high potential passing through the slip 15 ring from the rest of the CT unit. In this way arcing from the high poten-tial slip ring to electrical ground does not occur. Seals are provided to prevent - leakage o~ the dielectric fluid from the CT unit thereby maintaining the insulating fluid in contact 20 with the entire slip ring. Only the high potential slip ring arrangements are insulated since the low potential slip rings carry low power current and present no arcing danger.
The length along the axial dimension of the 25 CT unit embodying the improved high voltage slip-ring arrangement is short. This compact design allows the unit to be tilted about an axis transverse to the scanning axis by approximately 20 and allows the patient to be scanned in planes other than a 30 vertical cross section.
From the above, it is apparent that one feature and object of the present invention is to provide a simplified~ compact and safely insulated brush and slip-ring arrangement for providing both high 35 and low power to orbiting components of a CT scanning unit. A second advantage of the invention is to :.: : : , 11~95C,~ 7 provide a number of slip-rings thereby providing CT unit design flexibility. The compact nature of the apparatus allows the slip-ring arrangement to he tilted so the orbiting X-ray tube can transmit S radiation across non-vertical sross sections.
These and other features and advantages oE the invention will become more apparent as the invention - becomes better understood from the detailed description that follows, when considered in conjunction with 10 the accompanying drawings.
Brief_Description of the Drawings FIGURE 1 shows schematically the elements com-prising a CT scanning arrangement.
j FIGURE 2 schematically shows a source of X-rays 15 positioned to irradiate a patient cross section.
FI~URE 3A shows a front elevational view of elements of a CT scanner.
FIGURE 3B shows a partially sectioned view of the CT scanner shown in Figure 3A.
FIGURE 4 is an enlarged cross sectional view of a portion of the scanner shown in Figure 3B.
FIGURE 4A shows a further enlarged part of the cross sectional portion shown in Figure 4.
FIGURES 5A-5C sho~ wiring schematics for high 25 voltage energization of a CT X-ray tube.
Best Mode for Carrying Out the Invention Referring now to the drawings and Figure 1 in particular, a computed tomography system 10 designed for examining the internal structure of a patient 30 is shown. The system comprises a scanning unit 12, a couch 16, a signal processor ~0, and imager 22.
The scanning unit includes a housing 13 which covers the X-ray apparatus and provides an attractive appear-ance to the unit. Before a CT scan the couch 16 35 and a patient lying on the couch are moved into an aperture 14 in the housing 13. An X-ray tube within -;, ,. ... ~ .
. , ~. : .. . . .
the unit is energized and transmits X radiation, thereby irradiating the patien~.
The scanning unit 12 can be tilted about an axis 24 parallel to the floor. This movement provides 5 a flexibility in scanning without repositioning of the patient. Two support columns 23 mount the unit 12 for rotation about the axis 24. Rotational motion is applied by an AC motor 25, a right angle drive ;; 2~, and a pivot arm 27.
A series of X-ray detectors detect X-ray intensity af.er it passes through the patient and produce electrical signals in response to the radiation.
These electronic signals representing patient densities are sent from the scanning unit to the signal processor 15 20 by an electrical connection 15. The signal processor receives these signals and utlliæes known CT processing ; techniques to produce signals representing the varia-~ tions in patient density across a patient cross ; section. The signal processor then sends signals 20 to an imager 22 which provides an image o~ the patient.
Figure 2 schematically illustrates a CT X-ray source 30 and array of detectors 32 positioned about the patient aperture 14. The source 30 emits a spread of X radiation which passes through a collimator 25 34 which shapes the X radiation into a number of individual beams. One X-ray beam 33 is shown as it passes through the patient aperture and impinges upon a detector in the circular array 32 of X radiation detectors. The illustrated detectors are shown 30 positioned on the side of the patient aperture opposed from the source 30 and therefore certain of them detect radiation intensity a~ter that radiation has passed through the patient.
Although the Figure 2 -illustration shows a finite 35 num~er of detectors, so-called "stationary detector"
CT designs provide an array of detectors which com-pletely surround the patient aperture. Thus, it ~ J ~ ~_ is possible for the~X radiation detectors to remai stationary while the X radiation source 30 orbits about the patient~ aperture irradiating the patient from a number of different positions. The detec~ors 5 are of a known design and convert X radiation into an electrical signal whose outputs can be sen-t to the signal processor 20 ~or CT image formation.
All CT reconstruction algorithims require that the X radiation impinge upon the patient cross section 10 from a number of different positions so that intensity data from radiation originating ~rom various positions is obtained. By obtaining this multi-position intensity data it is possible to reconstruct a mapping or image of the density variations within the patient cross 15 section. To achieve this mul-ti~position irradiation the present invention includes a rotating assembly which supports the X-ray source 30 and is movable relative to the X-ray detector array 3~.
Movement of the X-ray source in a circular path 20 causes electrical energization problems which are compounded by the high voltage potential differences coupled to the X-ray tube.
Figures 3A and 3B illustrate a new and improved CT apparatus which facilitates the sending of potential 25 differences to the X-ray source for X-ray generation.
The CT apparatus shown includes a stationary gantry arrangement 40, a rotating assembly 42 and an X-ray tube housing 44. During operation a belt drive 48 causes the rotating assembly 42 to rotate within 30 the stationary gantry 40 thereby irradiating a patient cross section of interest from a number of different positions. The rotating assembly comprises a frame 50 attached to an annular portion of the assembly by eight connectors 43 (See Figure 3A) spaced evenly 35 about the patient aperture 14. The frame 50 carries the X-ray housing 44 Eor orbital rotation about the patient aperture 14.
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3 1 ~ 9 ~ o One aspect of the invention is ~he provision of high potential differences ~o the ca~hode and anode of the X-ray tube. In one embodiment of the invention the potential difference between cathode 5 and anode is on the order of 150,000 volts. This potential difference is provided by a positive and negative input each on the order of 75,000 volts removed from ground. To transmit electrical energy to the X-ray tube the stationary gantry 40 includes 1~ both a positive 46 and negative 47 high voltage electrical receptacle or connector. The positive voltage receptacle 46 shown ~n Figure 3B receives a voltage input of plus 75,000 volts from an external voltage source. The negative high voltage receptacle ~not shown in Figure 3B) receives an input voltage of approximately 75 t 000 negative volts.
The assembly further comprises a positive 56 and negative 58 slip ring portion which receive these high voltage inputs and transmit a high voltage 20 differential from the stationary gantry portion 40 to the rotating assembly 42 for transmittal to the X-ray tu~e. The first positive portion 56 includes only one slip ring which is coupled to the positive receptacle 46. The second negative portion 58 includes 25 four slip rings and is designed to receive more than one negative high voltage inputO The purpose of - this multiplicity in high voltage slip ring configura- -t~on is to allow control of the X radiation generation by utilization of either multiple focus or grid 30 potential voltage inputs.
After the high voltage potential is transmitted to the rotating assembly 42 it is further transmitted along cabling (shown in Fiyure 4 as reference numeral 120) to two high voltage receptacles 60, 62 mounted 35 to the frame 50. A first receptacle 60 receives the positive voltage and a second receptacle 62 receives ,.
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the ne~ati~e high vQl~age potentia7 inputs. Frcm these receptacles the high voltage is transmitted to the anode (positive) and cathode (negative) of the rotating X-ray tube.
The gantry is attached to a support 52 radially removed from the patient aperture by means oE suitable connectors 54 such as a nut and bolt arrangement.
This mounting serves to maintain the stationary gantry 40 in position while allowing the support 10 52 to be tilted about an axis perpendicular to the axis of CT scanning 36. If the support 52 is tilted while the patient maintained in a horizontal position the X radiation will traverse the patient aperture at a non vertical angle and thereby provide flexibility . 15 in CT scanning. If, for example, the support 52 is tilted 20 about an axis perpendicular to the scan axis 36 the cross section of patient irradiation ' will also be tilted 2~ to the vertical.
The geometrical configuration of the frame 50 20 and X-ray housing 44 is such that the rotating assembly 42 is well balanced about the scan axis 36. The frame 50 is much wider at a side 51 opposed from the X-ray housing and this width counterbalances the weight of the X-ray housing and enclosed tube 25 and provides a symmetrical mass distribution about ; the axis 36.
The stationary gantry 40 supports the rotating assembly 42 along an annular bearing connection 64, Figure 4 which allows free orbital rotation of the 30 assembly a~ about the axis 36. rhe compact design of the apparatus allows one bearing to provide sufficient support to the rotating assembly~
It is important in CT scanning that the position of the X-ray tube be precisely known during all times 35 of an X-ray exposure. For this reason, an encoder 66 in the form of an annular ring is a-~tachecl to , - . .: .
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112~564 : ' the rotating-assemblg ~. rrhis encoder 66 insludes - a number of marks equally spaced about the ring which indicate the angular orientation of the encoder.
As the annular ring moves a~out the center axls an 5 optical encoder 67 determines the posi~ion of the ring relative to the stationary gantry 40. In this way the precise position of ~the X~ray source can be de~ermined at all times cluring irradiation of the patient. Th;s position data is correlated with lO intensity readings from the X-ray detector array and utilized in reconstruction algorithms ~nown within the art.
Figures 5A-C illustrate three di~ferent X-ray tube input configurations for energization of an 15 X-ray tube. Each con~iyuration shows an anode 70 and a cathode 72 coupled to energi2ation inputs.
A series of these high voltage energiza~ion inpu~s 74 are shown transmitting potential differences to the tu~e.
In a single focus X-ray tube (See Figure 5A) three high voltage inputs are needed. A first input 76 is the positive input to th~ X-ray anode and in the preferred embodiment of the invention is input through a first positive p~rtion 56 of the slip ring 25 arrangement. Two negative inputs 78, 80 are used .o energize the cathode 72 and in the preferred embodiment are transmitted via the secon~ portion 58 of the slip ring arrangement. A transformer 82 supplies a filament current which causes electrons 30 84 to be emitted thermionically from the cathode for acceleration towards the high potential anode 70.
Figure 5B illustrates a double focus X-ray tube.
Three negative high voltage inputs 86-88 are transmitted 35 to the X-ray tube cathocle 7~. Through control of the voltages appearing on a primary oE the transformer ',,: , , - - .
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` 13 82, i-t i8 pos~:Lble~ to con~rol the high voltage inputs 86-B8 and pLo-vide a measure of x radiation control unavailable on the single focus tube.
An X-ray tube which includes a grid con~rol 5 is illustrated in Figure 5C. This tube includes a high voltage positive input 76 and three high voltage negative inputs 90-92. Two inputs 30, 91 transmit a voltage appearing across the secondary of the transformer 82. A third input 92 ser~es to 10 maintain a control voltage on a grid 94 within the X-ray tube. Through adjustment oE grid tube potential a means oE control over electron transmittal to the anode unavailable in the single focus tube is provide~.
From the illustrations in Figures 5A-5C it is 15 apparent that a plurality of high voltage negative inputs must be available if single focus, double focus and grid X-ray tube control is to be achieved.
The second negative portion 58 of the 51ip ring arrangement (See Figure 3B) includes a plurality 20 f 51ip rings for t~is purpose. In the preferr~d embodiment four slip rings are included to provide flexibility in CT scanner design. The volta~e inputs to these slip rings are ~t many thousands of volts below ground but are each separated by relatively 25 low voltag~s. In a single focus X-ray tube configura-tion, for example, the voltage separation between the two inputs 78, 80 need only be l~rge enough to cause a filament current to flow in the X-ray tube cathode.
Fisure 4 shows a more detailed cross sectional view of the slip ring arrangement shown in Figure 3B. That figure illustrates the X-ray tube housing 44, the rotating assembly 42 mounted by the bearing 64 inside the stationary gantry 40. The cross section 35 depicted shows the frame 50 and one of its eight mountiny connectors 43.
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The Fi~ure -,4 cross section shows the first positive 56 and second negative 58 slip riny portions noted with regard to Fiyure 3B. The first portion ~sends a positive high voltage signal to the X-ray `;5 tube and the second portion includes 4 individual sllp rings to provide the controlled energization 'of the cathode as mentioned above. Both the ~ir,s~
56 and second 58 portions of the slip ring arrangement are immersed in an oil bath in a cavity 11~. This 10 oil prevents arciny between high voltage portions of the slip ring arrangement and other portions oE
the CT apparatus which could damage both the control circuitry and the X-ray tube in prior art systems.
The portion o~ the stationary gantry 40 bordering 15 on this cavity 112 is prefera~ly of aluminum construction and the portion of the rotating assembly which borders the cavity is o~ a plastic construction. These light weight materials allow the apparatus to be readily tilted and the plastic rotating portions allow the 20 system to be more easily rotated by the belt drive.
Four elastomeric seals 114-117 maintain a dielectric fluid such as oil in the cavity. These seals are mounted to the nonrotating gantry 40 and are biased against the rotating assembly by means of spring 25 biasing members 118. As the assembly rotates with respect to the stationary gantry, these sprin~s maintain the seals in contact with the rotating portions and threby prevent leakaye o~ the insulating fluid from the cavity 112.
The transmission path o~ the positive high voltage signal is clearly illustrated in Figure 4. The high voltage signal (typically 75,000 volts) is input into the high voltage receptacle 46 transmitted to the ~irst slip ring portion 56 then through hlgh 35 voltage cabling to a second high voltage receptacle 60 attachecl to the rotating assembly for transmittal .
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to the anode portion of the X-ray tube. The hiyh voltage passes through a brush which is biased towards the slip ring by a spring to insure contact b~tween the brush and rotating slip ring. One type o cabling 5 used to transmi L the high voltages between the slip ring and the X-ray tube is Federal cabling which is known in the ark of X-ray CT scanning. The cabling 120 passes through a bore machined into the plastic portion of the rotating assembly.
The second portion 58 of the slip ring assembly includes four rotating slip rings 1~2-125 which transmit four separate negative high voltage signals to the X-ray tube. A more detailed schematic oE
this second 58 portion o the slip ring arrangement 15 is shown in Figure 4A. As seen in that figure each rotating slip ring is contac~ed by a biased brush 127 which in turn i5 connected to an electrical contact in a housing 126. In the embodiment illustrated a single focus tube has been utilized and therefore 20 only two nega-tive high potential inputs 128, 129 are required with two spares available should other tubes be used.
At a location removed from the high voltage slip ring arrangement are a number of low voltage 25 slip rings 130-135 for transmitting low voltage electrical signals from the stationary gantry to the rotating assembly. Since these slip rings transmit low voltages they need not be immersed in an oil bath to insure electrical isolation. Although only 30 six slip rings are shown in the figure for clarity~
16 low voltage slip are utili2ed in a preferred embodiment of one commercial CT unit. Three of the low voltage inputs are utili~ed to provide power to a motor located in the rotating assembly 42 which 35 cools the anode of the X-ray tube by rotating it.
Three more of the low voltage slip rings are used 1 , . : -,- ,.
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as common or ground potential. Four other low voltage slip rings are utilized as general alternating current power inputs. These inpu~s are used to operate a number of solenoids mounted ~o the assembly 42 which 5 must be powered by AC signals.
Five remaining slip rings are used to monitor and contxol the condition of three switches mounted to the rotating assembly which operate a shutter, a filter, and the collimator. The functioning of 10 these three components must be coordinated with X-ray generation in the CT imaging process. One of these five remaining inputs transmits a frequency proportional to a re~erence intensity from the rotating ; assembly 42 to the stationary imaging electronics 15 20. Two of the remaining four inputs are used to provide synchroni2ation and clock signals. The remaining two slip rings operate to send and receive digital data from a multiplexing board which both controls and monitors the condition of the three 20 switches.
Since there are 16 rotating slip rings and the function of only 15 inputs have been described one of these 16 slip rings has no function in the present design but is available for future design modification.
While the embodiment described above has been characteri2ed with some particularity, it should be appreciated to those skilled in the art that certain modification and changes could be insorporated without departing from the spirit or scope of the 30 invention as detailed in the appended claims.
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The assembly further comprises a positive 56 and negative 58 slip ring portion which receive these high voltage inputs and transmit a high voltage 20 differential from the stationary gantry portion 40 to the rotating assembly 42 for transmittal to the X-ray tu~e. The first positive portion 56 includes only one slip ring which is coupled to the positive receptacle 46. The second negative portion 58 includes 25 four slip rings and is designed to receive more than one negative high voltage inputO The purpose of - this multiplicity in high voltage slip ring configura- -t~on is to allow control of the X radiation generation by utilization of either multiple focus or grid 30 potential voltage inputs.
After the high voltage potential is transmitted to the rotating assembly 42 it is further transmitted along cabling (shown in Fiyure 4 as reference numeral 120) to two high voltage receptacles 60, 62 mounted 35 to the frame 50. A first receptacle 60 receives the positive voltage and a second receptacle 62 receives ,.
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the ne~ati~e high vQl~age potentia7 inputs. Frcm these receptacles the high voltage is transmitted to the anode (positive) and cathode (negative) of the rotating X-ray tube.
The gantry is attached to a support 52 radially removed from the patient aperture by means oE suitable connectors 54 such as a nut and bolt arrangement.
This mounting serves to maintain the stationary gantry 40 in position while allowing the support 10 52 to be tilted about an axis perpendicular to the axis of CT scanning 36. If the support 52 is tilted while the patient maintained in a horizontal position the X radiation will traverse the patient aperture at a non vertical angle and thereby provide flexibility . 15 in CT scanning. If, for example, the support 52 is tilted 20 about an axis perpendicular to the scan axis 36 the cross section of patient irradiation ' will also be tilted 2~ to the vertical.
The geometrical configuration of the frame 50 20 and X-ray housing 44 is such that the rotating assembly 42 is well balanced about the scan axis 36. The frame 50 is much wider at a side 51 opposed from the X-ray housing and this width counterbalances the weight of the X-ray housing and enclosed tube 25 and provides a symmetrical mass distribution about ; the axis 36.
The stationary gantry 40 supports the rotating assembly 42 along an annular bearing connection 64, Figure 4 which allows free orbital rotation of the 30 assembly a~ about the axis 36. rhe compact design of the apparatus allows one bearing to provide sufficient support to the rotating assembly~
It is important in CT scanning that the position of the X-ray tube be precisely known during all times 35 of an X-ray exposure. For this reason, an encoder 66 in the form of an annular ring is a-~tachecl to , - . .: .
~, ~ , . .
112~564 : ' the rotating-assemblg ~. rrhis encoder 66 insludes - a number of marks equally spaced about the ring which indicate the angular orientation of the encoder.
As the annular ring moves a~out the center axls an 5 optical encoder 67 determines the posi~ion of the ring relative to the stationary gantry 40. In this way the precise position of ~the X~ray source can be de~ermined at all times cluring irradiation of the patient. Th;s position data is correlated with lO intensity readings from the X-ray detector array and utilized in reconstruction algorithms ~nown within the art.
Figures 5A-C illustrate three di~ferent X-ray tube input configurations for energization of an 15 X-ray tube. Each con~iyuration shows an anode 70 and a cathode 72 coupled to energi2ation inputs.
A series of these high voltage energiza~ion inpu~s 74 are shown transmitting potential differences to the tu~e.
In a single focus X-ray tube (See Figure 5A) three high voltage inputs are needed. A first input 76 is the positive input to th~ X-ray anode and in the preferred embodiment of the invention is input through a first positive p~rtion 56 of the slip ring 25 arrangement. Two negative inputs 78, 80 are used .o energize the cathode 72 and in the preferred embodiment are transmitted via the secon~ portion 58 of the slip ring arrangement. A transformer 82 supplies a filament current which causes electrons 30 84 to be emitted thermionically from the cathode for acceleration towards the high potential anode 70.
Figure 5B illustrates a double focus X-ray tube.
Three negative high voltage inputs 86-88 are transmitted 35 to the X-ray tube cathocle 7~. Through control of the voltages appearing on a primary oE the transformer ',,: , , - - .
z~s~
` 13 82, i-t i8 pos~:Lble~ to con~rol the high voltage inputs 86-B8 and pLo-vide a measure of x radiation control unavailable on the single focus tube.
An X-ray tube which includes a grid con~rol 5 is illustrated in Figure 5C. This tube includes a high voltage positive input 76 and three high voltage negative inputs 90-92. Two inputs 30, 91 transmit a voltage appearing across the secondary of the transformer 82. A third input 92 ser~es to 10 maintain a control voltage on a grid 94 within the X-ray tube. Through adjustment oE grid tube potential a means oE control over electron transmittal to the anode unavailable in the single focus tube is provide~.
From the illustrations in Figures 5A-5C it is 15 apparent that a plurality of high voltage negative inputs must be available if single focus, double focus and grid X-ray tube control is to be achieved.
The second negative portion 58 of the 51ip ring arrangement (See Figure 3B) includes a plurality 20 f 51ip rings for t~is purpose. In the preferr~d embodiment four slip rings are included to provide flexibility in CT scanner design. The volta~e inputs to these slip rings are ~t many thousands of volts below ground but are each separated by relatively 25 low voltag~s. In a single focus X-ray tube configura-tion, for example, the voltage separation between the two inputs 78, 80 need only be l~rge enough to cause a filament current to flow in the X-ray tube cathode.
Fisure 4 shows a more detailed cross sectional view of the slip ring arrangement shown in Figure 3B. That figure illustrates the X-ray tube housing 44, the rotating assembly 42 mounted by the bearing 64 inside the stationary gantry 40. The cross section 35 depicted shows the frame 50 and one of its eight mountiny connectors 43.
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The Fi~ure -,4 cross section shows the first positive 56 and second negative 58 slip riny portions noted with regard to Fiyure 3B. The first portion ~sends a positive high voltage signal to the X-ray `;5 tube and the second portion includes 4 individual sllp rings to provide the controlled energization 'of the cathode as mentioned above. Both the ~ir,s~
56 and second 58 portions of the slip ring arrangement are immersed in an oil bath in a cavity 11~. This 10 oil prevents arciny between high voltage portions of the slip ring arrangement and other portions oE
the CT apparatus which could damage both the control circuitry and the X-ray tube in prior art systems.
The portion o~ the stationary gantry 40 bordering 15 on this cavity 112 is prefera~ly of aluminum construction and the portion of the rotating assembly which borders the cavity is o~ a plastic construction. These light weight materials allow the apparatus to be readily tilted and the plastic rotating portions allow the 20 system to be more easily rotated by the belt drive.
Four elastomeric seals 114-117 maintain a dielectric fluid such as oil in the cavity. These seals are mounted to the nonrotating gantry 40 and are biased against the rotating assembly by means of spring 25 biasing members 118. As the assembly rotates with respect to the stationary gantry, these sprin~s maintain the seals in contact with the rotating portions and threby prevent leakaye o~ the insulating fluid from the cavity 112.
The transmission path o~ the positive high voltage signal is clearly illustrated in Figure 4. The high voltage signal (typically 75,000 volts) is input into the high voltage receptacle 46 transmitted to the ~irst slip ring portion 56 then through hlgh 35 voltage cabling to a second high voltage receptacle 60 attachecl to the rotating assembly for transmittal .
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to the anode portion of the X-ray tube. The hiyh voltage passes through a brush which is biased towards the slip ring by a spring to insure contact b~tween the brush and rotating slip ring. One type o cabling 5 used to transmi L the high voltages between the slip ring and the X-ray tube is Federal cabling which is known in the ark of X-ray CT scanning. The cabling 120 passes through a bore machined into the plastic portion of the rotating assembly.
The second portion 58 of the slip ring assembly includes four rotating slip rings 1~2-125 which transmit four separate negative high voltage signals to the X-ray tube. A more detailed schematic oE
this second 58 portion o the slip ring arrangement 15 is shown in Figure 4A. As seen in that figure each rotating slip ring is contac~ed by a biased brush 127 which in turn i5 connected to an electrical contact in a housing 126. In the embodiment illustrated a single focus tube has been utilized and therefore 20 only two nega-tive high potential inputs 128, 129 are required with two spares available should other tubes be used.
At a location removed from the high voltage slip ring arrangement are a number of low voltage 25 slip rings 130-135 for transmitting low voltage electrical signals from the stationary gantry to the rotating assembly. Since these slip rings transmit low voltages they need not be immersed in an oil bath to insure electrical isolation. Although only 30 six slip rings are shown in the figure for clarity~
16 low voltage slip are utili2ed in a preferred embodiment of one commercial CT unit. Three of the low voltage inputs are utili~ed to provide power to a motor located in the rotating assembly 42 which 35 cools the anode of the X-ray tube by rotating it.
Three more of the low voltage slip rings are used 1 , . : -,- ,.
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as common or ground potential. Four other low voltage slip rings are utilized as general alternating current power inputs. These inpu~s are used to operate a number of solenoids mounted ~o the assembly 42 which 5 must be powered by AC signals.
Five remaining slip rings are used to monitor and contxol the condition of three switches mounted to the rotating assembly which operate a shutter, a filter, and the collimator. The functioning of 10 these three components must be coordinated with X-ray generation in the CT imaging process. One of these five remaining inputs transmits a frequency proportional to a re~erence intensity from the rotating ; assembly 42 to the stationary imaging electronics 15 20. Two of the remaining four inputs are used to provide synchroni2ation and clock signals. The remaining two slip rings operate to send and receive digital data from a multiplexing board which both controls and monitors the condition of the three 20 switches.
Since there are 16 rotating slip rings and the function of only 15 inputs have been described one of these 16 slip rings has no function in the present design but is available for future design modification.
While the embodiment described above has been characteri2ed with some particularity, it should be appreciated to those skilled in the art that certain modification and changes could be insorporated without departing from the spirit or scope of the 30 invention as detailed in the appended claims.
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Claims (20)
1. CT scanner apparatus comprising a) a gantry arrangement;
b) a rotatable assembly mounted on the gantry and defining a through patient aperture, said assembly including an X-radiation source;
c) a slip rink assembly around the aperture and having certain portions connected to the gantry and other portions forming a part of the rotating assembly for rotation relative to the certain portions, the slip ring assembly including at least one slip ring;
d) said other portions being electrically connected to the X-radiation source;
e) input means connected to the certain portions for receiving a high voltage electrical input and for transferring the electrical input to the slip ring assembly;
f) drive means for rotating the rotatable assembly relative to the gantry; and, g) said slip ring assembly being configured to provide a cavity for maintaining an insulating fluid in contact with substantially the entire slip ring as the slip ring portions rotate relatively.
b) a rotatable assembly mounted on the gantry and defining a through patient aperture, said assembly including an X-radiation source;
c) a slip rink assembly around the aperture and having certain portions connected to the gantry and other portions forming a part of the rotating assembly for rotation relative to the certain portions, the slip ring assembly including at least one slip ring;
d) said other portions being electrically connected to the X-radiation source;
e) input means connected to the certain portions for receiving a high voltage electrical input and for transferring the electrical input to the slip ring assembly;
f) drive means for rotating the rotatable assembly relative to the gantry; and, g) said slip ring assembly being configured to provide a cavity for maintaining an insulating fluid in contact with substantially the entire slip ring as the slip ring portions rotate relatively.
2. The apparatus of claim 1 wherein the slip ring is a high voltage slip ring and wherein further brushes and slip rings are provided for low voltage connections.
3. The apparatus of claim 2 wherein said further brushes and slip rings are not in the cavity for insulat-ing fluid.
4. The apparatus of claim 1 where the slip ring assembly includes a spring loaded brush for con-tacting the slip ring and maintaining a path of low electrical resistance between the receptacle and the slip ring.
5. The apparatus of claim 4 wherein the other portions of the slip ring assembly further include cabling which rotates with the assembly for transferr-ing the electrical input from the brush to the X-ray source.
6. The apparatus of claim 1 wherein the rotating assembly is mounted for tilting about a second axis transverse to the axis of the rotating assembly and which includes means for rotating the rotating assembly about this second axis.
7. CT apparatus comprising:
a) a gantry;
b) a rotatable assembly rotatably mounted on said gantry by a single annular bearing for rotation about a scanning axis;
c) the rotatable assembly including an X-radiation source which includes a cathode and an anode, said assembly and the gantry defining a patient receiv-ing through aperture circumscribed by said bearing;
d) an X-radiation detector supported by the gantry for responding to X-radiation intensity after it has been emitted by the source and attenuated by a patient;
e) a slip ring assembly having certain portions connected to the gantry and other portions forming a part of the rotating assembly for rotation relative to the certain portions, the slip ring assembly including at least one slip ring;
f) said other portions being electrically connected to the X-radiation source;
g) receptacle means connected to said gantry for receiving an electrical potential;
h) transmission means forming a part of said rotating assembly for transmitting the electrical potential to the source; and i) the slip ring assembly including a connection means for transmitting said electrical potential from the receptacle means to the transmission means; said connection means comprising a brush and the slip ring for providing an electrical path of low resistance from the receptacle means to the X-radiation source during rotation of the assembly.
a) a gantry;
b) a rotatable assembly rotatably mounted on said gantry by a single annular bearing for rotation about a scanning axis;
c) the rotatable assembly including an X-radiation source which includes a cathode and an anode, said assembly and the gantry defining a patient receiv-ing through aperture circumscribed by said bearing;
d) an X-radiation detector supported by the gantry for responding to X-radiation intensity after it has been emitted by the source and attenuated by a patient;
e) a slip ring assembly having certain portions connected to the gantry and other portions forming a part of the rotating assembly for rotation relative to the certain portions, the slip ring assembly including at least one slip ring;
f) said other portions being electrically connected to the X-radiation source;
g) receptacle means connected to said gantry for receiving an electrical potential;
h) transmission means forming a part of said rotating assembly for transmitting the electrical potential to the source; and i) the slip ring assembly including a connection means for transmitting said electrical potential from the receptacle means to the transmission means; said connection means comprising a brush and the slip ring for providing an electrical path of low resistance from the receptacle means to the X-radiation source during rotation of the assembly.
8. In CT scanning a method for transmitting large potential differences to a rotating CT assembly which surrounds a through patient receiving aperture comprising the steps of:
a) mounting an X-ray source to the rotating assembly in a position to irradiate a patient in a cross-sectional plane to gather X-ray attenuation data;
b) energizing said generator by coupling it to a stationary source of high voltage through a brush and a slip ring which circumscribes the patient aperture;
c) preventing electrical arcing by immersing said brush and slip ring in an insulating dielectric material; and d) scanning a plurality of patient cross-sections without moving the patient by tilting said CT assembly and attached X-ray source and radiating the patient with X-rays in another cross-sectional plane to gather further X-ray attenuation data.
a) mounting an X-ray source to the rotating assembly in a position to irradiate a patient in a cross-sectional plane to gather X-ray attenuation data;
b) energizing said generator by coupling it to a stationary source of high voltage through a brush and a slip ring which circumscribes the patient aperture;
c) preventing electrical arcing by immersing said brush and slip ring in an insulating dielectric material; and d) scanning a plurality of patient cross-sections without moving the patient by tilting said CT assembly and attached X-ray source and radiating the patient with X-rays in another cross-sectional plane to gather further X-ray attenuation data.
9. The method of claim 8 wherein both a positive and negative high voltage brush and slip ring arrange-ment are provided for X-ray voltage transmission and wherein both are immersed in an insulating cavity for electrical isolation.
10. The method of claim 8 which further comprises a step of providing a plurality of low voltage inputs for transmittal to the assembly through a plurality of brush and slip ring arrangements spaced from the dielectric material.
11. A computed tomography scanner comprising:
a) an annular assembly delineating a through patient receiving aperture;
b) the annular assembly including a sub-assembly surrounding the patient aperture, the sub-assembly having relatively rotatable structures de-lineating an interior, annular chamber;
c) one of the structures being fixedly supported by other portions of the assembly;
d) an X-ray tube assembly connected to the other of the structures and comprising a tube sub-assembly which is rotatable about an axis extending through the patient aperture;
e) at least one slip ring mechanism in the chamber including an annular conductor secured to a first of the structures and a coacting brush connected to a second of the structures so that when said other structure is rotated the brush and annular conductor rotate relatively while being maintained in electrically conductive relationship;
f) an electrical conductor carried by the one structure and connected to a selected one of the annular conductor and the brush;
g) a second electrical conductor forming a part of the tube sub-assembly for rotation therewith, the second electrical conductor forming an electrical connection between the other of the annular conductor and brush and a component of the tube sub-assembly:
h) seals interposed between the structures and rendering the chamber fluid tight;
i) a dielectric fluid substantially filling the chamber; and j) a prime mover connected to the tube sub-assembly for driving the sub-assembly and thereby orbiting the tube sub-assembly about said axis while the first and second conductors are maintained in electrical connection with one another through the slip ring mechanism.
a) an annular assembly delineating a through patient receiving aperture;
b) the annular assembly including a sub-assembly surrounding the patient aperture, the sub-assembly having relatively rotatable structures de-lineating an interior, annular chamber;
c) one of the structures being fixedly supported by other portions of the assembly;
d) an X-ray tube assembly connected to the other of the structures and comprising a tube sub-assembly which is rotatable about an axis extending through the patient aperture;
e) at least one slip ring mechanism in the chamber including an annular conductor secured to a first of the structures and a coacting brush connected to a second of the structures so that when said other structure is rotated the brush and annular conductor rotate relatively while being maintained in electrically conductive relationship;
f) an electrical conductor carried by the one structure and connected to a selected one of the annular conductor and the brush;
g) a second electrical conductor forming a part of the tube sub-assembly for rotation therewith, the second electrical conductor forming an electrical connection between the other of the annular conductor and brush and a component of the tube sub-assembly:
h) seals interposed between the structures and rendering the chamber fluid tight;
i) a dielectric fluid substantially filling the chamber; and j) a prime mover connected to the tube sub-assembly for driving the sub-assembly and thereby orbiting the tube sub-assembly about said axis while the first and second conductors are maintained in electrical connection with one another through the slip ring mechanism.
12. A computed tomographic system comprising:
a) a gantry delineating a patient receiving opening extending transversely therethrough;
b) a stationary housing structure connected to the gantry and including fixed end walls delineating the ends of a portion of a chamber around a space occupied by a patient when the system is in use, the fixed end walls terminating inwardly in circular surfaces;
c) a rotating housing structure telescoped within the stationary housing structure and including spaced movable end walls further defining such chamber, the movable end walls terminating radially outwardly in circular surfaces each of which is complemental to a fixed endwall surface;
d) spaced seals interposed between the complemental surfaces at each chamber end to effect a fluid seal between the housing structures and thereby provide a fluid tight chamber;
e) an annular bearing interposed between the housing structures and supporting the rotating structure for rotation relative to the fixed housing structure about an axis extending through the patient opening;
f) an X-ray tube assembly carried by the rotating housing structure and including an X-ray tube adapted to emit a highly collimated, substantially planar spread beam along a path which intersects said axis;
g) a plurality of annular slip rings con-nected to a selected one of the fixed and rotating housing structures;
h) a plurality of high voltage slip ring brushes each electrically connected to an associated one of the slip rings to form a slip ring assembly and connected to the other of the fixed and rotating structures whereby each associated slip ring and brush are relatively rotated whenever the rotatable housing structure rotates, the slip rings and brushes being positioned within said chamber;
i) electrical connectors carried by the fixed housing structure for effecting electrical con-nections between the slip ring assemblies and electrical devices external of the fixed housing structure;
j) other electrical connectors carried by the rotating housing structure and effecting electrical connections between at least some of the slip ring assembly components and X-ray tube components;
k) a dielectric medium sufficiently filling said chamber to reverse the high voltage brush to slip ring connections; and, l) further slip ring assemblies having respective components respectively connected to the structures external of that cavity that is filled with part of the dielectric medium.
a) a gantry delineating a patient receiving opening extending transversely therethrough;
b) a stationary housing structure connected to the gantry and including fixed end walls delineating the ends of a portion of a chamber around a space occupied by a patient when the system is in use, the fixed end walls terminating inwardly in circular surfaces;
c) a rotating housing structure telescoped within the stationary housing structure and including spaced movable end walls further defining such chamber, the movable end walls terminating radially outwardly in circular surfaces each of which is complemental to a fixed endwall surface;
d) spaced seals interposed between the complemental surfaces at each chamber end to effect a fluid seal between the housing structures and thereby provide a fluid tight chamber;
e) an annular bearing interposed between the housing structures and supporting the rotating structure for rotation relative to the fixed housing structure about an axis extending through the patient opening;
f) an X-ray tube assembly carried by the rotating housing structure and including an X-ray tube adapted to emit a highly collimated, substantially planar spread beam along a path which intersects said axis;
g) a plurality of annular slip rings con-nected to a selected one of the fixed and rotating housing structures;
h) a plurality of high voltage slip ring brushes each electrically connected to an associated one of the slip rings to form a slip ring assembly and connected to the other of the fixed and rotating structures whereby each associated slip ring and brush are relatively rotated whenever the rotatable housing structure rotates, the slip rings and brushes being positioned within said chamber;
i) electrical connectors carried by the fixed housing structure for effecting electrical con-nections between the slip ring assemblies and electrical devices external of the fixed housing structure;
j) other electrical connectors carried by the rotating housing structure and effecting electrical connections between at least some of the slip ring assembly components and X-ray tube components;
k) a dielectric medium sufficiently filling said chamber to reverse the high voltage brush to slip ring connections; and, l) further slip ring assemblies having respective components respectively connected to the structures external of that cavity that is filled with part of the dielectric medium.
13. CT scanner apparatus comprising:
a) a gantry arangement;
b) a rotatable assembly mounted on the gantry and defining a through patient receiving aperture through which an axis of rotation passes, the rotatable assembly including an X-ray source;
c) an annular slip ring assembly around said aperture and including certain portions connected to and forming a part of the rotatable assembly, the slip ring assembly including other portions connected to and forming part of the gantry;
d) input means connected to the gantry and adapted to receive a high voltage electrical input;
e) the slip ring assembly portions includ-ing relatively rotatable slip ring and brush components for transmitting such electrical input from the input means to the X-ray source;
f) drive means for rotating the rotatable assembly;
g) said gantry and rotatable assembly defining a cavity about the slip ring four maintaining an insulating fluid at a level above the slip ring to brush connections.
a) a gantry arangement;
b) a rotatable assembly mounted on the gantry and defining a through patient receiving aperture through which an axis of rotation passes, the rotatable assembly including an X-ray source;
c) an annular slip ring assembly around said aperture and including certain portions connected to and forming a part of the rotatable assembly, the slip ring assembly including other portions connected to and forming part of the gantry;
d) input means connected to the gantry and adapted to receive a high voltage electrical input;
e) the slip ring assembly portions includ-ing relatively rotatable slip ring and brush components for transmitting such electrical input from the input means to the X-ray source;
f) drive means for rotating the rotatable assembly;
g) said gantry and rotatable assembly defining a cavity about the slip ring four maintaining an insulating fluid at a level above the slip ring to brush connections.
14. The apparatus of claim 13 wherein the gantry and rotatable assembly are mounted for tilting about an axis transverse to the axis of rotation to allow the scanning of multiple patient cross-sections without moving a patient.
15. The apparatus of claim 13 wherein further slip rings including relatively rotatable electricity conducting components are provided external of the cavity.
16. A process of conducting a computed tomographic scan of a patient comprising:
a) positioning a patient on a support surface extending through and projecting axially from both ends of a patient aperture;
b) transmitting an X-ray beam from a source through the patient while energizing the source through a slip ring assembly disposed around the aperture;
c) orbiting the source around the patient through a plurality of revolutions in a single direction of orbit as the source is being energized;
d) detecting radiation transmitted through the patient; and, e) producing an image of the patient with data received from the detected radiation.
a) positioning a patient on a support surface extending through and projecting axially from both ends of a patient aperture;
b) transmitting an X-ray beam from a source through the patient while energizing the source through a slip ring assembly disposed around the aperture;
c) orbiting the source around the patient through a plurality of revolutions in a single direction of orbit as the source is being energized;
d) detecting radiation transmitted through the patient; and, e) producing an image of the patient with data received from the detected radiation.
17. The process of claim 16 further including the step of using a ring of detectors encircling the patient in the step of detecting transmitted radiation.
18. The process of claim 16 wherein the source orbits about an axis and the produced image is substan-tially in a plane and wherein another image is produced in a different plane by repeating steps b through d after the axis and the patient have been tilted rela-tively.
19. A computed tomographic system comprising:
a) a gantry delineating a patient receiving opening extending transversely therethrough;
b) a stationary housing structure connected to the gantry and including walls delineating portions of a chamber around a space occupied by a patent when the system is in use, the walls terminating in circular surfaces;
c) a rotating housing structure coacting with the stationary housing structure and including spaced movable walls further defining such chamber, the movable walls terminating in circular surfaces each of which is complemental to a fixed endwall sur-face;
d) spaced seals interposed between the complemental surfaces to effect fluid seals between the housing structures and thereby provide a fluid tight chamber;
e) an annular bearing interposed between the housing structures and supporting the rotating structure for rotation relative to the fixed housing structure about an axis extending through the patient opening;
f) an X-ray tube assembly carried by the rotating housing structure and including an X-ray tube adapted to emit an X-ray beam along a path which intersects said axis;
g) a plurality of annular, high voltage slip rings each connected to a selected one of the fixed and rotating housing structures;
h) a plurality of high voltage slip ring brushes each electrically connected to an associated one of the slip rings to form a slip ring assembly and connected to the other of the fixed and rotating structures whereby each associated slip ring and brush are relatively rotated whenever the rotatable housing structure rotates, the slip rings and brushes being positioned within said chamber;
i) electrical connectors carried by the fixed housing structure for effecting electrical con-nections between the slip ring assemblies and electrical devices external of the fixed housing structure;
j) other electrical connectors carried by the rotating housing structure and effecting electrical connections between at least some of the slip ring assembly components and X-ray tube components;
k) a dielectric medium sufficiently filling said chamber to immerse the high voltage brush to slip ring connections; and, l) further slip ring assemblies having respective components respectively connected to the structures external of that part of the cavity that is filled with dielectric medium.
a) a gantry delineating a patient receiving opening extending transversely therethrough;
b) a stationary housing structure connected to the gantry and including walls delineating portions of a chamber around a space occupied by a patent when the system is in use, the walls terminating in circular surfaces;
c) a rotating housing structure coacting with the stationary housing structure and including spaced movable walls further defining such chamber, the movable walls terminating in circular surfaces each of which is complemental to a fixed endwall sur-face;
d) spaced seals interposed between the complemental surfaces to effect fluid seals between the housing structures and thereby provide a fluid tight chamber;
e) an annular bearing interposed between the housing structures and supporting the rotating structure for rotation relative to the fixed housing structure about an axis extending through the patient opening;
f) an X-ray tube assembly carried by the rotating housing structure and including an X-ray tube adapted to emit an X-ray beam along a path which intersects said axis;
g) a plurality of annular, high voltage slip rings each connected to a selected one of the fixed and rotating housing structures;
h) a plurality of high voltage slip ring brushes each electrically connected to an associated one of the slip rings to form a slip ring assembly and connected to the other of the fixed and rotating structures whereby each associated slip ring and brush are relatively rotated whenever the rotatable housing structure rotates, the slip rings and brushes being positioned within said chamber;
i) electrical connectors carried by the fixed housing structure for effecting electrical con-nections between the slip ring assemblies and electrical devices external of the fixed housing structure;
j) other electrical connectors carried by the rotating housing structure and effecting electrical connections between at least some of the slip ring assembly components and X-ray tube components;
k) a dielectric medium sufficiently filling said chamber to immerse the high voltage brush to slip ring connections; and, l) further slip ring assemblies having respective components respectively connected to the structures external of that part of the cavity that is filled with dielectric medium.
20. In CT scanning a method for transmitting large potential differences to a rotating CT assembly which surrounds a through patient receiving aperture comprising the steps of:
a) positioning a patent in a position projecting through the aperture for irradiation by an X-ray source mounted on the rotating assembly;
b) energizing said generator by coupling it to a stationary source of high voltage through a brush and a slip ring which circumscribes the patient aperture;
c) preventing electrical arcing by main-taining said brush and slip ring immersed in an insulat-ing dielectric material; and d) scanning a plurality of patient cross-sections without moving the patient by tilting said CT assembly and attached X-ray source and radiating the patient with X-rays in another cross-sectional plane to gather further X-ray attenuation data.
a) positioning a patent in a position projecting through the aperture for irradiation by an X-ray source mounted on the rotating assembly;
b) energizing said generator by coupling it to a stationary source of high voltage through a brush and a slip ring which circumscribes the patient aperture;
c) preventing electrical arcing by main-taining said brush and slip ring immersed in an insulat-ing dielectric material; and d) scanning a plurality of patient cross-sections without moving the patient by tilting said CT assembly and attached X-ray source and radiating the patient with X-rays in another cross-sectional plane to gather further X-ray attenuation data.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7619379A | 1979-09-17 | 1979-09-17 | |
| US076,193 | 1979-09-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1129564A true CA1129564A (en) | 1982-08-10 |
Family
ID=22130508
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA353,328A Expired CA1129564A (en) | 1979-09-17 | 1980-06-04 | Computer tomography method and apparatus |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5657433A (en) |
| CA (1) | CA1129564A (en) |
| DE (1) | DE3034717A1 (en) |
| FR (1) | FR2464694A1 (en) |
| GB (1) | GB2061028B (en) |
| NL (1) | NL190630C (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3221791A1 (en) * | 1982-06-09 | 1983-12-15 | Philips Patentverwaltung Gmbh, 2000 Hamburg | DEVICE FOR HIGH-VOLTAGE TRANSMISSION BETWEEN TWO RELATIVELY REVOLVABLE PARTS |
| US4798540A (en) * | 1983-05-12 | 1989-01-17 | Tokyo Shibaura Denki Kabushiki Kaisha | Integrated CT scanner gantry |
| US4799245A (en) * | 1983-05-12 | 1989-01-17 | Tokyo Shibaura Denki Kabushiki Kaisha | Integrated CT scanner gantry |
| JPS6340536A (en) * | 1986-08-05 | 1988-02-20 | ジーイー横河メディカルシステム株式会社 | X-ray radiographic apparatus |
| IL96230A0 (en) * | 1990-11-02 | 1991-08-16 | Elscint Ltd | Gantry for nuclear medicine imaging systems |
| DE4207007C1 (en) * | 1992-03-05 | 1993-05-13 | Siemens Ag, 8000 Muenchen, De | Computer tomography appts. with continuous rotating measuring unit - feeds x=ray energy over current feed to x=ray detector via insulated annular rotating disc |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4051379A (en) * | 1975-11-28 | 1977-09-27 | Artronix, Inc. | Axial tomographic apparatus and detector |
| US4093859A (en) * | 1975-11-28 | 1978-06-06 | Artronix, Inc. | Axial tomographic apparatus |
| GB1568062A (en) * | 1976-01-29 | 1980-05-21 | Emi Ltd | Slip-ring connection |
| DE2606534A1 (en) * | 1976-02-18 | 1977-08-25 | Siemens Ag | ROENTINE LAYER FOR THE PRODUCTION OF TRANSVERSAL LAYER IMAGES |
| JPS6019113B2 (en) * | 1976-04-19 | 1985-05-14 | シ−メンス・アクチェンゲゼルシャフト | Rotating electrical supply device and method for tomography scanning device |
| NL7704119A (en) * | 1976-04-19 | 1977-10-21 | Varian Associates | TOMOGRAPHIC SCANNING DEVICE. |
| DE2619482C2 (en) * | 1976-05-03 | 1982-05-06 | Siemens AG, 1000 Berlin und 8000 München | X-ray film device for the production of transverse slice images |
| US4066901A (en) * | 1976-09-13 | 1978-01-03 | Varian Associates, Inc. | Tomographic scanning apparatus with improved collimator structure |
-
1980
- 1980-06-04 CA CA353,328A patent/CA1129564A/en not_active Expired
- 1980-09-11 GB GB8029465A patent/GB2061028B/en not_active Expired
- 1980-09-12 JP JP12784580A patent/JPS5657433A/en active Granted
- 1980-09-15 DE DE19803034717 patent/DE3034717A1/en active Granted
- 1980-09-16 NL NL8005171A patent/NL190630C/en not_active IP Right Cessation
- 1980-09-17 FR FR8020030A patent/FR2464694A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE3034717A1 (en) | 1981-03-19 |
| NL8005171A (en) | 1981-03-19 |
| JPS5657433A (en) | 1981-05-19 |
| GB2061028A (en) | 1981-05-07 |
| NL190630B (en) | 1994-01-03 |
| FR2464694A1 (en) | 1981-03-20 |
| JPS6353814B2 (en) | 1988-10-25 |
| FR2464694B1 (en) | 1983-12-30 |
| DE3034717C2 (en) | 1989-12-14 |
| GB2061028B (en) | 1983-07-06 |
| NL190630C (en) | 1994-06-01 |
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| MKEX | Expiry |