US3452203A

US3452203A - Triode type x-ray tubes and method and apparatus for irradiating x-rays

Info

Publication number: US3452203A
Application number: US574733A
Authority: US
Inventors: Koichiro Shiga; Motoshige Yoshida; Yoichi Haga
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1965-08-31
Filing date: 1966-08-24
Publication date: 1969-06-24
Anticipated expiration: 1986-06-24

Description

June 24, 1969 KOlCl-"RQ SHlGA ET AL 3,452,203

TRIODB TYPE X-RAY TUBES AND METHOD AND APPARATUS FOR IRRADIATING X-RAYS Filed Aug. 24, 1966 Sheet I of a FIG. I

FIG. 4 26 27 KO/cmk 0 Ji /64 I f i f f Ma res/nae Yaw/D14 & 3 3 rm, HA 6/! g| INVENTOR$ KOICHIRO SHIGA ET AL June 24, 1969 3,452,203 TRIODE TYPE X-HAY TUBES AND METHOD AND APPARATUS Sheet FOR IRRADIATING X-RAYS Filed Aug. 24, 1966 3* m 6E s a w mi June 24, 1969 KQ|H|RQ $H|GA ET AL 3,452,203

TRIODE TYPE X-RAY TUBES AND METHOD AND APPARATUS FOR IRRADIATING X-RAYS Filed Aug. 24, 1966 Sheet 3 of 3 FIG. 7

United States Patent US. Cl. 25099 6 Claims ABSTRACT OF THE DISCLOSURE An X-ray tube having first and second sets of triode members, each set comprising respective cathodes and grids and a common anode. The first triode set has a predetermined cut-off voltage and the second set exhibits a larger cut-off voltage. The cathodes are simultaneously energized and the grids are simultaneously biased with the same voltage, the biased voltage being controlled to selectively operate the first and second triode sets.

This invention relates to a novel triode type X-ray tube having two types of filaments and to a method of and apparatus for irradiating X-rays utilizing the novel X-ray tube.

In X-ray diagnosis it is often desirable to directly take photographs at suitable times while observing affected portions by means of fluoroscopy or recording the images of the aifected portions by a video tape recorder or observing said images through an X-ray television system or photographing said images on movie films. These are particularly desirable for producing projected images of hearts, blood-vessels, etc.

A dual foci-diode type X-ray tube has been known having two types of filaments, i.e. a first filament for producing small focus and a second filament for producing a large focus, wherein the first filament is energized for fluoroscopy and then switched to the second filament for,

direct photographing.

However, as the second filament has a large heat inertia, a time, for example from 0.5 to 1 second, has been required from the instant of its energization until it has heated up to an operating temperature at which.

the operating voltage could be applied. Therefore, such an X-ray apparatus is not suitable for taking direct radiographs of quickly moving internal organs such as a heart. For this reason, where fluoroscopy and direct radiographing are made after injecting a contrast medium it was necessary to inject it at each case separately, which is not desirable because the patient must bear the pain for several times. It is also desirable to reduce the number of injections of the contrast medium because such injections accompany some side effects for internal organs.

It is well known that the triode type X-ray tube is suitable for this purpose because in this type of X-ray tube it is very easy to start and stop the radiation of X-rays of controlling its grid bias voltage. However, ordinary triode type X-ray tube is provided with only one type of filament so that it is necessary to change the connection of the heating circuit of the filament to increase its current in order to take direct radiographs at a suitable instant subsequent to the fluoroscopy with small filament current. This is similar to said diode type X-ray tube. Thus, it takes a certain time until the filament is heated up to a temperature suflicient for direct radiographing, so that it is again difiicult to directly take radiographs of rapidly moving internal organs.

Accordingly, it is the principal object of this invention to provide a new and improved triode type X-ray tube which is capable of taking direct radiographs of an object at any suitable time while observing it by fluoroscopy, taking movie pictures in the ordinary way in connected relation with a cardio-pulse, X-ray video tape recording and fluoroscoping in X-ray television.

Another object of this invention is to provide a novel method and apparatus for X-ray radiation capable of instantly switching its operation from fluoroscopy to radiography or vice versa.

The triode type X-ray tube embodying this invention comprises an evacuated tube, a common anode electrode disposed therein, a first cathode electrode adapted to form a large focus, a second cathode electrode adapted to form a small focus, and grid electrodes respectively disposed between said first and second cathode electrodes and said common anode electrode, the grid bias voltage E viz. the anode current I characteristic of one set comprising said first cathode electrode for producing said large focus and associated .grid and anode electrodes being made to be of sharp cut-off type, whereas the grid bias voltage 13,, viz. the anode current I characteristic for the other set comprising said second cathode electrode for producing said small focus and associated grid and anode electrodes being made to be of remote cut-off type.

The method of this invention comprises the steps of .utilizing a triode type X-ray tube which comprises a single evacuated vessel containing a common anode electrode, a filament for forming a small focus, another filament for forming a large focus and control grids respectively disposed between said filaments and said anode electrode thus constituting two sets of triodes having different cutoff characteristics, normally impressing bias voltages to said grids sufiicient to prevent thermal electrons from said filament for said large focus from arriving at said anode electrode, thus causing thermal electrons from said filament for said small focus to continuously or periodically generate X-rays for fiuoroscopy and bringing said grid bias voltage close to zero to rapidly increase the tube current, thus generating X-rays for direct radiography.

While the specification concludes with claims particularly and distinctly claiming the subject matter'of this invention, other objects and advantages together with construction and operation thereof can be more fully understood from the following detailed explanation of the invention taken in connection with the accompanying drawings, in which:

FIG. 1a shows a schematic elevational view, partly in section, of the essential elements of a triode type X-ray tube embodying this invention showing the cathode, .grid and focussing electrodes;

FIG. 1b is a plan view to schematicallyshow the arrangement of cathode and grid electrodes of the focussing electrode assembly according to this invention;

FIGS. 2 through 4 show E 'I characteristic curves to explain the operation of the triode type X-ray tube according to this invention;

FIG. 5 shows one example of a connection diagram of .an X-ray irradiating apparatus according to this invention;

plan view of the assembly Referring nowto the accompanying drawings, more particularly to FIG. 1a a triode type X-ray tube is shown generally by the reference numeral 10, with its evacuated envelope omitted. The X-ray tube comprises a rotary anode 11 mounted upon a shaft 12 which is arranged to rotate in the evacuated envelope. The anode electrode 11 is disposed to be bombarded by accelerated thermal electrons and is provided with an inclined surface 13 to form a focus which radiates X-rays in the direction perpendicular to the direction of incoming thermal electrons. Since in the rotary anode type X-ray tube the point of incidence of the thermal electrons varies from time to time, the heating effect caused by the bombardment of thermal electrons is relatively small whereby it is possible to pass relatively large tube current thus radiating X-rays in large quantities. In addition, the wear of the anode electrode can be reduced thus elongating its useful life. However, it should be understood that the invention is by no means limited to such a type of X-ray tube but may be equally embodied in the stationary anode type X-ray tube.

A focussing electrode assembly, generally indicated at 14 includes a cup-shaped focussing electrode 15 which is opened at one end thereof facing to the anode electrode 11. At the upper portion of the focussing electrode 15 there are provided a pair of

slots

16 and 17 with their bottoms covering towards the center. An insulating bushing 18 for lead-in wires is mounted in the lower portion of the slot 16 to support a first filament 19, also a first grid 20 is disposed in the bottom portion of the slot 16. Similarly, an insulating bushing 21 for lead-in wires is disposed in the lower portion of the other slot 17 to support a second filament 22, and a second grid 23 is disposed in the bottom portion of the slot 17. The details of the configuration and arrangement of the first filament 19, first grid 20, the second filament 22 and the second grid 23 are shown in FIG. 1b.

When thermal electrons are radiated from the first filament 19 towards the inclined surface 13 of the rotary anode 11, a large focus 24 which is represented by a square will be formed to radiate X-rays for direct radiography therefrom. On the other hand, when thermal electrons are radiated from the second filament 22 towards the inclined surface 13 of the rotary anode 11, a small focus 25 for fiuoroscopy will be formed as shown by a small rectangle within the square 24. While in the above, the large and small foci are coincident with each other, it is not always necessary to arrange them in such a manner, but they may be disposed in closed spaced relation. The purpose of the focussing electrode 15 is to cause all thermal electron currents emanating from the first and the

second filaments

19 and 22 to converge to form foci '24 and 25, respectively. The magnitude of the tube current flowing through the large focus is of the order of 100 to 400 milliamperes, for example, and that through the small focus is of the order of about 1 to 20 milliamperes. As is evident from the data illustrated just above, since the tube current for fluoroscopy is small the anode electrode 11 may be held stationary, but in order to take direct radiographs at any desired time it is preferable to maintain the anode in continuous rotation.

Both

filaments

19 and 22 are energized simultaneously. and remain energized throughout the operative cycle of the tube.

Each of the first and

second grids

20 and 23 is maintained in electrical contact with the focussing electrode 15 so that they are maintained at the same potential.

A first triode member consisting of the first filament 19 adapted to form the large focus, the first grid 20 and the anode 11 is constructed and arranged to have an E -I characteristic of sharp cut-off whereas the second triode member consisting of the second filament 22, the second grid 23 and thecommon anode 11 to have an E 4,, characteristic of remote cut-01f. For example, in the construction shown in FIG. 1, the rating of the thermal electron emission of the first filament 19 is made several tens to several hundreds times larger than that of the second filament 22, the relative positions of the first and second grids being made similar but the spacing between grid wires of the first grid is made smaller than that of the second grid. For example, the first grid is constructed by a wire of 0.1 mm. diameter which is wound to have 8 to 12 turns per inch, whereas the second grid is made of a wire of 0.1 mm. diameter which is wound to have 15 to 20 turns per inch.

FIG. 2 illustrates the characteristics of the X-ray tube shown in FIG. 1 wherein a curve 26 represents the E I characteristic for large focus or of the first triode member where the anode voltage E is constant, and a curve 27 indicates the E, p characteristic for small focus or of the second triode member. Where the grid voltage E is maintained zero, the first triode member will pass a large tube current indicated by 1 so that it can be cut-off by a relatively small grid bias voltage E of the magnitude of from 500 to 1000 v., for example. On the contrary, where the grid voltage E is maintained zero, the second triode member will pass a relatively small current I which can be cut-off by a relatively deep grid biasing voltages E of 2000 v., for example. As'can be seen from FIG. 2, the second triode member still passes a tube current indicated by I at the biasing voltage E which is effective of cut-off the first triode member. Since the second triode has inherently small tube current and the remote cut-off characteristic the slope of the E l curve 27 is small so that the magnitudes of tube current I, and I do not differ materially.

Thus, it will be clear that, in order to effect fluoroscopy, the grid voltage may be selected to any suitable value in a range of from E to E to cut off the first triode member for the large focus. Further, it will also be clear that, in order to take direct radiographs it is only necessary to reduce the grid biassing voltage to zero.

FIG. 3 represents an E -I curve identical with that shown in FIG. 2 to explain said operation. In this example, at a suitable instant during the interval wherein the grid biassing voltage is selected to have a value in a range of from E to E the voltage E is reduced to zero to effect direct radiographing and thereafter the grid biassing voltage is again restored to a value within the range of from E to E to continue fluoroscopy. If the voltage E is selected to be larger than E the tube current I could be completely cut off to cease generation of X-rays. Upon bringing the voltage E in a range of from E t0 gLy the tube current will assume a value I to generate X-rays for fluoroscopy thus making it possible to effect fluoroscopy, image pick-up for television broadcasting or transmission. When the voltage E is reduced to zero at any desired time, the tube current will be increased to I +I thus enabling direct radiographing. After taking photographs the voltage E is again brought back to a value in a range of from E to B to restore the tube current 1,, thus continuing fluoroscopy. Since both

filaments

19 and 22 are always energized, said direct radiographing may be made at any instant and for any desired number of times without any time lag.

FIG. 4 shows one example of the E -I curve for effecting so-called angio-cardiographing. In this case, grid bias voltage is selected to be larger than Egs to completely cut off the tube current, but the grid biassing voltage 13,, is periodically reduced to a value falling in the range of from E to E whereby to periodically generate X-rays for fluoroscopy. As can be clearly noted from FIG. 4, the X-ray tube is operated in such a manner that currents for fiuoroscopy I, are periodically passed for each period t with spacings of t to take movie pictures. During the above operation, the grid voltages E is reduced 'to zero at any desired time to pass the tube current of an angio-cardiographing, wherein photographing of an X-ray movie film and fluoroscopy are made simultaneously and during which direct radiographing is also possible at any desired time. Thus, for example, an X-ray image intensifier tube providing an optical system disposed on the output side of it which functions to utilize a portion of the output fiuoroscence for effecting fluoroscopy and the remaining major portion for photographing movie pictures is utilized. The film for direct radiographing is fed in front of the X-ray image intensifier tube by a mechanism similar to a film changer for angio-cardiographing in synchronism with the photographing signal.

FIG. 5 shows one example of a circuit arrangement which is constructed to permit switching of grid biassing voltage in two stages. In FIG. 5, the reference numeral 28 designates a high voltage generator adapted to supply a high voltage across the anode and cathode electrodes of a triode type X-ray tube embodying this invention. A D-C source source 29 and a pentode type vacuum tube V are provided in order to give the required control grid voltage mentioned above to the X-ray tube 10. In order to protect the cathode electrode by by-passing flash over current across the anode and grid electrodes of the X-ray tube, a diode D is provided with its anode electrode connected to the grid electrode of the X-ray tube and its cathode electrode connected to the cathode electrode of the X-ray tube. The grid and cathode electrodes of the X-ray tube are respectively connected to the opposite terminals of an anode load resistor 30 of the pentode tube.

The output from a multivibrator comprised by a twin triode tube V is derived out through a potentiometer 31 and is then applied to the third grid electrode of the pentode type vacuum tube V via one of the stationary contacts of a change-over switch 32. Further, a constant negative bias voltage from a source of constant negative voltage 33 is supplied to the third grid of the vacuum tube V through the other stationary contact of .the change-over switch 32. On the input terminal of the multivibrator is provided a switch 34 which is operated in an interlocked relation with the change-over switch 32 to supply the trigger pulse of a movie camera to the multivibrator. The width of the output pulse of the multivibrator can be adjusted by varying the valve of a condenser 35 which interconnects the input and output stages whereas the amplitude of the output pulse can be adjustable by the potentiometer 31.

The operation of the circuit shown in FIG. 5 is as follows: If it is assumed now that switches 32 and 34 are thrown to their upper contacts and that a repeating pulse synchronized with the film feed speed is supplied from a movie camera to the input of the vacuum tube V which constitutes a multivibrator, a repeating pulse will be produced in the output side, which varies in the negative direction and is applied to the third grid of the vacuum tube V When the first grid of the vacuum tube V is maintained at a negative potential, the anode current flowing through this tube V will be reduced corresponding to the magnitude of the pulse for the interval during which the negative pulse is applied to its third grid. In the absence of this pulse the vacuum tube V is fully conductive to produce a voltage drop sufficient to cut ofi the X-ray tube 10 or a voltage larger than the voltage E shown in FIG. 4 across the resistor 30, thus stopping radiation of X-rays. However, when the anode current of the vacuum tube V is decreased as above described the voltage drop across the resistor 30 will have a value intermediate of E and E As a consequence the X-ray tube 10 will generate X-rays for fluoroscopy as long as the pulse persists. This operation is repeated corresponding to the period of the pulse, thus enabling to take X-ray movie pictures.

In order to enable direct radiographing an additional multivibrator comprising a twin triode tube V;, is provided, said multivibrator being of the same construction as the first one comprised by the tube V The output stage of the additional multivibrator is connected to the first grid electrode of the vacuum tube V and the output trigger pulse from a film changer is applied to the input thereof. With this arrangement so long as the output pulse is provided by the multivibrator V a negative biassing voltage will be impressed upon the first grid electrode of the vacuum tube V to render it cut off with a result that the grid voltage of the X-ray tube 10 is reduced to zero thus passing a tube current necessary for direct photographing. It will be clear that this operation can be repeated at any time during the period in which X-ray movie pictures are taken under the control of the ouput pulse from the multivibrator comprised by the vacuum tube V When the switch 32 is thrown to its lower contact a constant negative voltage from the constant voltage source 33 will be supplied to the third grid of the vacuum tube V thus permitting the X-ray tube 10 to continue to pass the current for fluoroscopy. In this case too, it becomes possible to directly take radiographs by applying the output pulse from the multivibrator V to the first grid electrode of the vacuum tube V FIGS. 6a and 6b illustrate a modified focussing electrode structure 14 in which only a single slot 36 is provided in a focussing electrode 15 and the filament 22 for the small focus and the filament 19 for the large focus are coaxially disposed in the slot 36.

Grids

20 and 23 are arranged on the same plane in juxtaposed relation. As shown, the mesh of the grid 23, for the small focus is slightly coarser than the grid 20.

In further modified focussing electrode structure 14 shown in FIGS. 7a and 7b, filaments for small and larger foci, respectively, are located in parallel in a single slot 36 of a focussing electrode 15 and a grid 37 is provided common to said filaments. More particularly, as shown in FIG. 7a, the distance between the filament 23 for the small focus and the grid 37 is made smaller than that between the filament 19 for the large focus and the grid 37 thus creating a diiference between cut-01f voltages. For example, a satisfactory result was obtained with a spacing of 0.3 mm. between the small focus filament 23 and the grid 37 and a spacing of from 1.6 to 1.8 mm. between the large focus filament 19 and the grid 37.

The X-ray tube 10 shown in FIG. 8 is of the stereo type and two focussing

electrodes

14 and 14 are arranged as shown, which may be any one of various types illustrated herein above. Electrodes 14 are operated to alternately emit thermal electrons thus permitting to independently observe by left and right eyes the fluorescent image caused by X-rays radiated from anode electrode 11. In this manner a stereofluoroscopy can be made. Likewise stereomovie pictures can also be made. While the invention has been described in terms of certain preferred embodiments thereof, it will be clear to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An X-ray tube comprising:

an evacuated envelope;

a first triode set in said envelope and including a common anode electrode, a first cathode electrode to form a large focus and a first control grid disposed between said first cathode electrode and said common anode electrode, said first triode set having a predetermined reverse bias cut-off voltage;

a second triode set in said envelope and including said common anode electrode, a second cathode electrode to form a small focus and a second control grid disposed between said second cathode electrode and said common anode electrode, said second triode set having a large reverse bias cut-off voltage than said first triode set;

means for simultaneously energizing said first and second cathode electrodes and for causing said cathode electrodes to remain energized throughout the operative cycle of said X-ray tube; and

means for simultaneously biasing said first and second control grids with the same voltage.

2. The X-ray tube according to claim 1 wherein said control grids are comprised of a single grid common to said first and second cathode electrodes.

3. The X-ray tube according to claim 1 wherein said large and small foci are formed in closed spaced relation.

4. The X-ray tube according to claim 2 wherein said large and small foci are formed in closely spaced relation.

5. The method of radiating X-rays from a triode type X-ray tube, said method comprising the steps of utilizing a triode type X-ray tube including a single evacuated vessel containing a common anode electrode, a filament for forming a small focus, another filament for forming a large focus and control grids respectively disposed between said filaments and said anode electrode thus constituting two sets of triodes having different cut-off characteristics; simultaneously impressing simultaneously bias voltages to said grids sufiicient to prevent thermal electrons from said filament for said large focus from arriving at said anode electrode, thus causing: thermal electrons from said filament for said small focus to continuously or periodically generate X-rays for fluoroscopy; and bringing said bias voltage close to zero to rapidly increase the tube current, thus causing electrons from said filament for said large focus to generate X-rays for directly taking radiographs or for fluoroscopy.

6. A triode type X-ray tube apparatus comprising a triode type X-ray tube including:

a single evacuated vessel which contains a common anode electrode, a filament for forming a small focus, another filament for forming a larger focus and control grids disposed between said common anode and said filaments, said anode, filaments and grids being constructed and arranged to constitute two triode members having difierent cut-off characteristics; means for simultaneously energizing said filaments; means for biasing said grids simultaneously with the same voltage;

v a pentode, the anode electrode of which is connected to said grids of said X-ray tube to control the biassing voltages of said X-ray tube;

means to apply a negative control voltage of a predetermined period to the third grid of said pentode to cause said X-ray tube to generate X-rays for fluoroscopy at a predetermined period; and

means to apply, at any suitable time, a negative control voltage from a direct photographing commanding device to the first grid of said pentode to cause a large tube current to flow through said X-ray tube for directly taking radiographs or for fiuoroscopy.

References Cited UNITED STATES PATENTS 2,691,735 10/1954 Boldingh 25094 X 3,103,591 9/1963 Rogers et al. 250-99 X 3,389,253 6/1968 Kok 250-61 ARCHIE R. BORCHELT, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

U.S. Cl. X.R. 250103; 313-56