US3675020A

US3675020A - X-ray tube control circuitry

Info

Publication number: US3675020A
Application number: US860603A
Authority: US
Inventors: Melvin P Siedband; Philip A Duffy Jr; Jack L James
Original assignee: CGR Medical Corp
Current assignee: CGR Medical Corp
Priority date: 1969-09-24
Filing date: 1969-09-24
Publication date: 1972-07-04
Anticipated expiration: 1989-07-04
Also published as: GB1287825A; FR2062548A5

Abstract

Simple unified circuitry for use in controlling an X-ray generator for combining a selected photomultiplier tube with an operational amplifier which is either in an integrator mode or signal amplifier mode depending on whether radiographic procedures, fluoroscopic procedures or cine procedures are to be used.

Description

I United States Patent [1 1 3,675,020

Siedband et al. 1 July 4, 1972 54] X-RAY TUBE CONTROL CIRCUITRY 2,962,594 11/1960 Duffy ..250/95 3,109,093 10/1963 Arrison et a1. 250/95 X 1 lnvemorsi Melvm Siedband, Bammofe; 1 3,491,239 1/1970 Dalman ..250/95 Duffy, Jr., Catonsville; Jack L. James, Balmore, of Primary ExaminerJames W. Lawrence Assistant Examiner-C. E. Church [73] Asslgnee. CGR Medical Corporation, Cheverly, Md. Atmmey F H. Henson and E. P. Klipfel [22] Filed: Sept. 24, 1969 AB TRACT [21] App]. No.: 860,603 [57] S Simple unified circuitry for use in controlling an X-ray generator for combining a selected photomultiplier tube with an [52] US. Cl ..250/93, 250/95 operational lifi which is either in an integrator mode or [51] int. Cl. g signal amplifier mode depending on whether radiographic [58] Field of Search ..250/95, 103, 207 procedures, fluoroscopic procedures or cine procedures are to be used.

[56] References Cited 8 Claims, 1 Drawing Figure UNITED STATES PATENTS 2,796,527 6/1957 Oosterkamp et a1 ..250/95 EXPOSURE EXPOSURE /70 TERMINATING CIRCUIT TO ALL PM TUBES X-RAY TUBE CONTROL CIRCUITRY CROSS REFERENCES TO RELATED APPLICATIONS The present invention may be utilized with other circuitry for controlling an X-ray generator, for example, as described and claimed in copending patent application, Ser. No. 742,463, filed July 3, 1968, entitled An RMS Current Regulator" by Melvin P. Siedband'and-Jack L. James now abandoned; copending patent application Ser. No. 860,687, filed Sept. 24, 1969 entitled A Brightness Stabilizer with Improved Image Quality" by Melvin R Siedband and Philip A. Duffy; copending patent application Ser. No. 860,686, filed Sept. 24, 1969 entitled Switching Circuitry for an X-Ray Generator" by Fred J. Eulerand Jack L. James; and copending patent application Ser. No. 28,665, filed Apr. 15, 1970 entitled Heat Sensing Circuit" by Melvin P. Siedband and Jack L. James now Patent No. 3,634,871; all applications being assigned to the present assignee.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to X-ray tube control circuitry and more particularly relates to simple circuitry capable of controlling an X-ray generator but flexible enough to operate in a number of procedural functions such as radiographic, fluoroscopic or cine.

2. Description of the Prior Art Independent systems are generally used to control an X-ray generator when radiographic, fluoroscopic, or procedures are desired to be used. Hence; a multiplicity of circuits and power supplies results in a rather expensive, and complicated piece of equipment. In any of these procedures it is desirable to control the output of the X-ray generator as a function of the detected radiation level. In addition, it is also necessary for the radiologist to select the site of the detector which will sense the radiation level. That is, the radiologist must decide whether he will detect energy at the spotfilm device, under the table, at the output phosphor of an image intensifier or whatever other location'he may select. The voltage applied to the selected photomultiplier tubes or other detectors must be adjusted to establish the proper gain factor to assure the appropriate sensitivity. The sensitivity will determine proper and optimum exposures and is a function of different X-ray attentuation factors to that detector input as well as normal detector variations.

The detector may be located at a spotfilm device, under the table, or at the output of an image intensifier to permit brightness stabilized fluoroscopy, motion pictures of constant density or properly exposed radiographs.

A prior art method of terminating radiographic X-ray exposures is to couple the output of a scintillator to a photomultiplier tube which feeds a thyratron arranged as an integrator so that when the output current of the phototube charges the capacitor to a predetermined level, the thyratron fires and energizes circuits to interrupt the primary current to the X-ray high voltage transformer.

Fluoroscopic brightness stabilizer systems for controlling X- ray generators for proper cine exposures operate by the use of a photomultiplier tube optically coupled to the output phosphor of an image amplifier. One such system is as described and claimed in the aforementioned copending application, Ser. No. 860,687 wherein the output of a photomultiplier tube is fed to a dc amplifier, the output of which is compared to a reference and used to control the X-ray tube filament circuits so as to automatically adjust Xray tube beam currents. If the X-ray beam current exceeds certain bounds, a motor driven transformer adjusts the primary voltage of the X- ray tube high voltage transformer to control the accelerating voltage of the X-ray tube. Stabilization about specific values of X-ray beam current and establishing the bounds within which the X-ray accelerating voltage will vary depends upon the particular procedure being followed; that is, whether cine frame rates or simple fluoroscopy is being used.

cine

The object of the present invention is to provide X-ray tube control circuitry capable of operation following radiographic, fluoroscopic, or cineprocedures.

Another object of the present invention is to provide X-ray tubes control circuitry which allows the radiologist to select the site of the detector to be utilized to sense the level of radiation.

Another object of the present invention is to provide X-ray tube control circuitry capable of appropriate sensitivity adjustments to obtain proper exposures under different X-ray attenuation factors as well as the usual variations within the detectors.

Another object of the present invention is to provide X-ray tube control circuitry allowing the selection of the magnitude of operating voltage for the selected detector and allowing the choice of radiographic, fluoroscopic or cine procedures.

Another object of the present invention is to provide an X- ray tube control circuitry which is simplier, less expensive, more reliable, and smaller in size than prior art circuitry utilized for simplier purposes.

SUMMARY OF THE INVENTION Briefly, the present invention accomplishes the above cited objects and other objects and advantages by providing circuitry flexible enough to operate in a number of procedural choices. The level of variation may be detected from any one of a number of detectors each positioned in a desired location. The present invention combines the selected radiation detector with an operational amplifier having an integrator mode of operation and a signal amplifier mode of operation depending upon what procedure is desired. Means are provided for calibrating the circuitry to assure appropriate sensitivity.

DESCRIPTION OF THE DRAWING Further objects and advantages of the following invention will be readily apparent from the following detailed description taken in conjunction with the drawing in which the sole FIGURE is an electrical schematic diagram of an illustrative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The level of radiation from an X-ray tube 2 may be sensed at a number of locations by a plurality of detectors, herein illustrated for example as

photomultiplier tubes

10, 20 and 30. Each photomultiplier tube has applied thereto an operating voltage determined by a power inverter 40. The selected photomultiplier tube is connected to an operational amplifier 50 where the output from the selected photomultiplier is either integrated over time to determine the length and extent of exposure or to amplify the output from the selected photomultiplier tube to provide an output indicative of the brightness of the resulting image. The operational amplifier 50 will function in either mode as determined by the selecting circuitry 60. The operational amplifier 50, when in the integrator mode, provides an exposure termination signal to circuitry 70 upon the integral of the selected detector current and elapsed time reaching a predetermined value. The operational amplifier 50, when in its signal amplifier mode, provides a brightness signal which is a function of the selected detector current to a brightness stabilization circuit 80. The brightness stabilization circuitry is utilized when fluoroscopic or cine functions are desired. The exposure terminating circuit 70 is utilized when the radiographic procedure is desired.

More particularly, assume that the radiologist desires to detect energy at a particular site and photomultiplier tube 10 is in that location. The photomultiplier tube 10, if used in a radiographic procedure, may detect radiation from the X-ray tube 2 coupled through a scintillator. If the photomultiplier tube 10 is to be used for fluoroscopic or cine procedures it will be optically coupled to the output phosphor of an image intensifier (not shown) radiated by the X-ray tube 2.

The selection of photomultiplier 10 is illustrated to be accomplished by closing switch 11. Of course any suitable selection means may be utilized and may include external logic circuits, punched cards, tape, etc. The selection at 11 by the connection of a conduct signal, say +24 volts, will render a transistor 12 conductive. The other select circuits will be at ground potential. Therefore transistor 12 will be conducting so that a potentiometer 13 in its collector circuit in conjunction with a resistor network 14 between a voltagesupply indicated at +24 volts and a point reference potential or ground will select an input current to an amplifier, indicated as a transistor 41. An emitter follower circuit 42 is connected to respond to the amplifier 41 and provide an output voltage as a function of the input current to transistor 41.

The inverter 40 will thus produce an output voltage, for example between 650 and -l,300 volts, as determined by the potentiometer 13 at the collector of transistor 12. If the potentiometer 13 is approximately at its mid-range, 900 volts will be applied to photomultiplier tube 10 or, if desired, 900 volts can be applied to all of the photomultiplier tubes. lf operating voltage is applied to all three detectors the physical arrangement of the X-ray generator should be such that very little light input will be provided to the other photomultiplier tubes so that only the selected detector 10 will have a significant output signal. At the same time selection is made at 11, a Zener diode l and ordinary diode 16 leading to the base-of a field effect transistor 17 will conduct such that the transistor 17 will be rendered conductive. The output current of the selected detector will be coupled through transistor 17 directly to an input field effect transistor 51 in the operational amplifier 50.

Field effect transistor 51 and field effect transistor 52 are connected as a differential amplifier feeding cascaded

transistors

53 and 54.

Prior to the initiating of an exposure an enabling circuit 90 grounds the input 51 to the operational amplifier 50. That is, the absence of an exposure gate signal at the input of transistor 91 feeding field effect transistor 92 grounds the input to transistor 51. Assuming the power supply connection for the differential amplifier of

transistors

51 and 52 to be 6.8 volts as indicated, the operational amplifier 50 will be forced to an initial condition at the output collector of transistor 54 of near 4 volts, approximately the saturation condition of transistor 54.

When an exposure is initiated, the gate signal is changed from 0 to +24 volts deenergizing transistors 91 and 92 thereby enabling the operational amplifier 50 to respond to the output current of the selected detector 10. Feedback for the operational amplifier 50 is provided through resistor 55 and capacitor 56 which couples the collector of transistor 54 to the input of field effect transistor 51 to provide the operational integration. The rate of change of voltage seen at the collector of transistor 54 is directly proportional to the output current of the photomultiplier tube 10 fed to the input of transistor 17. As the output of the operational amplifier 50 increases in a positive direction, the setting of a potentiometer 71 in the base circuit of output of transistor 72 and the output voltage of transistor 54 will determine when transistor 72 will begin to conduct. The collector of transistor 72 is connected to circuits 70 in the X-ray control timer to terminate the exposure when transistor 72 is conductive. Obviously, the length of exposure is inversely proportional to the brightness detected by the photomultiplier tube 10. As brightness diminishes, the current output of the photomultiplier tube 10 is reduced and therefore the integration time of the operational amplifier 50 is increased.

If the X-ray tube control circuitry is to be used for fluoroscopic or cine procedures the mode selecting circuitry 60 is activated, for example, by closing switch 61. For such procedure the operational amplifier 50 will be made to operate in a signal amplifier mode for use in stabilizing brightness as described and claimed, for example, in the aforementioned copending application, Ser. No. 860,687.

If the control circuitry is to be used for stabilization of brightness in fluoroscopy or cine procedures, the output collector of transistor 54 is coupled through a filter 57 illustrated as parallel connected resistor 58 and capacitor 59 to the input of field efi'ect transistor 51 via field eflect transistor 62 in the selecting circuitry 60. When the transistor 62 is rendered conductive as a result of the connection of a "select operational amplifier input through switch 61 the parallel combination of resistor 58 and capacitor 59 is connected directly to the input of transistor 51 so that the configuration of the operational amplifier 50 is changed from an integrator to a signal amplifier mode. The output voltage at the collector of transistor 54 will then be proportional to the current from the selected detector 10. The shunt capacity in the feedback path will now function, not as an integrator, but as a filter to establish a roll-off frequency of about 3 to 4 cycles per second. That is, the operational amplifier 50 will follow steady state variations of a few cycles per second but if the radiation intensity varies to a greater degree the shunt capacity will smooth out excess variations exceeding the thermal time constant of the X-ray generator tube to thereby assure good stability of the system.

Other photomultiplier tubes

20 and 30 may be selected at 21 and 31 respectively by energizing their associated gating

field effect transistor

27 or 37. Potentiometers 23 and 33 will similarly allow calibration of the high voltage output from the inverter 40 to properly operate the selected photomultiplier tube. The circuitry may then be programmed by the selecting circuitry 60 to operate the operational amplifier 50 to an integrator mode for exposure phototiming when the radiographic procedure is desired or the operational amplifier 50 may be selected to operate in its signal amplifying mode for brightness stabilization purposes when fluoroscopic or cine procedures are to be used.

The entire logic circuitry of FIG. 1 can be reduced to a few printed circuit cards and provide a flexibility heretofore unavailable. A higher order of performance is possible than with conventional vacuum tube circuits. The utilization of the same X-ray tube control circuitry for any desired procedure with any selected radiation detector greatly reduces costs since an appropriate single circuit is programmed to operate for any desired procedure. The present invention replaces a portion of the present multiplicity of circuits and power supplies that were previously necessary. The illustrated circuitry is compatible with and may be operable with the brightness stabilizing circuitry described and claimed in the aforementioned copending applications, Ser. No. 860,687.

While the present invention has been described with the degree of particularity for the purposes of illustration, it is to be understood that all modifications, alterations and the substitutions within the spirit and scope of the present invention are herein meant to be included. For example, while transistors and knife switches have been illustrated to perform various switching and amplifying functions, it is to be understood that any suitable devices capable of similar performance may be utilized. The specific operating parameters are merely by illustration and other operating voltages and power supplies are equally applicable. Any number of photomultipliers in selected location may be utilized. Three photomultiplier tubes were shown for purposes of illustration.

We claim as our invention:

1. X-ray tube control circuitry comprising, in combination: a plurality of radiation detectors each in a desired location; means for selecting a desired radiation detector; power supply means responsive to the selecting means for providing an operating voltage to the selected radiation detector; operational amplifier means having an integrator mode for exposure timing and a signal amplifier mode for brightness sensing; means responsive to the selection of a radiation detector for connecting the output current of the selected detector to said operational amplifier means; means for selecting the mode of said operational amplifier means; said operational amplifier means, when in said integrator mode, providing an exposure termination signal upon the integral of the selected detector current and elapsed time reaching a predetermined value; said operational amplifier means, when in said signal amplifier mode, providing a brightness signal functionally related to the selected detector current.

2. The combination of claim 1 wherein said operational amplifier means, when in the signal amplifier mode, provides a signal directly related to the output current of the selected detector.

3. The combination of claim 1 further comprising exposure initiating means for gating said operational amplifier means to respond to the output current of said selected detector.

4. The combination of claim 1 further comprising means for smoothing out variations exceeding a few cycles per second in the output current of the selected detector.

5. The combination of claim 1 further comprising means for individually calibrating the magnitude of the operating voltage from said power supply means for each radiation detector that may be selected.

6. The combination of claim 1 further comprising timing means responsive to the magnitude of output current from the selected detector for determining the length of exposure.

7. The combination of claim 6 further comprising an output stage responsive to the exposure termination signal from said operational amplifier means reaching a predetermined magnitude to activate exposure terminating circuitry.

8. The combination of claim 7 wherein said output stage includes variable means for controlling the gain of the output stage to determine the magnitude of signal from said operational amplifier means which will actuate said output stage.