US3675027A - System for continuously varying the size of the field of an x-ray image intensifier tube - Google Patents

Abstract

A system for continuously varying the size of the field of an Xray image intensifier tube, wherein the voltages impressed on the electrodes of the tube are so controlled that the size of the field of view of the tube changes in such a manner that each and every point of the output image of the tube moves at a substantially constant speed.

Description

United States Patent [151 3,675,027

Tsuda et al. July 4, 1972 541 SYSTEM FOR CONTINUOUSLY [56] References Cited VARYING THE SIZE OF THE FIELD OF AN X-RAY IMAGE INTENSIFIER TUBE UNITED STATES PATENTS 3,417,242 12/1968 Windebank ..250/213 VT [72] Inventors: lOOhlSfl Tsuda; Masao Yoshlmura, both 3,225,204 12/1965 Schagen t 250/213 VT Japan 3,303,345 2/1967 Wulms ..250/213 VT [73] Assignee: Shimadzu Seisakusho Ltd., Kyoto, Japan I Primary ExaminerArchie R. Borchelt [22] led: Sept 1970 Assistant ExaminerD. C. Nelms 211 App] 74 454 Att0rneyFidelman, Wolffe, Leitner & Hiney [57] ABSTRACT [30] Foreign Application Priority Data I A system for continuously varylng the size of the field of an X- Oct. 3, 1969 Japan "44/7 9463 my image i t ifi tube7 wherein the voltages impressed On the electrodes of the tube are so controlled that the size of the LS. Cl. VT, of iew of the tube changes in uch a manner that each l. In. 1 and every point of the output image of the tube moves at a [58] Field of Search .250/21 3 R, 213 VT, 83.3 HP, Substantially constant speed ISO/83.3 R, 77; 313/65 R, 94; 315/10 5 Claims, 4 Drawing Figures SYSTEM FOR CONTINUOUSLY VARYING THE SIZE OF THE FIELD OF AN X-RAY IMAGE INTENSIFIER TUBE This invention relates to a system for controlling the size of the field of view of an X-ray image intensifier tube and, more particularly, to a system for continuously varying or zooming" the size of that portion of the input image of an X- ray image intensifier tube which is reproduced on the output screen thereof.

X-ray image intensifier tubes generally comprise a vacuum envelope and an input and an output screen at the opposite ends thereof, with several control electrodes therebetween for focussing an X-ray image formed on'the input screen onto the output screen as a visible image. Generally the output screen is far smaller in size than the input screen, the latter being for example eleven inches in diameter while the former is only one inch in diameter. If the entire image on the input screen is reproduced on the output screen, the image is demagnified to one-eleventh but much intensified in brightness. If only a portion of the input image is reproduced on the entire area of the output screen, the output image is less demagnified or enlarged but less intensified. The size of that portion of the input image which is reproduced as an output image is called the field of view (or simply the field) of the tube, and the ratio of the input image size to the output image size is called the demagnification ratio, which will be designed by M. Since the size of the output screen is fixed in a particular tube, the demagnification ratio is determined by the size of the field of view.

In the type of X-ray image intensifier tubes this invention is concerned with, by varying the voltages impressed on the electrodes it is possible to continuously vary the field or the demagnification ratio to obtain an output image of a desired size can be obtained. The technique of continuously varying the field or the demagnification ratio to commonly referred to as zooming. Zooming is a very effective technique in observation through the X-ray image intensifier tube. Suppose that an examiner is viewing the entire area of an object, for example, a patient's chest cavity on the output screen. If he wishes to closely examine a small portion of the chest cavity, he may zoom up the image on the output screen by increasing the demagnification ratio. When the demagnification ratio is changed for zooming, each and every point of the image on the output screen'moves radially away from or toward the center of the screen as the image is zoomed, so that the examiner can trace and see the minute moving point of the image more easily and accurately than if the image remains stationary. Experience shows that a small object at a remote place or an object in a dark place can hardly draw our attention if it stands motionless, but that when it happens to move, it can be easily distinguished from the background. The phenomenon that a moving object can be more easily ob served than a stationary one may be called the tracing observation effect". Zooming provides this tracing observation effect in X-ray examination of various objects.

Obviously, it is preferable to effect zooming at a suitable speed. As previously mentioned, zooming is effected by varying the voltages impressed on the electrodes of the intensifier tube. The voltage to be applied to the annode and the subsidiary annode, however, is very high, sometimes as high as kV, so that in order to regulate the high voltage it is practically impossible to insert a potentiometer in the high direct current voltage output circuit connected to the electrodes. Moreover, since the voltage to be applied to the subsidiary annode must not pulsate (and this is true with the other control electrodes), a smoothing condenser having a large capacity is usually provided at the output side of a direct current power source to smooth the output voltage thereof to be applied to the subsidiary annode. When the voltage of the direct current power source is changed for zooming, the corresponding change in the subsidiary annode voltage is delayed due to the time constant of the condenser, with resulting disturbance of the proper relation between the voltages on the different electrodes. This materially defocuses the output image and deteriorates the resolution thereof.

In zooming, the size of the image on the output screen changes in inverse proportion to the change of the demagnification ratio M. Forexample, when the image on the output screen is zoomed from a small field to a larger one in such a manner that the diameter of the field of view changes as a linear function of time elapsed, the size of the output image changes at a lower speed in the larger field with a larger demagnification ratio than in the small field with a small demagnification ratio. In other words, a point in an image on the output screen radially moves more slowly in a large field than in a smaller field. This not only causes irritation to the observer but also detriorates the tracing observation effect.

Accordingly, it is one object of the invention to provide a system for continuously varying the output image of an X-ray image intensifier tube, wherein when the output image is zoomed, its size changes at a substantially constant speed from a small to a larger field and vice versa, so that the observer can view the image being zoomed with the tracing observation effect and without having any irritating feeling.

Another object of the invention is to provide a system for zooming the output image of an Xray image intensifier tube, wherein when any change for zooming in the voltages impressed on the electrodes of the tube results in a corresponding change in the size of the output image without substantial delay, so that no reduction of the resolving power occurs during the course of zooming operation.

Other objects, features and advantages of the invention will become apparent from the following description of a preferred embodiment thereof with reference to the accompanying drawings, wherein the same reference symbols or numerals in different figures denote corresponding parts, and wherein;

FIG. 1 is a schematic, longitudinal section of an image intensifier tube incorporated into the system of the invention;

FIG. 2 is a graph illustrating the relation between the size of the field of view of the tube and the voltages impressed on the electrodes thereof;

FIG. 3 is an electrical circuit diagram of the control circuit showing the intensifier tube; and

FIG. 4 is a diagram of a portion of FIG. 3 showing the detailed construction of the voltage regulators.

Referring first to FIG. 1, there is shown X-ray image intensifier tube generally designated by 10 and comprising a vacuum tube 11, an input screen 12 at one end of the tube, a first electrode or grid 13 connected to a terminal G1, a second electrode or grid 14 connected to a terminal G2, a subsidiary annode 15 connected to a terminal SA, an annode 16 connected to a tem'iinal A and an output screen 17 at the opposite end of the tube 11. The input screen 12 has a diameter of, say, 1 1 inches, which is far greater than the output screen 17 having a diameter of, say, only one inch. As is well known, the X-ray image of an object, not shown, formed on the input screen is changed into a beam of electrons carrying the image thereon, and the beam is condensed and focussed by the electrodes 13 -16 onto the output screen 17 so as to display thereon a visible image corresponding to the input image, demagnified insize but intensified in brightness. As previously mentioned, that portion of the image on the input screen 12 which is reproduced on the output screen 17 is called the field of view (or simply the field), and the ratio of the size of the input image to that of the output image is called the demagnification ratio M.

The size of the field or the ratio M can be changed by changing the voltages applied to the terminals of the electrodes of the tube in a correlated manner as shown in FIG. 2, wherein the diameter of the field inches is taken along the abscissa and the voltages on the terminals G1, G2 and SA, along the ordinate, with the SA voltage being scaled at the left-hand side and the grid voltages G1 and G2, at the right-hand side of the graph. With the annode voltage being kept at a constant value, by varying the other control voltages G1, G2 and SA as shown by the curves designated by the corresponding reference symbols, it is possible to vary the size of the field of 3 view through the output screen as shown along the abscissathat is, to obtain an image corresponding to that portion or area of the input, image the diameter of which is given along the abscissa, occupying the entire area of the output screen.

A circuit for varying the voltages applied to the electrodes is shown by way of example in FIG. 3. The reference symbols A, SA, G1 and G2 designate the terminals designated by the same reference symbols, respectively, in FIG. 1. A voltage regulator 18 has its slider 19 connected to the terminal G1 and its opposite ends, to the secondary side of a transformer 20, with a rectifying diode 21, a smoothing condenser 22 and a grounding resister 23 connected therebetween. Similarly, a voltage regulator 24 has its slider 25 connected to the terminal G2 and its opposite ends, to the secondary side of a transformer 26, with a rectifying diode 27, a smoothing condenser 28 and a grounding resister 29 connected therebetween.

The voltage regulators l8 and 24 regulate the voltages to be applied to the grids l3 and 14, respectively. The transformers and 26 have their respective primary windings connected to an alternating current source L. To operate the voltage regulators a constant speed motor 30 is provided, which mechanically mOves the sliders l9 and of the voltage regulators to regulate the level of the output voltages therefrom. The construction of the regulators constitutes an essential portion of this invention and will be described in detail later.

A transfer switch 31 is inserted between the alternating current source L and the motor to determine the direction of rotation of the motor.

As previously'mentioned, the voltages to be applied to the annode A and the subsidiary annode SA are very much higher than those applied to the grids G1 and G2 and therefore it is practically impossible to have a voltage regulator inserted in the output circuitof the transformer connected between the source and the electrodes A and SA, as in the case with the grids G1 and G2. Therefore, the terminal SA of the subsidiary annode 15 is connected to the secondary side of a transformer 32 through a series combination of a protective resistor 33 and a rectifying diode 34, with a parallel smoothing condenser 35. The primary side of the transformer 32 is connected to the source L, with variable transformer 36 inserted therebetween, the slider 37 of which is controlled by a servo-motor 38. A servo-amplifier 39 includes voltage regulators 40 and 48 similar to the previously mentioned regulators 18 and 24. The amplifier 39 amplifies the difference voltage between the sliders 41 and 49 and controls the operating voltage to be applied to the servo-motor 38. The slider 41 of the regulator 40 is controlled by the motor 30 which controls the sliders 19 and 25 of the regulators 18 and 24. Thus, a voltage corresponding to the resistance set by the regulator 40 is applied to the terminal SA, as will be described in detail later.

The terminal A of the annode 16 is connected to the secondary side of a transformer 42 through a protective resistor 43, a rectifying diode 44 and a smoothing condenser 45. The primary sidelof the transformer 42 is connected to a variable transformer 46, which is in turn connected to the source L.

The slider 47 of the variable transformer 46 is manually mova-- ble to set the annode voltage to a predetermined fixed value.

FIG. 4 shows the detailed structure of the voltage regulator 18, The other voltage regulators are of a similar structure to the regulator 18, so that the structure of the regulator 18 alone will sufficiently be described as a representative of the others. The regulator 18 comprises a plurality of serial section resistors r-l r2, r-3, r-n having different predetermined resistance values, with the slider 18 movable along the series combination, so that the voltage taken out therefrom is applied to the control grid G1. The resistance values of these section resistors are so selected that as the slider is moved, the voltage taken out of each of the regulators changes in a correlated manner to those from the other regulators so as to provide different sizes of the field as shown in FIG. 2. Strictly speaking, so long as the slider moves along one of the section resistors, the voltage taken out therefrom varies linearly, and when the slider moves intO the adjacent one of the resistors,

the voltage changes linearly but with a difierent inclination. The resistance values of the resistors are so selected that these short section lines having different inclinations or slopes approximately correspond to the curves G1, G2 and SA, and as 5 will be easily seen, the more section resistors there are provided, the closer approximation to the curves is attained.

The resistance values are also so predetermined that the change in the voltages applied to the electrodes causes each and every point of the output image to move at a substantially constant speed as the size of the field changes.

Let the linear dimension of an object on the input screen be A, and the linear dimension of the image of that. object on the output screen be x. Then we have the following equation:

x A/M 1 15 wherein M is the demagnification ratio as previously mentioned. Let the diameter of the field expressed as a function of time I elapsed be flt). Then M=f(t)B (2 wherein B is the diameter of the output screen. Substituting the equation (2) into the equation l we obtain x AB/flt) (3 The changing speed of the linear size x of the output image as it is being zoomed can be obtained as the time derivative of x.

As previously mentioned, what we intend to attain is to keep dx/dt constant. To accomplish this condition, the value x must take the following from:

x at B 4 wherein a and ,8 are arbitrary constants. From the equations (3) and (4), we obtain flr)=AB/at+,8 (5 Here, if the maximum field size is flO) and the minimum field size is flT),

we have AB AB 0 f( B H (6) and . AB fU) 01TH; 7

Substituting (6) into (7),

f(T)= zxT+.

Here. if

l 1 r l f( f( b no)" a and B can be expressed as:

zx= a (9) ,e ABb (10 Substituting (9) and (I0) into (5), we have Therefore, by changing the field of view in accordance with the above equation (11) it is possible to make the changing speed of the output image be kept constant.

To give one example, if the maximum field size is 1 1 inches; the minimum field size is 5 inches; and the time required for the field to change from the maximum to minimum sizes is T,

the following equation will result:

provide larger fields are higher, than they would be if the changing speed of the diameter of the field were constant, so

' that the changing rates of the voltages impressed on the electrodes for smaller fields become smaller and those for larger fields, greater. To put it in other words, the resistance values of the section resistors are so selected that for the same moving speed of the slider, the voltage taken out from those of the resistors which effect smaller fields changes at a smaller rate and the voltage taken out from those of the resistors which effect larger fields changes at a greater rate.

Thus, it has become apparent that the invention fully accomplishes its objects to provide a new and improved system for continuously varying the size of the field of view of an X- ray image intensifier tube. Although only one example of the invention has been illustrated and described, there can be modifications and changes thereof which are apparent to those skilled in the art.

What we claim is:

l. A system for continuously varying the size of the field of an X-ray image intensifier tube including a plurality of electrodes to control the size of said field, comprising:

a voltage source;

means for connecting said electrodes to said voltage source to apply a voltage to each of said electrodes;

, and means for controlling the voltage to be applied to at least one of said electrodes in such a manner that the size of said field flt) changes in accordance with the equation tor adapted to be driven by said motor to provide for said at least one electrode a voltage which changes so that the size of said field changes in accordance with 3. The system of claim 2, wherein said voltage regulator comprises a series combination of section resistors with a slider adapted to be moved by said motor along the length of said combination, the resistance values of said resistors being so selected that the rate of field change increases as the size of field goes from minimum to maximum.

4. A system for continuously varying the size of the field of an X-ray image intensifier tube including an input screen, an output screen, a first grid, a second grid, an annode and a subsidiary annode to control the size of said field, comprising:

a voltage source;

means for connecting said grids,.annode and subsidiary annode to said voltage source;

a constant speed motor;

first, second and third voltage regulators simultaneously driven by said motor to respectively provide a first voltage to be applied to said first grid, a second voltage to be applied to said second grid, and a third voltage to regulate a voltage to be applied to said subsidiary annode, said first, second and third voltages varying in such a correlated manner to each other that the size of said field flr) changes in accordance with the equation 1 f a T b wherein t is the time having elapsed since commencement of field change, T is the time necessary for the field to change from the maximum size f(0) to the minimum size fl T); and b 1/fl0 and a =1/flT) l/flO), thereby causing each and every point of the output image to move at a substantially constant speed.

5. The system of claim 4, wherein each said voltage regulators comprises a series combination of section resistors with a slider adapted to be moved by said motor along the length of said combination, the resistance values of said resistors being so selected that the rate of field change increases as the size of field goes from minimum to maximum.

Claims (5)

1. A system for continuously varying the size of the field of an X-ray image intensifier tube including a plurality of electrodes to control the size of said field, comprising: a voltage source; means for connecting said electrodes to said voltage source to apply a voltage to each of said electrodes; and means for controlling the voltage to be applied to at least one of said electrodes in such a manner that the size of said field f(t) changes in accordance with the equation wherein t is the time having elapsed since the commencement of field changes; T is the time necessary for the field to change from the maximum size f(0) to the minImum size f(t); and b 1/f(0) and a 1/f(T) - 1/f(0), thereby causing each and every point of the output image to move at a substantially constant speed.

2. The system of claim 1, wherein said voltage controlled means comprises a constant speed motor and a voltage regulator adapted to be driven by said motor to provide for said at least one electrode a voltage which changes so that the size of said field changes in accordance with

3. The system of claim 2, wherein said voltage regulator comprises a series combination of section resistors with a slider adapted to be moved by said motor along the length of said combination, the resistance values of said resistors being so selected that the rate of field change increases as the size of field goes from minimum to maximum.

4. A system for continuously varying the size of the field of an X-ray image intensifier tube including an input screen, an output screen, a first grid, a second grid, an annode and a subsidiary annode to control the size of said field, comprising: a voltage source; means for connecting said grids, annode and subsidiary annode to said voltage source; a constant speed motor; first, second and third voltage regulators simultaneously driven by said motor to respectively provide a first voltage to be applied to said first grid, a second voltage to be applied to said second grid, and a third voltage to regulate a voltage to be applied to said subsidiary annode, said first, second and third voltages varying in such a correlated manner to each other that the size of said field f(t) changes in accordance with the equatIon , wherein t is the time having elapsed since commencement of field change, T is the time necessary for the field to change from the maximum size f(0) to the minimum size f(T); and b 1/f(0) and a 1/f(T) - 1/f(0), thereby causing each and every point of the output image to move at a substantially constant speed.

5. The system of claim 4, wherein each said voltage regulators comprises a series combination of section resistors with a slider adapted to be moved by said motor along the length of said combination, the resistance values of said resistors being so selected that the rate of field change increases as the size of field goes from minimum to maximum.

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