GB1567956A - X-ray eqquipment - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO X-RAY EQUIPMENT (71) We, SCANRAY (INTER NATIONAL TESTING) LIMITED, a British Company, of Barton Road, Water Eaton Industrial Estate, Bletchley, Milton Keynes MK2 3LQ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to X-ray apparatus.

A primary object of the invention is to provide means for x-radiation from a thermionic device wherein the amplitude, duration and emission of x-rays can be precisely controlled by an electronic system which can be powered from a derived or static DC electrical source to provide a pulse which is substantially constant over the period of the pulse.

There have been prior proposals in which the output of an X-ray tube has been stabilized against external variations e.g., mains voltage variations, that occur over a comparatively long period of time.

However, the output of such tubes is substantially sinusoidal and not constant over the period of the pulse.

According to the invention, apparatus for the production of X-rays comprises a thermionic X-ray tube having an anode, a cathode, a filament or other element which is separate from the cathode and which when heated produces electrons, two inductors connected respectively to the anode and cathode, means for heating said filament or other element for the production of electrons thereat prior to their requirement for the production of Xradiation, and electronic control means for said inductors for setting up a substantially constant voltage between the anode and the cathode for driving electrons emanating from the filament or other element to the anode, the electronic control means being arranged to maintain said voltage for a controlled time whereby the radiation output from the tube is substantially constant for that time.

The invention enables large outputs of Xradiation to be achieved by either single or multiple pulses each of which can be maintained under precise and controlled conditions by an operator and such that tube currents in the range of 2x10-2 Amps to 2x10' Amps can be obtained. It is desirable to achieve this type of output, for example when producing a high speed radiograph. Previous equipment has not, so far as is known, been capable of maintaining radiation output at a constant level or for sufficiently long time to enable recording to take place of a sequence of events.Prior art devices could not provide a sufficiently even radiation pattern when recording by means of motion picture cameras or electronic cameras such as IMACON (Patent Nos 1016930, 1143444, 1304213, 1317434 manufactured by John Hadland Limited) to produce developed images showing no change in quality due to inherent variation of the radiation during recording.

The invention can be used for recording an object or group of objects travelling at high speed, for example, rotating machinery, ballistics, liquid to liquid or metal to liquid transitions, chemical reactions, casting processes and welding processes, under X-ray examination when the invention is used in conjunction with image intensifiers and the high speed cameras mentioned above.

In another example, the invention can be used in medical or veterinary applications whereby radiography of organs can be achieved by synchronization with the movement of an organ so that, for example, heart valves can be definitely radiographed in both open and closed or other other defined conditions.

There is a further advantage in that when operated under repeat pulse conditions, the unit can be successfully used to produce conventional radiography on X-ray sensitive film with the advantage that, due to the high output per pulse, the exposure time can be greatly reduced.

The apparatus cannot adequately be described by such prior art names or lables as constant potential, flash discharge, pulsed output, half wave or other defined technique. For the purpose of definition, the term controlled amplitude duration and emission equipment for X-ray (CADEX) may be used.

In general, not withstanding the foregoing, the invention can be used for any conventional techniques as well as hitherto difficult tasks or some tasks previously thought to be impossible involving the sequential X-radiation recording of fast events or moving objects.

As will be understood by those skilled in the art of X-ray technology, X-ray devices can be used at various voltages and powers in relation to the particular application. It can also be used with any conventional image recording or gathering medium such as film, fluoroscopes or radiation sensitive cameras.

The flexibility of the invention is to provide equipment that is able to produce Xradiation of defined voltages and powers in a conventionally housed unit or units to suit the desired application. Selection of these parameters can be achieved within the invention by selection of suitable components or by providing the necessary controls.

The invention enables an X-ray tube in an insulated housing to be operated by a power drive circuit of transistors and other semiconductors to produce the required high current pulses in the inductors, the filament or other electron producing element all controlled from an independent electronic system wherein the amplitude of the pulse, the length of pulse and the timing or synchronising of the pulse to external events may be controlled. The monitor of all important factors such as voltage across the X-ray tube, the current passed by the tube, the actual pulse length produced as well as signals to operate remote recorders such as camera shutters is provided from the electronic system. The supply of power to the whole equipment can be derived from either conventional AC supplies, generators or public supply, or from DC batteries of suitable quality.Adequate safety devices can easily be included such that the operators cannot produce radiation except when all conditions relating to the correct procedure have been complied with. In this respect, electromechanical interlocks may be used in important stages of the equipment, namely the main power feed to the X-ray tube inductors and the drive signal from the controls.

One embodiment of the invention is apparatus for producing radiation up to and including 200KeV (i.e., 200 thousand electron volts) X-radiation, which will now be described, by way of example only, with reference to the accompanying drawings, namely: Figure 1, which is a system diagram of the main components of the apparatus; Figure 2, which shows a sectional view of a unit comprising an X-ray tube and associated components; Figure 3, which is a circuit diagram showing the main features of a power drive circuit; Figure 4, which is a circuit diagram showing details of control circuits; and Figure 5, which shows a perspective view of the outside of the complete apparatus when assembled for use.

Referring to Figure 1, a circuit embodying the invention is shown in the form of symbolic block diagram. DC power to a voltage stabilizer 4 can be provided from either a mains derived supply 1 or battery pack 2 by means of a selecting switch 3. The voltage stabilizer 4 provides regulated voltages required by the circuit at various different levels.

A transistor semiconductor array 5 passes the main power required to produce in inductors 14 and 15 extra high tension voltages across an X-ray tube 16. This is controlled via a modulator 6 which is a current amplifier. A pulse generator 9 feeds this modulator under control of operator selected controls and an automatic sequencer 11. Safety interlocks at 12 and 13 prevent either power or drive signals from being applied until the system is ready.

Drive to the filament of tube 16 is provided by a transformer 17, connected to adjustable transformers at 8. A static invertor at 7 provides a required AC signal.

To consider each aspect of the circuit in greater detail, Figure 2 may first be referred to. This shows the assembly of components 14, 15, 16 and 17 of Figure 1.

A tube can 20 of steel construction is lined with thin gauge lead sheet 21 on the inside. A radiation port 22 is formed in the can and a window 24 of thin aluminium plate is positioned therein so that the centre of this plate relates to the centre of the focal spot of the X-ray tube 25. An epoxy resin moulding 23 mates with the main can 20 to form an oil tight barrier at the window 22.

A flanged plate 26 is fixed at one end of the can, an oil tight joint being provided between the can and plate 26. Through this plate pass a number of oil tight electrical connectors 27. A rubber expansion bellows 28 is positioned into this plate 26 so that when the cam 20 is filled with oil, the bellows 28 will allow for temperature expansion. An aluminium shield assembly 29 is constructed in two parts so that during assembly it can be easily placed about the anode inductor 14 in a sub-assembly 30.

An insulating support plate 31A constructed of a moulded epoxy resin, namely that known under the Registered Trade Mark Araldite, terminates the inner end of the sub-assembly 30 and positions it in relation to the anode connection of the X-ray tube 16. The inductor 14 comprises a grain oriented silicon iron core 31 manufactured in eight sections of C shape, so that when assembled, the effective cross sectional area is 22.5 cm2. The inductor 14 has windings 32 consisting of a primary winding of 230 turns of 2.5 mm wire on a paper former, each layer of wire being insulated with insulating paper, namely Kraft paper, and a secondary winding of stepped layer formation wound over the primary winding using 98,000 turns of 0.1 mm wire. Again, each layer is insulated with paper.The windings are terminated such that one end of the secondary winding is made into a spring loaded plunger 33 which makes contact with the anode terminal of the Xray tube 14. The other end of the secondary winding is taken to one of the connectors 27 along with both ends of the primary winding. The cathode inductor 15 is built in exactly the same way as the anode inductor 14 and is mounted in a cathode sub assembly 34 similar to the anode sub assembly 30.

The X-ray tube 14 has an anode 35 comprising a tungsten pellet set into a copper heat sink 36 sealed into a glass envelope 25. A cathode assembly, consisting of Wehnalt cyclinder 39 and pure tungsten coiled filament 40 is sealed at the opposite end of the envelope 25. The arrangement of anode and cathode is such that, when heated, the filament produces free electrons that are attracted through the aperture in the Wehnalt cylinder to the anode, which is made positive with respect to the cathode.

The geometry of the assembly is according to the state of the art technique understood by those skilled in the art.

The cathode end of X-ray tube 16 is electrically terminated to that the Wehnalt cylinder 39 is connected to one end of filament 40, the composite connection being taken to one of two pads 41 (only one pad 41 appearing in Figure 2) and the other end of filament 40 is brought out to the other of the two pads.

The filament transformer 17 is constructed of grain orientated silicon iron core of 8.4 cm2 cross section with windings 42 comprising a primary winding of 220 turns of 2.5 mm wire, each layer being insulated from the other by means of paper, and a secondary winding wound with 1,000 turns of 0.45 mm wire, again each layer being insulated. Both secondary connections are brought to spring copper strips 43 such that they mate with the aforesaid pads 41. The insulation between primary and secondary windings of transformer 17 is paper layers built up so that a dielectric strength in excess of 200 KV is obtained. Primary wires are taken to the terminals 27. Connection is made to the pad 41 for the aforesaid composite connection by one end of the secondary winding of cathode inductor 15, which, as already explained, is identical to the anode inductor 14.

An epoxy resin insulator 44 of similar construction to the anode insulating support plates 31 holds the sub-assembly 34 consisting of cathode inductor 15, filament transformer 17 and shield plates 45, and locates the sub-assembly in relation to can 20. The anode end of the can 20 is closed by a flanged plate 28A similar to the plate 26.

An end plate 46 fitted with oil seal 47 is screwed into place to form an oil tight barrier with can 20.

During assembly, the whole of end cover 26 is removed and the interior of the can 20 placed under vacuum of the order of 0.025 torr. Oil to Bs 148 is introduced and vacuum reapplied. When full of oil the cover 26 is placed over the can 20 and an oil tight seai made. A valve 49 of the Schrader type is used to adjust the pressure of the oil within the can 20. Electrical connections are made using standard insulated cable from terminals 27 to an external integral connector 50. A coiled tube 51 for a fluid cooling medium is provided in the sub assembly 30.

Figure 3, which shows details of components 5 and 6 of Figure 1 is a power drive circuit for providing power to the anode and cathode inductors 14 and 15. For clarity, the inductor primaries are shown as windings 72 and 87. A voltage +V1 is provided from the voltage stabilizer 4 such that for the required X-ray output in KeV, the input voltage of line 71 is chosen so as to provide approximately the output voltage +V1 Kv= x 103 volts.

0.8 Suitable quality connectors connect the ends of the primary windings 72 and 87 to a collector of a transistor array 73 (represented by 5 in Figure 1), the emitters of which are connected to ground. The array 73 in fact consists of a number of semi conductors arranged in parallel configuration. The bases of each unit in array 73 are brought together and thence through resistor 78 to the junction of resistors 80 and 81. The relationship between resistors 80 and 81 is selected on assembly to control the base voltage resistor 78 and the base emitter junction of the array 73.

A high speed recovery diode 76 is operated in flywheel configuration across the inductor primary windings 72 and 87.

This prevents the voltage at the start of each winding from going negative with respect to the end of the windings.

A resistor 75 and diode 74 are connected in parallel and hence in series with an electrolytic capacitor 77. When the voltage +Vl is applied on line 71, but transistor 73 is not conducting the capacitor 77 will charge to +V1. When the transistor array conducts, the capacitor is discharged via the diode 74 so that, at the end of the pulse time period, the capacitor is fully discharged. On the removal of drive from the bases of transistor array 73, the voltage +V2 at point 88 is maintained at the natural saturation voltage of the transistors for the time due to a time constant determined by the resistor 75 and capacitor 77. This allows out of phase components in the primary windings 72 and 87 'to disperse before voltage is built up across them.

In order to operate the drive circuit for the inductors 14 and 15, a drive pulse from the pulse generator 9 is applied at an input 86 (Figure 3) of positive magnitude, with respect to ground 90, causing a transistor 82 to conduct so that the voltage across resistor 85 becomes positive for the period of the pulse. A resistor 83 in the collector arm of the transistor 82 limits the gain of the stage and a resistor 84 is used to adjust voltage applied to the next stage, namely a transistor 79. A positive pulse on the base of the transistor 79 will cause the main transistor array 73 to conduct, as previously described, so that a current is generated in the primary windings 72 and 87 at the rate VWL, where L is the inductance and W is the frequency of the pulse rise time.Fuses 88 and 89 in the power supply lines are so selected that currents in excess of ten times design values will rupture the fuses.

In all cases, the voltage +V2 is maintained constant at the ratio l/lOth +V1, at 89 when full stabilisation is required, but +V2 can be made constant over a range of +V1 voltages if some fall in the X-ray output can be tolerated.

The input pulse at 86 is derived from state of the art technology components arranged as shown in Figure 4. Figure 4 shows details of components 7,8,9, 10 and 11 in Figure 1.

A semiconductor oscillator 101 of the type known as 'Phase Shift' is such that, on receipt of a positive signal from a logic gate 102, the oscillator will start producing sine wave oscillation starting from ground zero.

The voltage and frequency are predetermined and fixed within the oscillator 101.

The output is amplified and buffered by a large scale amplifier 103 so that a diode 104 which receives the output will only pass the positive half sine waves. These charge a capacitor 105 to the peak value of the oscillation. An amplifier 106 with gain preset by resistors 107 and 108 will therefore receive the pulse with a sinewave leading edge and thereafter a flat top after the style of waveform 111 as shown by insert A, Figure 4.

This voltage is attenuated by a potential divider consisting of resistor 109 and variable resistors 110 so that the output 112 suits the input 86 as shown in Figure 3.

The width of the pulse is controlled by the length of time the oscillator 101 is allowed to run. A conventional optical isolator 113 is connected to the logic gate 102. The diode drive of the isolator 113 is in turn powered from a flip flop 114. The timing, produced by a large scale integration device 116 has its time period operator controlled by an adjustable resistor 117. Another safety feature is that a transistor-transistor logic flip flop 121 starts the operation of the timer device 116 under the control push buttons 122 and 123 (control 10 in Figure 1) so that a reset function by the operator is required before a pulse can be produced. An auxiliary pulse from another timer 115 having its time period set by an adjustable resistor 119 and a resistor 120 is used as an external drive for a recording medium.By adjustment of the resistor 119 the length of a pulse signalled by pressing the buttons 122 and 123 can be determined.

To control the feed of the filament transformer (17 in Figure 1) the static inverter 7 of commercial quality rated at 250VA is used so that a constant sine wave output is produced at the wiper contact 131 of a relay 135. A separate timer 134 with preset time period set by resistors 136 and 137 is activated by operation of a switch 138 (control 10 in Figure 1). During the timing period, the relay 135 is energised and the contact 131 switches over from a variable transformer 132 to an alternative variable transformer 133. The transformers 132, 133 (8 in Figure 1) may be set so that the output 139 without the timer 134 in operation, receives from the transformer 132 a voltage of half that from the transformer 133. Thus, the heater voltage, via transformer 17 can be increased for a fixed time period just prior to operation of high voltage pulse.

This gives the filament a longer life characteristic.

Conventional power supplies and switches, not shown, are used to provide the various components within the circuit with stabilised voltages according to manufacturers' specifications.

In this example, the total equipment is housed in metal enclosures as shown in Figure 5.

Referring to Figure 5, the operation of the equipment will be described. The tubehead assembly in the cam 20 is connected to a unit 152 containing the power transistors (i.e., transistor array 5 and modulator 6) by a cable assembly 151. A standard multiway cable connects the unit 152 to a unit 153 containing the components 7, 8,9, 10 and 11.

When X-ray operation is required a power control 154 is placed in the on position such that all low voltages (V2) are applied to the circuit. A separate low voltage isolator 159 is fitted to the electronic package 153. Indicators 155 and 156 show the status of the main power fuses.

The width of the desired pulse is set on a multiturn dial 167 connected to the time setting resistor 117. A similar dial 168 controls the time setting resistor 119 for the delayed output pulse for remote control of recording instruments such as cameras.

An interlock key is arranged to actuate a power switch 158 for interlock 13 (Figure 1) and a control switch 160 for interlock 12 (Figure 1).

Controls 161, 163, 163b for operation of the initial filament heating and final filament heating power are available to the operator from front panel controls as shown or from standard connectors (not shown) at the rear of the units 152, 153. The control 161 (not shown in Figure 4) connects + V2 to the inverter 130 to the initial warming of the filament. The controls 163, 163b actuate switch 138 to raise the filament temperature to the temperature required immediately prior to firing. Immediately prior to firing a final arm key 164 (not shown in Figure 3) connects the high voltage +V1 into the inductor circuit.

A control 166 marked "Ready" is operated just prior to firing. This enables the logic circuits and oscillator 101 (Figure 4).

The actual point of fire is determined by either an operator control 165 marked "Fire" or by remote signal via rear connector (not shown). Control 165 actuates switch 122 (Figure 4).

At the exact point of fire, lamp indicators (not shown) indicate that the pulse has been completed. Unless a burst repeat facility is used no further pulses can occur until a reset button 166 (which actuates switch 123) is pressed.

Operation of the final arm key 164 ensures the removal of the DC high voltage +V1 from the system.

In practice, from time zero when the signal is applied to produce radiation, a short delay occurs in the build up of all parameters to maximum. This delay time is independent of applied KV, mA or other adjustable factors being inherent due to tolerances on the components used. In practice, this time is of the order of 0.5 mS.

Variations of actual KeV produced for applied voltage are dependent on the required mA or tube current required.

Again, the actual values are only determined during manufacture and test but the formula

gives an approximate indication of the KeV produced when Vl is the applied voltage, I1 is the measured tube current in with amperes and R1 is the source resistance of the circuit in kilo ohms. However, due tothe dynamic nature of the unit, an accuracy of +20 percent is possible by theoretical calculation and actual measurement must be made to determine calibrations with greater accuracy.

WHAT WE CLAIM IS: 1. Apparatus for the production of X-rays comprising a thermionic X-ray tube having an anode, a cathode, a filament or other element which is separate from the cathode and which when heated produces electrons, two inductors connected respectively to the anode and cathode, means for heating said filament or other element for the production of electrons thereat prior to their requirement for the production of Xradiation, and electronic control means for said inductors for setting up a substantially constant voltage between the anode and the cathode for driving electrons emanating from the filament or other element to the anode, the electronic control means being arranged to maintain said voltage for a controlled time whereby the radiation output from the tube is substantially constant for that time.

2. Apparatus according to Claim 1, in which the said means for applying voltages to the anode and cathode consist of two similar inductors connected respectively to the anode and cathode and each having a secondary winding connected to the anode and cathode and a primary winding connected to the electronic control means.

3. Apparatus according to Claim 2, in which the thermionic X-ray tube together with the two inductors are contained within a mass of oil confined in a container.

4. Apparatus according to any one of the preceding claims, in which the electronic

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. stabilised voltages according to manufacturers' specifications. In this example, the total equipment is housed in metal enclosures as shown in Figure 5. Referring to Figure 5, the operation of the equipment will be described. The tubehead assembly in the cam 20 is connected to a unit 152 containing the power transistors (i.e., transistor array 5 and modulator 6) by a cable assembly 151. A standard multiway cable connects the unit 152 to a unit 153 containing the components 7, 8,9, 10 and 11. When X-ray operation is required a power control 154 is placed in the on position such that all low voltages (V2) are applied to the circuit. A separate low voltage isolator 159 is fitted to the electronic package 153. Indicators 155 and 156 show the status of the main power fuses. The width of the desired pulse is set on a multiturn dial 167 connected to the time setting resistor 117. A similar dial 168 controls the time setting resistor 119 for the delayed output pulse for remote control of recording instruments such as cameras. An interlock key is arranged to actuate a power switch 158 for interlock 13 (Figure 1) and a control switch 160 for interlock 12 (Figure 1). Controls 161, 163, 163b for operation of the initial filament heating and final filament heating power are available to the operator from front panel controls as shown or from standard connectors (not shown) at the rear of the units 152, 153. The control 161 (not shown in Figure 4) connects + V2 to the inverter 130 to the initial warming of the filament. The controls 163, 163b actuate switch 138 to raise the filament temperature to the temperature required immediately prior to firing. Immediately prior to firing a final arm key 164 (not shown in Figure 3) connects the high voltage +V1 into the inductor circuit. A control 166 marked "Ready" is operated just prior to firing. This enables the logic circuits and oscillator 101 (Figure 4). The actual point of fire is determined by either an operator control 165 marked "Fire" or by remote signal via rear connector (not shown). Control 165 actuates switch 122 (Figure 4). At the exact point of fire, lamp indicators (not shown) indicate that the pulse has been completed. Unless a burst repeat facility is used no further pulses can occur until a reset button 166 (which actuates switch 123) is pressed. Operation of the final arm key 164 ensures the removal of the DC high voltage +V1 from the system. In practice, from time zero when the signal is applied to produce radiation, a short delay occurs in the build up of all parameters to maximum. This delay time is independent of applied KV, mA or other adjustable factors being inherent due to tolerances on the components used. In practice, this time is of the order of 0.5 mS. Variations of actual KeV produced for applied voltage are dependent on the required mA or tube current required. Again, the actual values are only determined during manufacture and test but the formula gives an approximate indication of the KeV produced when Vl is the applied voltage, I1 is the measured tube current in with amperes and R1 is the source resistance of the circuit in kilo ohms. However, due tothe dynamic nature of the unit, an accuracy of +20 percent is possible by theoretical calculation and actual measurement must be made to determine calibrations with greater accuracy. WHAT WE CLAIM IS:

1. Apparatus for the production of X-rays comprising a thermionic X-ray tube having an anode, a cathode, a filament or other element which is separate from the cathode and which when heated produces electrons, two inductors connected respectively to the anode and cathode, means for heating said filament or other element for the production of electrons thereat prior to their requirement for the production of Xradiation, and electronic control means for said inductors for setting up a substantially constant voltage between the anode and the cathode for driving electrons emanating from the filament or other element to the anode, the electronic control means being arranged to maintain said voltage for a controlled time whereby the radiation output from the tube is substantially constant for that time.

2. Apparatus according to Claim 1, in which the said means for applying voltages to the anode and cathode consist of two similar inductors connected respectively to the anode and cathode and each having a secondary winding connected to the anode and cathode and a primary winding connected to the electronic control means.

3. Apparatus according to Claim 2, in which the thermionic X-ray tube together with the two inductors are contained within a mass of oil confined in a container.

4. Apparatus according to any one of the preceding claims, in which the electronic

control means comprise a transistor array arranged, on being subjected to a control pulse, to cause a capacitor to discharge thereby terminating the required voltage between the anode and cathode after a controlled time.

5. Apparatus according to Claims 2 and 4, including a recovery diode connected in parallel with the primary windings to prevent a reversal of the voltage on these windings.

6. Apparatus according to Claim 4, or Claim 5, comprising means for producing a control pulse having a substantially sinewave leading edge followed by a substantially flat top of controllable length, and means for adapting the control pulse to actuate the transistor array.

7. Apparatus according to Claim 6, in which the means for producing the control pulse comprise an oscillator, a diode for transmitting half waves from the oscillator to the said adapting means, a flip-flop for controlling each oscillation over a predetermined time period and an adjustable device operative on the flip-flop for determining the length of the time period.

8. Apparatus according to Claim 7, in which the flip-flop and adjustable device are in circuit with a manually controlled flipflop for initiating each pulse and resetting the circuit prior to the initiation of the next pulse. ~~~~~~~~~~~~~~~~~

9. Apparatus according to Claim 7, or Claim 8, in which the said flip-flop for controlling each oscillation operates the oscillator by way of an optical isolator and a gate.

10. Apparatus according to any one of the preceding claims, in which the filament is arranged to be heated by way of a transformer fed by way of an inverter through one or other of two further transformers according to the setting of a relay manually controlled by way of a timing device, the two further transformers being arranged respectively for heating the filament or other element by two different amounts.

11. Apparatus according to Claim 10, when limited to Claim 3, in which the filament transformer is contained in the said mass of oil, the two further transformers being located outside the container.

12. Apparatus according to any one of the preceding claims, arranged to operate on power received from a derived or static DC electrical source.

13. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.