Portable X-ray system

Abstract: A portable x-ray system comprises an x-ray source (1); an internal power supply (3) for supplying an input voltage; and a voltage converter (2) in electrical connection between the power supply (3) and the source (1), the converter (2) being adapted to vary the input voltage from the power supply (3) to provide an output voltage useable in the x-ray source (1) to generate x-rays of a predetermined energy. The power supply (3) comprises a battery power store (7); a capacitor power store (6); and switching means (11) to selectively connect the power stores (7,6) to provide the input voltage to the voltage converter (2) during an exposure.

Description: The present invention relates to an X-ray system and in particular to a portable X-ray system equipped with an internal power supply. Prior art portable X-ray systems generally comprise an X-ray source which is usually an X-ray tube, a low voltage battery store (typically several hundred volts) power supply and a voltage converter for stepping up the voltage supplied by the power supply to the high voltage (typically several tens of kilovolts (kV)) needed by the X-ray source to create a field in which electrons are accelerated before hitting a metal target and generating the X-rays. These systems are then used in conjunction with any one of a number of known image gathering apparatus, such as photographic plates or fluoroscopes to generate an X-ray image of an object, such as part of a patient in a hospital environment. As the quality of the image thus created will generally depend on the penetration of the X-rays used and the exposure time (during which time any movement of the object will cause a blurring of the image), the known X-ray systems usually provide a user with selectivity in one or more of the dose and dose rate. The degree of selectivity of these parameters ultimately depends on the nature of the power supply used and in particular on the level and duration of the voltages that can be generated by the power supplies. One known type of portable X-ray system comprises an internal storage power supply having a battery power store consisting of a number of individual lead/acid accumulators connected in series to provide the required output voltage to the converter, which usually includes a step-up transformer. This type of arrangement has an advantage that such accumulators, or similar battery type energy storage media, provide a suitable voltage output over a relatively long time period. However, such batteries are relatively bulky and heavy which is a problem if the X-ray system is intended to be portable. This is particularly true if the system is required to generate a relatively high dose, short exposure time X-ray output, for example as needed for short duration, deep penetration depth examinations. In this case a correspondingly large voltage (typically 300-400 V) needs to be supplied from the power source which demands between 25 to 33 bulky 12 V lead acid accumulators. Thus reducing the portability of the system. Another known type of X-ray system is described in US 3,878,394. Here the battery store is used to charge a capacitor which, because of the electrical characteristics of capacitors, when discharged provides directly a sufficiently high voltage for use in the generation of a high dose, short exposure time X-rays much more readily than is the case with the battery store. However these same electrical characteristics mean that a relatively large capacitance, which in practice usually represents a large number of capacitors, is needed if long exposure times are required which is relatively expensive. It is an aim of the present invention to provide an X-ray system in which some of the disadvantages of the known power supplies are reduced. This is achieved by the invention according to and characterised by Claim 1. By providing a hybrid power supply that comprises both a battery store, for example rechargeable batteries such as lead/acid accumulators, and a capacitor store which are switchable during an exposure to provide an output from the supply that is generated by one or both (either sequentially or contemporaneously) of them. In this way a relatively high voltage, hence short exposure time, can be provided without the need of as high a number of batteries as would be required in a battery store only supply and a long exposure time can be obtained without the need for as high a number of capacitors as would be required in a capacitor store only supply. Thus an X-ray system having an increased flexibility in the choice of exposure time is provided while still remaining relatively portable and inexpensive. Preferably the switching means operates to sequentially connect first the capacitor store and then the battery store to the input of the converter. This enables short exposure times to be used since power is taken firstly from the capacitor supply which is better suited to providing a high dose short duration output necessary for short exposure times. Usefully, means may be provided to connect an alternating current, for example from the mains electricity supply, power supply from external the X-ray system, to charge the capacitor power store. This provides a further source of power supply to the X-ray source and may be used to extend the supply time of the battery power store. Additionally or alternatively, the battery power store may be used to charge the capacitor store. This has the advantage that several exposures may be made before the power store has to be either replaced or, preferably, recharged using an external power source. This permits the portable operation of the X-ray system over an extended period of time. An embodiment of the invention will now be described, by way of example only, with reference to the drawing of the accompanying figure of which: Figure 1 shows a system block diagram; Referring now to Figure 1, in which the solid lines connecting the blocks represent power connections whereas the broken arrows represent control signal connections, represented is an X-ray system according to the present invention. The system comprises an X-ray tube 1 which is supplied with a high voltage from the voltage converter 2 which itself receives an input voltage from a storage type power supply 3. The voltage converter 2 comprises an inverter 4 and a step-up transformer arrangement 5. The inverter 4 is configured in a standard manner, as a square wave inverter, to provide an alternating current (AC) output to the high voltage step up transformer arrangement 5. This transformer arrangement 5 then provides the direct current (DC) high voltage supply to the X-ray tube 1. The input to the voltage converter 2 is provided by the power supply 3 which includes a capacitor power store 6 (for example comprising 6 x 15 mF capacitors connected to provide a 350 V output) and a battery power store 7 (for example comprising 16 x 12 V lead/acid accumulators connected to provide a 192 V output). A switching means 8 which operates to enable the power supply 3 to selectively supply the voltage to the converter 2 from either the capacitor store 6 or the battery store 7 is also contained within the power supply 3. The switching means 8 comprises an inductor 9 and a rectifying diode 10, connected to enable a boosted voltage to be supplied from the battery store 7, and a MOSFET switch 11. The switch 11 is operable such that power from the battery is switched to the output of the power supply when the voltage from the capacitor store 6 falls to a predetermined level, dependent on the required exposure time and the required dose. A programmable controller 12 is also provided to receive user input information, such as desired X-ray energy, dose and exposure time, as well as information on the operation of the system, such as information on the voltage level output from the supply 3 and the filament temperature in the X-ray tube 1. The controller 12 then provides control signals to the power supply 3, the voltage converter 2 and the X-ray tube control unit 13 in order to control the X-rays output from the X-ray system in dependence of the received information. The X-ray tube control unit 13 is in electrical connection with the X-ray tube 1 so as to control the tube filament current and hence the number of electrons generated for acceleration in the electric field created by the applied high voltage. The programmable controller 12 also provides signals to the inverter 4, in order to control the frequency and pulse shape of the AC output so as to provide a stable high voltage supply to the tube 1. Optionally, an external AC or so-called "mains" supply can be connected to the system by means of the plug connector 14 and mains supply switch 15, as is shown in Figure 1. The switch 15 comprises a three state turn switch to allow the selection of one of three modes: battery charging; battery power; and mains power. In battery charging mode the mains supply switch 15 operates so that mains power passes to the battery charger 16 and through the ancillary power supply 17 to provide power to the programmable controller 12. In battery power mode the switch 15 is switched so that power to the ancillary supply 17 is provided from the battery store 7 which also provides power to a capacitor charger 18 which is used to charge the capacitor store 6 before an exposure is made. Finally, in mains power mode the switch 15 is switched so that power from the mains is fed to the capacitor charger 18. Optionally, when mains powered, the programmable controller 12 may control the power supply 3 so that no power is taken from the battery store 7 during an exposure. The X-ray system additionally comprises a carriage (not shown) on which are mounted the other components of the X-ray system. The carriage may conveniently be provided with wheels (not shown) that are driven with the aid of a DC motor 19 in a motor unit 20. The motor unit 20 additionally comprises a DC to DC converter 21 which receives a voltage from the battery power store 7 and converts it to one suitable for use with the motor 19. Thus in the present example the battery power store 7 is used to power the X-ray tube 1, to charge the capacitor store 6 and to drive the motor 19.

Claims: An X-ray system comprising an X-ray source (1); a power supply (3) having a battery power store (7) for supplying an input voltage independently of an external power source; and a voltage converter (2) in electrical connection between the power supply (3) and the source (1), the converter (2) being adapted to vary the input voltage from the power supply (3) to provide an output voltage useable in the X-ray source (1) to generate X-rays of a predetermined maximum energy characterized in that the power supply (3) further includes a capacitor power store (6) adapted to store charge during periods of no exposure for discharge during an exposure; and switching means (8) operable to sequentially connect the power stores (7,6) to provide the input voltage to the voltage converter (2) during the exposure. An X-ray system as claimed in Claim 1 characterized in that the capacitor store (6) is adapted to provide a first voltage input to the converter (2) variable from a higher level to a lower level as the capacitor store (6) discharges; in that the battery store (7) is adapted to provide a second voltage input to the converter (2) at a level intermediate of the lower and higher levels, and in that the switching means (8) is automatically operable to supply the converter (2) firstly from the capacitor store (6) and then from the battery store (7) if the level of the first voltage falls to that of the second voltage. An X-ray system as claimed in any preceding claim characterized in that the battery power store (7) is operable to charge the capacitor store (6) during the periods of no exposure. An X-ray system as claimed in any preceding claim characterized in that there is further provided means (15, 17) to connect the power supply (3) to a source of alternating current power located external of the X-ray system. An X-ray system as claimed in any preceding claim characterized in that there is further provided a motor unit (20) adapted to propel a carriage on which the X-ray source and the power supply are mountable, the motor unit (20) comprising an electric motor (19) and converter (21) adapted to vary a voltage supplied by the battery power store (7) to a voltage usable by the motor (19).

Inventors: ZETTERLUND LENNART, ZETTERLUND, LENNART
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1999
Main classification: H05G1
IPC codes: H05G1