NL1003044C2 - X=ray installation with image speed-synchronised to scanner - Google Patents

Abstract

An opaque strip (20) has a series of holes 2.5mm apart. Relative motion between the strip (20) and the LED (30) and detector (31) combination produces electrical pulses. A dc voltage (42) proportional to pulse frequency (f1) is adjusted to match the reduced optical dimensions of the image projected onto a CCD array. The dc output of the adjuster (43) is converted to a second pulse train with a frequency (f2). This controls the time-interval delay integration (TDI) to achieve speed synchronisation between the X-ray scanner and the reduced format electro-optical image.

Description

Title: X-ray imaging device.

The invention relates to a method for forming an X-ray image by means of an X-ray image device, or to an X-ray image device of the type in which the X-ray image to be formed is built up using an elongated X-ray detector, which can convert incident X-rays into a light image, and which, in operation with respect to an object to be imaged, performs a scanning movement in a direction transverse to the longitudinal direction of the elongated X-ray detector, wherein the light image is imaged in a reduced size by means of optical means on a photosensitive semiconductor device, which image is reduced in size by means of an time delay / integration process controlled by clock signals converts to electrical signals representing the x-ray image.

Such an X-ray imaging device may, for example, be a device for slit radiography, as described, for example, in the Dutch patent application 9102063. In such an device, an object or a patient is scanned with the aid of a flat fan-shaped X-ray beam, which, during at least one scanning stroke transverse to the plane of the fan-shaped beam is moved. Behind the object, being an object or a patient, an elongated X-ray detector moves synchronously with the X-ray beam in such a way that the radiation transmitted by the patient or object always substantially falls on the X-ray detector. The X-ray detector converts the received X-rays into a light image, which can be used to generate electric signals representing the X-ray image. The flat fan-shaped beam can be obtained, for example, with the aid of an X-ray source, which cooperates with a slit diaphragm. The X-ray source and the slit diaphragm are movable together or relative to each other such that the 1003044 -2 fan-shaped beam leaving the slit diaphragm performs the desired scanning movement. The diaphragm may, if desired, be provided with slit control means, as described, for example, in Dutch patent application 8400845. However, the invention is also applicable to other types of devices, which comprise an elongated X-ray detector which performs a scanning movement in order to scan a predetermined area. An example is described in Dutch patent application 8303156.

An elongated X-ray detector suitable for use in an X-ray image device of the above-described type is, for example, an X-ray image intensifier tube as described in Dutch patent 183914. For use in an X-ray image device suitable for thorax examination, the X-ray image intensifier tube must have an image plane of ± 400 to 500 mm long. . This size corresponds to the width of the thorax in most people and the fan-shaped beam. For example, in the scanning direction, the image plane can be + 20 25 mm high. In order to form a complete chest X-ray image, the X-ray image intensifier tube must cover an area of + 400 x 400 mm 2, which is accomplished by causing the X-ray image intensifier tube to scan in a direction transverse to the longitudinal direction of the X-ray image intensifier tube. During the scanning movement, the X-ray image intensifier tube provides a varying output image, which can be used to expose a photographic film, but which is preferably projected onto a photosensitive electronic device, which converts the incident light into corresponding electrical signals. The electrical signals can then, whether or not after further processing, be stored or used to form a video image or the like.

A light-sensitive semiconductor device such as an elongated 1003044 -3-CCD device (CCD = charge coupled device) can be used for converting the output signal of the X-ray image intensifier tube into electrical signals. Such CCD devices are commercially available, but have much smaller dimensions than the exit window of the elongated X-ray image intensifier tube. A suitable CCD device is, for example, the Dalsa I-FI-2048, which has 2048 x 96 pixels and a sensitive area of 28.7 x 1.34 mm. To this end, the output image of the elongated image intensifier tube is displayed in a reduced size on the CCD device. For this purpose, use can be made of a camera comprising a lens system, which reduces the output image of the X-ray image intensifier tube to the appropriate dimensions for the CCD device and images the output image of the X-ray image intensifier tube on the CCD device. In the CCD device, image integration takes place in a known manner by means of a time delay / integration process, also called TDI (= time delay and integration) process, in order to obtain electrical signals such that they accurately represent the X-ray image. During the scanning movement of the elongated X-ray detector, a strip-shaped image always moves transversely with respect to the longitudinal axis of the X-ray detector over the output screen (the anode) of the X-ray detector. The speed of this movement of the output image of the X-ray detector over the output screen of the X-ray detector is determined by the scanning speed, ie the speed with which the X-ray detector performs the scanning movement.

It is of great importance that the TDI process is accurately synchronized with the movement of the X-ray image over the output screen of the X-ray detector. A speed difference (corrected for the image ratio of the output image of the X-ray detector versus the image projected on the CCD device) between the output image of the X-ray detector and the TDI process results in blur in the output signals of the CCD device. form image. The TDI flow rate should therefore be as close as possible to the speed at which the image projected on the CCD device moves over the CCD device.

According to the known art, use is made for this purpose of a position synchronization. During the scanning movement, the position of the X-ray detector, and thus of the starting image thereof, is continuously accurately determined. This is done, for example, using a ruler, which alternately has transparent and opaque areas with a pitch of, for example, 0.1 mm or less. The ruler 10 is mounted along the scanning path of the X-ray detector. Position pulses are then generated via an optocoupler during the scanning movement which are counted with a counter and / or used as clock pulses for the TDI process. A problem is, however, that the imaging measure of the 15 conventional lenses through which the output image of the X-ray detector is projected on the CCD device has such a spread that the required synchronicity cannot be achieved, or not sufficiently, as the position pulses as clock pulses. 20 are used for the TDI process.

The object of the invention is to solve the outlined synchronization problem and in general to provide a method and device for efficiently, accurately and reliably forming an output signal of a CCD device of an X-ray image device of the type described above, which output signal represents an X-ray image obtained by scanning with an elongated X-ray detector.

To this end, according to the invention, a method of the above-described type is characterized in that speed synchronization is used between the scanning movement of the X-ray detector and the clock signals for the semiconductor device, the frequency of the clock signals being derived from a speed dependent on the scanning movement. electrical signal.

An X-ray imaging device of the above-described type is characterized according to the invention by first 1003044 -5 means for generating a first electric signal, which depends on the speed of the scanning movement and second means for converting the speed-dependent electric signal signal in a second signal, from which clock signals for the photosensitive semiconductor device can be derived, the second means being adjusted such that the ratio between the first and the second signal represents the imaging measure of the optical means.

In the following the invention will be further described with reference to the accompanying drawing of some exemplary embodiments.

Figure 1 shows schematically in side view / section an example of an X-ray imaging device according to the prior art; figure 2 schematically shows the device of figure 1 in top view; figure 3 shows schematically in side view a first exemplary embodiment of a device according to the invention; and Figure 4 schematically shows an example of a circuit for processing the output signals of the light barrier.

Figures 1 and 2 schematically show, in side view and top view, an example of a known X-ray imaging device 1. The device shown comprises an X-ray source 2, provided with a slit diaphragm 3 via which a flat fan-shaped X-ray beam 4 on a front of a house or cabinet 5. placed patient to be examined 6 or pointed at an object to be examined. In the example shown, the X-ray source 2 can pivot about an axis 6 together with the slit diaphragm 3, as indicated by an arrow 7. The fan-shaped X-ray beam 4 pivots in a direction transverse to the plane of the fan-shaped X-ray beam, as indicated by an arrow 8 in Figure 1, in order to scan the patient or the object, or at least a relevant part thereof, with the X-ray beam during one or more strokes.

1003044 -6-

The box 5 has a front wall 9 transparent to X-rays, behind which an elongated X-ray detector 10 is located. The X-ray detector is coupled in a manner not shown, but known from, for example, NL 8303156, to the X-ray source 2 pivoting in operation in such a manner that the X-ray radiation transmitted through the patient or the object 6 always falls on the entrance window of the X-ray detector 10. The X-ray detector 10 therefore moves synchronously with the flat fan-shaped beam 4, as indicated by arrows 11.

The X-ray detector 10 is arranged to convert the X-rays incident on the input side into a light image which is generated on the output side. In the example shown, a tubular X-ray detector 15 is used with an X-ray sensitive elongated cathode 12, which emits electrons under the influence of incident X-rays. Opposite cathode 12 is an elongated anode 13. The electrons emitted move from the cathode to the anode under the influence of a high voltage prevailing between the cathode and the anode. The anode converts the incident electrons into light quants. The light image thus formed on the anode side is projected via a lens or a lens system 14 onto a light-sensitive semiconductor device, such as a CCD 15, which converts the light image into corresponding electrical signals, which can be further processed and / or stored in a device not shown . The lens system 14 and the semiconductor device are part of a stationary camera spaced from the X-ray detector 10, so that the camera can capture the output image of the X-ray detector 10 and project it onto the semiconductor device in any position of the X-ray detector 10.

Between the anode of the X-ray detector and the camera, if desired, a system with one or more mirrors can be placed. More than one camera can also be used. Furthermore, the camera (s) and possibly also 1003044 -7- the mirror system can move along with the X-ray detector, as described, for example, in applicant's unpublished Dutch patent application 1002466, which is considered to be incorporated herein by reference.

During operation, the anode image slides, as it were, transversely across the anode of the X-ray detector in a direction opposite to the direction of movement of the X-ray detector. Therefore, if the X-ray detector 10 moves upwards in the situation shown in Figure 1, the image is always refreshed at the top and shifts, as it were, from the top edge of the anode to the bottom edge thereof. This image moving over the anode is displayed (reduced) on a CCD device and is integrated for a predetermined time interval (the TDI process) 15 each time in order to form the electrical signals representing the desired X-ray image. A detailed description of the TDI process is known from US patent 4,383,327. The TDI process must take place precisely in synchronization with the movement of the image over the anode of the X-ray detector 20 and thus with the scanning movement of the X-ray detector.

According to the invention use is made of speed synchronization for this purpose. The desired speed synchronization can be accomplished by generating first control signals corresponding to the speed of the X-ray detector during the scanning movement, and then forming second control signals from these first control signals, the image measure of the image by the optics of the anode image on the CCD device is fully taken into account such that the frequency of the second control signals corresponds to the speed of the reduced anode image. In this manner, it can be effected that the TDI flow rate accurately corresponds to the rate at which the anode image projected on the CCD-35 device moves across the CCD device.

1003044 -8-

For the generation of the first control signals, use can be made, for example, of a light barrier moving with the X-ray detector, consisting of one or more light-emitting elements, such as, for example, LEDs and one or more light-sensitive elements, for example, photosensitive transistors, which are located on either side of a stationary strip or the like. Where reference is made here in the context of the generation of the first control signals, this means not only visible light but also other, non-visible electromagnetic radiation such as infrared. The strip may then periodically comprise successive sections which are alternately transparent or opaque. When the X-ray detector makes a scanning movement, the or each photosensitive transistor or the like provides a series of pulses at a frequency corresponding to the speed of the scanning movement. According to a preferred embodiment of the invention, an equidistant opaque hole or ruler may be used. In a practical example, the holes 20 can have a pitch of 2.5 mm.

Figure 3 schematically shows an opaque strip 20 provided with holes 21. On one side of the strip there is a light barrier with a light-emitting element 22 and on the other side a light-sensitive element 23. The elements 22 and 23 are preferably jointly arranged on mounted a carrier, not shown in further detail, around the strip and moving up and down relative to the strip during operation, as indicated by an arrow 24. Although it is possible to move the strip and use a stationary light barrier, the carrier with the light barrier preferably moves along with the X-ray detector along the stationary strip in that case.

If desired, multiple combinations of the 35 photosensitive and light-emitting elements can be used for cooperation with one and the same hole strip or with multiple hole strips. In the following, 1003044 -9- is based on one light barrier, which works together with one hole strip.

When in operation the combination of the light-emitting element and the light-sensitive element moves along the hole strip 5, the light-sensitive element provides a pulsating output signal with a frequency corresponding to the speed at which the light barrier moves along the hole strip. According to the invention, this output signal is converted into a first DC voltage signal, the magnitude of which is proportional to the frequency of the pulsating output signal and thus to the speed of the scanning movement. For this purpose use can be made of one of the known frequency-voltage converters known for this purpose. Subsequently, a second DC signal 20 is digitally formed from the first DC voltage signal by means of, for example, a circuit having a resistance division with a fixed or adjustable resistance and in an analogous manner or by means of a digital device (for instance a programmable computer). The relationship between the first and second DC voltage is determined by the setting of the resistance division or of the digital device. That setting represents the imaging measure of the optics that maps the X-ray detector output image to the CCD device.

The second DC voltage is then applied to a voltage-frequency converter, also known per se. As a result, a second pulsating signal is obtained, the frequency of which reproduces not only the speed of movement of the output image of the X-ray detector, but also the image measure of the optics that images the output image on the CCD device and, therefore, also the speed with which the image over the CCD device moves and thus TDI-35 flow rate. The second pulsating signal is thus ideally suited to serve as a clock signal for the TDI process.

1003044 -10-

Figure 4 schematically shows an example of a circuit for processing the output signals of the light barrier. On either side of the hole strip 20, an LED 30 and a photosensitive transistor 31 are located opposite each other. The output signal of the transistor 31 is applied via a filter stage 32 to a first amplifier 33 and via a differentiation stage 34 to a second amplifier 35. The first amplifier provides a first pulse train 36 which is in phase with the signal provided by the photosensitive transistor 31, while the second amplifier provides a second pulse train 37 which has a phase difference of 90 'with the first pulse train. The capacitors C1, C2 convert the pulse trains 36,37 into peak-shaped pulses corresponding to the edges of the pulses, which are rectified by a double-sided rectifying stage 38 and then fed to a third amplifier 39. The output signal 40 of the third amplifier now exists from a series of short pulses, for each period of the input signal provided by the photosensitive transistor 31, four short pulses are present in the output signal 40. In the example shown, the pulse train provided by the third amplifier 39 is supplied to a frequency / voltage converter 41 which supplies a DC voltage at the output 42, the value of which is proportional to the frequency f l of the input pulse train. This DC voltage is supplied to a converter 43, which converts the DC voltage supplied into a second DC voltage. The setting of the converter 43 represents the imaging measure of the optics that maps the X-ray detector output image to the CCD device. The second DC voltage is then supplied to a DC / frequency converter 44, which converts the supplied second DC voltage into a pulse train of a frequency f2 proportional thereto. For example, the DC voltage / frequency converter and the frequency / DC converter may be formed using an integrated circuit of 1003044 -11- type VFC 32 from Analog Devices or from Burr-Brown. The converter 43 may, for example, comprise a resistance network shown in Figures 4a to 4c, with or without adjustable resistance, or a digital (computer) circuit. The signal of frequency f2 can be used as a clock signal for the CCD device, possibly via an adaptation circuit 45. In principle, it is not necessary to multiply the number of peaks in the signal provided by transistor 31 to four pulses, but the accuracy. The synchronization of 10 is improved by this. If only one of the amplifiers, for example amplifier 33 or a one-sided rectification, is used, two pulses are produced for each period of the input signal.

Furthermore, the conversion of the signal of frequency f1 into a suitable signal of frequency f2 can also be effected in a manner other than with the aid of the circuit shown.

A multiplication of the number of peaks in the input signal can furthermore also be obtained by using two or 20 more combinations of a light-emitting and a photosensitive element, which combinations are staggered mounted along the hole strip.

These and similar modifications are obvious to one skilled in the art and are understood to fall within the scope of the invention.

1003044

Claims (16)

1. A method of forming an X-ray image with an X-ray imaging device of the type in which the X-ray image to be formed is built up by means of an elongated X-ray detector, which can convert incident X-rays into a light image and which in operation with respect to an object to be imaged performs a scanning movement in a direction transverse to the longitudinal direction of the elongated X-ray detector, whereby the light image is imaged in a reduced size by optical means on a photosensitive semiconductor device, which converts the reduced light image into electrical signals by means of a time-delay controlled / integration process, which represent the X-ray image, characterized in that speed synchronization is applied between the scanning movement of the X-ray detector 15 and the clock signals for the semiconductor device, the frequency of the clock signals being derived from one of the speed of the scanning movement dependent electrical signal. Method according to claim 1, characterized in that the electrical signal dependent on the speed of the scanning movement is converted into a first pulse train with a first frequency, which is converted into a second pulse train with a second frequency, the conversion 25 being it is performed that the ratio between the first and second frequencies represents the imaging measure of the optical means, and the second pulse train is used to form the clock signals. 3. Method according to claim 1 or 2, characterized in that the electrical signal dependent on the speed of the scanning movement is generated by means of at least one light-emitting element which co-acts with at least one photosensitive element, which elements are on either side of an elongated member with alternating 1003044 -13- transparent and opaque sections moving with the scanning movement relative to the elongated member. Method according to claim 3, characterized in that an elongated strip 5 is used as the elongated member. Method according to claim 3 or 4, characterized in that the elongated member is arranged stationary. 6. A method according to any one of the preceding claims, characterized in that a first pulse train is formed from the electrical signal dependent on the speed of the scanning movement and comprises a plurality of pulses per period of the speed-dependent signal. Method according to claim 6, characterized in that the first pulse train is formed with four pulses per period of the speed-dependent signal. Method according to any one of claims 2 to 7, characterized in that the first pulse train is converted into a first DC voltage, the magnitude of which depends on the frequency of the first pulse train, the first DC voltage is converted into a second DC voltage, the ratio between the first and the second DC voltage representing the imaging measure of the optical means, and the second DC voltage being converted into the second pulse train, the frequency of the second pulse train being dependent on the magnitude of the second DC voltage. 9. X-ray imaging device of the type in which the X-ray image to be formed is built up by means of an elongated X-ray detector, which can convert incident X-ray radiation into a light image and which, in operation in a house of the device, performs a scanning movement in a direction transverse to the longitudinal direction of the elongated X-ray detector, wherein the light image is reduced by optical means on a photosensitive semiconductor device, which converts the reduced light image by means of a time delay / integration process controlled by clock signals to electrical 1003044-14 signals, representing the X-ray image, characterized by first means for generating a first electrical signal, which depends on the speed of the scanning movement, and second means for converting the speed-dependent electrical signal into a second signal, from which clock signals for the photosensitive semiconductor The device may be derived, the second means being adjusted such that the ratio between the first and the second signal represents the image measure of the optical means. 10. X-ray imaging device according to claim 9, characterized in that the first means comprise at least one light barrier with a light-emitting element and a photosensitive element, which provides an electrical output signal under the influence of light, as well as an elongated member with alternately transparent and opaque parts. wherein the light barrier and the elongated member in operation move relative to each other in the longitudinal direction of the elongated member, which movement is determined by the scanning movement of the X-ray detector. 11. X-ray imaging device according to claim 10, characterized in that the first means comprise a first pulse-forming stage and a parallel-connected second pulse-forming stage, the first and second pulse-forming stages forming first and second pulse trains from the output signal provided by the photosensitive element. wherein the first and second pulse trains have a phase difference of 90 '; and that the first and second pulse trains are combined into a third pulse train using a combination circuit. X-ray imaging device according to claim 11, characterized in that the combination circuit comprises a double-sided rectifying circuit. X-ray imaging device according to any one of claims 9 to 12, characterized in that the second means comprise an adjustment device formed by a programmable computer device. 1003044 -15- X-ray imaging device according to any one of claims 9 to 12, characterized in that the second means comprise a conversion device comprising at least one resistance division. 5 X-ray imaging device according to any one of claims 9 to 14, characterized in that the second means comprise a frequency / voltage converter and a voltage / frequency converter and an adjustment device connected between these converters. 10 16. X-ray imaging device according to any one of claims 10 to 14, characterized in that the elongated member is a regularly spaced opaque strip on either side of which a light-emitting element and a light-sensitive element are in operation with respect to the strip moving in the longitudinal direction of the strip. 1 003044