DE102006033716A1 - X-ray diagnosis apparatus, with digital imaging, has a dosage measurement sensor using part of the scintillating light with a matrix of detection sensors - Google Patents

Abstract

The X-ray diagnosis apparatus has a dosage sensor using part of the scintillating light. The light-sensitive layer of the scintillator (14), in a housing (27), is over an active pixel matrix (15) on a glass substrate (20). An optically sensitive detector matrix (28) is under the glass substrate, as a sensor to measure dosage. The detector matrix is connected (31) to an electronic board (29).

Description

The The invention relates to an X-ray diagnostic device with a high voltage generator for an X-ray source, with an X-ray detector, the an imager with a scintillator and with in a matrix arranged pixel elements and a dose sensor arranged behind it a dose measuring device, on which a transducer of the Dose measuring device connected to control the high voltage generator is.

since Change years digital x-ray detectors classic radiography or fluoroscopy, angio and cardangiography. Various technologies have been in use for some time Use or just before the market; digital technologies like Image intensifier camera systems, based on television or CCD cameras, imaging systems with integrated or external readout unit, systems with optical Coupling the converter foil to CCDs or CMOS chips, selenium-based Electrostatic reading detectors (e.g., Thoravision) and Solid state detectors with active readout matrices and direct or indirect conversion the X-ray radiation.

Especially For some years now, new types of solid state detectors (FD) for digital X-ray imaging have been available in the market launch, on active Auslesematrizen example of amorphous silicon (a-Si). The image information is in an X-ray converter, for example, cesium Iodide (CsI), converted in the photodiodes of the matrix as electrical Stored charge and then over a active switching element with a dedicated electronics read out and analog-digital converted and further processed by the image system.

Related technologies also use an amorphous silicon active read-out matrix, but a converter (e.g., selenium) that directly generates electrical charge that is then stored on an electrode. The stored charge is then read out via an active switching element with a dedicated electronics and analog-digital converted, as described below with reference to 2 will be described in more detail, and further processed by the image system. Other technologies are based on CCDs (charge coupled devices) or APS (active pixel sensors) or large area CMOS chips, such as in "Flat-panel detectors in X-ray diagnostics" by Spahn et al., Radiologist 43 (2003), pages 340 to 350 , is described.

all The technology described above is based on X-ray information ultimately digitally present, both in place by a two-dimensional Pixel structure, as well as in the signal height by gray scale with given Bit depth.

to Regulation of the dose will be common external ionization chambers used in front of the x-ray detector are attached. This arrangement corresponds to that, too for conventional Systems, i. Film foil, or imaging plate systems used become. The disadvantage of this arrangement is that the externally mounted Dose control unit is structured - she points, for example three X-ray sensitive Chambers on - and therefore dependent from the place different degrees of incoming X-rays absorbed.

• • Bei konventionellen Systemen (Film-Folie) werden die Ionisationskammern auf dem Film abgebildet. Da in diesem Fall keine Bildverarbeitung durchgeführt werden kann, d.h. immer die volle Dynamik des Films dargestellt wird, sind die Strukturen jedoch nur gering oder nicht sichtbar.
• • Im Falle von digitalen Systemen ist dagegen eine Bildverarbeitung möglich, z.B. eine Reduzierung des dynamischen Bereichs (beispielsweise durch Veränderung der "Center"- und "Window"-Werte). Dies kann dazu führen, dass die Strukturen der einzelnen Ionisationskammern deutlich sichtbar werden. Bei digitalen Bildaufnehmern (Festkörperdetektoren, CCDs, CMOS-Chips) wird zwar im allgemeinen eine Kalibrierung durchgeführt, durch die das angesprochene Problem aufgrund der notwendigen Bildvorverarbeitung (z.B. Offset- und Gainkorrekturen) in erster Ordnung korrigiert werden; sobald die Strahlenqualitäten, die bei der Kalibrierung und bei der eigentlichen Röntgenaufnahme nicht übereinstimmen – dies ist im allgemeinen der Fall – tritt der Artefakt jedoch wieder auf. Auch im dem Falle, dass die Kalibrierung mit der vorgelagerten Dosismesskammer und die Aufnahme ohne vorgelagerte Dosismesskammer, beispielsweise bei aus dem Tisch herausziehbarem Detektor, vorgenommen werden oder aber auch bei umgekehrter Anordnung der Dosismesskammer bei Kalibrierung und Aufnahme wird der Artefakt selbst bei gleicher Strahlenqualität in voller Höhe auftreten.
• • Eine externe Ionisationskammer muss auch separat synchronisiert werden, d.h. dann aktiviert werden, wenn der Detektor aufnahmebereit ist und die Röhre bzw. der Generator den Röntgenpuls einleitet. Dies führt zu zusätzlichem "logistischem" Aufwand beim Systemkontroller.

An external ionization chamber leads to several principal disadvantages:

• • In conventional systems (film foil), the ionization chambers are imaged on the film. Since no image processing can be carried out in this case, ie the full dynamics of the film is always displayed, the structures are only slight or invisible.
• • In the case of digital systems, on the other hand, image processing is possible, eg a reduction of the dynamic range (eg by changing the "center" and "window" values). This can lead to the structures of the individual ionization chambers becoming clearly visible. In the case of digital image sensors (solid-state detectors, CCDs, CMOS chips), calibration is generally carried out by which the problem addressed is corrected in first order due to the necessary image preprocessing (eg offset and gain corrections); however, as soon as the beam qualities that do not match during calibration and during the actual X-ray scan - this is generally the case - the artifact recurs. Also in the case that the calibration with the upstream Dosismesskammer and the recording without upstream Dosismesskammer, for example, be pulled out of the table detector, or even with the reverse arrangement of the Dosismesskammer during calibration and recording the artifact is even with the same beam quality in full Height occur.
• • An external ionization chamber must also be synchronized separately, ie activated when the detector is ready to record and the tube or generator initiates the X-ray pulse. This leads to additional "logistical" effort in the system controller.

• • zusätzliche Systemkosten,
• • zusätzliche Bauhöhe in Systemen,
• • zusätzliche Einstell- und Eichprozeduren (Aufwand, Kosten) sowie
• • eine weitere Komponente, die eventuell Service benötigt.

That conditionally

• • additional system costs,
• • additional height in systems,
• • additional adjustment and calibration procedures (effort, costs) as well as
• • another component, possibly service needed.

From the DE 102 39 804 A1 It is known to accommodate X-ray sensitive ionization chambers directly in the detector and thus to reduce the variety of components. In this case, an "ordinary" x-ray-sensitive dose measuring unit is essentially integrated in the detector. Part of the unabsorbed X-radiation is used for dose measurement.

X-rays penetrates any material, is only weakened and thus stands in each Fall behind the a-Si layer to disposal.

Farther are there any approaches the design of the amorphous silicon matrix to change that way that directly the imaging detector unit (the a-Si) for dose measurement is used. However, this has disadvantages as the design at the expense of the primary Using the detector to create an image goes. Specifically, it works this usually at the expense of the so-called fill factor, ie the pixel size related relative size of the photodiode. A reduced fill factor, however, means loss of image quality, such as reduced sensitivity and Deterioration of the signal-to-noise ratio.

The solution of the problem described is of particular relevance to portable detectors, i. those that are not used in a "Bucky-Lade" in which an external ionization chamber can be integrated. For portable Detectors, however, also for similar to free shots a film cassette are used, there is still today regarding dose measurement no solution.

Also for like that called dynamic detectors, for example, in angiography and cardiology, there is no procedure today the one dose shutdown for the current picture allows. Today's solutions are based on the determination of the dose from previous images. For a first Image in a series is therefore no dose control possible. Also This is not an ideal method when the object is from image to image Image changes.

The Invention is based on the task of an X-ray diagnostic device of the type mentioned in such a way that a simple, fast and safe dose measurement for controlling the X-ray system for the current Image of a single shot or a recording sequence done can.

The The object is achieved in that the dose sensor of a dose measuring device with an array of in a matrix arranged, large-scale, photosensitive elements for detection by the imager falling, the X-ray dose proportional residual light for controlling the high voltage generator is provided. Due to the separate arrangement of a photosensitive Dosensor, which emitted the scintillator, through the pixel matrix detects penetrating residual light, a signal proportional to the X-ray dose quickly and easily a transducer of the dose measuring device for Control of the high voltage generator can be supplied.

It has proved to be advantageous when the dose sensor in the detector integrated and discretely arranged by the imager.

In Advantageously, the imager can be a device for generating having a reset light.

According to the invention, the Device is optically transparent or partially transparent.

In Advantageously, the dose sensor for detecting the residual light have a matrix of discrete photodiodes, wherein the matrix integrated according to the invention can be.

alternative to photodiodes can Phototransistors can also be used. You have the advantage very much much higher Sensitivities to show what the application benefits. However, have she also has one for This application disadvantageous lower Ansprechschnelligkeit.

These Photodiodes or phototransistors can be made of crystalline or amorphous silicon, germanium, organic materials or other advantageous Materials exist.

It has proven to be advantageous if the dose sensor for detection of the residual light has an integrated matrix of CMOS sensors.

According to the invention can Matrix of Dosage Sensor Pre-Amplification, Be associated with analog / digital conversion and / or analysis circuits.

Of the Dose sensor for the detection of residual light can be extremely cost-effective, large area and especially thin when arranged in a matrix organic photodiodes having.

alternative the dose sensor for detecting the residual light can also be an a-Si converter be.

The Invention is described below with reference to the drawing Embodiments explained in more detail. It demonstrate:

1 a known complete system with digital X-ray detector, anti-scatter grid and dose measuring device,

2 a schematic structure of a solid-state detector,

3 a detail of an arrangement of four pixels of an a-Si matrix,

4 an X-ray detector with integrated matrix-shaped dose measuring system in cross section,

5 an X-ray detector with integrated matrix-shaped Dosismesssystem in cross section with reset light and

6 a structured arrangement of a matrix of large-area, photosensitive detectors for forming a Dosismesseinrichtung.

In the 1 is one of the DE 102 39 804 A1 known X-ray diagnostic device with a first tripod 1 shown at the height adjustable an X-ray source 2 is attached, the conically bundled X-rays 3 generated in the beam path of the X-rays 3 located object 4 penetrate. The X-ray diagnostic device has a second tripod 5 on, at which an x-ray detector 6 fixed in such a way that it is level with the X-ray source 2 is aligned so that through the object 4 weakened x-rays 3 on the x-ray detector 6 fall. In front of the x-ray detector 6 is a anti-scatter grid 7 arranged in the object to be examined 4 Suppressed scattered radiation suppressed. Behind the x-ray detector 6 is an X-ray sensitive dose sensor 8th a dose measuring device, for example an ionization chamber provided. A high voltage generator 9 with system control and transducers of the dose measuring device supplies the X-ray tube of the X-ray source 2 with high and heating voltage. Furthermore, the system control 9 with the X-ray detector 6 and the dose sensor 8th the dose measuring device via control lines, data lines and power supplies 10 connected.

The output signal of the X-ray detector 6 will continue to be an image calculator or image system 11 supplied with hardware and software. The picture system 11 may include computers, converters, image storage and processing circuitry. It is for viewing the acquired X-ray images with a control monitor 12 connected. The picture system 11 is via control and data lines 13 connected to the other components of the X-ray diagnostic device.

In the 2 is the x-ray detector 6 shown in perspective cross-section. The core component of the Röntgendetek sector 6 consists of a solid-state pixel matrix, row drivers and amplifiers. The solid-state pixel matrix has, for example, a layer with a scintillator 14 on, for example consisting of cesium iodide (CsI), which when irradiated by the X-rays 3 visible photons emitted and into a pixel matrix 15 made of amorphous silicon, which gives a visible X-ray image. Each of the pixels or pixels of this pixel matrix 15 exists, as in 2 is shown enlarged from a photodiode 16 and a switch 17 that with line wires 18 and column lines 19 connected is. The pixel matrix 15 is on a glass substrate 20 applied.

In each case, all pixels of a line are simultaneously driven by the control electronics 21 addressed and read out. In the simplest case, an image is progressively read line by line. The signals are via a read-out electronics 22 one in the image system, for example 11 arranged processing circuit in which the signals are processed in parallel in a plurality of amplifiers, merged by multiplexers and converted in an analog / digital converter (A / D converter) into a digital output signal for further digital processing.

In the 3 Fig. 12 is a detail of an arrangement of four of, for example, 1028 x 1028 pixels of the a-Si pixel matrix 15 of the 2 shown. The matrix-shaped photodiodes 16 take the largest area. Between the photodiodes 16 are for controlling perpendicular gate lines 23 and for reading horizontally data lines 24 arranged. At their intersections are TFTs as switches 25 (Thin film transistors) provided under which bias lines 26 are arranged. In the spaces between photodiodes 16 , TFTs 25 and wires 23 . 24 and 26 the scintillation light is not absorbed and falls on the underlying glass substrate 20 Where it can be used via appropriate decoupling, as described below.

In the 4 is an inventive X-ray detector 6 schematically illustrated, in which a matrix-shaped photosensitive dose sensor 8th is integrated. The x-ray detector 6 is based on the fact that a part of the scintillation light is not absorbed in the actual detector matrix, but behind it is available as a residual light available. This can be used, for example, for dose measurement. In a housing 27 is an x-ray sensitive layer, the scintillator 14 , arranged on the the active pixel matrix 15 follows that on the glass substrate 20 is applied. On the other side of the glass substrate 20 is an optical one sensitive detector matrix 28 as a dose sensor 8th arranged for dose measurement. Below the detector matrix 28 is an electronics board 29 provided that via connections 30 at the pixel matrix 15 connected. By means of cables 31 For power supply, control and transmission of image and measurement data is the electronics board 29 continue with the detector matrix 28 and outward with the picture system 11 and the transducers of the dose measuring device.

Now penetrate the X-rays 3 an object 4 For example, a patient, they fall according to the radiation transparency of the patient 4 weakened on the scintillator 14 , There they produce a scintillation light 32 that's on the pixel matrix 15 falls. Part of the scintillation light 32 penetrates in the spaces between the photodiodes 16 the pixel matrix 15 and falls as a low light 33 on the detector matrix 28 , Their output signal is then supplied to a, for example, in the system control arranged Dosismesssystem, the high voltage generator 9 controls accordingly.

In the 5 is a variant of an X-ray detector according to the invention 6 with integrated matrix-shaped photosensitive dose sensor 8th shown schematically. The structure is essentially the same as in 4 , only between glass substrate 20 and detector matrix 28 is a known device for generating a reset light 34 arranged, which in the radiation pauses the pixel matrix 15 illuminated to reset the charge.

In the 6 is an example of a structured arrangement of a detector matrix 28 represented by 8 × 8 photosensitive sensors, such as large-area pixels, as measuring fields 35 a dose sensor 8th be formed. As is known, an arbitrary spatial selection of the measuring fields can now be used 35 organ-dependent to the evaluation of the detected dose are selected, as by the colored fields 35 is marked. The measuring fields 35 are considerably larger than the area of the photodiodes 14 so they make up a large proportion of the residual light 33 accumulate on their active surface.

By the replacement according to the invention The ionization chamber has an internal, ie integrated in the detector Dose control unit for use. This dose control is discreet built, so independent attached by the actual imaging detector unit.

The essence is that some of the scintillation light 32 is not image-effective, ie not in the photodiodes of the a-Si matrix 15 is absorbed. This low light 33 falls through the lines 23 . 24 and 26 , Switching element 25 , etc. formed interstices of the pixel matrix 15 on the underlying substrate 20 (i. general glass), as in particular the 3 can be seen. There it is available for further analyzes, for example for dose measurement. So place an optical dose sensor 8th , or a detector matrix 28 from sensors according to 4 and 5 behind the substrate 20 Thus, a part of the light can be detected in this way, which is directly a measure of the incident dose to the X-ray detector 6 is.

• • CMOS-Sensoren,
• • Photodioden,
• • Phototransistoren oder
• • a-Si-Photodioden,

wobei die Sensoren jeweils aus einzelnen Elementen oder einer Matrix mehrerer Elemente bestehen können. Die Photodioden oder Phototransistoren können aus kristallinem oder amorphem Silizium, Germanium, organischem Materialien oder anderen vorteilhaften Materialien bestehen.Such a dose measuring device based on optical photons, that is, the residual light 33 in an indirectly converting detector 6 uses, the detector matrix can 28 be executed as follows:

• • CMOS sensors,
• • photodiodes,
• • phototransistors or
• A-Si photodiodes,

wherein each of the sensors may consist of individual elements or a matrix of several elements. The photodiodes or phototransistors may be made of crystalline or amorphous silicon, germanium, organic materials or other advantageous materials.

The matrix of the dose sensor 8th may be associated with pre-amplification, analog-to-digital conversion and / or analysis circuits, for example on-chip.

• • Die Detektor-Matrix 28 des Dosismesssystems kann hinter der a-Si-Matrix 15, dem Substrat 20 und dem Rücksetzlicht 34 angebracht sein. Im diesem Falle ist es notwendig, dass die Schicht des Rücksetzlichts 34 optisch transparent oder teiltransparent ist.
• • Die Detektor-Matrix 28 des Dosismesssystems kann zwischen Substrat 20 und Rücksetzlicht 34 angebracht sein. Dann muss die Detektor-Matrix 28 transparent oder teiltransparent sein.

On reset light 34 based, indirectly converting flat panel detectors according to 5 are used to either "reset" the photodiodes, ie to activate for the next X-ray shot, and / or to reduce ghost effects, such as lag or memory effects. The reset light 34 is usually located behind the amorphous silicon matrix when viewed from the direction of incidence of the X-ray radiation.

• • The detector matrix 28 of the dose measuring system can be behind the a-Si matrix 15 , the substrate 20 and the reset light 34 to be appropriate. In this case, it is necessary that the layer of the reset light 34 is optically transparent or semi-transparent.
• • The detector matrix 28 of the dose measuring system can be between substrate 20 and reset light 34 to be appropriate. Then the detector matrix has to be 28 be transparent or semi-transparent.

Alternatively, solutions for both of the above variants may also be based on using different parts of the optical spectrum. For example, the scintillation light is usually "green". If the reset light is "red", then k NEN variants with different optical absorption properties can be used.

Between substrate 20 and detector matrix 28 of the dose measuring system according to 4 In addition layers may be attached for better optical coupling. The same applies to the interface between detector matrix 28 of the dose measuring system and reset light 34 in the variant according to 5 ,

• 1. Die Dosissensoren müssen sehr schnell ausgelesen werden. Die Taktrate für das Auslesen und die Analyse muss ein Vielfaches der Taktrate sein, mit der die bildgebenden Detektoren ausgelesen werden, da ja während der Röntgenintegration in den bildgebenden Detektoren die Entscheidung getroffen werden muss, ob die Röntgenstrahlung zu beenden ist.
• 2. Die Größe der Dosissensoren kann deutlich größer sein, als die Größe der bildgebenden Detektorelemente. Damit wird das relativ geringe Signal pro Flächen- und Zeiteinheit, das auf diese Sensoren fällt, kompensiert, da nur ein Teil des Lichts durch die Zwischenräume der Photodioden fällt und für die Dosismessung verfügbar ist. Zudem werden die Sensoren i. Allg. in sehr viel kürzeren Taktraten ausgelesen als die bildgebenden Detektoren.

A geometric arrangement of individually selectable dose sensors as measuring fields 35 the detector matrix 28 for dose measurement is in 6 shown. It is advantageous to keep the number of dose sensors significantly lower than the number of picture elements of the pixel matrix 15 of the imaging detector. This has two reasons:

• 1. The Dosissenoren must be read out very quickly. The clock rate for the reading out and the analysis must be a multiple of the clock rate with which the imaging detectors are read out, since during the X-ray integration in the imaging detectors the decision must be made as to whether the X-radiation is to be ended.
• 2. The size of the dose sensors can be significantly larger than the size of the imaging detector elements. Thus, the relatively small signal per unit area and time that falls on these sensors is compensated because only a portion of the light falls through the interstices of the photodiodes and is available for dose measurement. In addition, the sensors i. Gen. read at much shorter clock rates than the imaging detectors.

By the training of the invention the X-ray diagnostic device with an array of arranged in a matrix, large area, receives photosensitive elements a residual light-based dose measuring device integrated in the flat detector, the discreet, so independent from the actual imaging detector unit is constructed.

The separate arrangement of a photosensitive Dosassesors can independently whether the detector is operated with or without reset light got to. It can Different variants of photosensitive Dosissenoren for Application, such as CMOS circuits, in intelligence like preamplification, analog-to-digital conversion and analysis can be realized on-chip can, organic photodiodes, the extremely cost-effective, large-area and above all thin produced can be and / or a-Si detectors.

Claims (13)

X-ray diagnostic device with a high-voltage generator ( 9 ) for an X-ray source ( 2 ), with an X-ray detector ( 6 ), which has an image converter ( 14 . 15 ) with a scintillator ( 14 ) and in a matrix ( 15 ) arranged pixel elements and a dose sensor arranged behind ( 8th ) of a dose measuring device with an array ( 28 ) arranged in a matrix, large-area photosensitive elements ( 35 ) for detecting by the image converter ( 14 . 15 ), the X-ray dose proportional residual light, on which a transducer of the dose measuring device for controlling the high voltage generator ( 9 ) connected. X-ray diagnostic device according to claim 1, characterized in that the dose sensor ( 8th ) integrated in the detector and discreetly from the image converter ( 14 . 15 ) is arranged. X-ray diagnostic device according to claim 1 or 2, characterized in that the image converter ( 6 ) a device for generating a reset light ( 34 ) having. X-ray diagnostic device according to one of claims 1 to 3, characterized in that the device ( 34 ) is optically partially transparent. X-ray diagnostic device according to one of claims 1 to 3, characterized in that the device ( 34 ) is optically transparent. X-ray diagnostic device according to one of claims 1 to 5, characterized in that the dose sensor ( 8th ) has a matrix of discrete photodiodes for detecting the residual light. X-ray diagnostic device according to one of claims 1 to 5, characterized in that the dose sensor ( 8th ) has a matrix of phototransistors for detecting the residual light. X-ray diagnostic device according to claim 6 or 7, characterized in that the matrix is integrated. X-ray diagnostic device according to one of claims 6 to 8, characterized in that the dose sensor ( 8th ) for detecting the residual light of crystalline or amorphous silicon, germanium or organic materials. X-ray diagnostic device according to one of claims 1 to 5, characterized in that the dose sensor ( 8th ) has an integrated matrix of CMOS sensors for detecting the residual light. X-ray diagnostic device according to one of claims 1 to 10, characterized that the matrix of the dose sensor ( 8th ) Preamplification, analog / digital conversion and / or analysis circuits are assigned on-chip. X-ray diagnostic device according to one of claims 1 to 5, characterized in that the dose sensor ( 8th ) for detecting the residual light arranged in a matrix organic photodiodes. X-ray diagnostic device according to one of claims 1 to 5, characterized in that the dose sensor ( 8th ) is an a-Si converter for detecting the residual light.