EP1250705A1

EP1250705A1 - Radiological image sensing system for scanning x-ray generator

Info

Publication number: EP1250705A1
Application number: EP00993753A
Authority: EP
Inventors: Paul Thomson-CSF Propriété IntellectuellE DE GROOT
Original assignee: Thales Electron Devices SA
Current assignee: Thales Electron Devices SA
Priority date: 1999-12-30
Filing date: 2000-12-28
Publication date: 2002-10-23
Anticipated expiration: 2020-12-28
Also published as: US6934360B2; DE60010521T2; US20050201518A1; WO2001050481A1; US7082187B2; FR2803394A1; FR2803394B1; EP1250705B1; DE60010521D1; US20020172327A1

Abstract

The invention concerns a radiological image sensing system capable of co-operating with a scanning X-ray generator (10) designed to generate a X-radiation (1) scanning a surface (2) whereof the image is to be produced. The X-radiation (1) irradiates successively portions (2') of the surface whereof the image is to be produced (2). The X-radiation derived from a portion (2') bears a radiological image of said portion. The sensing system comprises an image sensor (22, 52) which is stationary relative to the scanning and dimensioned so as to acquire an image of the whole surface (2) whereof the image is to be produced via the X-radiation derived from the portions (2'). It further comprises means (24, 240) for limiting, at a given time, the image sensor (22, 52) acquisition to that of the image of the irradiated portion (2') at said time, said limiting means being synchronised with the scanning and in geometric correspondence with the irradiated portion (2').

Description

RADIOLOGICAL IMAGE DETECTION SYSTEM FOR SCANNED X-RAY GENERATOR

The present invention relates to a radiological image detection system for a scanning X-ray generator capable of operating at high rate.

X-ray imaging systems grouping together a radiological image detection system associated with an X-ray generator are used in the medical field or in the field of non-destructive testing. In these types of application, it is sought to obtain images of very good quality and in particular well contrasted.

A conventional X-ray imaging system used in the medical field generally comprises an X-ray generator delivering X-radiation to which a patient is exposed and, opposite to the X-ray generator, a detection system which detects the radiation X having passed through the patient and who is then carrying a radiological image. The X-ray generator and the patient are positioned relative to each other so that the X-ray irradiation field covers the entire imaging surface of the patient at a given time. The stationary detection system then simultaneously detects the radiological image of the entire surface to be imaged.

However, a significant part of the X-rays passing through the patient is scattered, that is to say that it is deviated from its initial rectilinear trajectory. The deflected or scattered rays are still detected by the detection system and the detected image is deteriorated compared to that which would be provided only by useful x-rays, i.e. those which have not been deflected . This deterioration results in a degradation of the contrast.

To get rid of scattered X-rays, an anti-scattering grid is generally placed between the patient and the detection system. This grid absorbs a large part of the scattered X-rays but also absorbs part of the useful X-rays, and consequently requires a higher patient dose. This grid is currently the only solution for eliminating the scattering in detection systems using an X-ray image intensifier tube, which are currently the most used for real-time radiological imaging. Another solution to get rid of scattered X-rays without increasing the dose of X-rays is to use a scanning X-ray generator which irradiates the surface to be imaged in a progressive manner, the instant irradiated area being only a portion of the surface to be imaged. In this case, the X-ray generator is associated with a mobile detection system which is synchronized with the scanning movement of the X-ray and in geometric correspondence with the instantaneous irradiated zone. The detection system is generally formed of solid state sensor elements covered with a scintillating material and arranged in a bar, the dimensions of this bar are such that it receives only the image of the instantaneous irradiated zone. It therefore does not detect scattered X-rays which are deflected but only X-rays which have directly passed through the patient.

However, the implementation of such detection systems requires complicated mechanical devices.

The dimensions of the bar are conditioned by those of the instantaneous irradiated zone. It is therefore not possible, without changing the strip, to want to optimize the compromise between the dimensions of the irradiated area and the X-ray flow rate. It is not easy to move the strip of sensor elements to the state solid to the rhythm of the scanning X-ray, especially if the required scanning speed is high, as in fluoroscopy examinations in which several tens of images per second must be taken.

The precision mechanics used to move the detection system represents an important item in the cost of such detection systems.

Detection systems have also been proposed in which a slot in a mechanical shutter moves at the level of the detector, in synchronism with the scanning carried out by the X-ray beam. These mechanical systems do not allow a high scanning rate and are heavy and expensive. EP 0 083 465 gives an example.

The present invention, while continuing to eliminate the scattered radiological images, aims to overcome the aforementioned problems, in particular related to the doses to be administered to the patient, to movement mechanics of the image sensor or other parts such as slits in shutters on the detection side; it allows scanning speeds compatible with those required in fluoroscopy mode to be achieved.

To achieve this, the present invention provides a radiological image detection system capable of cooperating with a scanning X-ray generator intended to produce X-ray scanning a surface to be imaged, this X-ray irradiating portion after portion the surface to be imaged, the X-ray radiation from a portion carrying a radiological image of said portion. The system comprises an image sensor which is stationary with respect to the scanning and which is dimensioned so as to be able to acquire an image of the entire surface to be imaged via the X-ray radiation coming from the portions, the detection system further comprising means for limiting electronically, at a given instant, the acquisition of the image sensor to that of the image of the irradiated portion at this instant, these electronic limitation means being in synchronism with the scanning and in geometric correspondence with the irradiated portion.

The electronic limitation means are purely static, unlike the rotating or scrolling mechanical limitation means of the prior art. In a first configuration, the means for limiting the acquisition of the image sensor can be means for partially occulting the image sensor with respect to the surface to be imaged, external to the image sensor. A liquid crystal screen, the scanning of which is controlled in synchronism with the scanning of the X-ray beam, makes it possible to allow only a limited image area passing to a detection camera corresponding to that which is illuminated at this instant by the detector.

The image sensor can be a light image sensor and cooperate with means for converting the X-radiation from the portions into a light image. In another embodiment, the image sensor can be an electronic image sensor and cooperate with means for converting the X-ray radiation coming from the portions directly into an electronic image. Selenium sensors are able to do this direct conversion.

In both cases, the means for limiting the acquisition of the image sensor can be integrated into the image sensor, the latter being organized to prevent any image acquisition outside the area which corresponds to an image portion illuminated at an instant by the X-ray beam.

The image sensor can be of the solid state type and in particular of the CCD type, of the CMOS type, with photosensitive diodes, with capacitive elements. The image sensor can be a light image sensor formed from a plurality of photosensitive pixels in the solid state, the means for limiting the acquisition of the image sensor can control, just before a portion is irradiated, an erasure of the pixels of the sensor corresponding to the light image of said irradiated portion, and a reading of said pixels just after the irradiation of said portion.

The image sensor can be an electronic image sensor formed by a plurality of capacitive elements and the means for limiting the acquisition of the image sensor can control, just before a portion is irradiated, an update. zero of the charge of the capacitive elements corresponding to the electronic image of said irradiated portion and a reading of the charges stored in said capacitive elements just after the irradiation of said portion.

It is also possible that the light image sensor is of the photographic film or cinematographic film type; in this case, in principle, a liquid crystal screen will be used to perform the image limitation.

The means for converting the X-ray into a light image can be of the radiological image intensifier or scintillator type deposited on a photosensitive matrix in the solid state, while the means for converting the X-ray into an electronic image can be made on the basis of selenium.

The detection system may include means for processing the image captured by the image sensor so as to reconstruct a complete image of the radiological image of the surface to be imaged from images of the irradiated areas.

Other characteristics and advantages of the invention will appear on reading the following description illustrated by the appended figures which represent:

- Figure 1 a section of an example of image detection system associated with a scanning X-ray generator, in which the means of limitation of the acquisition of the image sensor are mechanical partial concealment means;

- Figure 2 a front view of the means limiting the acquisition of the image sensor used in the image detection system of Figure 1; - Figure 3 a section of a second example of image detection system associated with a scanning X-ray generator, in which the means for limiting the acquisition of the image sensor are means for partial occlusion mechanical;

- Figure 4 a front view of the means limiting the acquisition of the image sensor used in the image detection system of Figure 3;

- Figure 5 a section of a third example of an image detection system associated with a scanning X-ray generator, in which the means for limiting the acquisition of the image sensor are means for partial occlusion mechanical; - Figure 6 a section of a fourth example of an image detection system according to the invention associated with a scanning X-ray generator, in which the means for limiting the acquisition of the image sensor are means partial electronic and external concealment of the image sensor; - Figure 7 a front view of the partial concealment means used in the image detection system of Figure 6;

- Figures 8a, 8b, in section, two new examples of image detection system according to the invention in which the means limiting the acquisition of the image sensor are integrated into the image sensor; - Figures 9a, 9b, 9c three front views of the image sensor of Figure 8a, at different times, to understand the operation of the means limiting its acquisition;

- Figure 10, in partial section an electronic image sensor that can be integrated into an image detection system according to the invention.

In these figures the same elements have the same reference and the scales are not respected for the sake of clarity.

FIG. 1 represents an image detection system 20. This image detection system is used in medical imaging equipment comprising a scanning X-ray generator 10 which delivers a X-ray 1 scanning a surface to be imaged 2 of a patient 3 to be examined. At a given instant, the X-ray radiation 1 irradiates only a portion 2 ′ of the surface to be imaged 2. After a complete scan, the entire surface to be imaged 2 has been irradiated portion by portion. The scanning X-ray generator 10 can be with a scanning slot, that is to say with a slot which moves in front of an X-ray source or be with a fixed slot as described for example in the French patent application FR A- 2 795 864. In this case, it is by acting on the variable orientation of the electron beam relative to a target that the angle of incidence of the X beam on the body to be irradiated is varied: the speed sweep can be high, in the absence of movements of mechanical parts.

On the other side of the patient 3, that is to say opposite to the scanning X-ray generator 10 is the detection system 20. It detects the X-ray 1 having passed through the patient, this X-ray being carrier of a radiological image.

The image detection system 20 comprises an image sensor 22 intended to acquire, via the X-ray radiation coming from the portions, an image of the surface to be imaged. This image sensor 22 is stationary with respect to the scanning and it has dimensions allowing it to acquire an image of the entire surface to be imaged 2. (I is not set in motion nor limited in dimensions to those of the Irradiated portion. By eliminating the means for setting the sensor in motion since it is stationary, this eliminates in particular the mechanical problems encountered with a sensor displaceable at the rate of the scanning radiation. The image detection system 20 also comprises means

24 to limit, at a given instant, the acquisition of the image sensor 22 essentially to that of the image of the portion 2 'irradiated at this instant, these means being in synchronism with the scanning and in correspondence, geometric with the irradiated portion 2 '. A dotted link illustrates the synchronism between the scanning X-ray 1 and the means 24 limiting the acquisition of the image sensor 22.

In the example described, the image sensor 22 is a light image sensor and it cooperates with means 21 for converting the X-radiation carrying the radiological image into a light image received by the light image sensor 22 . One could consider using an electronic image sensor in place of the light image sensor as shown in Figure 10 described later. This sensor is intended to pick up electronic charges and it cooperates with means for directly converting the X-radiation carrying the radiological image into an electronic image.

In the example described in FIG. 1, the detection system 20 comprises as conversion means a radiological image intensifier tube 21 known by the acronym IIR, followed by the light image sensor 22. The means 24 limiting the acquisition of the light image sensor 22 are mechanical means for partially obscuring the light image sensor 22. These partial concealment means 24 are external to the light image sensor 22, they partially mask the image sensor 22 so that it only captures, at a given instant, the light image of the irradiated portion 2 'by scanning X-ray 1.

We will now see in more detail the image detection system in its embodiment of FIG. 1.

The IIR tube 21 conventionally comprises a vacuum-tight enclosure 200 closed at one end by an inlet window 201 through which the scanning X-ray 1 penetrating through the patient 3 penetrates.

The X-ray scanning 1 then meets an input screen 202 whose function is to translate the intensity of the X-ray into a quantity of electrons. This entry screen 202 is dimensioned so that it can be struck by X-ray radiation 1 regardless of the place of impact on the entry window 201. The entry screen 202 generally comprises a scintillator 203 associated with a photocathode 204. The scintillator 203 converts the scanning X-ray 1 into visible photons which are themselves converted into electrons by the photocathode 204.

A set of electrodes 205 accelerates the electrons and focuses them on a cathodoluminescent output screen 206. The luminescent output screen 206 is arranged near an output window 207 located opposite to the input window 201 The impact of the electrons on the luminescent screen 206 makes it possible to reconstruct the light image which has formed on the photocathode 204. This light image translates at a given moment the radiological image of the irradiated portion 2 ′. This bright image has the faults mentioned above because with only the scanning X-ray, scattered X-rays strike the photocathode 204 and their effect is visible on the output screen 206. The image displayed by the output screen 206 is then transmitted to the light image sensor 22. This light image sensor 22 is generally a CCD type sensor (for Charge-Coupled Device in English or charge-coupled device) included in a video camera 220, a cinematographic film placed in a cinematographic camera or a photographic film included in a camera. The CCD sensor can advantageously be replaced by a CMOS type sensor which functions in a very similar manner.

The transmission of the light image displayed by the output screen 206 to the light image sensor 22 is generally done by means of an optical coupling device 209, placed outside the IIR tube 21 and centered on a longitudinal axis XX ′ of the tube IIR, an axis around which the outlet screen 206. is also centered. This optical coupling device 209 may comprise lenses and / or optical fibers.

The light image sensor 22 is dimensioned to receive the entire image of the surface to be imaged 2, as is the case in conventional image detection systems with stationary X-ray beam.

It is associated with partial concealment means 24 synchronized with the scanning movement of the scanning X-ray radiation 1 and in geometric correspondence with the irradiated portion 2 ′ of the surface to be imaged. By being partially masked, the light image sensor 22 can only capture the light image of the portion irradiated 2 ′ by the scanning X 1 radiation. These concealment means 24 prevent the light image sensor 22 from capturing the trace of X-rays scattered in the patient 3.

The image detection system 20 may include a signal acquisition and processing device 23 which processes and stores signals relating to the image delivered to it by the light image sensor 22. After appropriate processing, these signals can be observed on a display device 25. In the example of FIG. 1, the light image sensor 22 is stationary with respect to the scanning while the partial concealment means 24 are mobile and more particularly rotary relative to the light image sensor 22. They are placed between the output screen 206 and the light image sensor 22.

They take the form of a disc 240 opaque to the light coming from the output screen 206, and provided with at least one window 241 allowing the light to pass. This window 241 can simply be an opening in the disc which lets the light image of the irradiated portion 2 ′ pass.

The disc 240 is rotated so that its window 241 moves in synchronism with the X-ray radiation 1 scanning the surface to be imaged 2. When the X-ray radiation 1 scanning has completely excursed the surface to be imaged 2, the window 241 has excursed the light image sensor and the latter has captured the entire radiological image of the surface to be imaged 2 converted into a light image, from a plurality of light images corresponding to the different irradiated portions 2 ′ during scanning. The speed of rotation of the disc 240 is synchronized with that of the scanning X-ray beam 1. It is assumed that the scanning of the scanning X-ray 1 is carried out on the surface to be imaged 2 from top to bottom as shown in FIG. 1. The X-ray scanning 1 emerges from a slit 4 whose length, perpendicular to the scanning direction, corresponds to the dimension of the surface to be imaged 2 also located perpendicular to the scanning direction, to an enlargement coefficient. This factor is a function of the distance separating the patient 3 from the X-ray generator 10. The width of the slot 4 located in the scanning direction is very small compared to the other dimension of the surface to be imaged 2 also located in the scanning direction. scanning. The slot 4 may be driven in a back-and-forth movement in translation, but one can envisage, to overcome this back-and-forth movement which is always difficult to achieve at high speed, use a rotating disc with one or more slots. In the case, the scanning is unidirectional.

The dimensions of the irradiated portion 2 ′ at a given instant are modeled on those of the slot 4 to the nearest enlargement coefficient. In the example of FIG. 1, the windows 241 are radial slots whose dimensions are modeled on those of the irradiated portion

2 ', to within a coefficient of proportionality, a function of the relative positions and the effects of the different elements located between the patient 3 and the concealment means 24.

These slots 241 are located at the periphery of the disc 240. It is preferable to distribute the windows 241 over the entire periphery of the disc, especially if the rate of the radiological images to be taken is high.

In the case where the scanning is done in translation, the disc 240 will have a large radius in front of the length of the windows 241 so that the displacement of a slot in front of the light image sensor 22 is comparable to a translation. We refer to figure 2.

The partial concealment means 24 can take the form of an opaque ribbon 242 provided with one or more windows 243 transparent to the light of the exit screen 206. This ribbon 242 can be configured in a loop and driven by rollers 244 as illustrated in FIG. 3. When it faces the light image sensor 22, it moves in translation. Its windows 243 are slits transverse to the direction of movement of the ribbon 242. Reference is made to FIG. 4. If the scanning movement is a two-way movement back and forth, the emission of X-rays may be stopped for a period of time. of the two paths if the partial concealment means are driven in a unidirectional movement in rotation or in translation.

In the two configurations described, the partial concealment means 24 are arranged between the output screen 206 and the light image sensor 22. In the case where an optical coupling device 209 is interposed between the output screen 206 and the light image sensor 22, the partial concealment means 24 can be either between the output screen 206 and the optical device of coupling 209 as in FIG. 1, or between the optical coupling device 209 and the light image sensor 22 as in FIG. 3.

It could also be envisaged that the partial concealment means 24 are placed between the patient 3 and the conversion means 21 and that they are directly exposed to X-ray radiation. In this variant, the image sensor could be a d electronic image. In the example illustrated in FIG. 5, the image sensor is a light image sensor and the conversion means 21 are materialized by an IIR tube. The differences with the configurations described above are that now the partial concealment means 24 are exposed directly to X-ray 1 having passed through the patient 3 and comprise an opaque part 247 to X-ray and one or more parts 248 which lets it pass. It is assumed in this FIG. 5 that the partial concealment means 24 take the form of a disc which forms the opaque part 247 and that this disc is provided with windows 248 in the form of slots which allow the radiological image of the portion to pass through. irradiated 2 '. These partial concealment means 24 having to be partially opaque to X-rays are made from lead and require more powerful means to be moved and more expensive than in the previous variants. The previous examples illustrate the principles of matching a body part, irradiated at a given time by the X-ray beam which scans the body, with a corresponding light image part and with an electronic image part. corresponding, or directly with a corresponding electronic image part when the system directly converts X-rays into an electronic image without passing through a bright image. But these examples also show that this matching is done by mechanical means, essentially in the form of slots which move in synchronism with the scanning of the X-ray beam. The present invention proposes to use electronic means, synchronized with the movement of X-ray scanning, to produce an electronic image only in an area which, at a given time, corresponding to the area irradiated, by the X-ray in scanning motion. These means are static and advantageously replace the mechanical means described above, in the various configurations envisaged.

Two main achievements are planned. In the first, which is applicable when part of the chain of conversion of X-rays into an electronic image passes through a bright image, a liquid crystal screen is inserted between the bright image and an image sensor. This image sensor is preferably electronic (such as the CCD or CMOS matrix sensor of an electronic camera) but it can also be envisaged that it is a simple photographic film which will be exposed zone by zone as and as the X-ray scans, the areas of film not corresponding to the area irradiated at a given time being masked at that time. The liquid crystal screen is made opaque everywhere except in an area (in principle a matrix line if the scanning allows line-by-line irradiation) corresponding to the image effectively irradiated by the X beam. The light image sensor, if it is electronic, does not collect a signal, except in this zone. X-rays which may have been scattered in scattered directions and which may have produced a light image not limited to the irradiated portion, will not influence the electronic sensor because it will only observe an area truly corresponding to the portion irradiated. In the second major variant, applicable whether there is conversion into a light image before the image is collected by an electronic light image sensor or there is direct conversion of X-rays into an electronic image, provides that the electronic integration means which convert the light image photons or the X image photons into electrons are organized to prevent the integration or the reading of charges outside the image zone which corresponds to the zone irradiated at a given time by the scanning X-ray.

Typically, if a line (or possibly a few lines) of light or electronic image sensor is irradiated at a given instant, we arrange to empty the charges of these lines just before the irradiation begins (thus discharging the charges from unwanted scattered radiation), the charges resulting solely from the irradiation of the irradiated area are integrated, and these charges are read immediately after the irradiation time. Reference is first made to FIGS. 6 and 7 which illustrate the invention.

The partial concealment means 24 are produced by a networked shutter 245 with liquid crystals, the transmission of which is controlled by the position of the portion irradiated 2 ′ by scanning X-ray radiation 1. These partial concealment means 24 are used to stop the light from the output screen 206 of the radiological image intensifier tube 21.

This shutter 245 can comprise a thin layer 31 of liquid crystals (for example of the nematic helical type) sandwiched between two transparent blades 32, 33 sealed together, themselves placed between two crossed polarizers 36.

Such a shutter 245 operates in the following manner. At least one of the transparent plates is provided with an array of electrodes, making it possible to apply an electric field to portions of the layer of liquid crystals. This is why the shutter 245 is said to be networked. By subjecting part of the liquid crystal layer to an electric field, it becomes opaque and stops the light coming from the output screen 206. This light can no longer reach the light image sensor 22. In the absence of an electric field, this part is transparent and lets the light coming from the output screen 206. This light can thus reach the light image sensor 22.

In the example described and shown in detail in FIG. 7, there is shown on each transparent strip 32, 33 a network 34, 35 of parallel transparent electrodes E1, E2 oriented transversely to the direction of scanning of the X-ray radiation 1. A electrode E1 of a network 34 is paired with an electrode E2 of the other network 35 and two paired electrodes are opposite. Each network 34, 35 is connected to a control device 37, 38 respectively making it possible to apply to its electrodes E1, E2 an appropriate potential and therefore to subject the portion of liquid crystals located between two paired electrodes to an appropriate electric field. make it opaque. The control of the potentials to be applied to the electrodes produced in synchronism with the scanning makes it possible, at all times, to include in the shutter 245 made opaque a transparent area 246 whose dimensions are such that the light image sensor 22 does not pick up than the radiological image of the irradiated portion 2 '. The dimensions of the transparent zone 246 are modeled on those of the irradiated portion 2 ′ to the nearest coefficient of proportionality.

The electrode patterns described in FIG. 7 are only nonlimiting examples and others are of course conceivable to delimit what must remain opaque and what must become transparent. A pattern conventional matrix can be used, provided that the control means, in principle line by line, are organized so as to correspond with the nature of the scanning X used.

A significant advantage of the means for limiting the acquisition of the image sensor associated with an X-ray image intensifier tube, in the configuration where they are located between the output screen and the image sensor is that these means limitation not only eliminate the light from the X-ray scattered in the patient but also the scattered light and the X-rays scattered over the entire path between them and the patient. In their absence, this light or this X-ray would be captured by the image sensor and the contrast would be degraded. The best gains in contrast are obtained by placing the limiting means as close as possible to the light image sensor.

Instead of being external to the image sensor, the means for limiting its acquisition can be integrated therein. In this second solution, it is the electronic image sensor which collects only one useful image area at a given instant. These variants are illustrated in FIGS. 8a, 8b, 9a to 9c and 10 with solid state image sensors.

We refer to Figure 8a. As in FIG. 1, we find the scanning X-ray generator 10 which delivers the X-ray radiation 1 scanning the surface to be imaged 2 of a patient 3 to be examined. On the other side of the patient 3 is the detection system 20 according to the invention with a light image sensor 22. It includes means 21 for converting the X-ray radiation coming from the portions 2 ′ into a light image of the IIR tube type. associated with the light image sensor 22. Now the light image sensor 22 is an electronic sensor of the CMOS type included for example in a video camera 220. The means 240 for limiting the acquisition of the light image sensor are integrated into the bright image sensor. They can either prevent the acquisition of an image outside a determined zone (corresponding to the zone irradiated by the X-ray beam) or effect a reset to zero of the acquired image in a determined zone (a line of sensor for example or a few lines) just before collecting a desired image in this area, and again in synchronism with the scanning of the X-ray. CMOS type sensors of recent design are starting to be used. They are very promising because they consume much less than CCD sensors, are much less bulky, offer new possibilities in the acquisition of portions of images, can operate at speeds higher than those of CCD sensors and are of lower costs. In such a sensor, each pixel does not only include a photosensor element, for example a photodiode, but also a CMOS transistor circuit with a reading amplifier function, making it possible to quickly read the quantity of charges stored at the level of each pixel which has been exposed to a light signal. On the same substrate there are also means for digitizing the signals stored by the pixels and used during reading.

In the configuration of FIG. 8a and of FIGS. 9a to 9c, the light image sensor 22 is formed of a plurality of photosensitive sensitive points or pixels P1 to P9 arranged in a matrix and connected between a column conductor Y1 to Y3 and a line conductor X1 to X3. These pixels are symbolized by a square. Only nine have been shown so as not to overload the figure. After exposure to a light signal, the pixels P1 to P3 connected to the same line conductor X1 are addressed at the same time by an addressing device 400 connected to the line conductors X1 to X3, the amount of light they have received is read at each pixel, the data read for each pixel being transferred by the column conductors Y1 to Y3 in an analog-digital conversion device 401 operating in parallel to be digitized there. The means 240 limiting the acquisition of the image sensor 22, in a first phase, just before a portion 2 'is irradiated, control the reset to zero, that is to say the erasure of the pixels P4 to P6 of the sensor corresponding to the light image of said portion, and in a second phase, just after the portion 2 ′ has been irradiated, control the reading of the pixels P4 to P6 corresponding to this light image. To acquire the bright image of the surface to be imaged 2, all the pixels are subjected to this succession of erasure, exposure and reading states.

FIGS. 9a to 9c are used to describe the operation of the limiting means 240. It is assumed that the scanning of the X-ray radiation 1 takes place linearly as in FIG. 1 and that a line of pixels corresponds to a 2 'irradiated portion. The arrow entering the block 240 symbolizing the limitation means indicates that these means are synchronized with the scanning movement of the X-ray.

In FIG. 9a, the line conductor X2 to which the pixels P4 to P6 are connected carries an arrow coming from the addressing device 400, which symbolizes that they have just been erased or set to zero. They have been cleared of all traces of previous exposure. The pixels P1 to P3 are exposed and are shown grayed out while the pixels P7 to P9 are read, which is symbolized by arrows on the column conductors Y1 to Y3 originating from the pixels P7 to P9 and directed towards the conversion device analog-digital 401.

In FIG. 9b, the pixels P4 to P6 are grayed out, which means that they have just been exposed to an illumination delivered by the radiological image intensifier tube. The pixels P1 to P3 are read, which is symbolized by arrows on the column conductors Y1 to Y3 coming from the pixels P1 to P3 and directed towards the analog-digital conversion device 401. The pixels P7 to P9 are erased which is symbolized by the arrow, coming from the addressing device 400, and carried by the line conductor X3 to which the pixels P7 to P9 are connected. In FIG. 9c, we wanted to illustrate the fact that the pixels P4 to P6 are read at this instant while the pixels P1 to P3 are erased and that the pixels P7 to P9 are exposed. The same symbols as before were used. In this way, the signals read do not include a broadcast.

• In FIG. 8b, we find, as in FIG. 1, the scanning X-ray generator 10 which delivers the X-ray radiation 1 scanning the surface to be imaged 2 of a patient 3 to be examined. On the other side of the patient 3 is the detection system 20 according to the invention. There is no IIR tube. It comprises an image sensor 22, 52 in the solid state which can be either of the light image sensor type 22 or of the electronic image sensor type 52. Its dimensions are substantially those of the surface to be imaged 2. The sensor cooperates with means 21, 51 for converting the X-ray radiation coming from the portions 2 ′ either into a light image or into an electronic image. If it is a conversion into a light image, the conversion means 21 are of the scintillator type which cover the light image sensor 22. If it is a conversion into an electronic image, the conversion means 51 are made from selenium which covers the electronic image sensor 52. The conversion means 21, 51 are directly facing the X-radiation which has passed through the patient. The light image sensor 22 can be a sensor whose pixels are formed formed of a photosensitive diode cooperating with a switch. This type of sensor is well known in digital radiology. The electronic image sensor 52 can be as shown in FIG. 10. The means 240 for limiting the acquisition of the image sensor are integrated into the image sensor 22, 52 and entirely comparable to what has has been described in FIG. 8a. The sensitive elements of the sensor are subjected to a succession of states: erasure or reset, exposure, reading.

Referring to FIG. 10, the electronic image sensor 52 is formed by a plurality of points 53 sensitive to electronic charges, each formed by a capacitive element 54 associated with a switching element 55 for example a TFT transistor ( for the Anglo-Saxon name Thin Film Transistor) activated in particular during reading, arranged in a network in the manner of the representations in Figures 9. These sensitive points are produced in particular using the technique of depositing thin films of semi-material conductors such as amorphous silicon. This electronic image sensor 52 cooperates with means for converting radiological image-electronic image based on selenium for example. The sensitive points are covered with a layer 51 based on selenium. By crossing the selenium-based layer 51, the X-ray radiation is directly converted into electronic charges (symbolized by an arrow). These electronic charges are stored on the capacitive elements 54. The means for limiting the acquisition of the electronic image sensor operate in a manner comparable to what has been described in FIGS. 8a and 8b. The charges stored „on the capacitive elements 54 are read sequentially line by line. By carrying out an operation of resetting the capacitive elements 54 of a line just before they receive electronic charges and an operation of reading the charges stored in these capacitive elements just after they have received charges, one achieves to eliminate the signal linked to the x-rays scattered in the acquisition of the radiological image. Instead of resetting a line to zero before subjecting it to light irradiation or X-ray irradiation, it could be envisaged to prevent the integration of photogenerated charges outside a determined line and to allow it only in the selected line. Finally, it should be noted that, in particular in the medical field, there is a tendency to replace the radiological image intensifiers (empty tubes) with solid state detectors, possibly of large dimensions, and that it is therefore possible directly adapt this observation limitation solution to a determined area in correspondence and synchronism with an X-ray scan.

The examples described are not limiting as regards the choices of association between the image sensor, the conversion means and the means limiting the acquisition of the image sensor, other combinations are possible without departing from the scope of the invention.

Claims

1. A radiological image detection system capable of cooperating with a scanning X-ray generator (10) intended to produce X-ray radiation (1) scanning a surface to be imaged (2), this X-ray radiation (1) irradiating portion ( 2 ′) after portion the surface to be imaged (2), the X-ray radiation from a portion (2 ′) carrying a radiological image of said portion, characterized in that it comprises an image sensor (22 , 52) which is stationary with respect to the scanning and which is dimensioned so as to be able to acquire an image of the entire surface to be imaged (2) via the X-ray radiation coming from the portions (2 ′), the detection system further comprising means electronic to limit, at a given instant, the acquisition of the image sensor (22,52) to an area corresponding to the irradiated portion (2 ') at this instant, these limiting means acting in synchronism with the scanning and in geometric correspondence with the irradiated portion (2 ').

2. Image detection system according to claim 1, characterized in that the image sensor is a light image sensor (22) and in that it cooperates with means for converting the X-ray radiation from the portions (2 ') in bright image.

3. Image detection system according to claim 2, characterized in that the means (24) for limiting the acquisition are produced by a network liquid crystal shutter (245), fixed relative to the image sensor ( 22) light and interposed between the means for converting the X-ray into a light image and the light image sensor.

4. Image detection system according to one of claims 1 and 2 characterized in that the means (240) for limiting the acquisition of the image sensor (22) are integrated into the image sensor.

5. An image detection system according to claim 4, in which the image sensor (22) is formed from a plurality of photosensitive pixels. the solid state, characterized in that the means (240) for limiting the acquisition of the image sensor (22) control, just before a portion is irradiated, an erasure of the pixels of the sensor corresponding to the light image of said irradiated portion, and a reading of said pixels just after the irradiation of said portion.

6. Image detection system according to claim 4, in which the electronic image sensor is formed of a plurality of capacitive elements (54), characterized in that the means (240) for limiting the acquisition of the image sensor (52) control, just before a portion (2 ') is irradiated, a resetting of the capacitive elements (54) corresponding to the electronic image of said irradiated portion and a reading of the charges stored in said capacitive elements (54) just after the irradiation of said portion (2 ').

7. Detection system according to one of claims 1 to 4, characterized in that the image sensor (22, 52) is of the solid state type and in particular of the CCD type, of the CMOS type, with photosensitive diodes, with elements capacitive.

8. Detection system according to claim 2, characterized in that the means (21) for converting the X-ray into a light image are of the radiological image intensifier or scintillator type.

9. Image detection system according to claim 1, characterized in that the image sensor (52) is an electronic image sensor and in that it cooperates with means (51) for directly converting the radiation X from portions (2 ') in electronic image.

10. Detection system according to claim 9, characterized in that the means (51) for converting the X-ray into an electronic image are produced on the basis of selenium.

11. Detection system according to one of claims 1 to 10, characterized in that it comprises means (23) for processing the image captured by the image sensor (22) so as to reconstruct a complete image of the radiological image of the surface to be imaged from images of the irradiated areas.

12. Detection system according to one of claims 1 to 3, characterized in that the light image sensor is of the photographic film or cinematographic film type.