Abstract:
Collimation device of the type intended to direct an energy beam in a given direction and at a given solid angle, the collimation device being capable of being installed on output of an energy beam generating means and of being connected to a control unit. The collimation device includes means for testing operation of the assembly formed by the energy beam generating means, the collimation device and the control unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 0007745 filed Jun. 16, 2000, the entire contents of which are incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention concerns the field of electromagnetic radiation beams used for different types of measurement and visualization. The invention is applicable notably to X-ray imaging or processing devices, for example, in the medical field.  
           [0003]    A radiology apparatus generally comprises means for an X-ray emission having equipped with an X-ray tube and a collimator, means for receiving the X-ray emissions separated from the means for emission by a distance sufficient to place there an object that it is desired to study. The collimator serves to determine the solid angle of aperture of the X-ray beam. The X-ray beam can thus be limited to the surface of the receiver. The collimator can also serve to further reduce the solid angle of the beam in order to limit it to a particular zone of interest of the object that is studied or processed, which makes it possible to prevent other parts of the object from being subjected to X-rays. The collimator can include a diaphragm made according to the principle of the diaphragm of a camera of articulated moving plane type. A diaphragm whose attenuating material consists of a deformable solid or of a fluid in a chamber is also disclosed in FR-A-2,601,544.  
           [0004]    In addition, a radiology apparatus further comprises an electronic control unit for the X-ray tube, collimator, receiver (provided, for example, with a scintillator), a high-voltage supply of the X-ray tube, etc.  
           [0005]    Such an apparatus must be calibrated in order to attain a sufficient qualitative and quantitative precision of the structures observed on an image. The calibration is generally done by means of a phantom that is placed at the object site on the path of the X-ray beam. A phantom is an object separate from the apparatus and comprising parts opaque to X-rays arranged according to a geometry defined and known. An image of the phantom is acquired under the geometric conditions of an angle of incidence that it is sought to be calibrated. The projections of the characteristic points are then recognized in the image. Each characteristic point of the object is associated with its trace in the acquired image. The system of equation describing the projection supplying the image is inverted in the mathematical sense and the set of parameters of the projection is finally obtained for the given vantage point. A phantom and method of calibration of an X-ray imaging system is disclosed in FR-A-2,700,909 and EP-A-0,874,536.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0006]    An embodiment of the present invention is directed to increasing the automation of calibration of a system using electromagnetic radiation. An embodiment of the present invention proposes controlling the calibration. Tan embodiment of the present invention proposes a phantom whose risks of deterioration are reduced.  
           [0007]    A collimation device, according to one embodiment of the invention, is of the type intended to direct an energy beam in a given direction and at a given solid angle. The collimation device is capable of being installed on output of an energy beam generating means and of being connected to the control unit. The collimation device includes means for testing operation of the assembly formed by the energy beam generating means, the collimation device, the control device and a receiver. The means can be integrated with the device, for example, by being adjacent to the collimation elements. The means can be connected to the control unit directly or indirectly. The collimation device advantageously includes means for calibrating the operating parameters intended to be used by the control unit. In an embodiment of the invention, the collimation device includes means for testing the operation of an X-ray tube emitting the energy beam. The means are preferably capable of being commanded by a control unit. In an embodiment of the invention, the means are capable of being remote-controlled by a computer installed on another site.  
           [0008]    In an embodiment of the invention, the means include a plurality of test tools with a position sensor of each tool. The collimation device can include a motion sensor of each tool. The progress or temporal change of the calibration can then be monitored.  
           [0009]    A radiology apparatus, according to one aspect of the invention, means for emitting an energy beam means of reception for the energy beam, a control unit and a collimation device, such as described above.  
           [0010]    A test kit, according to one embodiment of the invention, includes means for fastening to a collimation device, of the type designed to direct an energy beam in a given direction and at a given solid angle and means for testing the operation of the collimation device means for emitting energy beam and a control unit. The test kit can advantageously be equipped with means for communicating with the control unit. The test kit is therefore capable of being fastened to collimation device, notably, below the latter in the direction of propagation of the energy beam. The test kit can be fastened on a collimation device with little or no structural modifications.  
           [0011]    The invention also proposes a method for testing a radiology apparatus, in which the operation of the apparatus is tested by means of tools forming part of a collimation device, the tools making it possible to functionally define the operation of the means for emitting an energy beam of the collimation device and of a receiver.  
           [0012]    The invention is also directed to a computer program including means for providing a program code for applying the steps of the above-mentioned method.  
           [0013]    The invention likewise is directed to a storage medium capable of being read by a device for reading the program code which are stored there in and which are capable of applying the steps of the abovementioned method.  
           [0014]    The invention also makes possible a remote control of the quality of operation of an apparatus, notably of a radiology apparatus, by making possible a calibration remote-controlled from a maintenance center, for example, with telecommunication through an Internet-type network, or an automatic calibration at given time intervals or operating times, while providing for the possibility that a negative result of automatic calibration might trip an alarm in a maintenance center which can also be remotely situated.  
           [0015]    For that purpose, the collimation device may comprise: one or more lead plates for calibration of the X-ray tube that is done by emitting X-rays; one or more copper plates for calibration of the gain response of the entire information processing system formed by the apparatus, which makes it possible to characterize, notably, the aging of the X-ray tube; one or more aluminum plates for spectral characterization of the X-ray beam and dose measurement. Several aluminum plates will preferably be provided to determine at what thickness of aluminum the dose is divided by a given factor; one or more wires of radiation-absorbent material; one or more grids of radiation-absorbent material; one or more plates of radiation-absorbent material of thickness calibrated in steps to make calibration of the image quality possible.  
           [0016]    The persistence or kinetic blur due, for example, to the scintillator, which continues to emit an output signal when the input signal (X-rays) has been interrupted can be calibrated. The progress of presistence is monitored by placing one or more test objects in the beam, automatically controlling the speed and position of the test objects. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    An embodiment of the invention is illustrated by the attached drawings in which:  
         [0018]    [0018]FIG. 1 is a schematic view of a collimator;  
         [0019]    [0019]FIGS. 2, 4,  6  and  7  are schematic views in perspective of test tools;  
         [0020]    [0020]FIG. 3 is a schematic view of a test kit;  
         [0021]    [0021]FIG. 5 is a schematic side view in elevation of the test tool of FIG. 4;  
         [0022]    [0022]FIG. 8 is a diagram of steps of operation; and  
         [0023]    [0023]FIG. 9 is a diagram of an architecture of a radiology apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    In FIG. 1, a collimation device  1  comprises a casing  2  provided with an inlet  3 , an outlet  4  and a plurality of moving plates  5  to  12  opaque to X-rays. Plates  5  to  12  provide a collimation according to a rectangular format of an X-ray beam  13  represented by a line of dots and dashes being propagated on an axis  14 . The beam emanates from a focus  15  situated in an X-ray tube not represented. Collimation makes it possible to adapt the beam to the shapes of rectangular detectors of film, scintillator and CCD camera type, or solid state detectors, or organs crossed by the X-ray beam.  
         [0025]    The collimation device  1  also includes an additional casing  16  placed in contact with the lower aperture  4  of casing  2  and also arranged to be transparent to X-rays. Inside casing  16 , there is a disk  17  rotary-mounted and driven by a motor  18 , the rotation being detected by a sensor  19 , for example, of optical type reading an optical coder, not represented, which can comprise a sequence of alternate light and dark zones arranged on the upper surface of the disk  17 , close to its periphery, opposite the sensor  19 .  
         [0026]    An embodiment of the disk  17  is illustrated in FIG. 2. The disk  17  comprises a plurality, for example seven, of circular zones  22  to  28 . The diameter and the positioning of the circular zones  22  to  28  on the disk  17  are such that the X-ray beam  13  illustrated in FIG. 1 presents a diameter slightly less than that of one of the circular zones  22  to  28 , when it crosses one of the circular zones  22  to  28 . Circular zone  22  is empty and is used in normal operation of a radiology apparatus, for example, on taking an X-ray image of a patient. Circular zone  23  is an aluminum plate of given thickness that allows testing of the variation of spectral quality due to aging of the X-ray tube, which makes it possible to determine when it is advisable to change the tube in order to avoid a shutdown of the radiology apparatus due to a malfunction. The information on change of spectral quality can also be used for calibration of the exposure parameters, such as high service voltage of the X-ray tube, service current, etc. Circular zone  24  comprises a two-dimensional phantom such as a metal grid of given material and thickness. Circular zone  25  also comprises a phantom, for example, in the form of a sheet with defined beveled edges. Those two phantoms make possible an evaluation of image quality. Circular zone  26  comprises a plate of heavy metal, for example, 2 mm thickness of lead, which makes it possible to totally block the X-ray beam. Circular zone  27  comprises a copper plate of given thickness, for example, 2 mm. Circular zone  28  also comprises a copper plate of different thickness from circular zone  27 . Both circular zones  27  and  28  can be used for calibration of the X-ray dose without it being necessary to use a dosimeter.  
         [0027]    A motor  18  for turning the disk  17  on instruction of the radiology apparatus control unit  20 , allows the different steps of calibration to proceed automatically. The intervention of an operator can be reduced to the decision to initiate calibration. The operator can be located on site or at a remote maintenance center connected by digital link to the radiology apparatus. Calibration can also be carried out automatically, for example, outside of normal working hours of the radiology apparatus and the necessary adjustments of the parameters of the radiology apparatus can be made while being able to signal a fault requiring attention by means of a local alarm and/or to a remote maintenance center. A sensor  19 , makes it possible to ascertain the position and possibly the speed of rotation of the disk  17 , is also connected to the control unit  20  of the radiology apparatus.  
         [0028]    As can be seen in FIG. 1, the control unit  20  is joined by a wire connection  21  to the operation test means formed by the casing  16  equipped with the disk  17 , motor  18  and sensor  19 . However, a wireless link or even a connection through casing  2  could also be provided. The control unit  20  can be dedicated to the operation test means, or dedicated to the collimation device  1 , or can form a central control unit of the radiology apparatus to which the collimation device  1  is a part. The control unit  20  includes at least one processor, at least one memory and at least one set of control instructions stored in memory and capable of being executed by the processor.  
         [0029]    Casing  16  and casing  2  can be interlocked, for example, by means of screws, not represented. Casings  2  and  16  can also be made in a single unit. If casing  16  is separate from casing  2 , it can be arranged to add an operation test means to the collimation device in the existing radiology apparatus, as shown in FIG. 3. In the latter case, the test means may be in the form of a test kit  29  having a general shape similar to the test means of the embodiment of FIG. 1 and provided, in addition, with two lugs  30  and  31 , each provided with a screw  32 ,  33  capable of cooperating in corresponding tapped holes of a collimation device casing.  
         [0030]    In FIGS. 4 and 5, another test tool is illustrated, which can be placed inside a test means casing. The tool  34  has a cylindrical structure  35  around which is placed a plurality of rectangular elements  36  comprising the same type of elements as the circular zones  22  to  28  illustrated in FIG. 2.  
         [0031]    In the embodiment illustrated in FIG. 6, a test tool  37  comprises a plurality of square test elements  38  to  41 , each hinged at an angle on an axis  42  ready to be placed on the path of an X-ray beam  43  that is represented here as a beam of parallel lines.  
         [0032]    Of course, in both of the foregoing embodiments, the rotation of the tool  34  and of elements  38  to  41  of the tool  37  is motor-driven and monitored by sensor(s) so that the control unit receives information on the position and possibly the movement of these different elements.  
         [0033]    In the embodiment illustrated in FIG. 7, the test tool  44  comprises two blocks  45  and  46  made of a given radiation-absorption material and each having a half-parallelepiped shape cut along a diagonal. The two blocks  45  and  46  complement each other, in the sense that, on bringing them in contact, a rectangular parallelepiped is formed. The X-ray beam  43  crosses the two blocks  45  and  46 , the spacing of which determines the thickness of material crossed by the X-ray beam  43 . The relative position of the blocks  45  and  46  is detected by sensor and is controlled by means of a motor.  
         [0034]    Different steps used by a radiology apparatus control unit are illustrated by way of example in FIG. 8 by means of a routine stored in an internal memory of the control unit or outside the control unit.  
         [0035]    At step  50 , a routine of the control unit, which is dedicated to calibration, verifies the time elapsed since the last calibration and compares it with a predetermined ceiling. If the time elapsed is greater than the ceiling, one then proceeds to step  51 ; otherwise the program is halted in order to be resumed later, for example, the next day at the same time or after a few minutes of non-use of the radiology apparatus. At step  51 , the program controls the movement of a test tool and, by considering the disk  17  of FIG. 2, the positioning of circular zone  23  in place of circular zone  22 , which is empty, on the path of the beam  13 . Then, a standard calibration is carried out with the circular zone  23 . At steps  52  to  56 , the program controls the corresponding operations for circular zones  24  to  28 .  
         [0036]    At stage  57 , the routine controls the movement of the disk  17 , so that circular zone  22 , which is empty, is placed on the path of the beam  13 . If, in the course of one of steps  52  to  56 , calibration reveals a fault which the control unit cannot remedy by itself, the program controls an alarm stage  58  either on site, for example, on a screen of the radiology apparatus, or at a remote maintenance center, the alarm being advantageously accompanied by a message relating to the nature of the fault, its seriousness, a down time of the radiology apparatus, etc. Otherwise, calibration is terminated and the time elapsed since the last calibration is reset at step  59 .  
         [0037]    In FIG. 9, the radiology apparatus comprises, in addition to the central unit  20  and collimation device  1 , an X-ray tube  60  integral with the collimation device  1 , a high-voltage generator  61  for powering the tube  60 , a receiver  62 , provided, for example, with a scintillator and a matrix camera, and a monitor  63  provided with a screen  64  for the display of X-ray images.  
         [0038]    The present invention makes it possible to design tools for automatic testing of an electromagnetic ray imaging and processing apparatus. The test tools can come in the form of a kit that is added to an existing collimator or can be integrated with a collimator. Remote image quality control can thus be carried out with diagnosis in real time and preventive maintenance. The test tool rests permanently on the imaging apparatus and possesses a deactivated position in which the beam of electromagnetic rays does not encounter any obstacle. The image taken in normal operation of the imaging apparatus does not therefore undergo any attenuation or diminution of quality.  
         [0039]    It is important to know precisely the movement of a tool across the beam in order to be able to deduce therefrom an estimate of the remanence and to monitor the progress of remanence in the course of time, that is, aging of the receiver  62  and, notably, of the scintillator. For that purpose, a tool will be moved in a few milliseconds in the X-ray beam intermittently and at constant speed.  
         [0040]    The radiology apparatus whose control unit is connected to the test tool is advantageously provided with a remote link, digital, for example, to a maintenance center, which makes it possible to perform a number of maintenance operations without the service call of a maintenance operator.  
         [0041]    Other maintenance operations can be carried out with the service call of a maintenance operator, who will have identified the component to be replaced before his trip, which will also make it possible to reduce the number of trips.  
         [0042]    The handling of a phantom separate from the apparatus becomes superfluous, which reduces the risks of loss or deterioration of the phantom likely to distort the calibration.  
         [0043]    Various modifications in structure and/or steps and/or function may be made by one skilled in the art without departing from the scope and extent of the invention as recited in the claims.