WO1991009567A1

WO1991009567A1 - Method and installation for determining an intervention straight line segment in a non homogenous structure

Info

Publication number: WO1991009567A1
Application number: PCT/FR1990/000939
Authority: WO
Inventors: Jean-Baptiste Thiebault; Michel Scriban; Jean-François UHL
Original assignee: Diadix S.A.
Priority date: 1989-12-22
Filing date: 1990-12-21
Publication date: 1991-07-11
Also published as: JPH05508082A; FR2656211A1; FR2656211B1; EP0506810A1

Abstract

In order to determine an intervention straight line segment (PE-PC) in a non homogenous structure from an input point in the structure, a first radioscopic image (I1) of the structure is effected in a plan parallel to an estimated direction of the segment and of non position with respect to a fixed reference system. Said image is digitalized, stored and displayed; tracings are effected on the image which tracings represent a reference plane (P1) wherein must be situated the segment and of its boundaries; coordinates of the reference plan and of the boundaries in the fixed reference system are determined in stored by means of said non position and said tracings. Said coordinates and a sighting means (100, 110) integral with the radioscopy device, a second image (I2) of the structure is obtained, which is situated in a plane perpendicular to the plane of the first image and to the reference plane, and such that the sighting means aims at the region of the input point. Said second image is digitilized, stored and displayed; a reference center (CR) corresponding to the sight is also displayed; an authorized passage area (PD) for the intervention is identified; the radioscopy device is displaced by servo-controlling thereto a displacement of the image with respect to the reference center in order to center said center to the area; the sight direction (DV) providing then the direction of the segment, while its length is provided by said coordinates.

Description

METHOD AND INSTALLATION FOR DETERMINING A RIGHT OF INTERVENTION SEGMENT IN A NON-HOMOGENEOUS STRUCTURE

The present invention relates generally to the field of assistance with local intervention within a non-homogeneous structure.

It relates more particularly to a method for determining an optimal line segment for intervention in such a structure, from a determined entry point, and an installation for its implementation, using only the radioscopic technique. Here, by radioscopy, we mean any device comprising an X-ray source and an X-ray sensor capable of delivering an electrical signal representative of the image formed as a function of the attenuation of the rays by the non-homogeneous structure. In the prior art, an X-ray radioscopy device conventionally comprises a mobile carriage housing the power source and supporting the base of a hoop. The generally semicircular arch comprises at one end the X-ray source and at the other end the X-ray sensor, such as an image intensifier or the like, intended to form a video image as a function of the attenuations undergone by rays having passed through the non-homogeneous structure (for example an area of a patient's body). The video image is displayed on a monitor located in the vicinity of the device.

Also known, for example from DE-A-2 108 657 and EP-A-0 269 801, radiographic tracking devices in which the position of an radiographic device is permanently identified with respect to a fixed frame of reference. Thus, using two images, one can determine the coordinates in the fixed frame of reference of an area such as an area to be treated.

But in these two patents, it is assumed that two radiographic images can be produced from any point of view, and in particular in two planes perpendicular to each other and essentially parallel to an estimated direction of intervention, so extremely easily determine the coordinates of this direction for subsequent intervention. However, in certain situations, there are constraints regarding the taking of images. For example, in view of the intervention on a vertebra or the like, one can only make frontal cuts and saggital cuts, that is to say that one can only take a single view in a parallel plane to the estimate of the intervention direction. The devices of the aforementioned patents are incapable, in such a context, of precisely determining a segment of intervention line. The present invention aims to overcome these drawbacks of the prior art and to propose a method and an installation for assistance with intervention in a non-homogeneous structure which makes it possible to provide the operator with precise coordinates as to a straight line segment d 'intervention, in the kind of situation mentioned above, while considerably minimizing the doses received by the structure.

To this end, it first proposes a method for determining an intervention line segment inside a non-homogeneous structure from an entry point into the structure, using a movable radioscopy, characterized in that it comprises the stages consisting in: producing a first radioscopic image of the non-homogeneous structure, located in a plane essentially parallel to an estimated direction of the line of intervention and position known by compared to a fixed frame of reference, digitize this first image, store it in memory and display it on a screen, carry out on the first image present on the screen geometric lines deduced from this image and representative of a reference plane in which the intervention line segment and the limits of this segment must be located, determining, from the known position data of the first image and of said plots, coordinate data of said plane of reference and said limits in the fixed reference frame, and memorize them, using said coordinate data and a sighting means secured to the radioscopy device, to produce a second radioscopic image of the non-homogeneous structure, situated in a plane perpendicular to the reference plane and arranged substantially transversely to the plane of the first image, and such that the sighting means targets the region of the entry point and the sighting direction (DV) of said sighting means is a first estimate of the direction of the line segment intervention, digitize this second image, put it in memory and display it on the screen, also display a screen on the screen reference frame corresponding to the aiming direction of said aiming means, identify on the second image a passage area authorized for the intervention, move the radioscopy device and enslave therein a relative displacement of the reference center and of said second image, in such a way that the reference center is essentially centered on said authorized passage area, the sighting direction then providing the direction of the line of intervention, while the length of said segment is provided by said coordinate data.

In a first embodiment, the step of moving the radioscopy device is carried out manually. In a second embodiment, the method comprises, between the step of identifying the authorized passage area and the step of moving the radioscopy device, the additional step consisting in performing another image on the second image. path representative of the center of the authorized passage area, while the step of moving the radioscopy device is carried out automatically as a function of the mutual positions of the reference center and of said path of the center of the authorized passage area.

Advantageously, there is also provided the step consisting in determining from the position of the radioscopy device, following the displacement step, second coordinate data, the first and second coordinate data being stored to define reference data for the intervention line segment.

In order to assist the operator in the subsequent intervention, it is particularly preferable to also provide for the step consisting of simultaneously displaying on the screen said fixed reference frame in three dimensions as well as the first and second digital images, positioned relative to said reference frame. and shown in perspective. The present invention also relates to an installation for determining a line segment of intervention inside a non-homogeneous structure from an entry point into the structure, characterized in that it comprises: a device movable radioscopy, means for controlling the movements of the radioscopy device with respect to a fixed reference frame, digitization means for digitizing radioscopic images supplied by the radioscopy device, means for storing and displaying on a screen said radioscopic images, graphic tracing means for carrying out plots on the displayed images, sighting means integral with the radioscopy device and indicating the instantaneous direction of sighting of said device and to which corresponds on the screen a reference trace, means for controlling the position of the radioscopic image relative to the reference trace as a function of the displacements of the radioscopy device, means for determining from position data of the detection device radioscopy and of said plots of geometric data relating to the intervention line segment, a first radioscopic image making it possible to determine a reference plane in which the intervention line segment is contained, as well as the limits of said segment, while a second image, perpendicular to the plane of the first image and to the reference plane, and co corresponding to an aiming direction which is an estimate of the direction of the line of intervention, makes it possible, by servo-control of its position as a function of the movements imparted to the radioscopy device using the aiming means, to determine the position of the segment in the reference plane.

Most preferably, the sighting means comprises a laser beam located on the x-ray axis of the radioscopy device and emitted from an x-ray emitter and / or an x-ray receiver of the device x-ray.

The installation can advantageously be coupled to a servo-controlled intervention tool holder. Other aspects, aims and advantages of the present invention will appear more clearly on reading the following description. Figure 1 is a combined perspective / block diagram view of an installation according to the present invention, Figure la is a partial detail view of the installation of Figure 1, Figure 2 is a horizontal section through a human vertebra, FIG. 3 is a diagrammatic view of part of the installation of FIG. 1 and of a patient's body, in a first relative position, FIG. 4 schematically represents a radioscopic image obtained in the relative position of FIG. 3, FIG. 5 is a schematic view similar to FIG. 3, in a second relative position of the part of the installation and of the patient, FIG. 6a schematically represents a radioscopic image obtained in the relative position of FIG. 5, FIG. 6b is represents the radioscopy of FIG. 6a in an offset position, FIGS. 7, 7a and 7b are sectional views similar to FIG. 2, corresponding to three situations of which cell es of Figures 6a and 6b, and Figure 8 illustrates a screen representation of two x-rays.

It will first be indicated that, from one figure to another, identical or similar elements or parts are designated by the same reference numbers. We will first describe with reference to Figure 1 an installation according to the present invention.

The installation conventionally includes a fixed operating table TO, associated with a also fixed reference frame [0, x, y, z], denoted Ro, where Ox is the direction transverse to the table, Oy is the vertical direction and Oz is the longitudinal direction of the table.

A mobile radioscopy device, generally indicated at 10, comprises a frame 11 capable for example of sliding along a rail 12 fixed to the ground and extending in the longitudinal direction of the table TO. The frame 11 carries a part 13 which is movable in a plane perpendicular to the direction of the rail 12 (using for example slide means not shown) and which itself carries a base of a hoop 14 of form general semicircular by means of an arm 14a. The roll bar comprises at one end a source of X-rays 15 and at the other end, opposite, a receiver 16 of X-rays, in this case an amplifier of - _| 5 brightness which makes it possible to reconstruct an x-ray of a part of the body of a patient arranged between the source 15 and the receiver 16 in the form of a video image. The central axis of the X-ray emission and reception is indicated in DV. ( _j Such an image intensifier is capable of delivering to a display screen or monitor 17 an appropriate video signal to display the radioscopic image on the screen.

In the prior art, the assembly 5 comprising the hoop 14, the source RX 15 and the receiver RX 16 is mounted on a trolley on wheels entirely independent of the table TO, and there is in this case no possible geometric correlation between the position of the fluoroscopic device and the Ro reference frame. _Q According to a first essential aspect of the present invention, the radioscopic device 10, made up of the elements described above, is designed so that its various movements are referenced with respect to the Ro reference system, using servo motors of _b positioning in association with position sensors of any suitable type. Preferably, the RX source 15 and the receiver 16 facing each other can be driven jointly according to six degrees of freedom (translations along x and y and z and rotations around these axes). More precisely, the frame 11 can slide in a regulated and controlled manner along the rail 12 in the longitudinal direction of the table (axis Oz), while the part 13 which carries the arch can be adjusted in the vertical directions (Oy ) and transverse (Ox) to the

'û table using slide means or the like not shown. In addition, the arch support arm 14a is mounted on the part 13 of the frame by means of a ball joint 18, which allows it to pivot around two axes respectively parallel to Ox and Oy. Finally

^ the arch 14 is capable of pivoting around a fictitious center (point CF) by a mutual ent slide between said arch and a termination 14b in the form of an arc of a circle of the arm 14a.

The means used concretely to achieve

This controlled movement command and the position measurements associated with six degrees of freedom are conventional means, which will not be described here in order to avoid adding to the description.

According to another aspect of the invention, provision is made

25 a computer 20 of conventional type which includes as specific elements a high resolution display screen 25 as well as a tool 28 for carrying out graphic plots on the screen. Such a tool 28 can consist of a mouse, a digitizing tablet or

3ύ other equivalent means.

The other components of the computer 20 are neither described nor shown, since they are well known.

The computer 20 is also connected to the servo motors of the device 10, for controlling them,

35 via an interface 23 and electrical conductors 24. In addition, the position sensors correspondents are connected to the computer 20 via a line with several conductors 21 and an interface 22.

The image intensifier 16 is also connected to the computer 20 via a digitizer 26, of a type known per se, capable of converting the video output signal of said image intensifier into a set of digital image signals capable of being stored, processed and displayed by the computer 20, equipped with appropriate image processing software.

As a variant, it is possible to replace the assembly constituted by the image intensifier 16 and the digitizer 26 by a sensor of the "CCD" type (Charge Coupled Device or charge transfer system) sensitive to X-rays, known per se in technique, suitable for outputting digital image signals which can be applied to the computer 20 via a simple interface. More precisely, and as will be seen in detail below, the computer 20 is capable of producing on the screen 25 either full-screen radioscopic images, in two dimensions, or even a "two and a half dimensions" view showing on the one hand the axes of the fixed reference frame Ro in three dimensions and on the other hand digitized fluoroscopic images contained in image plans displayed in perspective and positioned with respect to the frame of reference Ro, using the information provided by the various position sensors to determine the position and orientation of these plans in relation to said fixed reference system. These sensors give the complete coordinates of the X-ray source and of the image intensifier as well as of the direction of emission DV of the X-rays, and it is easy to derive the coordinates of each image plane in the repository Ro to ensure the positioning of this plane in said reference frame.

According to another aspect of the present invention, the radioscopic device 10 comprises means for aiming and / or materializing an axis intended in particular to allow the alignment of the DV axis of emission / reception of X-rays at a given point.

In the present example, and now with reference to FIG. 1 a, these means comprise a source of low power laser beam 100 associated with optical means designed so that this beam is superimposed on the axis DV of the transmission / reception of X-rays. Such a beam can be emitted from the X-ray source and / or from the image intensifier. In the present example, these optical means consist of a mirror made of a material inert with respect to X-rays and oriented at 45 ° with respect to the DV axis of the X-rays and interposed on their path, the source 100 emitting the beam from the side towards this mirror. As a variant, one can imagine a means of the riflescope type in which the operator observes the superposition of a test pattern and the area of the non-homogeneous structure, the test pattern comprising at least one central reference materializing the axis of the rays X. The aiming means have the advantage, inter alia, of making it possible to frame the radioscopy device in such a way that the central part of the rays is located on the area of greatest interest of the non-homogeneous structure. This makes it possible to work with areas of the image having the lowest distortion, as opposed to the edge areas of the image in which the distortion can be very large.

In association with the sighting means, means are provided for a screen center to appear on the screen on each radioscopic image (digitized image on the screen 25 and possibly video image on the screen 17). reference (for example a central cross) corresponding to the trace on the image of the direction of aiming DV).

Finally, the computer 20 is capable of creating a control of the relative displacements between the reference center and the image displayed on the displacements of the radiographic device 10; for example, the image can remain fixed on the screen, while the reference center is moved by an appropriate graphic program as a function of the signals supplied by the position sensors of the device 10. In this case, this prevents the computer 20 has to perform a large number of calculations necessary for the controlled displacement of the image. But as a variant, it is of course possible to move the image and leave the center of reference fixed.

We will now describe with reference to FIGS. 2 to 7 an example of application carried out using the installation described above in order to determine a certain number of parameters useful in the context of the installation of a nail or screw in the pedicle of a vertebra.

These parameters essentially consist of the length of the nail to be implanted as well as in the direction in which the implantation must be carried out from an entry point either predetermined, or of which at least one of the coordinates constitutes a parameter to determine.

There is shown in Figure 2 a schematic horizontal section of a vertebra V, comprising a vertebral body CV and two pedicles respectively left and right, PG and PD, located on either side of the spinal cord ME.

In a manner known per se, the consolidation nail must be introduced from an entry point PE located _SU r the posterior face FP of the vertebra, passing through one of the pedicles (here PD) most centrally possible and as parallel as possible to the general direction thereof, on the one hand to avoid any risk of breakage or cracking of the pedicle if the nail passes too close to its edges, and on the other hand in order to Avoid any risk of injury to the spinal cord or neighboring organs if the nail comes out laterally from the pedicle.

The optimal direction for positioning a nail is indicated by the dashed line DI (Direction u Implantation) in Figure 2.

On the other hand, it is necessary to determine on the optimal axis DI a point located in the vertebral body CV and that the front end of the nail must not exceed. Thus, FIG. 2 shows a target point 5 PC, located at a substantial distance from the anterior limit of the vertebral body, which is the point at which the point of the nail must stop at the end of the positioning of this one.

The determination of such a PC point is imperative 0 to avoid that the nail arriving too close to the front wall of the vertebra, with a risk of embrittlement or even damage to the neighboring organs, while seeking to use a length of nail as large as possible for consolidation as effective as possible.

Initially, the operator has cleared the vertebra, the posterior surface of which is exposed, and can then determine at least approximately the entry point PE of the nail. 0 On the other hand, it does not know for the moment either the direction of implantation DI from the entry point PE, nor the position of the target point PC, and neither in this case the distance between PE and PC, this is i.e. the depth of the hole to be drilled and the length of the nail

J5 or the screw to use. The procedure, during which the patient is kept in a strictly fixed position, is as follows. First, the operator takes a lateral X-ray image II of the vertebra, the line of sight

5 of the radioscopy device being parallel to Ox. More generally, we seek here to produce an image whose plane is essentially parallel to a prior estimate of the orientation of DI. The position of the fluoroscopy device in relation to the TO table and

- _{| 0} to patient P is shown diagrammatically in FIG. 3. This image, denoted II, is located in a plane parallel to yOz. It is digitized at 26, stored in the computer 20 and displayed on the screen 25 first of all in full screen mode. She is shown

- _j , diagrammatically in FIG. 4.

Then, using the graphic drawing tool 28, the operator draws on this image a point PE which will correspond to the entry point of the nail. In practice, the point PE can be chosen by comparing the visual observation 0 of the vertebra on the patient, after appropriate exposure of the latter, and the X-ray image of FIG. 4.

As a variant, the projection of the entry point PE onto the image II can be carried out by placing on the entry point PE visually located on the vertebra 5 exposed a small reference made of a material chosen so that it appear clearly on image II; in this case, the simple pointing of a cursor on this visible mark on the image makes it possible to determine within the calculator a straight line DPE on which the entry point 0 is located, and to memorize its coordinates.

The operator chooses and then draws on the image II a straight line DI which passes as centrally as possible through the right pedicle PD observed on II, starting from the entry point PE. 5 The operator chooses and then draws a target point PC located on the right DI in the vertebral body CV, the position of PC being chosen according to the constraints indicated above. This determines a straight line Dpc on which the target point must be located, and whose coordinates are stored in the computer.

In addition, the line DI plotted on the screen makes it possible to determine a plane PI, perpendicular to the plane of the image Il and which must contain the direction of intervention DI, and whose inclination α relative to the horizontal H can be calculated easily. Furthermore, and for the purposes explained below, it is possible to measure on image II an approximate distance between the entry point PE and the central region of the right pedicle, this distance being denoted DEP. Given that these tracings are carried out on an image contained in a plane parallel to yOz, without knowledge for the moment of the depth of the geometrical elements considered (approximately according to Ox), the tracing steps above did not make it possible to determine for the moment all the coordinates of the parameters sought. More precisely, and now with reference to FIG. 7, this initial step only made it possible to determine, in addition to the aforementioned inclination α of the plane PI, the two lines DPE and Dpc located on either side of the line NI normal to image II and contained in the plan PI, on which are located, at an unknown dimension, the points PE and PC.

More precisely, neither the exact situation of the line DI in the plane PI, nor if necessary the position of the entry point PE on the line DPE, have been determined.

The next step is to bring the x-ray device 10 into a second specific orientation. This new orientation is obtained by a rotation of the radioscopy device in the PI plane determined previously. More specifically, the calculator automatically positions the fluoroscopic device so that its direction of aiming DV is on the one hand contained in the plane PI, and on the other hand located in a plane close to the plane of image II, that is to say parallel to yOz or of slight inclination with respect to this plane.

In the case where the entry point PE is well located, the position of the point PE on the right DPE is determined by the subsequent step which consists in bringing, under the sole control of the operator, the direction of sight DV of the radioscopy device to pass through the entry point located on the vertebra, and this by moving the radioscopic device (for example by translation along Ox) so that the current direction of sight DV remains in the plane PI. In practice, this operation can be carried out by affixing on the vertebra a clearly visible mark corresponding to the entry point PE, then by moving the radioscopic device substantially parallel to the axis Ox so that the thin beam of laser light strikes the vertebra at this mark. The position sensors of the installation are then able to provide the position of PE on DPE, and consequently the three coordinates of PE in the frame of reference Ro, these coordinates then being memorized. It should be noted that the displacement of the radioscopic device to effect this adjustment can be carried out either manually (the installation being in this case brought into a state in which only a displacement in the required direction is possible, to avoid any drift in translation or in rotation according to the other coordinates), or again by using appropriate control buttons on the radioscopic device or on the computer 20 to actuate the servo motor or motors driving the device in the appropriate direction. The next step consists, in this determined position of the radioscopy device indicated diagrammatically in FIG. 5, to take a second radioscopy of the vertebra, to digitize it at 26, to store it in the computer 20 and to display it on the screen 25, initially in "full screen" mode.

The image obtained is designated by I2a shown in Figure 6a. Furthermore, the computer 20 traces on the image I2a, as indicated above, the reference center CR of the image corresponding to the position of the axis DV and of the laser beam (normal N2 in image 12), this center of reference corresponding to the projection onto this image of the entry point PE.

It can be seen in FIG. 6a that there is a shift between the projection of the entry point and the center CpD of the right pedicle PD through which the nail is to be implanted. This offset is indicative of the angular difference which exists at that moment between the direction along which the DI nail to be implanted ^e t the direction of current referred DV fluoroscopy device. Since the current lines DI and DV both pass through the entry point PE, this angular deviation can be estimated with satisfactory precision by the fact that an estimate of the distance DEP between the entry point PE and the pedicle PD, which is obtained from image II as indicated above, and on the other hand an estimate δD of the distance between the reference center of the image corresponding to the projection from the entry point PE and the center of the pedicle, this value δD being determined by the computer 20 following the plotting of the point CPD.

Figure 7a shows the situation at this time, observed along the Oz axis. The value of the angular offset β between the current sighting axis DV (normal ∑a) and the direction of implantation DI sought is given by the relation:

The device 10 can then be brought automatically, by controlled pivoting of the line of sight DV around the point PE, of the aforementioned angle β, while remaining in the plane PI, to arrive at a position such as the axes DV and DI are confused. The final position obtained is illustrated in Figures 6b and 7b, the latter showing in particular the new normal N2b combined with the intervention line DI.

Another solution for carrying out this final step, which is particularly suitable when it is desired to avoid the influence of the imprecision of the estimated value DEP, consists in translating the radioscopy device, in a direction for example parallel to Ox , so that the center of reference on the screen and the center of the CpD pedicle are superimposed. This step determines a new entry point, and it is clear that this second solution can be adopted in particular when the entry point PE is not perfectly determined and / or can vary within given limits. Thus this variant allows, if necessary, to make a fine adjustment according to Ox (and if necessary according to Oz) of the entry point PE when the latter is not visually located on the patient with sufficient precision.

It is important to note here that, whatever the mode of implementation chosen, it is in no way necessary to capture a third radioscopic image of the vertebra. Indeed, thanks to the use in the computer 20 of a graphics program capable of adjusting in real time the position of the reference center CR with respect to the frame of reference Ro as a function of the displacements imparted to the radioscopy device 10, it is possible to center the direction of aiming DV of said device on the center of the pedicle simply by observing the screen 25 during said movements, and by controlling these movements until the centering of CR on the pedicle is effective.

Once the above operations have been carried out, the aiming direction DV, materialized by the laser beam, becomes the implantation direction, and the entry point PE is located at the point of impact of said beam.

The final coordinates of the device 10 can be stored at this time in the computer together with the coordinates stored following the capture of the first radiological image. And this data can serve as a basis for ordering an intervention means such as a slave tool holder (indicated diagrammatically at 30 in FIG. 1), for drilling and placing the nail.

Furthermore, and now with reference to FIG. 8, the program installed in the computer 20 is designed, in a final step, to display on the screen 25 the images II and 12, suitably positioned one relative to the other, in perspective, and to also display the Ni and Nz normals in images II and 12 in three dimensions. The installation of the present invention thus makes it possible to perform a so-called "two and a half dimensions" reconstruction of the non-homogeneous structure , to check the consistency of the observations and plots made and help the operator in his intervention. And concretely, the step of "adjusting" the direction of intervention (rotation or possibly translation of the normal 12 to superimpose CR and CPD) can be accompanied by a corresponding movement, enslaved, of the normal Nz on the two and a half dimensional image, until this normal passes through the center of the pedicle, while images II and 12 remain fixed on the screen.

Of course, the present invention is in no way limited to the embodiment described above and shown in the drawings, but a person skilled in the art will know how to make any variant or modification in accordance with his spirit.

In particular, the invention applies very generally to any type of intervention in a non-homogeneous structure.

In the case of an intervention on a patient, the invention can be used to advantage in many cases where it is necessary to determine an intervention length and an intervention direction prior to the operation itself, and for example for the installation of screws, nails or various prostheses or also for guiding catheters.

Finally, given the ability of the method and of the installation of the present invention to locate specific points of a non-homogeneous structure with respect to a fixed frame of reference Ro, the invention can also be used quite advantageously as a means marking to adjust in a computer two- or three-dimensional representations previously stored (for example a set of sections obtained by NMR and spatialized imagery) of a structure that is not homogeneous with the actual position of the structure relative to a fixed reference frame, in accordance for example to French patent application No. 89 13028 filed on October 5, 1989 in the name of the Applicant.

In this case, the computer 20 can be designed to display on the screen not only the radioscopic images obtained in real time but also, calibrated in the same frame of reference, three-dimensional images previously determined and stored. Furthermore, as a variant, the radioscopic device used in the present invention may comprise two sets of X-ray source / image intensifier (or CCD sensors), so as to be able to take the two radioscopic images II and 12 simultaneously or practically simultaneously. An appreciable saving of time can thus be obtained.

In addition, in the above case, given the ability of the installation to simultaneously generate _Q on a screen two radioscopic images, the installation can be advantageously used to perform stereoscopic vision. More specifically, by taking two images of the same area along two viewing axes slightly inclined with respect to each other, and in _j - using for example two offset polarizers to distinguish the two images at the level of ocular vision , an observation in relief of the interior of the zone considered of the non-homogeneous structure can be carried out.

Claims

1. Method for determining an intervention line segment (DI, PE, PC) inside a non-homogeneous structure from an entry point into the structure, using a radioscopy device movable, characterized in that it comprises the steps consisting in: producing a first radioscopic image (II) of the non-homogeneous structure, situated in a plane essentially parallel to an estimated direction of the line of intervention and position line known with respect to a fixed frame of reference, digitize this first image, store it in memory and display it on a screen, carry out on the first image present on the screen geometric plots deduced from this image and representative of a reference plane (PI) in which the intervention line segment and the limits of this segment must be located, determine, from the known position data of the first image and said plots, coordinate data of said reference plane and of said limits in the fixed reference frame, and memorizing them, using said coordinate data and a sighting means (100, 110) integral with the radioscopy device, producing a second radioscopic image

(12) of the non-homogeneous structure, located in a plane perpendicular to the reference plane and disposed substantially transversely to the plane of the first image, and such that the sighting means targets the region of the entry point and that the sighting direction (DV) of said aiming means, ie a first estimate of the direction of the line of intervention segment, digitize this second image, save it and display it on the screen, also display on the screen a reference center (CR) corresponding to the sighting direction (DV) of said sighting means, identify on the second image an authorized passage area (PD) for the intervention, move the radioscopy device and enslave therein a relative displacement of the reference center and said second image, in such a way that the reference center is essentially centered on said authorized passage area, the direction of view (DV) then providing the direction of the line segment d intervention, while the length of said segment is provided by said coordinate data.

2. Method according to claim 1, characterized in that the step of moving the radioscopy device is carried out manually.

3. Method according to claim 1, characterized in that it comprises, between the step of identifying the authorized passage area and the step of moving the radioscopy device, the additional step consis¬ as to be performed on the second image another plot (CPD) representative of the center of the authorized passage area, and in that the step of moving the radioscopy device is carried out automatically as a function of the mutual positions of the reference center and of said plot of the center of the authorized passage area.

4. Method according to one of claims 1 to 3, characterized in that it further comprises the final step of determining from the position of the radioscopy device following the step of moving the second coordinate data , the first and second coordinated data being stored to define reference data for the intervention line segment.

5. Method according to one of the preceding claims, characterized in that it further comprises the step consisting in simultaneously displaying on screen said fixed reference frame in three dimensions as well as the first and second digital images, positioned relative to said reference frame and shown in perspective.

6. Installation for the determination of an intervention line segment (DI, PE, PC) inside a non-homogeneous structure from an entry point (PE) in the structure, characterized in that '' it comprises: a movable radioscopy device (10), slave control means (21-24) of the movements of the radioscopy device relative to a fixed reference frame (Ro), digitization means (26) for digitizing images radioscopic means provided by the radioscopy device, means (20, 25) for storing and displaying on a screen said radioscopic images, graphic tracing means (28) for carrying out tracings on the displayed images, a sighting means ( 100, 110) integral with the radioscopy device and indicating the direction of instantaneous sighting (DV) of said device and to which corresponds on the screen a reference trace (CR), means (20) for controlling the position of the x-ray image with respect to the reference plot as a function of the displacements of the radioscopy device, means for determining from position data of the radioscopy device and from said plots of geometrical data relating to the line segment of intervention, a first radioscopic image (II ) to determine a reference plane (PI) in which is contains the intervention line segment, as well as the limits (PE, PC) of said segment, while a second image (12), perpendicular to the plane of the first image and to the reference plane, and corresponding to a direction of aiming which is an estimate of the direction of the line of intervention, allows, by slaving its position as a function of the movements imparted to the radioscopy device using the aiming means, to determine the position of the _Q segment in the plane of reference.

7. Installation according to claim 6, characterized in that the sighting means (100, 110) comprises a laser beam located on the axis of the X-ray of the radioscopy device and emitted from an X-ray emitter ( 15) and / or an X-ray receiver (16) of the radioscopy device.

8. Installation according to one of claims 6 and 7, characterized in that it is coupled to a servo-tool holder (30) intervention.