Method of guiding a stereotaxic instrument at an intracerebral space target point

What is claimed is:

1. A method of guiding a stereotaxic instrument at an intracerebral space target point, comprising the steps of:

injecting a roentgenocontrast medium into the cerebral cavity of a patient to produce contrast of the intracerebral points thereof;

securing to the patient's cranium at least four detachable roentgenocontrast markers having known distances therebetween, with one of said detachable roentgenocontrast markers being offset from a straight line joining any two of other said detachable roentgenocontrast markers;

effecting a first roentgenography of the patient's head;

effecting a second roentgenography of the patient's head with said second roentgenography being effected under projection conditions differing from projection conditions of said first roentgenography;

removing said detachable roentgenocontrast markers from the patient's head;

identifying a position of said detachable roentgenocontrast markers relative to said intracerebral points as references by using the roentgenograms available from said first and second roentgenographies, the distances between said detachable roentgenocontrast markers and the positions of the roentgen radiation source relative to the roentgen films in the course of said first and second roentgenographies;

identifying a position of the intracerebral space target point relative to said intracerebral reference points;

constructing an intracerebral space physical model presenting the relative position of said intracerebral reference points, said detachable roentgenocontrast markers and said target point, said intracerebral space physical model including at least three points, each of which is adapted to simulate one of said detachable roentgenocontrast markers, and a point adapted to simulate said target point;

placing a sterotaxic apparatus on the patient's head;

recurrently securing to the patient's cranium said detachable roentgenocontrast markers in exactly the same position as they had relative to the patient's cranium in the course of said first and second roentgenographies;

identifying the positions of said detachable roentgenocontrast markers, simulated in said intracerebral space physical model, relative to said stereotaxic apparatus and fixing in a stereotaxic apparatus model these indicated positions of said detachable roentgenocontrast markers relative to said stereotaxic apparatus;

orienting said intracerebral space physical model relative to said stereotaxic apparatus model by placing said three points of said intracerebral space physical model adapted to simulate said detachable roentgenocontrast markers in the specified positions of said detachable roentgenocontrast markers relative to said stereotaxic apparatus set forth in said stereotaxic apparatus model;

mounting a guiding arrangement with a stereotaxic instrument upon said stereotaxic apparatus model and adjusting an operative end of said stereotaxic instrument to the specified point of said intracerebral space physical model adapted to simulate the specified target point, with the position of said stereotaxic apparatus being rigidly secured at said guiding arrangement;

drilling a trepanation aperture; and

mounting said guiding arrangement with said stereotaxic instrument upon said stereotaxic apparatus and introducing said stereotaxic instrument into said trepanation aperture.

2. A method of guiding a stereotaxic instrument as recited in claim 1, wherein the step of identifying positions of said detachable roentgenocontrast markers, simulated in said intracerebral space physical model, relative to said stereotaxic apparatus and fixing in a stereotaxic apparatus model these specified positions of said detachable roentgenocontrast markers relative to said stereotaxic apparatus, is effected by sequential adjustments of the stereotaxic instrument to said detachable roentgenocontrast markers while securing the position of said stereotaxic instrument at the guiding arrangement at each such adjustment and transferring said guiding arrangement with said stereotaxic instrument following each such adjustment from said stereotaxic apparatus onto said stereotaxic apparatus model.

3. A method of guiding a sterotaxic instrument as recited in claim 2, wherein the steps of:

securing to the patient's cranium said detachable roentgenocontrast markers is preceded by fastening at least four complementary roentgenocontrast markers in the bones of his cranium, which is followed by performing said first and second roentgenographies;

injecting a roentgenocontrast medium into the cerebral cavity of the patient is effected subsequent to performing said first and second roentgenographies and removing said detachable roentgenocontrast markers from the patient's head;

injecting a roentgenocontrast medium into the cerebral cavity of the patient is followed by performing third and fourth roentgenographies of the patient's head, with said third roentgenography differing in projection conditions from said fourth roentgenography;

identifying a position of said detachable roentgenocontrast markers relative to said intracerebral reference points is effected on the basis of said four roentgenographies by identifying a position of said detachable roentgenocontrast markers relative to said complementary roentgenocontrast markers and identifying a position of said complementary roentgenocontrast markers relative to said intracerebral reference points, with distances between said complementary roentgenocontrast markers being calculated while identifying a position of said detachable roentgenocontrast markers relative to said complementary roentgenocontrast markers; a position of said detachable roentgenocontrast markers relative to said complementary roentgenocontrast markers being identified by using the roentgenograms available from said first and second roentgenographies, distances between said detachable roentgenocontrast markers and positions of the roentgen radiation source relative to the roentgen films in the course of said first and second roentgenographies; while a position of said complementary roentgenocontrast markers relative to said intracerebral reference points being identified by using the roentgenograms available from said third and fourth roentgenographies, distances between said complementary roentgenocontrast markers and positions of the roentgen radiation source relative to the roentgen films in the course of said third and fourth roentgenographies.

4. A method of guiding a stereotaxic instrument as recited in claim 3, wherein the step of securing said detachable roentgenocontrast markers to the patient's cranium is effected by the patient's biting a dental impression of his upper jaw having said detachable roentgenocontrast markers clamped thereto.

5. A method of guiding a stereotaxic instrument as recited in claim 1, wherein the steps of:

securing to the patient's cranium said detachable roentgenocontrast markers is preceded by fastening at least four complementary roentgenocontrast markers in the patient's skull which is followed by performing said first and second roentgenographies;

injecting a roentgenocontrast medium into the cerebral cavity of the patient is effected subsequent to performing said first and second roentgenographies and removing said detachable roentgenocontrast markers from the patient's head;

injecting a roentgenocontrast medium into the cerebral cavity of the patient is followed by performing third and fourth roentgenographies of the patient's head, said third roentgenography differing in projection conditions from said fourth roentgenography; identifying a position of said detachable roentgenocontrast markers relative to said intracerebral reference points is effected on the basis of said four roentgenographies by identifying a position of said detachable roentgenocontrast markers relative to said complementary roentgenocontrast markers and identifying a position of said complementary roentgenocontrast markers relative to said intracerebral reference points, with distances between said complementary roentgenocontrast markers being calculated while identifying a position of said detachable roentgenocontrast markers relative to said complementary roentgenocontrast markers; a position of said detechable roentgenocontrast markers relative to said complementary roentgenocontrast markers being identified by using the roentgenograms available from said first and second roentgenographies, distances between said detachable roentgenocontrast markers and positions of the roentgen radiation source relative to the roentgen films in the course of said first and second roentgenographies; while a position of said complementary roentgenocontrast markers relative to said intracerebral reference points being identified by using the roentgenograms from said third and fourth roentgenocontrast markers and positions of the roentgenradiation source respective to the roentgen films in the course of said third and fourth roentgenographies.

6. A method of guiding a stereotaxic instrument as recited in claim 1, wherein the step of securing said detachable roentgenocontrast markers to the patient's cranium is effected by the patient's biting a dental impression of his upper jaw having said detachable roentgenocontrast markers clamped thereto.

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FIELD OF THE INVENTION

The present invention relates generally to the field of medicine, and more specifically, to methods of guiding a stereotaxic instrument at an intracerebral space target point, and may find application in stereotaxic operations performed on the brain in humans.

The term "target point" is defined herein as a n intracerebral space point located in the region of a cerebral structure to be subjected to stereotaxic effect.

The term "guiding a stereotaxic instrument at a target point" is defined herein as imparting to a stereotaxic instrument such a spatial position which, if the stereotaxic instrument has been set appropriately in a stereotaxic apparatus, will ensure the adjustment matching of the stereotaxic instrument to the intracerebric space target point, as well as the adjustment matching proper.

BACKGROUND OF THE INVENTION

In the prior state of the art there is known a method of guiding a stereotaxic instrument at a target point incorporating the employment of a stereotaxic apparatus disclosed in U.S.S.R. Inventor's Certificate No. 283,494, and a method similar to it incorporating the employment of a stereotaxic surgical apparatus disclosed in U.S. Pat. No. 3,457,922. The method in question comprises injecting a roentgenocontrast substance into the ventricles of the patient's brain, movably securing to the patient's head a stereotaxic instrument, X-raying the patient's head in two projections, identifying through the coordinate system definable by the intracerebral reference points a position of the target point in the coordinate system of the X-ray pictures, spatially locating a relative position of the target point and the stereotaxic instrument by the projections thereof on the X-ray pictures, moving the stereotaxic instrument for the purpose of assigning thereto such a spatial position as required for guiding at the target point, recurrently X-raying for the purpose of spatially locating a position of the target point and stereotaxic instrument after having it moved, and matching the stereotaxic instrument to the intracerebral space target point.

A disadvantage of the aforedescribed method consists in the low accuracy of spatially locating a position of the target point in the coordinate system involving the X-ray pictures owing to the absence of control over the orthogonality of the coordinate system involving the X-ray picture, the coordinate system defined by the intracerebral reference points and also the low accuracy of spatially locating the relative position of the target point and stereotaxic instrument by their projections on the X-ray pictures, inasmuch as it is next to impossible to guarantee the orthogonality of the coordinate system involving the stereotaxic apparatus, and by the coordinate system involving the X-ray picture. Hence, the accuracy of guiding the stereotaxic instrument at the target point will be insufficient in the above method. Another disadvantage of the method is the high degree of traumatization caused by the lengthy procedure of guiding and the necessity of exposing the patient to repeated irradiation in the course of the guiding procedure.

In the prior art there is known a method of guiding a stereotaxic instrument at a target point incorporating the employment of a stereotaxic neurosurgical apparatus disclosed in U.S. Pat. No. 3,357,431 comprising the steps of injecting an X-ray contrast substance into the ventricles of the patient's brain, movably fixing to the patient's cranium a stereotaxic instrument associated with two X-ray contrast point markers so that said markers and said stereotaxic instrument are established along the same straight line perpendicular to the mid-sagittal plane of the brain, X-raying the patient's cranium in two respectively perpendicular projections, locating by means of the coordinate system defined by the intracerebral reference points a spatial position of the target point in the coordinate system involving X-ray pictures, locating a spatial position of the target point relative to the X-ray contrast point markers, moving the stereotaxic instrument along the plane parallel to the mid-saggittal plane of the brain for the purpose of matching the projections of the X-ray contrast point markers to the projection of the target point on the profile X-ray picture and moving the stereotaxic instrument along the straight line perpendicular to the mid-saggital plane of the brain for the purpose of matching on the frontal X-ray picture the projection of the stereotaxic instrument to the projection of the plane parallel to the mid-sagittal plane of the brain and extending across the projection of the target point, and matching the stereotaxic instrument to the target point within the brain.

The guiding accuracy provided by this method is somewhat higher than that of the foregoing method, yet even this accuracy is not adequate by reason of the insufficiently high accuracy of locating, by means of the coordinate system defined by the intracerebral reference points, a spatial position of the target point in the coordinate system involving X-ray pictures since the orthogonality of the coordinate system involving the intracerebral reference points, the coordinate system involving X-ray pictures, fails to be controlled effectively. Another disadvantage of this method is the considerable traumatization resulting from the overly protracted guiding procedure. Furthermore, a disadvantage of the method described lies in the restrictions imposed on the availability of surgical access to the target point because upon matching the stereotaxic instrument to it, the instrument is capable of moving only along the plane parallel to the mid-sagittal plane of the brain.

Also known in the prior art is a method of guiding a stereotaxic instrument at a guiding point assuming the employment of a stereotaxic neurosurgery apparatus disclosed in U.S. Pat. No. 3,508,552 featuring the steps of injecting an X-ray contrast substance into the ventricles of the patient's brain, fastening to the patient's skull X-ray contrast markers made in the form of double grids with parallel rectangular passages forming a regular square pattern, X-raying the patient's skull in two respectively perpendicular projections, locating a spatial position of the target point in the coordinate system involving X-ray pictures by means of the coordinate system defined by the intracerebral reference points, determining in the grid arranged parallel to the mid-sagittal plane of the brain the specific rectangular passage having a projection thereof matched to a projection of the target point on the profile X-ray picture, determining in the grid arranged perpendicular to the mid-sagittal plane of the brain the specific rectangular passage having a projection thereof matched to a projection of the target point on the frontal X-ray picture, and adjusting the stereotaxic instrument to the target point within the brain by introducing the stereotaxic instrument through one of the specific rectangular passages of one of the grids to a depth corresponding to the distance from this grid to the other specific passage.

Disadvantages inherent in this method consist of the low accuracy of guiding a stereotaxic instrument, the objectionably high degree of traumatization and the limitations imposed on the availability of surgical access to the target point. The guiding accuracy provided by the present method is slightly lower than that of the preceding method owing to the fact that both of these methods are characterized by the insufficiently high accuracy of locating a spatial position of the target point in the coordinate system involving the X-ray pictures by means of the coordinate system defined by the intracerabral reference points, while the accuracy of matching the stereotaxic instrument to the target point is largely dependent on the dimensions of the rectangular passages and the distances between the adjacent passages. The traumatization level due to the time interval taken by the guiding procedure is somewhat lower in this method as compared to the foregoing one because the guiding procedure can be accomplished more quickly inasmuch as there is no need for repeated X-raying. The surgical access can be effected not only parallel to one plane, as in the preceding method, but parallel to two planes.

The abovementioned disadvantages are partially eliminated in a method of guiding a stereotaxic instrument at an intracerebral space target point described in a paper by T. Riechert "Die Stereotaktischen Hirnoperation", Deutsche Medischen Wissenschrift, 1959, vol. 84, pp. 1669-1683. This method contemplates injecting an X-ray contrast substance into the ventricles of the patient's brain, placing a stereotaxic apparatus on the patient's head, fastening detachable X-ray contrast markers to the patient's cranium, taking two X-ray pictures of the patient's head including an image of the intracerebral reference points under different projection conditions, locating a position of the intracerebral reference points relative to the X-ray contrast markers, locating a position of the intracerebral reference points relative to the target point, constructing an intracerebral space physical model including a point simulative of the target point and sequentially matching the stereotaxic instrument to the point of the physical model simulative of the target point and to the intracerebral space target point. PG,9

Subsequent to injecting an X-ray contrast substance the patient's head is placed movably in the stereotaxic apparatus made integral with an operation table and X-ray film holders. The base ring of the stereotaxic apparatus has four X-ray contrast point markers attached thereto and arranged along the two respectively perpendicular diameters of the ring. These markers define a coordinate system of the stereotaxic apparatus.

The injection of the X-ray contrast substance is effected through a specially drilled trepanation aperture.

The fastening of the X-ray point markers to the patient's cranium is effected by placing under X-ray control and rigidly fixing the patient's head in the stereotaxic apparatus. As this takes place, it is essential that the coordinate planes of the coordinate system defined by the intracerebral reference points be orthogonal to the planes of the X-ray films and the main rays of the X-ray tubes.

The X-ray pictures are taken simultaneously by two X-ray tubes when they are strictly centered with respect to the X-ray contrast point markers and the films.

The films obtained provide an image of the intracerebral reference points which is followed by constructing a coordinate system based on these points, determining the coordinates of the target point according to the stereotaxic atlas and plotting them on the films with allowance made for the enlargement coefficient of the films. A coordinate system of the stereotaxic apparatus is constructed by the projections of the four X-ray contrast point markers and the coordinates of the target point are determined in this system.

The intracerebral space physical model is constructed on the basis of a stereotaxic apparatus model representing an exact copy of the base ring of the stereotaxic apparatus. A point simulative of the target point is set forth in the intracerebral space physical model in the coordinate system of the stereotaxic apparatus.

The procedure of adjusting the stereotaxic instrument to the point of the intracerebral space physical model simulative of the target point is effected by transfering a guiding device with the stereotaxic instrument from the base ring of the stereotaxic apparatus onto the ring of the stereotaxic apparatus model. Making use of the available degrees of freedom of the guiding device therewith, the stereotaxic instrument is adjusted to the point simulative of the target point and this position of the stereotaxic instrument is fixed, whereafter the guiding device with the stereotaxic apparatus is again transferred onto the base ring of the stereotaxic apparatus and in the process of introducing the stereotaxic apparatus into the trepanation opening in the patient's skull the instrument is adjusted to the intracerebral space target point.

The aforedescribed method has significant disadvantages. Making X-ray films, determining the coordinates of the target point and adjusting the stereotaxic instrument thereto are to be accomplished as soon as the X-ray contrast substance is injected into the cavities of the patient's brain which causes the brain to swell and leads to a change of the spatial position of the cerebral structures relative to the intracerebral reference points as compared to their position specified in the stereotaxic atlas. Consequently, inaccuracy in the guiding procedure of the stereotaxic instrument may result. This disadvantage is also due to the necessity of very accurately placing the patient's head and centering the X-ray tubes, during which operations the coordinate planes of the coordinate system defined by the intracerebral reference points must be orthogonal to the planes of the films and the main rays of the X-ray tubes, which is impracticable in the actual conditions of neurosurgical intervention and brings about errors in the calculations.

Another disadvantage of the method described above is the high degree of traumatization. This is attributable to the necessity of rigidly fastening the patient's head, drilling a special trepanation opening for the injection of the X-ray contrast substance since with the patient's head being fastened it is impossible to inject a gasiform X-ray contrast substance through a lumbar puncture. The necessity of X-raying to check the fastening of the X-ray contrast markers to the patient's cranium and the adjustment of the stereotaxic instrument to the target point within the brain leads to a slow healing process of the operation injuries. The high degree of traumatization is produced due to the fact that the fastening of the patient's head, the injection of an X-ray contrast substance, the X-raying procedure, the handling of the films, the determination of the coordinates of the target point, the construction of the intracerebral space physical model and the adjustment of the stereotaxic instrument to the point of the physical model simulative of the target point are effected directly in the course of the neurosurgical operation, which, as a consequence, lasts not less than three hours. Throughout this time the patient is lying on the operation table with a trepanation opening.

The long duration of the operation does not permit guiding the stereotaxic instrument at more than three target points.

Further, when fastening the patient's head in the course of X-raying the contrasting qualities of the required cerebral cavities shown on the X-ray film are apt to deteriorate, which tends to complicate the identification of the intracerebral reference points to such an extent that occasionally it becomes indispensable either to utilize an X-ray contrast substance of improved contrasting qualities or to inject an X-ray contrast substance once again. Additionally, the rigid fastening of the head generally disagrees with certain patients, e.g. those suffering from epilepsy.

Other disadvantages of the aforesaid method consist in that in the X-raying process, the patient's head is placed in the stereotaxic apparatus comprising steel elements, which hamper the implementation of the X-raying process.

Further, in order to practice the method as described above it is necessary to have a specialized operating theater equipped with a special X-raying instrumentation, which can not be used for other purposes.

SUMMARY OF THE INVENTION

An object of the present invention is to increase the accuracy of guiding a stereotaxic instrument at an intracerebral space target point.

Another object of the invention is to reduce the degree of traumatization when guiding a stereotaxic instrument at a target point.

A further object of the invention is to cut down the duration of a stereotaxic operation.

Broadly stated, the invention resides in injecting a roentgenocontrast medium into the cavities of the patient's brain, securing to the patient's cranium at least four detachable roentgenocontrast markers having known distances therebetween; sequentially performing two roentgenographies under different projection conditions, removing the detachable roentgenocontrast markers from the patients head; identifying a position of the detachable roentgenocontrast markers relative to the intracerebral reference points by using the roentgenograms available from said roentgenographies, distances between the detachable roentgenocontrast markers and a position of the roentgen radiation source respective to the X-ray films in the course of said roentgenographies. Subsequently a position of the target point is identified with respect to the intracerebral reference points and an intracerebral space physical model is constructed, wherein included are three points adapted to simulate the three detachable roentgenocontrast markers, and a point adapted to simulate the target point. The method further comprises placing a stereotaxic apparatus on the patient's head, securing again to the patient's cranium the detachable roentgenocontrast markers in exactly the same position they had in the course of the roentgenographies, identifying a position of the detachable roentgenocontrast markers simulated in the intracerebral space physical model respective to the stereotaxic apparatus and fixing in a stereotaxic apparatus model the specified positions of the detachable roentgenocontrast markers respective to the stereotaxic apparatus. Subsequently the intracerebral space physical model is oriented relative to the stereotaxic apparatus model by placing the three points thereof adapted to simulate the three detachable roentgenocontrast markers in the specified positions of the detachable roentgenocontrast markers relative to the stereotaxic apparatus set forth in the stereotaxic apparatus model; mounting a guiding arrangement with a stereotaxic instrument upon the stereotaxic apparatus model, adjusting the operative end of the stereotaxic instrument to the point of the intracerebral space physical model adapted to simulate the target point, with the position of the stereotaxic apparatus being rigidly secured at the guiding arrangement; drilling a trepanation aperture, mounting the guiding arrangement with the stereotaxic instrument upon the stereotaxic apparatus and introducing the stereotaxic instrument into the trepanation aperture.

Advantages of the present invention are as follows. Owing to the possibility of reproducing a position of the detachable X-ray contrast markers relative to the patient's cranium the proposed method enables dividing in time the injection of a roentgenocontrast substance into the cavities of the patient's brain, performing the roentgenographies of the patient's head, identifying a position of the detachable roentgenocontrast markers relative to the intracerebral reference points and constructing an intracerabral space physical model, on one hand, and adjusting the stereotaxic instrument to the point of the physical model adapted to simulate the target point, and to the intracerebral space target point, on the other hand. While this takes place, a time interval between the stated groups of operations can be arbitrarily large and, as a consequence, sufficient for:

(a) the changes of the spatial position of the cerebral structures caused by the injection of the roentgenocontrast medium to vanish by the moment of adjusting the stereotaxic instrument to the intracerebral space target point which steps up the accuracy of guiding the stereotaxic instrument; and

(b) the intracerebral space physical model can be constructed well before the adjusting procedure, which reduces the duration of the stereotaxic operation and, consequently, reduces the traumatization caused by the guiding method.

The accuracy of guiding the stereotaxic instrument is also improved due to the fact that in the proposed method the necessity of accurately placing the patient's head and strictly centering the X-ray tubes relative to the roentgenocontrast markers and the films, has been ruled out.

Since there is no need for rigidly fastening the patient's head to the operation table in the course of the roentgenographies, the risk of traumatizing the patient when he makes involuntary movements, as for instance, in an epileptic seizure, is avoided. In the proposed method there is no necesity for drilling a trepanation opening in the patient's skull because it affords a possibility of injecting a roentgenocontrast medium through a lumbar puncture.

In addition, the traumatization level in the proposed method is decreased since the procedure of adjusting the stereotaxic instrument to the target point is accomplished without exposing the patient to the X-ray radiation, which contributes to a speedy healing of his surgical wounds.

The steps of identifying the positions of the detachable roentgenocontrast markers, simulated in the intracerebal space physical model, relative to the stereotaxic apparatus, and fixing the specified positions of the detachable roentgenocontrast markers relative to the stereotaxic apparatus in the stereotaxic apparatus model can be effected by sequentially adjusting the stereotaxic instrument to the detachable roentgenocontrast markers while securing the positions of the stereotaxic instrument at the guiding arrangement at each such adjustment and transferring the guiding arrangement with the stereotaxic instrument after each such adjustment from the stereotaxic apparatus onto the stereotaxic apparatus model.

Such a procedure ensures simplicity and high accuracy in identifying the positions of the detachable roentgenocontrast markers relative to the stereotaxic apparatus and fixing these positions in the stereotaxic apparatus model. The stereotaxic apparatus and its model need not be equipped with additional appliances therewith.

According to an embodiment of the invention, it is contemplated that securing to the patient's cranium the detachable roentgenocontrast markers is preceded by fastening four complementary roentgenocontrast markers in the bones of his cranium, which is followed by performing said two roentgenographies; injecting a roentgenocontrast medium into the cavities of the patient's brain is effected subsequent to performing said roentgenographies and removing the detachable roentgenocontrast markers from the patient's head; injecting a roentgenocontrast medium into the cavities of the patient's brain is followed by sequentially performing two more roentgenographies differing in projection conditions; identifying a position of the detachable roentgenocontrast markers relative to the intracerebral reference points is effected on the basis of said four roentgenographies by means of identifying a position of the detachable roentgenocontrast markers relative to the complementary roentgenocontrast markers and identifying a position of the complementary roentgenocontrast markers relative to the intracerebric reference points, with distances between the complementary roentgenocontrast markers being calculated while identifying a position of the detachable roentgenocontrast markers relative to the complementary roentgenocontrast markers, a position of the detachable roentgenocontrast markers relative to the complementary roentgenocontrast markers being identified by using the roentgenograms available from the initial two roentgenographies, distances between the detachable roentgenocontrast markers and positions of the roentgen radiation source relative to the roentgen films in the course of the initial two roentgenographies, while a position of the complementary roentgenocontrast markers relative to the intracerebral reference points being identified by using the roentgenograms available from the second two roentgenographies, distances between the complementary roentgenocontrast markers and positions of the roentgen radiation source relative to the roentgen films in the course of the second two roentgenographies.

The fastening of the complementary roentgenocontrast markers as bones of the patient's cranium for use in the auxiliary points in the intermediate calculations involving the identification of the position of the detachable roentgenocontrast markers relative to the intracerebral reference points permits the roentgenography of the patient's head with the roentgenocontrast medium being injected into the cavities of his brain without having the detachable roentgenocontrast markers secured to his cranium. The absence of the detachable roentgenocontrast markers in the course of the contrast roentgenography allows one to choose any placement of the patient's head, including those which produce the best X-ray views of the intracerebral reference points.

It is desirable that the fastening of the detachable roentgenocontrast markers to the patient's cranium be effected by having the patient bite a dental impression of his upper jaw having these roentgenocontrast markers attached thereto.

This fastening is atraumatic and permits one to definitely secure the detachable roentgenocontrast markers to the patient's skull in the course of the roentgenographies as well as in the course of the stereotaxic operation for the purpose of orienting the intracerebric space physical model relative to the stereotaxic apparatus model.

The foregoing and other objects and advantages of the present invention will become more apparent from the ensuing detailed description of the embodiments thereof given by way example with reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the patient's head with the detachable roentgenocontrast markers secured to his cranium according to the invention;

FIG. 2 represents the patient's head with the detachable roentgenocontrast markers secured to his cranium and the complementary roentgenocontrast markers fastened in the bones thereof according to the invention;

FIG. 3 represents the intracerebral space physical model according to the invention;

FIGS. 4a, b, c represent the patient's head with the stereotaxic apparatus placed thereon and the deatachable roentgenocontrast markers secured to his cranium;

FIGS. 5a, b, c diagrammatically represent the fixing of the specified positions of the detachable roentgenocontrast markers relative to the stereotaxic apparatus in the stereotaxic apparatus model according to the invention;

FIG. 6 is a perspective view of the intracerebral space physical model oriented relative to the stereotaxic apparatus model according to the invention;

FIG. 7 diagrammatically represents the means for adjusting the stereotaxic instrument to the point of the intracerebral space physical model adapted to simulate the target point according to the invention; and

FIG. 8 shows the patient's head with a trepanation aperture and the stereotaxic instrument introduced thereinto.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The procedure of guiding a stereotaxic instrument at an intracerebral space target point according to the invention is accomplished as follows.

A few days before, for example, a week before the forthcoming neurosurgical operation a roentgenocontrast medium, e.g. air, is injected through a lumbar puncture into the ventricles 1 (FIG. 1) of the patient's brain. It is permissible instead of air to inject into the cerebral cavities some other roentgenocontrast media--both gasiform and liquid, by means of a ventricular puncture.

Then four detachable roentgenocontrast point markers 2, 3, 4 and 5 are secured to the patient's head so that they assume a rigidly fixed position with regard to the patient's cranium. It is essential that the roentgenocontrast point markers 2, 3, 4 and 5 have such a relative position in which three of them, for instance, the markers 2, 3 and 4 are not arranged along one straight line. The detachable roentgenocontrast markers 2, 3, 4 and 5 are, for example, the points of metallic pins 6 attached to a plate 7 so that the distance between each of the two of the roentgenocontrast markers 2, 3, 4 and 5 can be measured easily and accurately. The plate 7 with the pins 6 is attached, for example, to a plaster dental impression of the patient's upper jaw, which allows the roentgenocontrast markers 2, 3, 4 and 5 to be rigidly secured to the patient's cranium inasmuch as the upper jaw remains stationary with regard to the cranium.

The plaster dental impression of the patient's upper jaw is made well in advance of the procedure described. For this purpose the patient bites a tray profiled according to the arch configuration of his upper jaw and filled with plaster. Thereafter the tray containing an impression is removed from the teeth and dried. When biting this impression the patient's upper jaw teeth fit individually in the corresponding indentations on the impression, owing to which the roentgenocontrast point markers 2, 3, 4 and 5 attached thereto assume one and the same reproducible spatial position relative to the patient's cranium at each biting of the impression. Such a manner of securing the detachable roentgenocontrast markers 2, 3, 4 and 5 is atraumatic and does not cause disagreeable sensations in the patient.

The securing of the detachable roentgenocontrast markers to the patient's cranium can be effected otherwise, for example, by means of placing in the bones of the patient's cranium two slots made of stainless steel, which are adapted to receive the pins carrying the plate with the roentgenocontrast markers. The slots are removed from the cranium after the operation.

In the embodiment of the invention described herein the number of the detachable roentgenocontrast markers 2-5 is equal to four. It should be borne in mind that the stated number is required as a minimum to practice the proposed method. According to the invention there may be provided more than four, e.g. five or six detachable roentgenocontrast markers and in this case the "redundant" roentgenocontrast markers, above the required four, can be used to check the results of the calculations involving the construction of the intracerebral space physical model as described below.

Then two roentgenographies of the patient's head are performed sequentially with the aid of a conventional diagnostic X-ray apparatus comprising one tube with the patient's head being placed arbitrarily and a known position of the roentgen radiation source 8 relative to a roentgen film 9. These two roentgenographies differ in projection conditions, that is in a relative position of the roentgen radiation source 8, the roentgen film 9 and the patient's head, with the placement of the patient's head being selected so as to provide in the roentgenograms images of the intracerebral reference points 10, 11 and 12, for example, anterior commissure, posterior commissure and vault apex respectively, and images of the detachable roentgenocontrast markers 2, 3, 4 and 5 carried by the plate 6. After the roentgenographies have been performed, the plaster impression with the roentgenocontrast markers 2, 3, 4 and 5 are taken off the patient's upper jaw.

In case it proves difficult to obtain in one roentgenogram the images of all the intracerebral reference points 10, 11 and 12, then the first and/or the second roentgenographies as are repeated many times as necessary in order to obtain in the