Method of determining the position of a medical instrument

The invention relates to a method for determining the position of an object to be examined in a partially inserted medical instrument in a three-dimensional Image data set of the object as well as an arrangement for carrying this method.

A method and an arrangement for determining the position of a medical Instruments in a two-dimensional image data set are known from EP 857 461 A2. Here are intraoperatively by means of a C-arm x-ray apparatus X-ray images the examination area of ​​an examination object, for example a patient, recorded, at the same time by means of an optical position measuring device the position of the object or the patient table and the medical instrument relative to the X-ray device is measured. can the position of the medical instrument then in a position relative to one or more of the detected X-ray images be converted, so that the current position in each case in one or more to view X-ray images. Such a method can be used as navigation aid serve for the doctor during the treatment of a patient. However, there is the Disadvantage that intraoperatively for navigation no three-dimensional image information be available. Although it is possible to intervene on the basis of a pre-operative planning three-dimensional dataset, intraoperatively but always only two-dimensional X-ray images are acquired, and the position of the medical instrument can only in this intraoperatively detected two-dimensional be determined and displayed X-ray images.

It is true that methods are known in which the position of a medical instrument is determined intraoperatively and relative to a detected preoperatively in a position three-dimensional image data set can be converted. For this purpose, however, must in detecting the three-dimensional image dataset pre-operatively special markers be patient attached that displayed in the three-dimensional image data set with be and approached immediately before surgery using a special pointer in order to determine their spatial positions. By means of the then in spatial Coordinates and known in 3D image coordinate positions of these markers can then a intraoperatively measured spatial position of a medical instrument in a Position relative to the three-dimensional image data set to be converted. Such However, processes have the disadvantage that no image information of the anatomy of the patient are used and that the anatomy during the intervention is changed regularly over the state of the anatomy in the preoperative Acquisition of the 3D image data set.

The invention is therefore based on the object, a method for determining the Position of a partially inserted into an object medical instrument indicate in a three-dimensional image data set of the examination subject, wherein which the mentioned disadvantages are avoided, in particular, a high accuracy to be achieved at the least possible expense. In addition to a correspondingly configured arrangement for performing the method are given.

These objects are achieved by a method according to claim 1 and by a The arrangement of claim 9 solved.

The invention starts from the realization that an intra-operative two-dimensional X-ray image can be advantageously exploited, which also intraoperatively measured position of the medical instrument in a position relative to a three-dimensional Image data set, which will be detected preoperatively usually convert. According to the invention to intraoperatively addition to the position of the medical instrument also determines the spatial position of the X-ray image. Using a suitable Registration procedure is then the spatial relationship between this X-ray image and the three-dimensional image data set is determined, resulting in quasi gives spatial position of the three-dimensional image data set. Using this knowledge it is now easily possible, the position of the medical instrument relative to the to determine the three-dimensional image data set, since the spatial position of the medical Instruments detected just before. With the invention it is thus in a simple manner possible to the position of a medical instrument in a to determine three-dimensional image data set, without that in capturing the image data set special attached with markers on the patient to be imaged need that again must be registered immediately before surgery. also intraoperatively acquired image data is processed, the exact statements about Allow the patient's anatomy, thereby improving the accuracy of position determination is increased.

The advantageous embodiment according to claim 2 utilizes known means for determining the spatial position of the X-ray image, which is also for determining the spatial Position of the medical instrument can be used. The used to Position-measuring device may be configured differently, for example with optical Cameras, infrared cameras and / or electromagnetic detectors, the three-dimensional position of corresponding markers, for example, optical LEDs, infrared diodes or electromagnetic transmitters can be determined.

The developments according to claims 3 to 5 are options for determining the spatial relationship between the X-ray image and the three-dimensional Image data set. For this, the three-dimensional image data set as a whole, or several partial volumes, individual contained in the image data set particularly conspicuous Objects or structures or individual voxels of the image data set to the X-ray image compared or searched in the radiograph. This is preferably done iteratively. A Such an advantageous comparison method is defined in claim 5 and from EP 880 109 A2, which is hereby expressly referred to and the disclosure of to be considered as incorporated in the present application. Here are from three-dimensional image data set pseudo-projection images created and with the X-ray image compared, wherein the creating the pseudo-projection image based lying Parameters such as magnification, projection direction so as long iteratively varied be until the pseudo-projection image and the X-ray image coincide optimally. Then, the spatial relationship between X-ray image and 3D image data set found.

Preferably, the method is intraoperatively and be carried out continuously according to claim 6 designed so that during the treatment of a patient as the physician can serve navigation aid and constantly updated information on the anatomy and can provide the position of the medical instrument.

According to the advantageous development as claimed in claim 7 is from the three-dimensional Picture record an image created, in which the position of the medical instrument or the Instrument itself is displayed. This also serves to support the treating Physician during surgery. It may be of different images shown are, for example layer images or projection images from the three-dimensional image data set created and by means of intraoperative X-ray device used not be generated, such as combining images captured from preoperatively and intraoperatively captured image data, vessel trees or preoperatively created navigation plans.

Particularly advantageous is the embodiment according to claim 8, wherein the three-dimensional Image data set präoperation by any imaging device has been detected and when intraoperatively Röntgenfluroskopieeinrichtung, including a C-arm X-ray device, is used. This allows the physician during treatment also images from different imaging modalities with different Information content presented intraoperatively.

An inventive arrangement with which the method described particularly advantageously can be carried out, with an X-ray device, a Position measuring device and an arithmetic logic unit disclosed in claim. 9

The invention will be explained in more detail with reference to the drawings. Show it:<sl><li>Fig. 1 is a schematic representation of an arrangement according to the invention,</li><li>Fig. 2 is a diagram for explaining the procedure and</li><li>Fig. 3 is a block diagram for explaining the method according to the invention.</li></sl>

Fig. 1 shows a computer tomograph 1, with that of a patient 3 before the start of a surgical procedure, a sequence is made by CT scans, the parallel to the longitudinal axis of the patients represent 3 vertical layers. These computer scans form a three-dimensional image data set to the three-dimensional representation the examination area of ​​the patient can be 3. On the basis of this data set For example, the later performed surgical procedure to make a plan.

By means of an X-ray device 2 are continuously dimensional during surgery X-ray images of the arranged on an operating table 4 patients 3 created. For this, a C-arm X-ray device is used herein, when an X-ray source 6 and an X-ray detector 7 are arranged on a C-arm 5, by an Tripod not shown is supported. 8 The C-arm is at least in the direction of arrow 9 pivotable about a horizontal axis. The X-ray image 7 provides its output signals via the analog-to-digital converter 11 to an image memory 12, the is connected to a computing unit 20th The control of the X-ray device 2 by means of a control unit 10th

Next, a position measuring device 13 is provided with two infrared CCD cameras 14, which are arranged laterally next to the examination region on a tripod. With this can be spatial positions of correspondingly designed IRED determine. To the position of a medical used during surgery Instruments 16, here a biopsy needle to determine, are on the from the Patients protruding end of the biopsy needle 16 at defined positions three such Infrared light-emitting diodes 17 are arranged. In order to further the position of the X-ray device 2 or the imaging geometry of the X-ray device 2 in the preparation of x-ray images during the operation to determine each of the X-ray source 6 and to the X-ray detector 7, three such light-emitting diodes 18 and 19. From the thus determined Imaging geometry can be the spatial position of a detected X-ray image determine, that is, the position of the X-ray image relative to the patient 3. This calculation and storage of the determined positions takes place in a position computing unit 15, the results of which are in turn passed on to the computing unit 20th

The computing unit 20 is the addition to the intra-operatively acquired X-ray images and measured positions and the detected preoperatively from the CT scanner 1 Image data set supplied. There is from this information by means of a yet to be detailed Comparison method, the spatial relationship between the two-dimensional X-ray image and the three-dimensional image data set is determined. After determining this allocation rule, it is possible, the spatial position of the medical Instruments 16 to be converted into a position relative to the three-dimensional image data set and from the three-dimensional image data set and / or intraoperatively create created radiograph of one or more images on a monitor 21 can be displayed and in which the position of the medical instrument may be displayed.

In FIG. 2, the individual process steps are again in a flow chart shown. In the preoperatively performed step 101 is a three-dimensional Image data set CT detected with the aid of computed tomography, the absorption distribution, the dimensionally reproduces within an examination volume. Out this may also be a sub-volume CT_p are selected, the one for the later comprises especially engagement region of interest. This selection can be performed manually or automatically by segmentation.

The shown below intraoperatively performed steps 102 to 104 can continuously or repeatedly during an operation at desired intervals or be performed at specific times. In step 102 simultaneously a two-dimensional X-ray image I_r and the positions of the imaging geometry and the medical instrument determined. Between the X-ray image I_r and the total volume CT or the sub-volume CT_p the three-dimensional Image data set is then in step 103 the allocation rule certainly. This will ultimately be used in step 104 to the position the medical instrument in the total volume CT or the partial volume CT_pto determine the image data set and, if necessary to create appropriate images.

Referring to FIG. 3 is the comparison method to determine the allocation rule are explained in detail. The three-dimensional image data set CT is determined from several detected by the computer tomograph slice images CT1, CT2, ..., CTX formed.

This is a partial volume CT_p selected that is relevant for later engagement and in the case shown, for example, represents a vertebral body.

The spatial transformation or mapping between the image of the patient, particularly the segmented vertebral body through the CT data and the location This vertebral body in space by means of intraoperatively acquired radiograph I_r determined. These are from the sub-volume CT_p Pseudo-projection images I_pgenerated. The size of the pseudo-projection image I_p is this the size of the X-ray image I_r correspond. The position of the projection point from which the partial volume CT_p in the Pseudo-projection image I_p is projected, corresponding to the position of the X-ray source (or the the X-ray emitting focal spot of the X-ray source) with respect to the X-ray detector in the X-ray. Usually agree the first selected Starting position of the partial volume CT_p with respect to the projection point and the projection direction not with the position and the orientation of the real part volume in the generation of the X-ray photograph with respect to the X-ray source and the X-ray detector agreement. Therefore, these projection parameters of the sub-volume CT are_p in with respect to the projection point and the plane of the projection image I_p changed as long until in one of the difference between the X-ray image I_r and the pseudo-projection image I_p derived difference image I_d the picture of the vertebral body CT_p preferably good extinguishes. This is the case when the pseudo-projection image I_p underlying Location and Orientation of the vertebral body CT_p with the location and orientation of the real Vertebral body with respect to the X-ray source and the X-ray detector coincides. For a further explanation of this process is again the EP 880 109 A2 referenced.

The described method allows the correlation between the X-ray image I_rand the three-dimensional image data set CT in the two X-ray radiation direction perpendicular directions determined very accurately. In the direction of the central X-ray beam is the determination, however, significantly less precise. However, this can be improved by that a second X-ray image with a perpendicular to the first radiograph Beam path will be painted and the comparison process with the second of these X-ray exposure is performed.

The invention is not limited to the embodiment shown, the exemplary only is to be understood. The three-dimensional image data set can also be by means of a other imaging system to be detected, the other can intraoperatively used X-ray device and the position measuring device can be configured differently, as long as the required functionality is met. The concrete embodiment of the method steps, in particular the determination of the assignment rule between the three-dimensional Image data set and the two-dimensional X-ray images, can fully done differently. The comparison method described is merely an example of the Provision of this assignment.