Method for positioning a catheter in a vessel, and device for implementing the method

[0002] 1. Field of the Invention

[0003] The present invention is directed to a method for positioning a catheter that has been inserted into a vessel and to a device for implementing the method, the device being particularly for conducting an angiographic examination of a subject.

[0004] 2. Description of the Prior Art

[0005] In angiographic examinations, i.e. in radiological examinations of blood vessels or lymphatic vessels, a catheter is inserted into the examined vessel, by means of which a specific contrast agent can be injected into the vessel in order to improve the contrast of the captured X-ray image at the examined location, the corresponding vessel being brought into prominence in the X-ray image by the contrast agent injection. For this purpose the catheter must first be led to the respective target location, i.e. to the desired examination location. The positioning of the catheter in angiographic examinations thus has a special significance, since what is particularly important in the positioning of the catheter to follow the branchings of the vessel accurately and to reach the desired target location (where there is a stenosis or an aneurism [sic], for example) precisely and without interruption.

[0006] For this reason, a technique known as the road map technique (pathfinder technique) has long been used, which facilitates positioning of the catheter in a vessel that is to be examined. In this technique, a small amount of contrast agent is injected into the vessel via the catheter while transirradiating the vessel, and, as soon as the vessel gives an image, the transirradiation is interrupted and the last radiographic image is stored as a mask. After the transirradiation has been restarted, individual images are captured of the catheter inserted in the vessel that is to be examined, and these are superimposed on and subtracted from the stored mask image, so that an examiner can visually localize and place the catheter in the contrasted image by observing the superimposed total image.

[0007] The above-described road map technique requires that the instantaneous images of the catheter in the vessel be captured from the same exposure angle or projection angle of the X-ray device as the previously stored mask image, since otherwise these images can not be compared to the stored mask images, by being superimposed on them. As a result, in order to mark the individual vessels, it is necessary to make new contrast agent injections for each projection direction or for each exposure angle, so that difficult interventional procedures, such as those employed in the field of neuroradiology must be used. Since these procedures entail relatively frequent contrast agent injections, this makes rapid positioning and localizing of the catheter in the vessel to be examined difficult and prolongs the treatment period for the examination subject.

[0008] An object of the present invention is to provide a method for positioning a catheter which has been inserted into a vessel, as well as a corresponding device, which make it possible to position the catheter more rapidly and simply in the vessel which is to be examined and to avoid frequent contrast agent injections, in particular.

[0009] The basic idea of the aforementioned road map technique is also relied upon in the present invention for positioning the catheter in a vessel to be examined; that is, after a contrast agent has been injected, a contrast agent image is captured and stored as a mask of the respective vessel, the mask being superimposed by a subsequently captured single image of the vessel with inserted catheter, in order to be able to localize and place the catheter in the contrasted vessel using the thus-acquired total image. This is augmented in the present invention to achieve the above object by generating and storing a three-dimensional image of the vessel as the mask, this three-dimensional image being computed from a number of individual images that have been picked up from various projection angles or exposure angles with an X-ray device, by transirradiating the contrasted vessel. This procedure-makes it possible to select that individual image of the three-dimensional mask image whose projection direction, or whose exposure angle, most optimally corresponds to the instantaneous exposure angle of the instantaneous image, depending on the projection direction of the subsequent instantaneous exposure of the examined vessel. This selected individual image is subsequently displayed with the individual instantaneous images superimposed thereon, in order to be able to localize and place the catheter visually in the contrasted vessel.

[0010] Using the invention, only a one-time contrast agent injection is required in order to generate a three-dimensional mask image. The individual images, which, when reconstructed, yield the three-dimensional mask image of the contrasted vessel, can be captured by rotating the pickup system of the X-ray device around the examination location. The invention thus guarantees that, despite a single one-time contrast agent injection, it is always possible to select the appropriate mask image and to superimpose the instantaneous images thereon, regardless of the actual projection direction used to capture the instantaneous images of the vessel to be examined, so that new injections of contrast agent are not required for each new positioning direction. Using the present invention, it is thus possible to rapidly and precisely localize and position the catheter in the vessel, so that the catheter can likewise be guided in the vessel rapidly and precisely to the desired target location, (the location of the examination).

[0011] The present invention also makes it possible, subsequent to capturing the three-dimensional mask image of the vessel, to select the projection direction or the exposure angle for capturing the instantaneous images which is optimal for catheter guidance, and to adjust the X-ray device accordingly. For this purpose, it is merely necessary to select the individual image of the three-dimensional mask image that corresponds to the projection direction that has been set, in order to be able to subsequently superimpose the instantaneous images thereon.

[0012] The present invention can be used either in a monoplanar transirradiation or in a biplanar transirradiation of the examination location, the instantaneous images being captured from only one projection direction or from two different projection directions, respectively. It can be guaranteed by appropriate matchings that the selected mask image is always displayed congruently to the captured instantaneous image, by employing the known pixel shifting technique for this purpose.

[0013] FIG. 1 is a simplified block diagram of a device for the angiographic examination of a subject in which the present invention is employed.

[0014] FIG. 2aand FIG. 2billustrate a measure to make the mask image congruent to a captured instantaneous image.

[0015] The device illustrated in FIG. 1 is for angiographic examination of a subject 1, wherein fluoroscopic images are obtained of vessels of the subject 1 in order to be able to detect constrictions of the vessel or the like. The X-ray device includes a radiation source 2 (illustrated in FIG. 1) and an image capturing system 3, which includes an X-ray image amplifier and a monitor, in particular. The image capturing system 3 of this X-ray device is connected to an image processing unit 10, which evaluates or combines the fluoroscopic images captured by the X-ray device and displays them on a monitor 7. This allows an examiner to visually localize and place the catheter, which as been inserted into a vessel for purposes of angiographic examination, by observing the monitor 7, in order to be able to accurately follow branchings of the vessel and to guide the catheter continuously and precisely to the desired target location, for example.

[0016] The examination can proceed as follows:

[0017] First, a contrast agent is injected into the vessel in which the catheter is to be guided, in order to highlight the vessel path more sharply, and a mask image of the corresponding vessel is captured using the X-ray device, this being a matter of a three-dimensional image of the vessel. This three-dimensional mask image of the contrasted vessel is composed of a number of individual mask images which are captured by transirradiation of the vessel from different projection angles or exposure angles. This can ensue by rotating the radiation source 2 and the image capturing system 3, which are mounted on a C-arm, once around the corresponding body parts of the subject 1, with a number of individual mask images of the contrasted vessel being captured from different projection directions. The image data of these individual mask images are fed by the image capturing system 3 to a 3D mask image memory 4, which processes the image data and combines them into the three-dimensional mask image of the location of examination with the corresponding vessel; i.e., the 3D mask image memory 4 generates a three-dimensional image record which is obtained by combining the image data of the individual mask images that are captured from different projection directions. This three-dimensional image record is stored in the 3D mask image memory 4.

[0018] The above described procedure i s executed only once; that is, it is only necessary to perform a single injection of contrast agent into the vessel to be examined, i.e., into the corresponding examination location, in order to obtain the three-dimensional mask image.

[0019] The examiner subsequently selects the projection direction of the X-ray device which is optimal for catheter guidance and positions the radiation source 2 and the image capturing system 3 accordingly. The positioning of the X-ray device can occur either manually or automatically; that is, the examiner prescribes the desired projection direction to the device, and the radiation source 2 and the image capturing system 3 are positioned by a suitable drive corresponding to the desired projection direction, in order to be able to subsequently execute the instantaneous exposures, required for the road map technique, of the corresponding vessel.

[0020] Next, dependent on the selected direction of projection, the image data of that individual mask image whose projection direction corresponds to the selected direction is selected from the three-dimensional image record of the 3D mask image memory 4. If this is not possible, that individual mask image is selected whose projection direction most optimally corresponds to the direction of projection of the X-ray device that has been set. The selection of the image data of the individual mask image to be selected can ensue manually. An automatic selection, however, is preferable; that is, depending on the desired direction of projection, the 3D mask image memory 4 may have processing capability allowing it to automatically select the image data of that individual mask image, from the three-dimensional image record of the previously obtained three-dimensional mask image of the contrasted vessel, whose projection direction best corresponds to the desired projection direction. However selected, the data for this image are supplied to an image processor 6, which superimpose the individual mask image on the subsequently captured instantaneous images of the vessel (examination location), and to displays these latter images on the monitor 7.

[0021] The corresponding body part of the subject 1 is subsequently transirradiated again, and an instantaneous image of the vessel is captured with the catheter inserted, which image is fed to an image memory, which may also have computing capability 5. This image memory 5 processes the image data of the instantaneous image which is captured from the previously set projection direction and feeds the image data to the image processor 6, so that the processor 6 can superimpose the previously selected individual mask image of the three-dimensional mask image, which is supplied from the 3D mask image memory 4, on the image data of the instantaneous image and can display this resulting image data on the monitor 7. The processor 6 thus always superimposes an individual mask image, which is previously selected corresponding to the desired projection direction, of the three-dimensional mask image of the contrasted vessel, on an instantaneously captured individual image. By using the monitor 7, an examiner can thus localize and place the catheter in the contrasted vessel.

[0022] The device illustrated in FIG. 1 is for angiographic examination of the subject 1, wherein a monoplanar transirradiation is performed; that is, an instantaneous exposure of the respective vessel always occurs from one previously set projection direction. The present invention can be applied just as well for biplanar transirradiation, in which instantaneous exposures are performed from two different directions of projection. To this end, the device illustrated in FIG. 1 is expanded by an additional image memory 5 along with an additional processor 6, the instantaneous image of the desired examination location from a different projection direction being fed to this additional image memory 5. In this case, the additional processor 6 receives the corresponding image data of the additional image memory 5 and would access the shared 3D mask image memory 4 in order to select that individual mask image of the previously obtained three-dimensional mask image which corresponds optimally to the projection direction, and to superimpose the individual mask image thereon. In this way, a second superimposed total image of the examination location of the subject 1 is generated, which may be displayed on a separate monitor or together with the previously described first superimposed total image on the same monitor 7, so that the examiner can observe the catheter guidance in the vessel from different viewing angles.

[0023] The captured instantaneous image, which is stored in the image memory 5, is distorted to a certain extent by the X-ray image amplifier contained in the image capturing system 3. In order to be able to compare this instantaneous image to the corresponding individual mask image, and to be able to superimpose this mask image thereon despite this distortion, it is necessary either to correct the distortion of the instantaneous image according to the X-ray image amplifier distortion or to correspondingly distort the selected individual image mask of the 3D mask image memory 4 according to the X-ray image amplifier distortion, so that equally corrected or equally distorted individual images are superimposed by the processor 6 and displayed on the monitor 7. Correction of the distortion of the instantaneous image, or the distortion of the individual mask image, can be performed by appropriate image processing software in the processor 6.

[0024] When the instantaneous image of the image memory 5 is superimposed with the selected individual mask image from the 3D mask image memory 4, the image background, i.e. bones and the like, can still be seen on the monitor 7. In order to be able to display only the catheter with the individual mask image of the three-dimensional mask image of the 3D mask image memory 4 on the display 7, it is possible to execute an additional instantaneous image capture of the examination location without contrast agent injection and without a catheter, that is, given a withdrawn catheter, prior to the actual transirradiation with the previously set projection direction of the X-ray device, the corresponding image data for this image also being stored in the image memory 5, for example. The image memory 5 then subtracts the image data forming this “empty” image from the image data of the instantaneous images that are obtained subsequently by transirradiation with the catheter present, and supplies the image data representing this revised image to the processor 6. The processor 6 superimposes the individual mask image, supplied by the 3D mask image memory 4, of the three-dimensional mask image on this revised instantaneous image, or subtracts the individual mask image therefrom, in order to display a corresponding total image on the monitor 7. Alternatively, it is also possible to generate a series of empty images which are subtracted from the respective instantaneous images acquired during transirradiation with the catheter present, so that the three-dimensional mask image is acquired as a series of subtraction images produced by the subtraction of an instantaneous image, which is captured during transirradiation, from a corresponding empty image.

[0025] The X-ray device can have certain mechanical device tolerances which may lead to imprecisions in the image capture and consequently in the positioning of the catheter. To this end, prior to the actual initial operation of the X-ray device, a test run of the C-arm with the radiation source 2 and the image capturing system 3 can be conducted, with a calibrating phantom disposed in the examination field of view and with image data from the phantom being detected during the trial, in order to subsequently have the ability to calculate the device tolerances or device deviations and to take these into account in the image processing of the captured images. Only the device tolerances for the specified motion plane of the C-arm of the X-ray device, however, can be computed and taken into account by means of this calibration run. A calibration run for every arbitrary device position, which would amount to a complete three-dimensional calibration, cannot be performed for reasons of outlay and complexity. Nevertheless, when another base positional setting of the device is selected for transirradiating the subject 1, it is still possible, as described above, to select, from the three-dimensional image record of the 3D mask image memory 4, that individual mask image whose image projection direction best corresponds to the instantaneous projection direction. Due to the device tolerances, however, which are not calibrated for this device position, there are convergence errors between the selected individual mask image and the instantaneous image which is captured in the set direction of projection and which is stored in the image memory 5. A postprocessing of the images thus is necessary, in order to make the instantaneous image congruent to the individual mask image. This postprocessing can be executed automatically or semiautomatically by the processor 6 in the form of a two-dimensional or three-dimensional matching, whereby preferably either the image structures used for this are the same in the selected individual mask image of the three-dimensional mask picture of the 3D mask image memory 4 and in the instantaneous image of the image memory 5, or there must necessarily be a correlation between them. This is described in detail below.

[0026] For example, it is possible to bring the instantaneous image into congruence with the selected individual mask image of the three-dimensional mask image by bringing the individual pixels into congruence by x and y shifting. This method is termed pixel shifting and can be performed automatically by the processor 6, for example. In a biplanar exposure, the matching or aligning between the two instantaneous images of the different projection directions and a corresponding individual image mask of the three-dimensional mask picture can ensue in succession or in alternation in a three-dimensionally interactive manner; i.e., the two instantaneous images of the examination location, which are captured from different projection directions, are brought into congruence with the correspondingly selected individual mask image of the previously captured and stored three-dimensional mask image separately from one another.

[0027] When the catheter is already situated in the vicinity of the target region or the desired examination location, a direct matching is performed for the catheter with the vessel representations of the mask image of the three-dimensional mask picture. The fact that the catheter must be located in the corresponding vessel is exploited for this purpose. FIG. 2aillustrates the display on the monitor 7 for the case when the representation of a vessel 8 which is obtained by means of a selected individual mask image of the three-dimensional mask image of the 3D mask image memory 4 is not congruent to the representation of the catheter 9, this representation having been obtained by means of the instantaneous pickup with the image memory 5. Since it is necessary for the catheter 9 to be situated in the vessel 8, the individual mask image of the three-dimensional mask image, or alternatively the instantaneous exposure image of the transillumination, can be shifted such that the catheter 9 comes to be situated in the vessel 8, as is illustrated in FIG. 2b.

[0028] If the catheter is already situated in the vicinity of the target region, another alternative is to perform a trial injection of the contrast agent during transirradiation and the captured and stored individual image of the vessel obtained as a result can be brought into congruence with the identical vessels of the previously captured mask image of the three-dimensional mask image, in order to guarantee that the instantaneous image of the image memory 5 that is captured in the corresponding device position is congruent to the individual mask image of the three-dimensional mask image of the 3D mask image memory 4.

[0029] The above-described matching measures cause the instantaneous image of the examination location, i.e., of the corresponding vessel, obtained during transirradiation, to be brought exactly into congruence with the previously captured vessel image of the three-dimensional mask image, so that the inventively executed road map technique leads to the result of a reliable and certain localization and placement of the catheter in the corresponding vessel.

[0030] Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.