Abstract:
In a medical navigation system and an operating method therefor, a navigation device, having a field of view, detects a position indicator attached to a subject within the navigation field of view, and the navigation device, and thus the navigation field of view, are varied in position by a motorized drive connected to the navigation device. The current attitude of the navigation device and the position indicator are detected, and based on this detection, the motorized drive is operated and controlled so as to always maintain the position indicator within the navigation field of view of the navigation device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention concerns a method to operate a medical navigation system, and a medical navigation system. 
         [0003]    2. Description of the Prior Art 
         [0004]    For medical procedures on patients—for example diagnoses, therapies or operative procedures—a spatial accuracy that is as high as possible is desirable. In surgical procedures—for example on the brain or the spinal column of a patient—it is even indispensable to operate on a precisely determined location in the patient with a medical instrument. Systems known as medical navigation or tracking systems for this purpose have existed for a long time. Systems that operate optically or electromagnetically are significantly different. A medical navigation system operates such that a location indicator in the form of a marker is attached to each of the patient and to the surgical instruments to be used. This marker—a trihedron made of spheres that can be easily detected optically in the optical case, for example; a sensor coil in the electromagnetic case—interacts with a navigation device (mounted so as to be stationary) of the navigation system, in the optical case one or more cameras and in the magnetic case one or more field coils. In the optical case, the camera detects the spatial position of the marker; in the electromagnetic case the spatial position is determined by evaluating the field of the field coil that is received in the sensor coil. In ceiling-based navigation systems, the navigation device is attached to the room ceiling, for example of the operating room. Mobile systems contain a camera mounted on a stand as a navigation device which can be placed arbitrarily freely in space, for example in the operating room. 
         [0005]    Such a navigation device covers only a certain spatial volume (known as the tracking volume) as a navigation region, which the position of the position indicator can be detected only by this navigation region. In particular in optical navigation systems, the optical camera systems must be readjusted given a change of the OP setup if the camera no longer has a line of sight to markers on instruments or patient. In the case of an optical occlusion—for example as a result of a relocation of the patient—the user must thus manually reposition the optical tracking system, i.e. shift the camera arranged on a stand or on the OP room floor, for example, in order to ensure sufficient visibility of the position indicator in the region of interest (for example the situs). In electromagnetic navigation systems, the field generator merely generates a magnetic field in a limited spatial region, in which magnetic field the receiver coils function with sufficient precision. The field generator must then be occasionally displaced. 
         [0006]    With regard to the OP workflow, such adjustments are not desired since effort is necessary and time delays result; the OP workflow is disrupted. For example, the tracking is stopped as soon as there is no line of sight. If the position indicator no longer lies in the tracking volume, the current location of a surgical instrument is temporarily unknown to the navigation system. Without the position information, the medical procedure must be interrupted. For example, in procedures on the spinal column of a patient in proximity to the spinal cord this is problematic since here unintended injuries can lead to complications for the patient. Given known navigation systems, the OP personnel therefore specifically ensure that in every conceivable situation of the procedure the position indicators are situated in the navigation region, or ensure that the navigation device generates a suitable navigation region and the navigation region is not disrupted by the OP setup in any situation of the procedure. 
         [0007]    In known systems—thus in the aforementioned cases—the navigation device must thus be readjusted manually, for example by a physician or OP personnel. In a sterile OP environment it is an additional complication that maintaining a sterile environment must be taken into account. The navigation system is normally unsterile and is provided with appropriate sterile coverings or wrapping that must be displaced as well given tracking of the system. Manual contact with the unsterile navigation system is particularly problematical. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the invention is to provide an improved method to operate a medical navigation system and an improved medical navigation system. 
         [0009]    The above object is achieved in accordance with the invention by a method to operate a medical navigation system, wherein the navigation system has a navigation device that is associated with a limited navigation region. The navigation system moreover has at least one position indicator that can be attached to a subject to be located and that can be located only within the navigation region. The navigation system has a motorized drive for position and attitude variation of the navigation device. By the spatial variation of the navigation device, the attitude and alignment of the navigation region ultimately coupled with it are also varied. The navigation system also has a detection device to detect the current attitude and alignment of navigation region and position indicator. According to the invention, the navigation system detects the attitude variation of the navigation device that is implemented by the motorized drive. An ongoing regulation of the coordinates of the attitude variation additionally controls the drive via a control signal such that the navigation region contains always the position indicator at any given time. For this purpose, the regulation uses an input signal from the detection device that provides information about the current attitude of the navigation region of the position indicator. 
         [0010]    The invention is based on the insight to always move the navigation device via a motorized drive and a correspondingly suitable controller or regulator, to cause the tracking volume—and thus the navigation region—to always be aligned on the presently required spatial region at any time. The spatial region is thus always automatically held or selected by the controller so that the necessary position indicator (for example of the medical instrument) and the patient reference (thus the position indicator attached to the patient) are always located inside said spatial region. 
         [0011]    In other words, the navigation system or its navigation device can be optimally aligned by the integrated regulator even when instruments with corresponding position indicators are held or moved at disadvantageous angles or distances relative to the navigation device, for example. The regulator thus always seeks an optimal or improved position as long as the position indicator by varying the navigation region, can be better placed in this improved position. A manual readjustment of the navigation device—for example by OP personnel—is no longer necessary. The user of the navigation system loses no time and in general does not have to worry about the suitable placement of the navigation device, for example does not need to think about the setting of optimal visibility conditions for a navigation camera. The user does not need to make himself or herself unsterile due to contact with components of the navigation system and loses no time with work that is inconvenient for the user. The navigation is more comfortable to use due to this method and thus its acceptance is increased. The risk to the patient is markedly reduced. 
         [0012]    In a preferred embodiment of the invention, the regulator activates the drive such that the navigation device has a defined distance from the position indicator. For example, an optimal distance between camera and marker or field generator and receiver coil is preselected (thus defined) for a given navigation system, and the navigation device is held at a correspondingly optimal distance by the controller. 
         [0013]    The medical navigation system normally has at least two position indicators. In a preferred embodiment of the method, the regulator controls the drive such that the navigation device is centered with regard to the position indicator. In other words, the navigation device passes to a position that, for example, enables an average, optimally identical distance from the different position indicators or the position distances between navigation device and the position indicators exhibit an optimally small fluctuation range around an optimal distance. 
         [0014]    In a further preferred embodiment of the method, the navigation device operates optically and operates simultaneously as a detection device. In other words, for example, a tracking camera is used simultaneously for the actual navigation but also to detect the current navigation region, even the viewing angle or field of view of the navigation camera. An additional, separate detection device is accordingly superfluous. 
         [0015]    In an alternative method variant, the navigation device operates electromagnetically and the position indicator simultaneously operates as a detection device. In other words, here a sensor coil is us used both for navigation and to measure the electromagnetic field generated by the navigation device in order to thus determine the navigation region. An additional separate detection device is likewise not necessary here. 
         [0016]    In the case of an electromagnetic navigation device, in a further embodiment of the method the regulator also activates the drive such that the electromagnetic field generated by the navigation device at the location of the position indicator has a specific alignment. For example, the controller can always align the field coil such that the generated field at the location of the sensor coil always has optimal field alignment, for example it is perpendicular to this. 
         [0017]    In a further embodiment of the method, the detection device monitors the navigation region for interfering foreign objects. In the case of a tracking camera, for example, the detection device monitors its field of view for the penetration of interfering foreign bodies (i.e. foreign bodies that occlude the camera&#39;s view), for example OP personnel or a voluminous instrument (for example an x-ray C-arm). The spatial position of the corresponding foreign objects can then be detected, and the regulator can determine a new position for the navigation device so that again there is free view of the position indicator. 
         [0018]    In a further embodiment of the method, the detection device monitors the navigation region with a camera coupled with an image processing system. A monitoring of the navigation region for foreign objects thus is possible in a particularly simple manner. 
         [0019]    In an embodiment of the method, additional knowledge or additional data is or are detected via redundant or additional components of the detection device. For example, a larger navigation region can be tracked via a second camera. If a camera becomes “blind” due to occlusion, the second (thus redundant) camera delivers additional tracking information. At this time the occluded system—thus the first camera—serves for a new, optimal position. The controller then uses these data or, respectively, the knowledge for the optimization of the position of the navigation device. Redundant or additional components are, for example, a second optical tracking system or a video camera with connected image processing that can acquire and evaluate the image information with regard to movements, position displacements of components of the OP setup, etc. For optical navigation systems, such a second optical tracking system could for example be installed in the navigation device that bears the navigation camera. For example, given a technically complex realization additional knowledge or data are then position information about the OP setup, participating personnel, the geometry of the OP room etc. 
         [0020]    With regard to the navigation system, the object is achieved by a medical navigation system of the aforementioned embodiment which, according to the invention, thus includes a detection device and a correspondingly operating regulator. The medical navigation system, together with its advantages and the embodiment according to the invention, has already been explained in detail in connection with the method according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  schematically illustrates a medical navigation system constructed and operating in accordance with the present invention, in an optically operating embodiment. 
           [0022]      FIG. 2  schematically illustrates a medical navigation system constructed and operating in accordance with the present invention, in an electromagnetically operating embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  shows an operating (thus OP) room  2  with a bed  4  on which a patient  6  is borne. An optical navigation system  8  is installed in the OP room  2 . A surgical procedure that requires high spatial precision with regard to the procedure location of the instrument  10  at the patient  6  is conducted on the patient  6  with the aid of an instrument  10 . The procedure is therefore spatially coordinated with the aid of the navigation system  8 . Subjects to be localized are thus the patient  6  and the instrument  10 . 
         [0024]    The navigation system  8  has two optical markers in the form of the position indicator  12   a  (which is attached to the patient  6  so as to be stationary) and the position indicator  12   b  (which is attached to the instrument  10  so as to be stationary). A double camera is used as a navigation device  14  and detects the spatial positions P a  and P b  of the position indicators  12   a  and  12   b . The navigation device  14  has as an optical detection region (field of view) a navigation region  16  within which the markers  12   a  and  12   b  must be kept so that their spatial positions P a  and P b  can be determined in the navigation system  8 . 
         [0025]    According to the invention, the navigation device  14  is mounted on the ceiling  18  of the OP room  2  with the use of a rail system  20  that includes two electrical motors  22 . With its use the navigation device  14  can be displaced to an arbitrary position P N  in the direction of the arrows x and y. The position P E  of the navigation region  16  thus can also be displaced. The navigation system  8  moreover has a detection device  24  integrated into the navigation device  14  and the controller  28 , which detection device  24  determines both the current attitude or position P E  of the detection region  16  in the current position of the navigation device  14 , and the positions P a  and P b  of the position indicators  12   a  and  12   b . In an alternative embodiment, the detection device is a separate module that is installed or can be moved independently of the navigation device  14 . In the embodiment shown in  FIG. 1 , the cameras of the navigation device  14  simultaneously form a portion of the detection device  24  since their images are also used to evaluate or determine position or attitude P E  of the navigation region  16 . The cameras can moreover be used to observe the navigation region  16  in that they monitor this for the penetration of foreign objects  34   a  and  34   b , for example a person occluding the view of the camera or a voluminous medical apparatus. 
         [0026]    The detection unit  24  determines the detected positions P a , P b  and P E  as measurement variables  26  that are supplied to a regulator  28  that is used by the navigation system  8 . From the measurement variables  26  the regulator calculates a control signal  30  to operate the electromotors  22 . The controller  28  determines the control signals  30  such that the navigation device  14  is moved to a position P N  along the arrows x, y with the aid of the electromotors  22  or the rail system  20 , in which position P N  the detection region  16  is directed—thus has such an attitude P E —such that the position indicators  12   a  and  12   b  lie within this detection region  16 . The regulator  28  is an automatically operating controller and regulator. In an alternative embodiment, the cameras in the navigation device  14  can additionally also be rotated and pivoted by additional motors (not shown) in order to be able to correspondingly flexibly align the detection region  16  in suitable positions P E . 
         [0027]    In an alternative embodiment, the regulator  28  activates the motors  22  such that the distances d a  and d b  from navigation device  14  to the position indicators  12   a  and  12   b  correspond to a predetermined distance, or deviate from this as little as possible or by optimally the same or a maximum amount. 
         [0028]      FIG. 2  shows the OP room  2  from  FIG. 1  with the patient  6  on whom a different medical measure is conducted with an alternative instrument  10 , however. The navigation system  8  in  FIG. 2  is an electromagnetic navigation system that uses a field coil as a navigation device  14 . Receiver coils as position indicators  12   a  and  12   b  are attached both to the instrument  10  and to the patient  6 , which receiver coils correspondingly determine the spatial position of patient  6  as position P a  and instrument  10  as position P b  relative to the navigation device  14 . 
         [0029]    Here the navigation device  14  is attached via the rail system  20  to the bed  4  and can be displaced along the arrows x and y via motors  22  relative to its spatial position P N . The navigation system  8  includes a controller  28 . In this embodiment the detection device  24  is integrated into the controller  28 . The detection device  24  again detects the positions P a , P b  and P E  of navigation region  16  and position indicators  12   a  and  12   b . In the present case, the navigation region  16  is the spatial region surrounding the field coil, in which spatial region this field coil generates a magnetic field that is sufficiently strong and homogeneous for receiver coils. In  FIG. 2  the controller  28  also correspondingly receives measurement variables  26  from which it determines the optimal position P N  of the navigation device  14  and activates the motors  22  correspondingly in order to move this to the suitable position so that the position indicators  12   a  and  12   b  lie securely and optimally in a navigation region  16 . In this embodiment the alignment R of the electrical field generated by the field coil is hereby taken into account. The field coil in the form of the navigation device  14  is suitably rotated for this so that the direction R of the field optimally perpendicularly traverses the position indicators  12   a  and  12   b  in the form of the receiver coils. 
         [0030]    In one embodiment, an additional camera  32  which serves to detect foreign objects  34   a  and  34   b —namely a mounting plate interfering with the navigation region and an ultrasound head—is present as an extension of the detection device  24 . Both are metallic and interfere with the field connection between the position indicators  12   a  and  12   b  and the navigation device  14 . The controller  28  is connected with the camera  32  via an image processing system  36  in order to suitably evaluate the image information and from this to newly calculate the position P N  of the navigation device  14  so that the aforementioned interferences are eliminated, meaning that the foreign objects no longer interfere with the navigation region  16  in the relevant region of the position indicators  12   a  and  12   b.    
         [0031]    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 heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.