Patent Publication Number: US-2019192230-A1

Title: Method for patient registration, calibration, and real-time augmented reality image display during surgery

Description:
TECHNICAL FIELD 
     The present disclosure relates to surgical navigation systems, in particular to a system and method for operative planning, image acquisition, patient registration, calibration, and execution of a medical procedure using an augmented reality image display. 
     BACKGROUND 
     Some typical functions of a computer-assisted surgery (CAS) system with navigation include presurgical planning of a procedure and presenting preoperative diagnostic information and images in useful formats. The CAS system presents status information about a procedure as it takes place in real time, displaying the preoperative plan along with intraoperative data. The CAS system may be used for procedures in traditional operating rooms, interventional radiology suites, mobile operating rooms or outpatient clinics. The procedure may be any medical procedure, whether surgical or non-surgical. 
     Surgical navigation systems are used to display the position and orientation of surgical instruments and medical implants with respect to presurgical or intraoperative medical imagery datasets of a patient. These images include pre and intraoperative images, such as two-dimensional (2D) fluoroscopic images and three-dimensional (3D) magnetic resonance imaging (MRI) or computed tomography (CT). 
     Navigation systems locate markers attached or fixed to an object, such as surgical instruments and patient. Most commonly these tracking systems are optical and electro-magnetic. Optical tracking systems have one or more stationary cameras that observes passive reflective markers or active infrared LEDs attached to the tracked instruments or the patient. Eye-tracking solutions are specialized optical tracking systems that measure gaze and eye motion relative to a user&#39;s head. Electro-magnetic systems have a stationary field generator that emits an electromagnetic field that is sensed by coils integrated into tracked medical tools and surgical instruments. 
     Incorporating image segmentation processes that automatically identify various bone landmarks, based on their density, can increase planning accuracy. One such bone landmark is the spinal pedicle, which is made up of dense cortical bone making its identification utilizing image segmentation easier. The pedicle is used as an anchor point for various types of medical implants. Achieving proper implant placement in the pedicle is heavily dependent on the trajectory selected for implant placement. Ideal trajectory is identified by surgeon based on review of advanced imaging (e.g., CT or MRI), goals of the surgical procedure, bone density, presence or absence of deformity, anomaly, prior surgery, and other factors. The surgeon then selects the appropriate trajectory for each spinal level. Proper trajectory generally involves placing an appropriately sized implant in the center of a pedicle. Ideal trajectories are also critical for placement of inter-vertebral biomechanical devices. 
     Another example is placement of electrodes in the thalamus for the treatment of functional disorders, such as Parkinson&#39;s. The most important determinant of success in patients undergoing deep brain stimulation surgery is the optimal placement of the electrode. Proper trajectory is defined based on preoperative imaging (such as MRI or CT) and allows for proper electrode positioning. 
     Another example is minimally invasive replacement of prosthetic/biologic mitral valve in for the treatment of mitral valve disorders, such as mitral valve stenosis or regurgitation. The most important determinant of success in patients undergoing minimally invasive mitral valve surgery is the optimal placement of the three dimensional valve. 
     Typically, one or several computer monitors are placed at some distance away from the surgical field. They require the surgeon to focus the visual attention away from the surgical field to see the monitors across the operating room. This results in a disruption of surgical workflow. Moreover, the monitors of current navigation systems are limited to displaying multiple slices through three-dimensional diagnostic image datasets, which are difficult to interpret for complex 3D anatomy. 
     SUMMARY OF THE INVENTION 
     When defining and later executing an operative plan, the surgeon interacts with the navigation system via a keyboard and mouse, touchscreen, voice commands, control pendant, foot pedals, haptic devices, and tracked surgical instruments. Based on the complexity of the 3D anatomy, it can be difficult to simultaneously position and orient the instrument in the 3D surgical field only based on the information displayed on the monitors of the navigation system. Similarly, when aligning a tracked instrument with an operative plan, it is difficult to control the 3D position and orientation of the instrument with respect to the patient anatomy. This can result in an unacceptable degree of error in the preoperative plan that will translate to poor surgical outcome. 
     The augmented reality systems allow overlaying a virtual image over a real-world image, such that these images are correctly collocated, depending on the viewpoint of the surgeon. In order to do so, it is essential to track the position of the surgeon&#39;s head and direction of view with respect to the real anatomy. This, in turn, requires performing a preoperative scan of the real anatomy and registering the scan with respect to the same coordinate system in which the surgeon&#39;s head is tracked. Performing and registering a pre-operative scan of patient anatomy is not a trivial task. 
     One aspect of the invention is a method for registering patient anatomical data in a surgical navigation system, the method comprising: placing a registration grid over the patient at a first position, wherein the registration grid comprises a plurality of fiducial markers; by means of a medical scanner, scanning both a patient anatomy of interest and the registration grid to obtain patient anatomical data; providing a pre-attached tracking array comprising a plurality of fiducial markers that is attached to the patient at a second position; by means of a fiducial marker tracker, capturing the 3D position and/or orientation of the pre-attached tracking array and the registration grid; and registering the patient anatomical data with respect to the 3D position and/or orientation of the pre-attached tracking array as a function of the relative position and/or orientation of the registration grid and the pre-attached tracking array. 
     The pre-attached tracking array may be pre-attached to the patient internal anatomy around the surgical field 
     The fiducial marker tracker may use an optical, electromagnetic or acoustic technology for capturing the 3D position and/or orientation. 
     The method may further comprise: using the tracker for real-time tracking of the pre-attached tracking array; generating, by a surgical navigation image generator, a surgical navigation image comprising the patient anatomical data adjusted with respect to the 3D position and/or orientation of the pre-attached tracking array; showing the surgical navigation image by means of a 3D display system such that an augmented reality image, collocated with the surgical field, is visible to a viewer looking towards the surgical field. 
     The method may further comprise: by means of the tracker, real-time tracking of at least one of: a surgeon&#39;s head, a 3D display and surgical instruments to provide current 3D position and/or orientation data; and adjusting the surgical navigation image with respect to the tracked current 3D position and/or orientation data. 
     The method may further comprise: by means of the tracker, real-time tracking of a robot arm marker array; and generating the surgical navigation image further comprising the robot arm virtual image adjusted with respect to the tracked position and orientation of the robot arm marker array. 
     The method may further comprise identifying the fiducial markers of the registration grid in the volumetric data provided by the medical scanner using a convolutional neural network. 
     Another aspect of the invention is a method for registering patient anatomical data in a surgical navigation system, the method comprising: by means of a medical scanner, scanning a volume comprising a patient anatomy of interest and a registration grid placed over the patient at a first position, to obtain patient anatomical data, wherein the registration grid comprises a plurality of fiducial markers; by means of a fiducial marker tracker, capturing a 3D position and/or orientation of a pre-attached tracking array that has been pre-attached to the patient at a second position and of the registration grid placed over the patient at the first position, wherein the pre-attached tracking array comprises a plurality of fiducial markers; and registering the patient anatomical data with respect to the 3D position and/or orientation of the pre-attached tracking array as a function of the relative position and/or orientation of the registration grid and the pre-attached tracking array. 
     In some embodiments, the intended use of this invention is both presurgical planning of ideal surgical instrument trajectory and placement, and intraoperative surgical guidance, with the objective of helping to improve surgical outcomes. 
     These and other features, aspects and advantages of the invention will become better understood with reference to the following drawings, descriptions and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Various embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein 
         FIG. 1  shows a layout of a surgical room employing a surgical navigation system, in accordance with an embodiment of the invention; 
         FIG. 2  shows components of the surgical navigation system in accordance with an embodiment of the invention; 
         FIG. 3A  shows one example of an augmented reality display in accordance with an embodiment of the invention; 
         FIG. 3B  shows another example of an augmented reality display in accordance with an embodiment of the invention; 
         FIG. 4  shows an overview of the operating room during the registration procedure in accordance with an embodiment of the invention; 
         FIG. 5  shows an overview of a method for patient anatomy registration in accordance with an embodiment of the invention; 
         FIG. 6A  shows a registration grid placed on the patient in accordance with an embodiment of the invention; 
         FIG. 6B  shows the registration grid in accordance with an embodiment of the invention; 
         FIG. 6C  shows a tracking array attached to the patient in accordance with an embodiment of the invention; 
         FIG. 6D  shows capturing the 3D position and/or orientation of both the tracking array and the registration grid in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention. 
       FIGS. 1, 2, 3A and 3B  show an example of a surgical navigation system employing augmented reality display, for which the method for patient registration as described later herein is applicable. This is only an example and the method for patient registration can be used with other systems as well. 
     The example of the surgical navigation system as presented herein in  FIG. 1  comprises a 3D display system  140  to be implemented directly on real surgical applications in a surgical room. The 3D display system  140  as shown in the example embodiment comprises a 3D display  142  for emitting a surgical navigation image  142 A towards a see-through mirror  141  that is partially transparent and partially reflective, such that an augmented reality image  141 A collocated with the patient anatomy in the surgical field  108  underneath the see-through mirror  141  is visible to a viewer looking from above the see-through mirror  141  towards the surgical field  108 . 
     A patient  105  lies on the operating table  104  while being operated on by a surgeon  106  with the use of various surgical instruments  107 . The surgical navigation system as described in details below can have its components, in particular the 3D display system  140 , mounted to a ceiling  102 , or alternatively to the floor  101  or a side wall  103  of the operating room. Furthermore, the components, in particular the 3D display system  140 , can be mounted to an adjustable and/or movable floor-supported structure (such as a tripod). Components other than the 3D display system  140 , such as the surgical image generator  131 , can be implemented in a dedicated computing device  109 , such as a stand-alone PC computer, which may have its own input controllers and display(s)  110 . 
     In addition, the system may comprise a robot arm  191  for handling some of the surgical tools. The robot arm  191  may have two closed loop control systems: its own position system and one used with the optical tracker as presented herein. Both systems of control may work together to ensure that the robot arm is in the right position. The robot arm&#39;s position system may comprise encoders placed at each joint to determine the angle or position of each element of the arm. The second system may comprise a robot arm marker array  126  attached to the robot arm to be tracked by the tracker  125 , as described below. Any kind of surgical robotic system can be used, preferably one that follows standards of the U.S. Food &amp; Drug Administration. 
       FIG. 2  shows a functional schematic presenting connections between the components of the surgical navigation system. 
     The surgical navigation system comprises a tracking system for tracking in real time the 3D (i. e. in three dimensions) position and/or orientation of various entities to provide current position and/or orientation data. For example, the system may comprise a plurality of arranged fiducial markers, which are trackable by a fiducial marker tracker  125 . Any known type of tracking system can be used—for example in case of a marker tracking system, 4-point marker arrays are tracked by a three-camera sensor to provide movement along six degrees of freedom. A head position marker array  121  can be attached to the surgeon&#39;s head for tracking of the position and orientation of the surgeon and the direction of gaze of the surgeon—for example, the head position marker array  121  can be integrated with the wearable 3D glasses  151  or can be attached to a strip worn over surgeon&#39;s head. 
     Alternatively, the tracker may use optical, electromagnetic, acoustic, or any other technology for capturing the 3D position and/or orientation of markers. 
     A display marker array  122  can be attached to the see-through mirror  141  of the 3D display system  140  for tracking its position and orientation, since the see-through mirror  141  is movable and can be placed according to the current needs of the operative setup. 
     A patient anatomy marker array  123 , also called herein a tracking array  123 , can be pre-attached (before performing the registration procedure) at a particular position and/or orientation of the anatomy of the patient. 
     A surgical instrument marker array  124  can be attached to the instrument whose position and orientation shall be tracked. 
     A robot arm marker array  126  can be attached to at least one robot arm  191  to track its position. 
     Preferably, the markers in at least one of the marker arrays  121 - 124  are not coplanar, which helps to improve the accuracy of the tracking system. 
     Therefore, the tracking system comprises means for real-time tracking of the position and/or orientation of at least one of: a surgeon&#39;s head  106 , a 3D display  142 , a patient anatomy  105 , and surgical instruments  107 . Preferably, all of these elements are tracked by a fiducial marker tracker  125 . 
     A surgical navigation image generator  131  is configured to generate an image to be viewed via the see-through mirror  141  of the 3D display system. It generates a surgical navigation image  142 A comprising data of at least one of: the pre-operative plan  161  (which are generated and stored in a database before the operation), data of the intra-operative plan  162  (which can be generated live during the operation), data of the patient anatomy scan  163  (which can be generated before the operation or live during the operation) and virtual images  164  of surgical instruments used during the operation (which are stored as 3D models in a database), as well as virtual image  166  of the robot arm  191 . 
     The surgical navigation image generator  131 , as well as other components of the system, can be controlled by a user (i.e. a surgeon or support staff) by one or more user interfaces  132 , such as foot-operable pedals (which are convenient to be operated by the surgeon), a keyboard, a mouse, a joystick, a button, a switch, an audio interface (such as a microphone), a gesture interface, a gaze detecting interface etc. The input interface(s) are for inputting instructions and/or commands. 
     The surgical navigation image generator  131  is configured to control the steps of the method described with reference to  FIG. 5  and calculate necessary data to perform the method. 
     All system components are controlled by one or more computer(s) which are controlled by an operating system and one or more software applications. The computer(s) may be equipped with a suitable memory which may store computer program or programs executed by the computer in order to execute steps of the methods utilized in the system. Computer programs are preferably stored on a non-transitory medium. An example of a non-transitory medium is a non-volatile memory, for example a flash memory while an example of a volatile memory is RAM. The computer instructions are executed by a processor. These memories are exemplary recording media for storing computer programs comprising computer-executable instructions performing all the steps of the computer-implemented method according the technical concept presented herein. The computer(s) can be placed within the operating room or outside the operating room. Communication between the computer(s) and the components of the system may be performed by wire or wirelessly, according to known communication means. 
     The aim of the system is to generate, via the 3D display system  140 , an augmented reality image such as shown in  FIG. 3A  or  FIG. 3B . When the surgeon looks via the 3D display system  140 , the surgeon sees the augmented reality image  141 A which comprises: 
     the real world image: the patient anatomy, surgeon&#39;s hands and the instrument currently in use (which may be partially inserted into the patient&#39;s body and hidden under the skin); 
     and a computer-generated surgical navigation image  142 A comprising at least one of: the pre-operative plan  161 , data of the intra-operative plan  162 , data of the patient anatomy scan  163  (supplemented by different orthogonal planes of the patient anatomical data  163 : coronal  174 , sagittal  173 , axial  172 ), virtual images  164  of surgical instruments used during the operation, virtual image  166  of the robot arm, a menu  175  for controlling the system operation. 
     If the 3D display  142  is stereoscopic, the surgeon shall use a pair of 3D glasses  151  to view the augmented reality image  141 A. However, if the 3D display  142  is autostereoscopic, it may be not necessary for the surgeon to use the 3D glasses  151  to view the augmented reality image  141 A. 
     The surgical navigation image  142 A is generated by the image generator  131  in accordance with the tracking data provided by the fiducial marker tracker  125 , in order to superimpose the anatomy images and the instrument images exactly over the real objects, in accordance with the position and orientation of the surgeon&#39;s head. The markers are tracked in real time and the image is generated in real time. Therefore, the surgical navigation image generator  131  provides graphics rendering of the virtual objects (patient anatomy, surgical plan and instruments) collocated to the real objects according to the perspective of the surgeon&#39;s perspective. 
     The 3D display system described above makes use of a 3D display  142  with a see-through mirror  141 , which is particularly effective to provide the surgical navigation data. However, other 3D display systems can be used as well to show the augmented image, such as 3D head-mounted displays. 
     The virtual image of the patient anatomy  163  is generated based on data representing a three-dimensional segmented model comprising at least two sections representing parts of the anatomy. The anatomy can be for example a bone structure, such as a spine, skull, pelvis, long bones, shoulder joint, hip joint, knee joint etc. This description presents examples related particularly to a spine, but a skilled person will realize how to adapt the embodiments to be applicable to the other bony structures or other anatomy parts as well. 
     The model is generated based on a pre-operative scan of the patient. 
     The following description will present a method for registering a pre-operative or intra-operative scan of the patient. 
       FIG. 4  shows an overview of the operating room, with the elements shown that are similar to that shown in  FIG. 1 . In addition, a medical intraoperative image scanner (IIS)  180  is present, to perform patient anatomy scanning to obtain the patient anatomical data  163 . The presented example of the IIS  180  is a computer tomography (CT) scanner, but other types of scanners can be used as well. 
       FIG. 5  shows steps of a method for patient anatomy registration and other supportive actions. 
     In step  501 , a registration grid  181  is placed on the patient  105  at a first position  105 A, as shown in  FIG. 6A . 
     In step  502 , a volume comprising the patient anatomy of interest and the registration grid is scanned with the IIS  180 . 
     The registration grid  181 , as shown in  FIG. 6B , is a device that has a base  181 A and an array of fiducial markers  181 B that are registrable both by the HS  180  and the fiducial marker tracer  125 . For highly accurate registration results, the grid  181  may comprise five markers  181 B, forming three groups of three markers each (some markers may belong to more than one group), each group arranged on a different plane. The registration grid  181  can be attached to the patient for example by an adhesive, such that it stays in the position during the scan. Registration grids with other amount and arrangement of markers can be used as well, depending on the needs. 
     The fiducial markers of the registration grid  181  in the volumetric data provided by the medical scanner can be identified using a convolutional neural network (CNN). 
     Therefore, the scan of the patient anatomy performed in step  502  comprises data of the patent anatomy and of the registration grid, in particular the markers  181 B. 
     In step  503 , the tracking array  123  is provided that has been pre-attached to the patient, at a second position  105 B, as shown in  FIG. 6C . Attachment of the tracking array  123  to the patient can be done in a surgical or a non-surgical procedure. For example, the tracking array can be inserted into the iliac crest or a bony anchor point. The tracking array can be also attached by means of a dedicated holder to the body of the patient that does not require invasion inside the human body. The tracking array  123  can be attached to the patient in step  501 , along with the grid  181  or even before step  501 . In step  504 , the fiducial marker tracker  125  is used to capture and record the 3D position and/or orientation of both the tracking array  123  and the registration grid  181 , as shown in  FIG. 6D . During this section of the process, the relative position and/or orientation of the pre-attached tracking array  123  and the registration grid  181  is determined. The relative position and/or orientation works as the reference to keep track of the position and/or orientation of the anatomy of the patient when the registration grid  181  is removed. 
     Steps  501 ,  503  related to arrangement of the registration grid  181  and of the fiducial marker tracker  125  with respect to the patient body can be performed by different personnel than the steps of scanning  502  and capturing  504  of images. These steps  501 ,  503  can be considered as not forming an essential part of the method for patient anatomy registration, but as supportive actions. These steps  501 ,  503  can be performed in advance and separately from the steps  502 ,  504 . 
     Next, in step  505 , the registration grid  181  can be removed from the patient. Even though the registration grid is removed, the patient&#39;s anatomy is still tracked properly because the tracking array  123  keeps that relative reference to display the anatomy in place. 
     In step  506 , the patient anatomical data  163  is registered with respect to the 3D position and/or orientation of the tracking array  123  as a function of the relative position and/or orientation of the registration grid  181  and the tracking array  123 , in particular as the function of their fiducial markers  181 B,  123 B. The 3D display system may be then activated to present an augmented reality image, such as shown in  FIG. 3A or 3B . The patient anatomy virtual image can be then displayed on collocation with the real physical anatomy of the patient. Therefore, the augmented reality image comprises the patient anatomical data  163  (as well as other virtual images (such as virtual instrument images  164 )) registered with respect to the position of the tracking array  123  and preferably also the position of the structure system  140  and the head of the surgeon  106 . 
     The surgical procedure can be performed now with the use of the surgical navigation system, wherein the patient anatomical data  163  is precisely aligned with the position and/or orientation of the tracking array  123 , the position and/or orientation of which is real-time tracked by the fiducial marker tracker  125  during the surgical procedure. 
     Moreover, if some of the surgical tools can be handled by the robot arm  191 , the position and/or orientation of which is tracked via the robot arm marker array  126 , the augmented reality image may further comprise a virtual image  166  of the robot arm collocated with the real physical anatomy of the patient, as shown in  FIG. 3B . Furthermore, the augmented reality image may comprise a guidance image  166 A that indicates, according to the preoperative plan data, the suggested position and orientation of the robot arm  191 . 
     The virtual image  166  of the robot arm may be configurable such that it can be selectively displayed or hidden, in full or in part (for example, some parts of the robot arm can be hidden (such as the forearm) and some (such as the surgical tool holder) can be visible). Moreover, the opacity of the robot arm virtual image  166  can be selectively changed, such that it does not obstruct the patient anatomy. 
     The advantage of the presented method in some embodiments is that the patient anatomical data  163  is precisely scanned by the IIS  180  along with the registration grid  181 , which can be positioned at the first position  105 A in a very close vicinity of the area of interest to be scanned, therefore an accurate scan of the anatomy and the grid can be performed. After the scan is complete, the position and/or orientation of the grid  181  is recorded with respect to a position and/or orientation of the tracking array  123 , which can be attached to the patient&#39;s body at the second position  105 B, at some distance away from the area of interest, and next the registration grid  181  can be removed from the patient. As a result, the tracking array  123  is positioned at the second position  105 B away from the operating area and does not disrupt the surgeon during the operation, while still allows to track the position and/or orientation of the tracking array  123  and therefore determine the corresponding position and/or orientation of the patient anatomy subject to the operation. 
     Once the anatomy of the patient is registered for the operation, the virtual images can be correctly collocated with the real world image, such as shown in  FIGS. 3A, 3B . 
     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Therefore, the claimed invention as recited in the claims that follow is not limited to the embodiments described herein.