JP5667988B2 - System and method for dynamic metal strain compensation of electromagnetic tracking system - Google Patents

Description

  The present invention relates to an electromagnetic tracking system, and more particularly to a system and method for dynamic metal distortion compensation using an active reference marker.

  The result of a minimally invasive medical procedure uses an electromagnetic tracking system (EMTS) to track the position of the medical device and display information about the medical image, thereby guiding the medical device to a target location within the living tissue Improved by helping to

  EMTS generates a local electromagnetic field at the site for treatment, and the medical device works by using an electromagnetic (EM) field generator with a suitable small sensor coil. A current that is a function of the position and orientation of the associated sensor coil of the electromagnetic field generator is induced in the sensor coil. The EMTS can calculate the position of the sensor coil and thus the position of the medical device. A particular advantage of EMTS is that no field of view is required because the electromagnetic field can penetrate the human body so as not to affect it. Thus, EMTS is particularly suitable for tracking needles or catheters within anatomical structures.

  One of the main challenges of EMTS used in the medical environment is the existence of objects with metallic conductivity or ferromagnetism in close proximity to electromagnetic fields. These objects are to introduce distortions or metal artifacts that lead to errors in the location and orientation of tracking the medical device. In the medical environment, there are many objects that result in metal artifacts in EMTS. The main strain source is provided by a medical imaging device (eg, CT gantry, CT table, X-ray C-shaped arm, etc.) on which the patient lies. Other strain sources are movable medical devices or tools (ECG monitors, metal tools, etc.) that move in the vicinity of the EMTS. These sources of distortion distort the electromagnetic field and thus distort the position and orientation from the EMTS, resulting in tracking errors. Such errors can directly affect the results of medical treatment using EMTS. Currently, the clinical usefulness of EMTS cannot be assured in the presence of metal strain in the accuracy of EMTS location and orientation.

  US Patent Application Publication No. 2005/0107687 by Anderson provides a system and method for analysis and reduction of strain in EMTS. The tracking improvement unit relies on a predetermined distortion model for each particular tool or device being tracked. The predetermined model has been developed through an analytical process including magnetic field mapping and / or modeling / simulation that also takes into account sensor placement and shielding. The tracking analysis unit generates a map and / or model of the distortion characteristics of the device, which is essentially a lookup table for the device. This system does not attempt to reduce the distortion caused by objects that are stationary in the environment.

  US Patent Application Publication No. 2008/0079421 by Jensen proposes a static mapping of the strain field produced by an object in an embodiment. An electromagnetic sensor array is positioned within the predetermined volume, and the array of sensors is sampled to obtain a signal representative of the position of the electromagnetic sensor within the array. Since the array is fixed, the electromagnetic field distortion can be calculated. This system cannot be used in real time during a medical procedure and cannot take into account the electromagnetic field distortion caused by moving medical devices and tools within a given volume.

  International Publication No. 2007/113719 by Shen et al. Proposes a system for local metal distortion correction that improves the accuracy of EMTS in a medical environment. The system includes a magnetic field generator that monitors a medical device having an appropriate sensor coil, and a correction function derived by an error correction tool is applied to the sensor coil position and fold edge hand readings. The error correction tool has a plurality of electromagnetic sensors arranged in a fixed and known geometric configuration and is positioned surrounding a target site of a medical procedure. In addition, strain mapping can be performed utilizing an optical sensor for relative positioning reading along with an electromagnetic tracking system sensor.

  There remains a need for systems and methods that can efficiently compensate for metal strain in real time so as to improve the accuracy and reliability of EMTS in a medical environment. Accordingly, it would be desirable to have a system and method that can compensate for static strains caused by the environment and strains caused by the medical device and the tool itself.

US Patent Application Publication No. 2005/0107687 US Patent Application Publication No. 2008/0079421 International Publication No. 2007/113719 Pamphlet

  According to one aspect of the exemplary embodiment, a method for dynamic metal strain compensation using an electromagnetic tracking system (EMTS) comprises generating an electromagnetic field with at least one electromagnetic field generator. A plurality of fiducial markers are provided, each fiducial marker having at least one electromagnetic sensor, the electromagnetic sensors being oriented with a plurality of sensor orientations, at least a portion of the sensors being proximate to a predetermined volume. Is positioned. The reference marker is imaged to provide at least one baseline position of the reference marker in image space. The method uses EMTS to monitor position readings of a plurality of electromagnetic sensors, and calculates a metal distortion correction function by comparing the position readings of the electromagnetic sensors in the electromagnetic field and the position of the reference marker in the image space. And further. The position reading of a medical device moving through a predetermined volume is monitored using EMTS, the device having at least one electromagnetic sensor. In that case, a strain correction function is applied to the medical device position reading to compensate for the metal strain. The correction is dynamic and takes place in real time and comes close during the procedure to allow compensation for objects / distortions.

  The positioning of the at least one fiducial marker can be changed during position monitoring. At least a portion of the fiducial marker is positioned in a frame around at least a portion of the patient's body during the medical procedure and / or at least a portion of the fiducial marker is positioned directly on the patient's skin during the medical procedure. . Alternatively or additionally, at least one of the fiducial markers can be positioned within the patient's body during the medical procedure.

  Some of the position readings of the plurality of electromagnetic sensors are selected to contribute to the metal distortion correction function. The selection of the electromagnetic sensor can be dynamically based on selection criteria. The selection criteria can include selecting a sensor having an orientation that is closest to the orientation of the medical device being tracked to compute the compensation. In other configurations, the selection criteria can include selecting a sensor having a spatial location that is close to the spatial location of the medical device being tracked to compute the compensation. In a further configuration, the selection criteria can comprise selecting a sensor having a spatial position proximate to a target position within the patient's body to compute a compensation. In a further configuration, the selection criteria can comprise selecting a sensor based on a target position within the patient's body and the shape of the associated spatial position of the tracked medical device to compute a compensation. . In all configurations, the selection criteria can change as at least one of the orientation and spatial position of the medical procedure being tracked changes.

  The method for calculating the medical strain correction function can be selected based on the selection of the electromagnetic sensor. For example, if the overall transformation (affine) computation method is used, the overall transformation computation method using interpolation computation is outside the geometric coverage of the selected sensor, The used and / or extrapolation method can be used when the medical device being tracked is outside the geometric coverage of the selected sensor. The method of calculating the metal strain correction function can be changed dynamically as the selection of the electromagnetic sensor is changed due to the movement of the medical device being tracked.

  In accordance with other features of the exemplary embodiment, a system for dynamic metal strain compensation using an electromagnetic tracking system (EMTS) has at least one electromagnetic field generator that generates an electromagnetic field. Having a plurality of fiducial markers, each fiducial marker having at least one electromagnetic sensor, the plurality of electromagnetic sensors being directed to a plurality of sensor orientations, at least a portion of the sensors being proximate to a predetermined volume Positioned and the fiducial marker is visible in the image space. A processor is included for computing a metal distortion correction function by comparing the position reading of the electromagnetic sensor and the position of the reference marker in the image space in the electromagnetic field. At least one electromagnetic sensor is attached to the medical device. The processor applies a calculated strain correction function to the medical device position reading to compensate for metal strain.

  At least a portion of the reference marker is provided on a frame adapted to surround at least a portion of the patient's body during the medical procedure. At least some of the reference markers have a plurality of electromagnetic sensors, and the plurality of electromagnetic sensors in such a reference marker can have different sensor orientations.

  These and other features and advantages of the present invention will be apparent from and will be apparent to those skilled in the art from the following detailed description, the accompanying drawings and the appended claims.

It is a figure which shows the general structure of the component of this invention. FIG. 6 shows an abdominal phantom having a plurality of active reference markers provided on the frame. It is a figure which shows image acquisition. It is a figure which shows route planning. It is a figure which shows baseline position alignment. It is a figure which shows specifying the active reference marker in image space. It is a figure which shows the navigation accompanied by electromagnetic distortion compensation. FIG. 4 shows an example showing active criteria in three different orientations provided around a target.

  The present invention relates to an electromagnetic tracking system (EMTS) for medical devices and other structures. Exemplary embodiments of the present invention are applicable to many types of structures, including cardiac and vascular applications, needle biopsy, percutaneous radiofrequency ablation therapy, cryoablation, prostate cancer treatment, and other cancer applications. Those skilled in the art need to understand that they can be applied, but are not limited thereto.

  Referring initially to FIG. 1, an electromagnetic tracking system (EMTS) 10 having an electromagnetic (EM) field generator 12 is shown. In one embodiment, the electromagnetic field generator 12 can generate a local electromagnetic field that can track sensor data from EM sensors included in the active reference marker 14 and the medical device 16. Markers 14 are provided around the patient's body 18. The markers 14 are visible in the medical image space and also have sensor coils that provide position information and orientation information in the electromagnetic tracking space, so that these markers can also be positioned in the electromagnetic tracking space. During the medical procedure, the medical device 16 is typically entered into the patient's body under the skin relative to the target location. The electromagnetic sensor coil is incorporated in the medical device 16, for example, in the vicinity of the tip of the medical device 16 when the medical device 16 is a needle or includes a needle. A current is induced in the sensor coil that is a function of the position and orientation of the sensor coil relative to the electromagnetic field generator 12. The EMTS 10 can calculate the position of the sensor coil and thus the position of the medical device 16. A particular advantage of EMTS is that no viewing direction is required. Thus, EMTS is particularly suitable for tracking needles or catheters inside human tissue.

  With reference to FIGS. 2-8, during a medical procedure, the active fiducial marker 14 can be positioned on a surface of the patient's skin or on a fixed frame 20 that is designed to be movable around the patient. (In the configuration shown, the abdominal phantom 18 is shown in place of the patient so that it can be used for testing purposes). The marker 14 can be positioned to surround an appropriate area proximate to an entry point on the patient's skin or close to a target location in the patient's body. Those markers can be connected to the EMTS 10 with wires 22, the patient 18 and the frame 20 on the table 24 with the electromagnetic field generator 12 positioned above the table 24, or any suitable It can be positioned at any place. An image of the relevant patient anatomy is acquired. The active fiducial markers 14 can be clearly identified in the medical image and the position of those markers in the image space can be determined (by application of software). This forms a true baseline for the position of the active reference marker 14. Those positions from the EMTS are used to compute the compensation by comparing the true baseline image position with the EMTS position. If a metal strain source is present, one or more positions of the active reference marker 14 will be distorted or inaccurate. Comparing with the baseline image position allows the correction to be computed. The correction can be performed in a variety of ways, including rigid body alignment, affine alignment, and many interpolation methods.

  In fiducial markers with a single sensor orientation, such as tangential to the skin, primarily the tracked medical device, such as a needle, is inserted perpendicular to the skin surface, so the sensor is In the end results in a relatively low consistency. When the marker is attached to the patient's skin with a sensor oriented inwardly perpendicular to the skin surface, the active reference marker 14 obtains usable correction or compensation in the first manner. Used as follows. Efficiency is optimal when the medical device 16 being tracked is oriented in the same direction as the sensor at the active reference marker. However, it is not always or quite often that the medical device being tracked and the sensors in the active fiducial marker are not in close proximity.

  In a first configuration, the disclosed system and method uses multiple arrays of active reference markers 14, each array having a different sensor orientation. In other configurations, the disclosed systems and methods can use a plurality of active basic markers 14 having various orientations that need not be organized into an array of specific orientations. Either an array of active reference markers 14 with the closest sensor orientation to the tracked medical device 16 or an array of individual active reference markers 14 with the closest sensor orientation to the tracked medical device 16 Is selected. The selected array or sensor is then used to compute the distortion correction. Because the marker 14 need only be identifiable in the medical image for the baseline position used to compute the compensation, the active reference marker 14 is not accurate and is positioned around the patient's body. Is possible, i.e. a priori position is not required. This gives the freedom to reposition the marker if needed during a medical procedure.

  By positioning the active reference marker 14 on the frame 20 surrounding the patient 18, the effects of breathing motion are eliminated. If the active reference marker 14 is under constant movement due to respiration, this will affect the ability to compute compensation. If breathing motion is estimated, the active fiducial marker 14 can be positioned directly on the patient's skin. The position read from the active reference marker 14 needs to be synchronized with the inspiratory level during image acquisition. This is accomplished via a gating process when the patient is connected to a respiratory device or when a bellows device is used. Alternatively, an internal active reference marker or similar marker can be used to predict respiratory status using EMTS or a similar tracking system.

  To use EMTS, a patient is first imaged using any suitable imaging system (see FIG. 3). A target path for the invasive medical procedure is then identified (see FIG. 4). These two steps can be performed immediately before the start of the medical procedure, during the medical procedure, or before the medical procedure. A baseline registration between image space and electromagnetic tracking space is obtained (see FIG. 5). Baseline registration is the first registration between the image space and the electromagnetic tracking space. This step is optional because the transformation between the two spaces is computed using the active reference marker 14 during the compensation computation. However, performing this step provides a baseline conversion between the image space and the electromagnetic tracking space in the event that the electromagnetic compensation operation fails. Furthermore, this step is useful if the software application allows a user selection of electromagnetic distortion compensation (ie, to switch it on or off).

  The position of the active reference marker 14 is then specified in the image space (see FIG. 6). The EMTS position information of the active reference marker 14 is then read and the EMTS computes a conversion or interpolation between the EMTS position and the image space position that performs distortion compensation. Once distortion compensation is computed, the image is corrected and the corrected image can be provided to the physician so that invasive navigation is performed with real-time distortion compensation (FIG. 7). The orientation of the medical device 16 being tracked is thus monitored in real time.

  The compensation is computed using the position reading from the sensor at the active reference marker 14 that has the same orientation (within the threshold) as the medical device 16 being tracked. In most cases, the tracked medical device 16 is not fixed because it dynamically changes as the medical device 16 is repositioned. Thus, by using multiple sensors with different orientations, the sensor with the orientation closest to the orientation of the medical device 16 being tracked can be selected to compute the compensation. Alternatively, the sensor closest to the medical device 16 can be selected, or the selection can be based on the sensor's geometric position relative to the medical device 16. As the orientation of the medical device 16 being tracked changes, an appropriate sensor can be dynamically selected to compute the compensation. In all cases, the minimum number of sensors needs to be used to calculate the correction, but the actual minimum number depends on the method used to perform the calculation.

  The selection of the sensor used for the computation can be used to determine the compensation method employed for the correction. For example, if only a few sensors meet the selection criteria, compensation can be performed by a global affine transformation. However, if a sufficient number of sensors are selected with appropriate geometric coverage, an interpolation method can be used. In some configurations, when the orientation of the medical device being tracked does not accurately correspond to the minimum number of orientations of the actual reference sensor, the interpolation is calculated by the sensor that best fits in the orientation. Is possible. Similarly, if the tracked medical device 16 deviates from the effective sensor geometric coverage, the overall transformation method may be better than the extrapolation method.

  The speed or frequency of compensation is two events and is limited only by obtaining the position read from the actual reference marker 14 and the compensation operation. Depending on the actual number of fiducial markers used, the speed of the EMTS and the compensation algorithm used, one compensation can be performed in a fraction of a second. True continuous real-time compensation may or may not be necessary in a medical environment.

  One method of sensor selection for use in the compensation operation is to use a plurality of sensor arrays, each array having a plurality of sensors that are substantially the same orientation or closest to the medical device 16. Based on the orientation of the medical device 16 being tracked, an appropriate array of sensors is selected to compute the compensation. The selection can be made through software identification of the appropriate array or by a hardware multiplexer / selector. Each individual sensor array has appropriately spaced sensors around the target site. The second method is to use a plurality of individual sensors (not configured in an array) with different orientations. Based on the orientation of the tracked medical device 16, the sensor having the orientation closest to the orientation of the tracked medical device 16 is selected to compute the compensation. Selection is most likely made through software identification of the appropriate sensor.

  The simplest exemplary embodiment of the sensor configuration is illustrated in FIG. 8 by a group of sensors 26 in three different orientations (they are represented by lines representing their orientation). Each group of sensors 26 can be located at an actual reference marker 14, or each actual reference marker 14 can be included in one sensor and grouped together in an array. It is. The number of orientations need not be limited to three, for example, two orientations can be used, or four or more orientations can be used.

  In other configurations, at least one fiducial marker 14 improves the accuracy of compensation within the patient during the procedure, eg, proximate to the medical device 16 being tracked, proximate to the target site, or It can be temporarily positioned at any suitable location.

  Electromagnetic tracking is a means of improving medical procedures including catheter tracking in cancer applications such as cardiac and vascular applications, cancer applications, and needle biopsy, costly radiofrequency ablation therapy, cryoablation, prostate cancer therapy, etc. . Errors caused by metal interference can affect the accuracy of medical procedures using electromagnetic tracking systems. By providing real-time dynamic error compensation, the disclosed method and system can improve the accuracy of electromagnetic tracking medical processing, making the use of EMTS more realistic and practical, and There are many opportunities for integration of medical imaging with medical device tracking in minimally invasive applications. These medical applications include the use of CT systems, X-ray systems, and ultrasound systems, and the technology is generally used in most situations where the physician needs to guide the medical device to a location in the anatomy. Is also applicable.

  The present invention having the methodological steps described above can be implemented in hardware, software, or a combination of hardware and software. The present invention can be implemented centrally in a single computer system or in a distributed manner in which different elements are passed across multiple interconnected computer systems. Any type of computer system or other apparatus adapted to perform the methods described herein is suitable. A typical combination of hardware and software can be a general purpose computer system having a computer program that controls the computer system to perform the methods described herein when loaded and executed. is there.

  The present invention having multiple steps of the above methodology can be incorporated into a computer program product. The computer program product is incorporated into a computer program having computer-executable code for instructing a computing device or computer-based system to perform the various processes, processes, and methods described herein. It is possible to have a computer readable storage medium. The computer program described here performs certain functions directly or after either a) conversion into other languages, codes or notations, b) reproduction in different types of materials, It means any representation in any language, code or notation of a set of instructions intended to be executed by a system having information processing capabilities.

  The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments, and utilize the structures described herein. It is not intended to serve as a complete representation of all the elements and features of the devices and systems that are possible. Many other embodiments can be utilized and derived from those embodiments, and thus structural and logical substitutions and variations depart from the scope of the present invention. Can be performed without The figure is also just a representation and is not drawn to scale. While ratios in the figures may be exaggerated, other figures may be reduced. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive.

  Thus, although specific embodiments are illustrated and described herein, it is possible to replace specific embodiments where any configuration calculated to achieve the same purpose is shown. It needs to be understood. This document is intended to cover any and all adaptations or variations of various embodiments. Those skilled in the art will appreciate when considering the above description that combinations of the above embodiments and other embodiments not specifically described herein are possible. Accordingly, the description is not to be construed as limited to the particular embodiments disclosed as the best mode contemplated for carrying out the invention, which is encompassed by the appended claims. It is intended to cover all embodiments that fall within the scope.

  The term “comprising” and its derivatives should not be considered as excluding additional elements. A singular representation of an element should not be considered as excluding multiple elements. The expression “or” should be interpreted as including, in other words as “and / or”.

Claims (14)

A method for dynamic metal strain compensation using an electromagnetic tracking system (EMTS) comprising:
Generating an electromagnetic field by at least one electromagnetic field generator;
Providing a plurality of fiducial markers, each fiducial marker having at least one electromagnetic sensor, the at least one electromagnetic sensor being oriented in a plurality of sensor orientations, at least a portion of the electromagnetic sensors being predetermined Positioned in proximity to the volume;
Imaging the reference marker to provide at least one baseline position of the reference marker in image space;
Using the EMTS to monitor position readings of the plurality of electromagnetic sensors;
Calculating a metal distortion correction function by comparing the position reading of the electromagnetic sensor and the position of the reference marker in image space in the electromagnetic field;
Monitoring the position reading of a medical device moving through the predetermined volume using the EMTS, the medical device having at least one electromagnetic sensor ;
Applying the metal strain correction function to position readings of the medical device to compensate for the metal strain; and
Selecting a portion of the position readings of the plurality of electromagnetic sensors to contribute to the metal distortion correction function;
Having a method.   The method of claim 1, wherein the positioning of the at least one fiducial marker is changeable in monitoring the position.   The method of claim 1, wherein at least a portion of the fiducial marker is positioned on a frame surrounding at least a portion of a patient's body during a medical procedure.   The method of claim 1, wherein at least a portion of the fiducial marker is positioned directly on a patient's skin during a medical procedure.   The method of claim 1, wherein at least one of the fiducial markers is positioned within a patient's body during a medical procedure. The method of claim 1 , wherein the selection of the electromagnetic sensor is dynamically based on selection criteria. The method of claim 6 , wherein the selection criteria comprises selecting a sensor having an orientation closest to the orientation of the tracked medical device to compute the compensation. The method of claim 6 , wherein the selection criteria comprises selecting a sensor having a spatial position proximate to the spatial position of the tracked medical device to compute the compensation. The method of claim 6 , wherein the selection criteria comprises selecting a sensor having a spatial position proximate to a target position within a patient's body to compute the compensation. 7. The method of claim 6 , wherein the selection criteria comprises selecting a sensor based on a target position in a patient's body and a shape of an associated spatial position of the tracked medical device to compute the compensation. . The method of claim 6 , wherein the selection criteria changes as one of the orientation and the spatial position of the tracked medical device changes. The method of claim 1 , wherein the method of calculating the metal strain correction function is selected based on the selection of the electromagnetic sensor. The method according to claim 12 , wherein an overall transformation calculation method is used. The method according to claim 12 , wherein an interpolation operation is used.

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