Patent Application
20140142419
The present invention relates generally to intra-body probe tracking, and particularly to methods for compensating patient movements during intra-body probe tracking.
Methods for locating the position of medical devices in the human body by magnetic and imaging procedures are known in the prior art. For example, U.S. Patent Application Publication 2011/0160569, whose disclosure is incorporated herein by reference, describes a method and a system for mapping a volume of an anatomical structure. The system includes a processor for computing a contour of a medical device as a function of positional and/or shape constraints, and to translate the contour into known and virtual 3D positions.
U.S. Patent Application Publication 2011/0054308, whose disclosure is incorporated herein by reference, describes a system for superimposing virtual anatomical landmarks on an image. The system includes a medical positioning system (MPS) for producing location readings with respect to points within a region of interest in accordance with an output of a location sensor disposed in a medical device.
U.S. Pat. No. 7,706,860, whose disclosure is incorporated herein by reference, describes methods and systems for navigating medical devices. A patient is imaged while a medical device is moved within the patient. A position (e.g., a location and/or orientation) of the moving medical device is detected within a coordinate system (e.g., a three-dimensional coordinate system), a position of the imaging field of view relative to the patient is adjusted based on the detected medical device position, such that the relevant tissue region of the patient is within the field of view.
U.S. Pat. No. 4,662,379, whose disclosure is incorporated herein by reference, describes a method of imaging a blood vessel such as a coronary artery which includes the steps of a dual energy providing radiation source and a radiation detector on opposing sides of a target area and at a plurality of angular positions through the target area.
U.S. Patent Application Publication 2010/0145197, whose disclosure is incorporated herein by reference, describes a device and method for generating a motion-corrected 3D image of a cyclically moving object by means of an ultrasound probe, comprising the steps of providing at least one 3D reference image of the object, the 3D reference image showing the object substantially at one particular phase in its cyclic movement; acquiring a set of sub-images of the object by sweeping the ultrasound probe over the moving object; registering at least two, preferably all, of the sub-images with the 3D reference image, thereby generating at least two motion-corrected sub-images; and reconstructing a motion-corrected 3D image from the motion-corrected sub-images. The invention is also directed to a corresponding device, computer program, and digital storage medium.
An embodiment of the present invention that is described herein provides a method including receiving a position of an intra-body probe inserted into an organ of a living body in a first coordinate system. Fluoroscopic images of the body are received. A movement of the body in the fluoroscopic images is measured in a second coordinate system. The received position of the intra-body probe in the first coordinate system is corrected using the movement identified in the second coordinate system.
In some embodiments, measuring the movement includes identifying a hard tissue of the body in the fluoroscopic images, and assessing the movement of the hard tissue between a first fluoroscopic image and a subsequent fluoroscopic image. In other embodiments, assessing the movement includes defining multiple anchor points on the hard tissue, and assessing the movement of the anchor points between the first fluoroscopic image and the subsequent fluoroscopic image. In yet other embodiments, correcting the received position of the intra-body probe includes applying the movement of the anchor points, which was assessed in the second coordinate system, to the received position of the intra-body probe in the first coordinate system.
In some embodiments, receiving the position includes defining the first coordinate system relative to one or more body patch sensors using a magnetic tracking system, and wherein receiving the fluoroscopic images includes identifying the body patch sensors in the fluoroscopic images and defining the second coordinate system relative to the identified body patch sensors. In other embodiments, correcting the received position using the measured movement of the body is performed upon determining that the movement of one or more body patch sensors, which are disposed on the body and detected by a magnetic tracking system, exceeds a predefined threshold.
In some embodiments, receiving the fluoroscopic images includes, for a given fluoroscopic image, receiving two or more fluoroscopic sub-images acquired at different angles in the second coordinate system. In other embodiments, measuring the movement of the body includes constructing first and second three-dimensional models of hard tissue of the body from respective first and second fluoroscopic images, and measuring the movement of the hard tissue between the first and second three-dimensional models of the hard tissue. In yet other embodiments, the method also includes tracking a movement of heart anchor points, so as to improve an accuracy in correcting the received position of the intra-body probe.
There is additionally provided, in accordance with an embodiment of the invention, an apparatus including an interface and a processor. The interface is configured to receive a position of an intra-body probe inserted into an organ of a living body in a first coordinate system, and to receive fluoroscopic images of the living body. The processor is configured to measure a movement of the body in the fluoroscopic images in a second coordinate system, and to correct the received position of the intra-body probe in the first coordinate system using the movement identified in the second coordinate system.
There is also provided, in accordance with an embodiment of the invention, an apparatus including a magnetic intra-body probe tracking system, a fluoroscopic imaging system, and a patient movement compensation system. The patient movement compensation system is configured to receive from the magnetic intra-body probe tracking system a position of the intra-body probe inserted into an organ of a living body in a first coordinate system, to receive from the fluoroscopic imaging system fluoroscopic images of the living body in a second coordinate system, to measure a movement of the body in the fluoroscopic images in the second coordinate system, and to correct the received position of the intra-body probe in the first coordinate system using the identified movement.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
Embodiments of the present invention that are described herein provide improved methods and systems for compensating for patient movements during the tracking of an intra-body probe, such as a catheter, within an organ or cavity of a living body.
In an example embodiment, a magnetic tracking system (MTS) is used to track the position of the distal tip of the catheter during navigation in the body, in combination with body patch probes that are placed on surface of the patient whose positions are also tracked by the MTS. The MTS measures the positions of the body patch probes, which are then used as a frame of reference for the position measurements of the catheter distal tip.
If the patient moves during the procedure, the MTS frame of reference defined by the body patch probes will be shifted, and the measurement of the location of the catheter distal tip will become inaccurate. The MTS frame of reference may be corrected by tracking the movement of the body probes. However, if the patient movement is too excessive, the MTS may not be able to compensate for it. It is possible in principle to recalibrate the reference frame of the MTS in order to compensate for the movement. The recalibration cycle, however, is time consuming and disruptive to the procedure.
The methods and systems described herein compensate for patient movements by processing fluoroscopic images acquired by a fluoroscope imaging system (FIS). In an example embodiment, if the patient movements exceed the MTS movement threshold, a patient movement compensation system (PMCS) uses successive fluoroscopic images to measure the patient movement by detecting the movement of hard tissue, such as the bones in the rib cage.
The PMCS typically receives both the position of the distal tip of the catheter and the body patches from the MTS, as well as the fluoroscopic images of the patient from the FIS. A processor of the PMCS is configured to assign anchor points on landmarks on the hard tissue of a first fluoroscopic image and to measure the position of the anchor points on one or more successive fluoroscopic images. The patient movement is typically measured by computing a translation vector and rotation of the movement of the assigned anchor points. The translation and rotation are then applied to resynchronize the frame of reference of the MTS restoring the accuracy of the catheter tracking without the need for an MTS recalibration cycle.
One or more magnetic skin patch probe sensors 32 are attached to the surface of patient body 17 and connected to MTS 20. One or more magnetic field generators 26 create a magnetic field through the body of the patient, which induce signals in catheter sensor 22 and body patch sensors 32, which are typically placed on the patient's back. The induced signals are used by MTS 20 to track and locate the position of sensor 22 in the catheter distal tip. The tracked position of the catheter distal tip is typically displayed to an operator 70 on an output display monitor 50.
Catheter position sensor 22 typically comprises one or more miniaturized coil sensors. In a tri-axial sensor (TAS) used in magnetic tracking systems, such as the CARTO system (Biosense Webster, Diamond Bar, Calif.), three coils are orthogonally configured at the distal tip of the catheter to create a received signal in response to the magnetic field in order to measure the local vector magnetic field at the distal tip by using the induced electrical signals in the sensor coils. In other systems, sensor 22 can be configured as a single axis sensor (SAS) comprising one coil as shown in
The MTS typically assigns a first coordinate system, also referred to herein as a catheter frame of reference or a human coordinate system, for tracking the distal tip of the catheter relative to magnetic field generators 26. The MTS assigns a second. The MTS assigns another frame of reference (denoted herein as the patient frame of reference or sensor coordinate system) for monitoring the position of body patch sensors 32 relative to field generators 26. Body patch sensors 32 may also be referred to as back patch sensors as used in the CARTO system described above. In order to display the catheter position relative to the patient, the MTS typically registers the two frames of reference with one another.
If patient 17 moves on gurney 19 (and thus relative to field generators 26) during the operation of MTS 20, as detected by a change in position of body patch sensors 32, the catheter frame of reference shifts and should be subsequently updated by the measured change in the patient's frame of reference. Otherwise, the measured position of catheter distal tip 24 may no longer be accurate.
In some embodiments, a patient movement compensation system 30, connected to MTS 20, is configured to monitor patient movement, and to resynchronize the patient and catheter frames of reference. Since the MTS measures both the patient and catheter frames of reference, the two frames of reference are functionally related to one another, and in fact can be the same frame. The term “MTS frame of reference” can be used interchangeably herein to refer to either the patient or catheter frames of reference, or both. The MTS frame of reference is also referred to herein as the first coordinate system.
MTS 20 can accommodate small changes in the patient frame of reference within a “movement envelope” of the system due to the patient's movement. However when the patient movement exceeds a predefined threshold, by exceeding the movement envelope of the MTS, the MTS can no longer compensate for it.
In some embodiments of the present invention, when patient movement compensation system 30 detects that the patient movement exceeded the predefined threshold outside of the MTS movement envelope window, measurements from a fluoroscope imaging system (FIS) 40 are then used in conjunction with the MTS to resynchronize the MTS frame of reference described above without the need for an MTS recalibration cycle.
Initially, when MTS 20 is first calibrated as body patch sensors 32, which are opaque in the FIS, are placed on the surface of the patient body, a first fluoroscopic image is also acquired by a fluoroscopic detector 42 which is mounted above the patient. The first fluoroscopic image encompasses body patch sensors 32, the catheter in heart 28 and a hard tissue of the patient. For a cardiac procedure, the hard tissue typically comprises the rib cage, sternum bone, or spine of the patient.
The fluoroscopic image may comprise a full three-dimensional image model constructed from one or more fluoroscopic sub-images, e.g., single fluoroscopic image “snapshots.” Typically in the CARTO system as an example embodiment, the first fluoroscopic image comprises a pair of images from two different angles, e.g., left anterior oblique (LAO) and right anterior oblique (RAO) images, which together enable three-dimensional reconstruction of the imaged volume, including the hard tissue.
The images can be viewed on output display monitor 50 by operator 70 along with the images or other cardiac signals from the MTS, such as an electrocardiogram signal and other information about the cardiac procedure for the operator.
The system and PMCS configurations shown in
Initially, processor 36 defines a second coordinate system, also referred to as an image frame of reference, using the positions of body patch sensors 32 from the first fluoroscopic image. Typically, processor 36 identifies the positions of body patch sensors in the first fluoroscopic image, e.g., the LAO and RAO images described previously. Using this identification, processor 36 is able to register the first image (the second coordinate system) with the MTS frame of reference (first coordinate system).
If processor 36 detects that the patient movement exceeded the predefined threshold outside of the MTS movement envelope window, a subsequent fluoroscope image is acquired by FIS 40 and provided to processor 36 via interface 34. The movement of the patient is then measured by processor 36 from the FIS data by comparing the position of the hard tissue in the first and subsequent fluoroscopic images as described below. Processor 36 then corrects the position measurements of the MTS (in the first coordinate system) so as to compensate for the patient movement (measured in the second coordinate system).
Processor 36 assigns a first set of anchor points, such as P1 and P2, on the hard tissue to the first image. In the present example the hard tissue comprises a rib cage 75 within the chest of patient 17 for cardiac procedures as shown in
If the patient moves on the gurney laterally, the origin of (X,Y,Z) is shifted to a new origin 85 of coordinate system (X′,Y′,Z′) as defined by a translation vector {right arrow over (T)} as shown in
Similarly, if the patient movement is a rotation about the axis through the spine while lying on the gurney, origin 80 of the coordinate system (X,Y,Z) remains the same in the rotated coordinate system (X″,Y″,Z″) where Z″=Z. The rotation of the body can be expressed as a rotation of angle θ of the X,Y axes to the X″,Y″ axes in the rotated coordinate system as shown in
The patient movement on the gurney is typically a superposition of both a translation and a rotation operating on (X,Y,Z) with a coordinate transformation defined by the translation vector {right arrow over (T)} and rotation vector {right arrow over (θ)} of the hard tissue. Processor 36 then relays this data from the second coordinate system back to MTS 20, and MTS 20 applies the coordinate transformation defined by the translation vector {right arrow over (T)} and rotation {right arrow over (θ)} to the first (MTS) coordinate system to resynchronize the MTS frame of reference with the patient movement computed from the FIS frame. This correction restores the accuracy of the measured position of the distal tip of catheter within the patient body during the therapeutic procedure by the MTS without the need to recalibrate the MTS.
The fluoroscopic image of the hard tissue typically comprises two or more fluoroscopic sub-images received successively in order to create a three-dimensional (3D) model of the anatomical structure for analysis by operator 70. The anchor points are placed on the hard tissue on various landmarks of the anatomical structure, such as a joint, bend, or junction in the bones of the rib cage, which can then be easily identified by system 30 from the images after translation and rotation. Typically, digital fluoroscopic imaging processing techniques are used to resolve the landmarks.
In some embodiments, a first set of anchor points are defined on a first fluoroscopic three-dimensional model of the hard tissue, which is constructed by receiving, or acquiring, two fluoroscopic sub-images at different angles. A second subsequent fluoroscopic three-dimensional model comprises receiving, or acquiring, two sub-images at different angles on which the second set of anchor points are defined. The rotation {right arrow over (θ)} and the translation vector {right arrow over (T)} are computed from the change of the position anchor points between the first and second sets.
In other embodiments, system 10 can be configured to create an initial three-dimensional (3D) fluoroscopic model of the hard tissue and to generate a reconstructed 3D model by applying single fluoroscopic images. A first 3D reconstruction of the hard tissue can be made from a first fluoroscopic single image on which a first set of anchor points are defined. A second 3D reconstruction of the hard tissue can be made from a second subsequent fluoroscopic single image on which a second set of anchor points are defined. The rotation {right arrow over (θ)} and the translation vector {right arrow over (T)} are computed from the change of the position anchor points between the first and second sets, which are subsequently applied to the MTS frame of reference to correct patient movement on the gurney in the position measurement of the catheter distal tip.
The embodiments shown in
In a third acquiring step 130, FIS/MTS interface 34 acquires an image of hard tissue 78 of patient and skin patch positions from fluoroscopic imaging system 40 (FIS). In a defining step 140, processor 36 defines anchor points on the hard tissue relative to a second coordinate system (X,Y,Z), e.g., image frame of reference as shown in
In a first decision step 150, if the MTS detects that the skin patch probe positions did not move more than a predefined threshold, e.g., outside of the movement envelope window, due to the patient movement on the gurney during the procedure, patient movement compensation system 30 resynchronizes the MTS frame of reference with the skin patch movements in a first resynchronizing step 160. The system then continues to monitor patient movement in first acquiring step 100.
If the patient moved more than the predefined threshold in decision step 150, FIS 40 acquires a subsequent fluoroscopic image 170 in a fourth acquiring step 170. In a second computing step 180, processor 36 computes a translation vector and rotation of hard tissue between successive fluoroscopic images of the patient as shown in
In a second decision step 200, if intra-body probe tracking system 10 assesses that the therapeutic procedure is complete, the procedure is terminated in a terminating step 210. If not, patient movement compensation system 30 continues to monitor patient movement in first acquiring step 100.
To further improve the accuracy of the distal tip position measurement in the PMCS, a more accurate position measurement of the heart can be obtained by defining multiple anchor points in the heart itself, in addition to the anchor points defined on the skeletal hard tissue as shown in
In some embodiments, heart anchor points can be defined while locating the position of the catheter distal tip at known landmarks in the heart, such as the right ventricular apex (RVA) and left atrial pulmonary veins. In other embodiments, additional heart anchor points may be obtained from anatomical points in the heart, such as the left ventricular apex (LVA) and heart valves, identified in the fluoroscopic images.
Alternatively, a more accurate catheter position measurement can be obtained from other imaging techniques used to identify additional heart anchor points. In some embodiments, heart anchor points can be defined by processor 36 as identified from landmark anatomical structures in the heart from images generated by rotational angiography. In other embodiments, heart anchor points can be defined by processor 36 as identified from landmark anatomical structures in the heart from ultrasound images generated by ultrasound catheter transesophageal echocardiography (TEE). Although the embodiments described herein mainly address catheter position tracking in cardiac procedures, the methods and systems described herein can also be used in other applications, such as catheter tracking in the bladder of the urinary tract, or in the stomach.
It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.
