Abstract:
Cardiac catheterization is carried out by importing image data of a heart of a living subject into an image-processing computer system, representing the image data as a first model of the heart and the coronary sinus in a first coordinate space, and introducing a probe into the coronary sinus. Thereafter fluoroscopic image data of the probe are used to prepare a second model of the coronary sinus in a second coordinate space, and the first model is transformed into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to cardiac physiology. More particularly, this invention relates to the evaluation of electrical propagation in the heart. 
         [0003]    2. Description of the Related Art 
         [0004]    The meanings of certain acronyms and abbreviations used herein are given in Table 1. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Acronyms and Abbreviations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 CS 
                 Coronary Sinus 
               
               
                   
                 LAO 
                 Left Anterior Oblique 
               
               
                   
                 RAO 
                 Right Anterior Oblique 
               
               
                   
                 CT 
                 Computed Tomography 
               
               
                   
                 MRI 
                 Magnetic Resonance Image 
               
               
                   
                   
               
             
          
         
       
     
         [0005]    Cardiac arrhythmias such as atrial fibrillation are an important cause of morbidity and death. Commonly assigned U.S. Pat. No. 5,546,951, and U.S. Pat. No. 6,690,963, both issued to Ben Haim and PCT application WO 96/05768, all of which are incorporated herein by reference, disclose methods for sensing an electrical property of heart tissue, for example, local activation time, as a function of the precise location within the heart. Data are acquired with one or more catheters having electrical and location sensors in their distal tips, which are advanced into the heart. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. Pat. No. 6,226,542, and U.S. Pat. No. 6,301,496, both issued to Reisfeld, which are incorporated herein by reference. As indicated in these patents, location and electrical activity is typically initially measured on about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface. The preliminary map is often combined with data taken at additional points in order to generate a more comprehensive map of the heart&#39;s electrical activity. Indeed, in clinical settings, it is not uncommon to accumulate data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity. The generated detailed map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart&#39;s electrical activity and to restore normal heart rhythm. 
         [0006]    Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096, issued to Ben Haim, which is incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart. 
         [0007]    Electrical activity at a point in the heart is typically measured by advancing a multiple-electrode catheter to measure electrical activity at multiple points in the heart chamber simultaneously. A record derived from time varying electrical potentials as measured by one or more electrodes is known as an electrogram. Electrograms may be measured by unipolar or bipolar leads, and are used, e.g., to determine onset of electrical propagation at a point, known as local activation time. 
         [0008]    Currently, large amounts of anatomical and functional data are gathered during catheter-based cardiac procedures. Maintaining alignment of this data with the actual position of the patient&#39;s heart and understanding the relationship of the catheter to anatomic structures are both important to the success of the procedure. In one approach the catheter is registered to images taken by another modality. 
         [0009]    An example of this approach is proposed in U.S. Pat. No. 7,720,520 to Willis. A reference catheter or reference element is placed in contact with the anatomical body. A physical structure within a navigational coordinate system is located using the reference elements or reference catheter. An image reference within an image coordinate corresponding to the physical structure is located. Location of the image reference can be accomplished, e.g., by displaying the medical image and electronically marking the displayed image reference, or by automatically locating image data corresponding to the image reference. The navigational and image coordinate systems are then registered based on the location of the physical structure within the navigational coordinate system and the location of the image reference within the image coordinate system, which allows graphical information to be merged with the medical image data. 
       SUMMARY OF THE INVENTION 
       [0010]    According to disclosed embodiments of the invention, a reconstruction of the heart is prepared prior to catheterization from cardiac image data, such as CT or MRI data. The reconstruction takes into consideration motion of the cardiac structures such as the coronary sinus due to cardiac and patient motion. Using the reconstruction, the coronary sinus is catheterized and reconstructed using fluoroscopic image data. The reconstruction of the coronary sinus is placed in registration with the reconstruction of the heart, so that the resulting image has a coordinate space consistent with that of a functional electroanatomic images of the heart that may be displayed or generated, for example a CARTO map. Cardiac structures of interest may then be identified on the functional electroanatomic image by an operator. 
         [0011]    There is provided according to embodiments of the invention a method, which is carried out by importing image data of a heart of a living subject into an image-processing computer system, representing the image data as a first model of the heart and the coronary sinus in a first coordinate space, and introducing a probe into the coronary sinus. Thereafter, the method is further carried out acquiring fluoroscopic image data of the probe, using the fluoroscopic image data to prepare a second model of the coronary sinus in a second coordinate space, and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model. 
         [0012]    The image data is obtained by computed tomography or magnetic resonance imaging of the heart. 
         [0013]    According to an aspect of the method, the first model is a 3-dimensional model. 
         [0014]    According to still another aspect of the method, preparing a second model includes reconstructing a 2-dimensional path of the probe. 
         [0015]    According to an additional aspect of the method, preparing a second model includes estimating a 3-dimensional path of the probe from the 2-dimensional path. 
         [0016]    Another aspect of the method includes locating a cardiac structure in the transformed first model in the second coordinate space. 
         [0017]    There is further provided according to embodiments of the invention an apparatus, including a cardiac catheter adapted for introduction into a coronary sinus of a heart of a living subject, a display, and a processor. The processor is cooperative with a fluoroscopic imaging device for performing a method, which is carried out by importing image data of the heart into an image-processing computer system, representing the image data as a first model of the heart and the coronary sinus in a first coordinate space, and introducing a probe into the coronary sinus. Thereafter, the method is further carried out acquiring fluoroscopic image data of the probe, using the fluoroscopic image data to prepare a second model of the coronary sinus in a second coordinate space, and transforming the first model into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first mode. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]    For a better understanding of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 
           [0019]      FIG. 1  is a pictorial illustration of a system for performing cardiac catheterization procedures, which is constructed and operative in accordance with an embodiment of the invention; 
           [0020]      FIG. 2  is a flow-chart of a method of registration of cardiac images using a coronary sinus catheter in accordance with an embodiment of the invention; and 
           [0021]      FIG. 3  is a composite image illustrating a stage in the process of coronary sinus reconstruction as applied to a 3-dimensional model of the heart, in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily needed for practicing the present invention. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily. 
         [0023]    Aspects of the present invention may be embodied in software programming code, which is typically maintained in permanent storage, such as a computer readable medium. In a client/server environment, such software programming code may be stored on a client or a server. The software programming code may be embodied on any of a variety of known non-transitory media for use with a data processing system, such as USB memory, hard drive, electronic media or CD-ROM. The code may be distributed on such media, or may be distributed to users from the memory or storage of one computer system over a network of some type to storage devices on other computer systems for use by users of such other systems. 
         [0024]    Embodiments of the invention enable identifying cardiac structures during the medical procedure. When the position of the coronary sinus is accurately known based on fluoroscopy of a coronary sinus catheter, its position can be related to the position of other portions of the heart provided there is a common coordinate system to locate the other portions, the embodiments of the invention place the coronary sinus, as determined from fluoroscopy, in registration with a 3-dimensional model of the heart prepared using another imaging modality. 
       System Overview 
       [0025]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for performing catheterization procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the invention. The system comprises a catheter  14 , which is percutaneously inserted by an operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The operator  16 , who is typically a physician, brings the catheter&#39;s distal tip  18  into contact with the heart wall at an ablation target site. Electrical activation maps, anatomic positional information, i.e., of the distal portion of the catheter, and other functional images may then be prepared using a processor  23  located in a console  24 , according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whose disclosures are herein incorporated by reference. One commercial product embodying elements of the system  10  is available as the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765, which is capable of producing electroanatomic maps of the heart as required for the ablation. This system may be modified by those skilled in the art to embody the principles of the invention described herein. 
         [0026]    Areas determined to be abnormal, for example by evaluation of the electrical activation maps, can be ablated by application of thermal energy, e.g., by passage of radiofrequency electrical current through wires in the catheter to one or more electrodes at the distal tip  18 , which apply the radiofrequency energy to the myocardium. The energy is absorbed in the tissue, heating (or cooling) it to a point (typically about 60° C.) at which it permanently loses its electrical excitability. When successful, this procedure creates non-conducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway causing the arrhythmia. The principles of the invention can be applied to different heart chambers to treat many different cardiac arrhythmias. 
         [0027]    The catheter  14  typically comprises a handle  20 , having suitable controls on the handle to enable the operator  16  to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator  16 , the distal portion of the catheter  14  contains position sensors (not shown) that provide signals to a positioning processor  22 , located in the console  24 . 
         [0028]    Ablation energy and electrical signals can be conveyed to and from the heart  12  through the catheter tip and/or one or more ablation electrodes  32  located at or near the distal tip  18  via cable  34  to the console  24 . Pacing signals and other control signals may be conveyed from the console  24  through the cable  34  and the electrodes  32  to the heart  12 . Sensing electrodes  33 , also connected to the console  24  are disposed between the ablation electrodes  32  and have connections to the cable  34 . 
         [0029]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system. The electrodes  32  and the body surface electrodes  30  may be used to measure tissue impedance at the ablation site as taught in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein incorporated by reference. A temperature sensor (not shown), typically a thermocouple or thermistor, may be mounted on or near each of the electrodes  32 . 
         [0030]    The console  24  typically contains one or more ablation power generators  25 . The catheter  14  may be adapted to conduct ablative energy to the heart using any known ablation technique, e.g., radiofrequency energy, ultrasound energy, freezing technique and laser-produced light energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, which are herein incorporated by reference. 
         [0031]    The positioning processor  22  is an element of a positioning subsystem in the system  10  that measures location and orientation coordinates of the catheter  14 . 
         [0032]    In one embodiment, the positioning subsystem comprises a magnetic position tracking arrangement that determines the position and orientation of the catheter  14  by generating magnetic fields in a predefined working volume and sensing these fields at the catheter, using field generating coils  28 . The positioning subsystem may employ impedance measurement, as taught, for example in U.S. Pat. No. 7,756,576, which is hereby incorporated by reference, and in the above-noted U.S. Pat. No. 7,536,218. 
         [0033]    A fluoroscopic imaging device  37  has a C-arm  39 , an x-ray source  41 , an image intensifier module  43  and an adjustable collimator  45 . A control processor (not shown), which may be located in the console  24 , allows an operator to control the operation of the fluoroscopic imaging device  37 , for example by setting imaging parameters, and controlling the collimator  45  to adjust the size and position of the field of view. The control processor may communicate with the fluoroscopic imaging device  37  via a cable  51  to enable and disable the x-ray source  41  or restrict its emissions to a desired region of interest by controlling the collimator  45 , and to acquire image data from the image intensifier module  43 . An optional display monitor  49 , linked to the control processor, allows the operator to view images produced by the fluoroscopic imaging device  37 . When the display monitor  49  is not included, the fluoroscopic images may be viewed on a monitor  29 , either via a split screen or in alternation with other non-fluoroscopic images. 
         [0034]    As noted above, the catheter  14  is coupled to the console  24 , which enables the operator  16  to observe and regulate the functions of the catheter  14 . The processor  23  is typically a computer with appropriate signal processing circuits. The processor  23  is coupled to drive the monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by the above-noted sensors and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14  and analyze the electrical signals from the electrodes, and generate desired electroanatomic maps. 
         [0035]    Typically, the system  10  includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system  10  may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, to provide an ECG synchronization signal to the console  24 . As mentioned above, the system  10  typically also includes a reference position sensor, either on an externally-applied reference patch attached to the exterior of the subject&#39;s body, or on an internally-placed catheter, which is inserted into the heart  12  maintained in a fixed position relative to the heart  12 . Conventional pumps and lines for circulating liquids through the catheter  14  for cooling the ablation site are provided. 
       Operation 
       [0036]    Reference is now made to  FIG. 2 , which is a flow-chart of a method of registration of cardiac images using a coronary sinus catheter in accordance with an embodiment of the invention. The process steps are shown in a particular linear sequence for clarity of presentation. However, it will be evident that many of them can be performed in parallel, asynchronously, or in different orders. Those skilled in the art will also appreciate that a process could alternatively be represented as a number of interrelated states or events, e.g., in a state diagram. Moreover, not all illustrated process steps may be required to implement the method. 
         [0037]    At initial step  53  a CT (or MRI) image of the heart is obtained. This may be accomplished prior to the current session, but in any case prior to introduction of a cardiac catheter. The image created in this step has a scale and coordinate system that is specific to the image acquisition device employed, which is referred to for convenience as “CT coordinates”. The term “CT coordinate space” describes a 3-dimensional space having points described in CT coordinates. The coronary sinus is defined in CT coordinates on the image. 
         [0038]    Next, at step  71  the CT image is imported into an image processing computer, e.g., the above-described CARTO 3 system. At this stage, the imported image occupies CT coordinate space. However, images normally produced using the image processing computer have another coordinate system and occupy a different coordinate space. This coordinate system and space are referred to herein for convenience as “CARTO coordinates” and “CARTO coordinate space”, respectively. It will be understood that the use of this terminology does not limit the application of the method to the CARTO 3 system. Rather the steps may be performed by many other types of image processing computers. 
         [0039]    Next at step  55 , using the image processing computer of step  71 , a 3-dimensional model of the heart in CT coordinate space is prepared from the CT image. This can be done using the CARTOMERGE™ module, available from Biosense Webster. 
         [0040]    Next, at step  73  a coronary sinus catheter is introduced into the coronary sinus under fluoroscopic control. 
         [0041]    Next, at step  75 , with the coronary sinus catheter in place, the coronary sinus is reconstructed by the image processing computer using the techniques taught in commonly assigned copending application Ser. Nos. 14/621,570 and 14/621,581, which are herein incorporated by reference. Briefly, a 3-dimensional path of the coronary sinus catheter may be estimated using epi-polar geometry or iterative reconstruction of linear segments. In one method of reconstructing the coronary sinus, the patient&#39;s heart position is tracked over time. In order to compensate for heart movement, an algorithm reconstructs a path or track of the coronary sinus catheter in three dimensions, based on two 2-dimensional fluoroscopic images acquired before and after a movement, and synchronized in the cardiorespiratory cycle. A transformation between the two reconstructed catheters is computed and used to align the data. The reconstructed coronary sinus is motion-compensated, and exists in CARTO coordinate space. 
         [0042]    Reference is now made to  FIG. 3 , which is a composite image illustrating a stage in the process of coronary sinus reconstruction as applied to a 3-dimensional model  81  of the heart as described in step  55 , in accordance with an embodiment of the invention. In the lower portion of the figure, taken from a fluoroscopic frame, a corridor  83  is outlined and sampled around a CS catheter path  85  (represented by a broken line). The catheter path  85  was defined from previous frame and may have been annotated by a human operator. The divergence of CS catheter  87  from the catheter path  85  is compensated by suitable transformations, as explained in further detail in the above-noted application Ser. Nos. 14/621,570 and 14/621,581, 
         [0043]    Referring again to  FIG. 2  together with  FIG. 3 , at step  77  the reconstructed coronary sinus is placed in registration with the 3-dimensional model that was prepared in step  55  by aligning coronary sinus  89  in the model  81  with the transformed catheter path  85  obtained from analysis of the fluoroscopic image. It will be recalled that the 3-dimensional model  81  exists in CT coordinate space. The model  81  is now transformed into CARTO coordinate space. The CARTOMERGE™ image integration module, available from Biosense Webster, is suitable for performing the image registration and coordinate transformation. Since the position or the coronary sinus is closely related to the position of other portions of the heart, the remainder of the heart on the model  81  will be in registration with other cardiac images generated and displayed by the image processing computer. 
         [0044]    Then in final step  79 , the coronary sinus and the other cardiac structures can now be accurately located on the image processing computer display in CARTO coordinate space. 
         [0045]    It will be appreciated by persons skilled in the art 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 that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.