Abstract:
Cardiac ablation is monitored to detect hemopericardium by iteratively acquiring magnetic resonance imaging (MRI) data that includes the pericardium, measuring the pericardium by analyzing the sets of MRI data, making a determination that a measurement of the pericardium in consecutive sets of MRI data differ, and responsively to the determination reporting a change in configuration of the pericardium.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to cardiac catheterization. More particularly, this invention relates to improvements in detecting complications of cardiac catheterization. 
     Description of the Related Art 
     The meanings of certain acronyms and abbreviations used herein are given in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Acronyms and Abbreviations 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 MRI 
                 Magnetic Resonance Imaging 
               
               
                   
                 ECG 
                 Electrocardiogram 
               
               
                   
                   
               
             
          
         
       
     
     Cardiac arrhythmias, such as atrial fibrillation, occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. 
     Procedures for treating such arrhythmias include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to interrupt or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. 
     Verification of physical electrode contact with the target tissue is important for controlling the delivery of ablation energy while avoiding excessive contact force that might cause damage to the cardiac tissues. Attempts in the art to verify electrode contact with the tissue have been extensive, and various techniques have been suggested. For example, U.S. Pat. No. 6,695,808 describes apparatus for treating a selected patient tissue or organ region. A probe has a contact surface that may be urged against the region, thereby creating contact pressure. A pressure transducer measures the contact pressure. This arrangement is said to meet the needs of procedures in which a medical instrument must be placed in firm but not excessive contact with an anatomical surface, by providing information to the user of the instrument that is indicative of the existence and magnitude of the contact force. 
     In an invasive procedure performed on the heart, particularly a procedure involving mapping and ablation, there is a concern that the myocardial wall may be perforated, leading to unwanted entry of blood into the pericardial sac (hemopericardium) and development of a life threatening cardiac tamponade. Such a perforation is typically small. However, the flow rate of blood from the ventricular or atrial chamber into the pericardial space varies from low to high. Accordingly, it may take from a few minutes to a number of hours before the existence of the perforation is apparent. 
     A detailed description of the pericardial anatomy is given in the document  Cardiac MRI: Part  2 , Pericardial Diseases , Prabhakar Rajiah, American Journal of Roentgenology. October 2011; Vol. 197:W621-W634 (Rajiah), which is herein incorporated by reference. As is explained in Rajiah, the so-called “black blood” magnetic resonance imaging (MRI) technique may include weighted T1 and T2 sequences. The technique is useful to visualize normal pericardial anatomy, as well as effusions of blood into the pericardial sac. The black blood technique is a spin-echo MRI mode, in which high-velocity signal loss occurs. The technique employs excitation and refocusing pulses, which are 90° out of phase. Blood flowing within the heart in a slice of interest at the time of the 180° pulse will not have received the 90° pulse. Therefore, there is no magnetization in the transverse plane of the slice to refocus to an echo, and only a dark area appears on the resulting image. Pericardial fluid, which is not in rapid motion, appears as a white band on the image. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention operate the black blood MRI protocol as a computer process in order to detect real-time perforation of the myocardial wall during an ongoing cardiac catheterization procedure. Typically, MRI and ablation are performed concurrently using a combined, MRI and CARTO electroanatomical mapping system, or suite. In order to detect perforation, an image-processing program is operated periodically in background on black blood imaging data. The computer processor runs an automatic image-processing algorithm that compares successive images in order to detect changes in the anatomy of the pericardium. The images may be analyzed by the processor without the images being actually displayed. Alternatively or additionally, the processor may run the black blood protocol in background when perforation is suspected, for example, after a specific predefined contact force was exceeded during catheter manipulation, mapping or an ablation. 
     In some embodiments the processor is configured to check specific susceptible regions of the pericardium, where there is an expectation that blood is most likely to start accumulating. 
     The black blood protocol as described herein allows nearly instantaneous intraoperative detection of perforation of the epicardium. Its automatic mode of operation is transparent to the operator, and does not interfere with the ongoing catheterization procedure unless an abnormal event is detected. 
     There is provided according to embodiments of the invention a method, which is carried out by inserting a probe into a heart of a living subject, navigating the probe into a contacting relationship with a target tissue of the heart, and performing a medical procedure on the target. The method is further carried out during the medical procedure by iteratively acquiring magnetic resonance imaging (MRI) data that includes the pericardium, including a first set of MRI data and a second set of MRI data, measuring the pericardium by analyzing the sets of MRI data, making a determination that a measurement of the pericardium in the second set of MRI data differs from the measurement of the pericardium in the first set of MRI data, and responsively to the determination reporting a change in configuration of the pericardium. 
     According to an aspect of the method, acquiring the MRI data comprises black blood imaging of the pericardium. 
     According to still another aspect of the method, measuring the pericardium comprises detecting a separation of the visceral layer from the parietal layer of the pericardium. 
     According to another aspect of the method, making the determination comprises failing to detect the separation on the first set of MRI data and detecting the separation on the second set of MRI data. 
     According to one aspect of the method, making the determination comprises detecting a change in a distance between the visceral layer and the parietal layer that exceeds a predetermined value, which can be 0.1 mm. 
     According to still another aspect of the method, the separation is detected in a superior recess of the pericardium, adjacent to a posterolateral wall of the heart or adjacent to an inferolateral right ventricular wall of the heart. 
     According to yet another aspect of the method, iteratively acquiring is performed at intervals of between 5 sec and 3 minutes. 
     There is further provided according to embodiments of the invention a medical apparatus, including a probe, adapted for insertion into a heart, a memory having programs stored therein, a display, and a processor linked to the display and coupled to access the memory to execute the programs. The processor is connectable to a MRI apparatus. The programs include a MRI control module and an image analysis module, wherein the programs cause the processor to perform the steps of iteratively acquiring magnetic resonance imaging (MRI) data that includes the pericardium by invoking the MRI control module to communicate control signals to the MRI apparatus. The MRI data includes a first set of MRI data and a second set of MRI data. The processor is operative for measuring the pericardium by analyzing the sets of MRI data using the image analysis module, making a determination that a measurement of the pericardium in the second set of MRI data differs from the measurement of the pericardium in the first set of MRI data, and responsively to the determination reporting a change in configuration of the pericardium, wherein iteratively acquiring, measuring, making a determination, and reporting are performed while performing a medical procedure on a living subject. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       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: 
         FIG. 1  is a pictorial illustration of a system for performing catheterization procedures on a heart, in accordance with a disclosed embodiment of the invention; 
         FIG. 2  shows MRI images illustrating discovery of pericardial fluid in accordance with an embodiment of the invention; 
         FIG. 3  is a pictorial block diagram of an embodiment of the system shown in  FIG. 1 , in accordance with an embodiment of the invention; 
         FIG. 4  is a flow-chart of a method of evaluating the pericardium during cardiac catheterization, in accordance with an embodiment of the invention; 
         FIG. 5  is a detailed flow-chart illustrating details of the method shown in  FIG. 4 , in accordance with an embodiment of the invention; and 
         FIG. 6  is a detailed flow chart of a method of automatic detection of hemopericardium, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 always 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. 
     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. 
     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  10  typically comprises a general purpose or embedded computer processor, which is programmed with suitable software for carrying out the functions described hereinbelow. Thus, although portions of the system  10  shown in  FIG. 1  and other drawing figures herein are shown as comprising a number of separate functional blocks, these blocks are not necessarily separate physical entities, but rather may represent, for example, different computing tasks or data objects stored in a memory that is accessible to the processor. These tasks may be carried out in software running on a single processor, or on multiple processors. Alternatively or additionally, the system  10  may comprise a digital signal processor or hard-wired logic. 
     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  22  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. 
     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 50° 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. 
     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 . 
     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 . 
     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 . 
     The console  24  typically contains one or more ablation power connections. 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. 
     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 . 
     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. 
     A MRI imaging device  37  is linked to a control processor  47 , which may be located in the console  24 . An operator may select or override automatic operation to control the operation of the MRI imaging device  37 , for example by revising imaging parameters. The control processor  47  may communicate with the MRI imaging device  37  via a cable  51  to enable and disable the MRI imaging device  37  to acquire image data. An optional display monitor  49 , linked to the control processor  47 , allows the operator to view images produced by the MRI imaging device  37 . When the display monitor  49  is not included, the images may still be viewed on a monitor  29 , either via a split screen or in alternation with other images. 
     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  22  is typically a computer with appropriate signal processing circuits. The processor  22  is coupled to drive the monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14  and the MRI imaging device  37 , 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 , analyze the electrical signals from the electrodes and generate desired electroanatomic maps. The above-described arrangement works well when a shared coordinate system is shared between system components, e.g., a combined CARTO-MRI system. This is especially true when ablating the atria, as its wall is very thin, and it is necessary to define its boundaries. Despite advances in image processing, edge detection of the endocardial wall continues to be challenging, and conventionally requires manual analysis of sequential slice images. However, with a trackable, MRI-compatible, indwelling catheter that touches the endocardial wall and measures contact-force, manual analysis can be avoided. 
     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. 
     Reference is now made to  FIG. 2 , which shows MRI images illustrating discovery of pericardial fluid in accordance with an embodiment of the invention. At the left side of the figure is a black blood intraoperative MRI frame  53  showing a four-chamber view of a normal heart  55  and pericardium  57 . The distal portion of a cardiac catheter  59  is shown in contact with endocardial surface  61  of the heart  55 . A relatively small amount of fluid in the pericardial space appears as a narrow black band  63  lying between thicker white strips  123 ,  125 . The strips  123 ,  125  correspond to the parietal and visceral pericardium, which are often inseparable on images of this sort. In  FIG. 2  the two pericardial layers can be resolved as a result of a physiologic amount of pericardial fluid. 
     At the right of  FIG. 2  is a diagram comprising another intraoperative black blood MRI frame  65  with the cardiac catheter  59  superimposed thereon. Blood has accumulated within the pericardium, presumably originating from the cardiac chamber. If the MRI frame  65  were presented visually, as shown in  FIG. 1 , the operator would recognize the hemopericardium as an intraoperative complication of the catheterization. Alternatively, the control processor  47  would have acquired successive MRI frames, and would have identified the MRI frame  65  as significantly deviating from previous frames, e.g., the MRI frame  53 . In  FIG. 2 , a hemorrhagic pericardial effusion has occurred as a complication of cardiac catheterization. The blood appears on the MRI frame  65  as a region of low signal intensity, indicated by arrows  67 ,  69 ,  71 ,  73 . Typically, the earliest collection of pericardial fluid occurs adjacent to the posterolateral left ventricular wall or the inferolateral right ventricular wall, after which pericardial fluid accumulates in the superior recess. 
     Reference is now made to  FIG. 3 , which is a pictorial block diagram of an embodiment of the system  10  ( FIG. 1 ) for detecting perforation of the epicardium during cardiac catheterization using magnetic resonance imaging, in accordance with an embodiment of the invention. A control processor  75  communicates with catheter  14  while it is in the heart  12  via cable  51  and deals with routine aspects of a medical procedure involving the catheter  14 , using any of a position tracking position tracking module  77 , an ablation generator  79  and a mapping module  81 . MRI acquisition unit  83  may be activated from time to time by the operator to acquire and prepare MRI images using the facilities of an image processor  85  and a display  87  to assist the operator in visualizing the cardiac anatomy and optionally visualizing the distal portion of the catheter  14  in embodiments in which sensing elements appropriate to MRI techniques are included with the catheter  14 . In addition, a MRI control program  89  executing in the control processor  75  transmits control signals to the MRI acquisition unit  83  causing MRI images to be acquired by the MRI acquisition unit  83  according to a predefined schedule or responsively to calculations of an image analysis module  91 , which operates on data obtained from the image processor  85 . The image processor  85  may be provided in the MRI acquisition unit  83 , or may be integral with the control processor  75 , or be a separate entity as shown in  FIG. 3 . As is explained in further detail below, the image analysis module  91  is programmed to detect an increase in the volume of the pericardial space during the course of the catheterization, and when conditions are met, to alert the operator by a notification on the display  87 , audibly via a speaker  93 , or both. 
     Reference is now made to  FIG. 4 , which is a flow-chart of a method of evaluating the pericardium during cardiac catheterization, in accordance with an embodiment of the invention. At initial step  95 , a cardiac catheter is introduced into a subject and navigated to a target, typically within a chamber of the heart. This may be accomplished using the facilities of the above-mentioned CARTO system, optionally aided by an imaging modality, e.g., MRI. 
     Next, at an optional step  97 , contact between the catheter and the target is verified and the contact force adjusted if necessary. Contact force determination can be accomplished using the teachings of application Ser. No. 13/589,347, entitled “Machine Learning in Determining Catheter Electrode Contact” and U.S. Patent Application Publication No. 2013/0172875, entitled “Contact Assessment Based on Phase Measurement”, both of which are commonly assigned and are herein incorporated by reference. 
     At step  99 , a medical operation is carried out by the operator, e.g., mapping or ablation at an area of interest. 
     During the performance of steps  97 ,  99  an iterative procedure involving MRI is carried out: 
     An MRI image of the field of interest is acquired at step  101 , and analyzed to evaluate the configuration of the pericardial space. The first iteration of step  101  constitutes a reference against which image data from subsequent iterations are compared. 
     Next, at decision step  103 , it is determined if analysis of the image data shows increased separation between the parietal and visceral pericardium in at least a portion of the pericardial space, indicating the formation of a hemopericardium. Width of the pericardial sac is an exemplary indication of the volume of the pericardial sac, and hence its liquid content. Other indicators of pericardial volume that can be determined on MRI images will occur to those skilled in the art. In some embodiments, the analysis may be accomplished with the aid of a conventional image processing program provided by the manufacturer of the MRI imaging device, optionally supplemented by the image analysis module  91  ( FIG. 3 ). Alternatively, the image analysis module  91  may be programmed to evaluate raw or partially processed image data so as to recognize any intraoperative change in the pericardial anatomy, for example, in a comparison of the parietal and visceral pericardial layers in the two images in  FIG. 2 . One set of images is compared with a baseline set or a previous performance of decision step  103 . In any case, the evaluation of the image data is performed automatically, and may be executed as a background process by the control processor  75  ( FIG. 3 ). If the determination at decision step  103  is negative, then after a predetermined delay interval control returns to step  101  for acquisition of new image data. 
     If the determination at decision step  103  is affirmative then control proceeds to step  105 . An alert to the operator is issued. 
     Final step  107  is performed upon completion of step  99  or step  105 , whichever occurs first. The procedure accordingly terminates normally or abnormally. 
     Reference is now made to  FIG. 5 , which is a flow-chart illustrating details of decision step  103  ( FIG. 4 ), in accordance with an embodiment of the invention. Normal pericardial thickness ranges from 1.2 to 1.7 mm on MRI images. When fluid accumulates in the pericardium quickly, pericardial pressures can increase substantially and produce well-known hemodynamic effects. One method of automatically evaluating MRI image data of the heart and pericardium in successive iterations of decision step  103  ( FIG. 4 ) exploits information known from the above-noted Rajiah document: pericardial fluid does not necessarily spread homogeneously. Rather, the earliest collection of pericardial fluid occurs adjacent to the posterolateral left ventricular wall or the inferolateral right ventricle wall, after which pericardial fluid accumulates in the superior recess. Moderate-sized collections of fluid (100-500 mL) tend to accumulate in the anterior aspect of the right ventricle as well. Large effusions are seen anterior to the right atrium and right ventricle. 
     At initial step  109 , a baseline or scout MRI image of the heart and pericardium is obtained. This may be conveniently done at the beginning of the catheterization session, or may be a previously obtained image. The images described in this method are obtained using the above-noted black blood technique. 
     Next, at step  111  the following target areas are identified: the posterolateral left ventricular wall, the inferolateral right ventricle wall, and the superior recess. 
     Next, at step  113 , MRI images are acquired to include at least the target areas that were identified in step  111 . In some embodiments, the images are selected or acquired to synchronize with cardiorespiratory motions. Measurements of the distances between the visceral and parietal pericardium are recorded at the target areas. This may be accomplished using routines provided by the image analysis module  91  ( FIG. 3 ). The measurements may include defining spatial regions of interest for the posterolateral left ventricular wall, and the inferolateral right ventricular wall, and analyzing the data in the regions of interest, respectively. 
     Next, at decision step  115 , it is determined if the measurements obtained in step  113  vary from a previous iteration (or the scout image) by more than a predetermined value. A suitable threshold of variation for this purpose depends upon the strength of the MRI magnetic field and is 0.1-0.3 mm for 3 T and 1.5 T, respectively. It will be recalled from the discussion above that normally almost no separation is evident between the parietal and visceral and visceral layers of the pericardium on black blood MRI images. However, in some patients, there is a very small physiological pericardial effusion, which represents a normal anatomical variant. Appearance of any discernable separation on a new iteration of step  113  when it was not detectable on a previous iteration may be a significant change in the images. 
     If the determination is affirmative, then an alert is reported at step  117 . Otherwise, a negative report is communicated at step  119 . 
     After performing either of steps  117 ,  119 , delay step  121  is performed. The delay interval is not critical, but should be small enough to detect significant changes in the pericardium before hemodynamic changes occur. A delay interval of 5 seconds is suitable. However, longer delay intervals may be tolerated, and the intervals may vary in different phases of the medical procedure. For example during ablation, the intervals may be shortened, while during mapping longer intervals may be chosen. Thereafter, a new iteration begins at step  113 . 
     Reference is now made to  FIG. 6 , which is a detailed flow chart of a method of automatic detection of hemopericardium, in accordance with an embodiment of the invention. The steps shown in  FIG. 6  are discussed with reference to the following pseudocode, and represent computer-implemented functions. 
     Step  127 : V]=Perform_3D_Anatomy_Scan(x0,y0,z0, size_X,size_Y,size_Z,O). This function receives coordinates, orientation and image size and performs a 3D volumetric scan. The scan can be rendered also as a 2D scan. 
     Step  129  [M]=Perform_Magnetic_Mapping_with_tagging_possible_perforation_regions (x,y,z,is_dangerous). This function receives coordinates, and a Boolean parameter if the current region is dangerous or not and returns a value M, which is binary 3D mask of 1 for dangerous pixels and 0 otherwise. 
     Tagging can be manually pre-defined or performed in real time according to the following criteria: 
     Mode==1: Pre-defined manually 
     Mode==2: if current_tissue_thickness&gt;former_tissue_thickness 
     Mode==3: Contact_Force_value&gt;threshold_CF 
     Mode==4: Blood_Pressure&lt;threshold_BP 
     Mode==5: Is_Abnormal_Ablation_Parameter_exist 
     Step  131  [L,O]=Get_Location (B1,B2,B3). This function returns catheter position and orientation relative to MRI system of coordinates according to a magnetic field B received from the location pad. 
     Decision step  133  [is_true]=Is_potential_perforation_region(L,O,M). This function receives a mask (3D volumetric binary data of the mapping and anatomy) and returns Boolean value whether the current location is potential perforation region or not. If the Boolean value is false, step  131  is performed. 
     If the Boolean value in decision step  133  is true, then step  135  is performed: [Data]=Bring_MRI_volumetric_data(L,O). This function scans quickly a very small region defined by location and orientation via black blood sequence and returns the grey level data. 
     If conditions are appropriate as noted above, a new 3D scan is performed at step  137   
     Step  139  represents analysis of the data thus far obtained, and is performed by a group of functions: 
     [Is_perforated=Analyze(mode) This function receives a mode, which defines which of several analysis types will be applied: 
     If mode==1 then call Analyze_via_Image_Algebra 
     Else if mode==2 call Analyze_via_gradient_analysis 
     Else call Analyze_via_tissue thickness. 
     Decision step  141  can be performed by invoking one or more of the following functions: 
     [is_peforated]=Analyze_via_Image_Algebra(Initial,Current).] The ImageAlgebra tool provided by Philips may be used for this function. This function receives an initial volumetric data (from Perform_3D_Anatomy_Scan) as well as current data (from step  135 ), normalize it by: 
     Initial=Initial/mean(Initial) 
     Current=Current/mean(Current) 
     Apply Image algebra: deviation=abs(Initial-Current) 
     Max_deviation=max(deviation) 
     If Max_deviation&gt;threshold→alert. 
     [is_peforated]=Analyze_via_gradient_analysis(Initial,Current,L,O). Trace a ray from current catheter location, which is in contact with current catheter orientation and derivate the gray level. If there are global minima in the middle, then there is perforation because pericardial sac as well as tissue will provide constant gradient change. But if there is blood (which is black) between the sac and tissue there will be a local minimum (according to Fermat&#39;s Law). 
     [is_peforated]=Analyze_via_tissue thickness (Initial,Current,L,O) 
     If current_tissue_thickness-initial_tissue_thickness&gt;threshold_TS then is_peforated==true. 
     Steps  143 ,  145  concern alerting the operator and taking corrective action, respectively, when a possible or actual perforation is detected at decision step  141 . In step  145 , the function Apply_Safety_Procedure(is_preforated) disconnects ablation option and may apply lifesaving procedures, which are outside the scope of this disclosure. 
     If no blood is detected in the pericardial sac at decision step  141 , then data is updated and stored at step  147 . The algorithm then iterates at step  131 . 
     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.