Abstract:
In a medical apparatus including a medical imaging system and a medical position and navigation system (MPS), the medical imaging system including an imaging transmitter, periodically emitting imaging radiation and an imaging detector, the medical position and navigation system including at least one MPS transmitter periodically transmitting MPS radiation and at least one MPS detector, the MPS radiation electromagnetically interfering with at least one mode of operation of the imaging detector, a device for eliminating interference to the imaging detector caused by positioning radiation, the device comprising a synchronizer, coupled with the medical imaging system and with the medical position and navigation system, synchronizing the imaging detector and each the at least one MPS transmitter, so that neither of the at least one MPS transmitter transmits during the at least one mode of operation of the imaging detector.

Description:
FIELD OF THE DISCLOSED TECHNIQUE 
     The disclosed technique relates to medical imaging in general, and to methods and systems for reducing electromagnetic interference in an image, obtained by a medical imaging system, in particular. 
     BACKGROUND OF THE DISCLOSED TECHNIQUE 
     Electromagnetic radiation medical imaging systems are known in the art. Such systems are generally used to create a representation in the form of an image of the anatomy of a region of interest of a patient. Such electromagnetic radiation medical imaging systems are, for example, X-ray, CT, MRI, US or PET systems. 
     Medical positioning systems (MPS) are known in the art. Such systems are generally used to track and mark the location of an object (e.g., catheter) in or around the body of a patient. Medical positioning systems may employ electromagnetic radiation to determine the location of a body in a reference coordinate system. More specifically, these systems employ the relationship between the strength of the signal associated with this radiation, as detected by a detector, and the distance of this detector from the source of the radiation. For example, such medical positioning systems may include three electromagnetic radiation transmitters, in the form of transmitting coils, positioned such that the axes normal to the plane crated by one of the turns of each coil are mutually orthogonal. These systems may employ detectors in the form of one or more receiving coils, positioned such that the axes, normal to the plane crated by one of the turns of each coil, are mutually orthogonal. Each coil corresponds to an axis in a reference coordinate frame. 
     A Medical imaging system may be employed in conjunction with a medical positioning system to obtain the image of the anatomy of a patient and the location of an object within or on the patient. For example, during a catheterization procedure, knowledge of the position of the catheter within the body of a patient, and an image of the anatomy of the region in which the catheterization procedure is performed, may be necessary. 
     Reference is now made to  FIG. 1 , which is a schematic illustration of a system, generally referenced  10 , for navigating an object, such as a distal tip of a catheter, in conjunction with images of the anatomy of a portion of a body of a patient as, detected by a medical imaging system, which is known in the art. System  10  includes medical imaging system  28 , a medical positioning system (MPS)  34 , a catheter  16 , a display unit  32  and a table  14 . Medical imaging system  28  includes an imaging radiation transmitter  30  and an imaging radiation detector  26 . Catheter  16  includes a distal end  18 . Distal end  18  includes magnetic position radiation detectors (not shown). This position radiation detector may be a single coil detector or a multiple coil detector (not shown). The detector is operative for detecting magnetic fields. Medical positioning system  34  includes positioning radiation transmitters  20 ,  22  and  24 . Positioning radiation transmitters  20 ,  22  and  24  are, for example, three coils. 
     Display unit  32  is coupled with imaging radiation detector  26 . Positioning radiation transmitters  20 ,  22  and  24 , and catheter  16  are coupled with medical positioning system  34 . Catheter  16  is inserted to a patient  12 , subjected to a treatment, and navigated towards a region of interest (e.g., the cardiovascular system). Imaging radiation transmitter  30  transmits radiation that passes through patient  12 . The radiation, detected by imaging radiation detector  26 , is a representation of the anatomy of a region of interest of patient  12 . An image representing the anatomy of the region of interest of patient  12  is formed on display unit  32 . The image includes catheter  16  and distal end  18 . Positioning radiation transmitters  20 ,  22  and  24  transmit magnetic fields which are mutually orthogonal, corresponding to axes of a reference coordinate frame. The detector at distal end  18  detects the magnetic fields generated by positioning radiation transmitters  20 ,  22  and  24 . The detected signal is related to the position of distal end  18 , for example, by the Biot Savart law, know in the art. Thus, the position of distal end  18  is obtained by medical positioning system  34 . Positioning radiation transmitters  20 ,  22  and  24  are located on imaging radiation detector  26  so as to register the coordinate system associated with imaging radiation detector  26  and the coordinate system associated with MPS  34  and to maximize the signal to noise ration of the signals detected by the positioning radiation detector. 
     However, imaging radiation detector  26  acquires the imaging radiation transmitted by imaging radiation transmitter  30 , concurrently with positioning radiation transmitter  20 ,  22  and  24 . Thus, due to the proximity of the positioning radiation transmitters to the imaging radiation detector, the magnetic field generated thereby, may affect imaging radiation detector  26 . Consequently the image formed on display unit  32  may be corrupted. 
     U.S. Pat. No. 6,810,110 to Pelc et al. entitled “X-Ray Tube for Operating in A Magnetic Field” is directed to a method wherein an x-ray source, including a cathode, an anode and magnetic means. The magnetic means produce a magnetic field having magnetic field lines passing from the cathode to the anode to compensate or correct an otherwise undesired magnetic field. The magnetic means may include an electromagnet or permanent magnets. The electromagnet may be electromagnetic windings or coils mechanically coupled to the x-ray source. The permanent magnets may be integrated inside or positioned outside of the x-ray source. 
     U.S. Pat. No. 6,828,728 to Levinson, entitled “Processing images for removal of artifacts” directs to a method wherein interference in an X-Ray image is removed by processing the image after the acquisition thereof. The method to Levinson, initially identify a region in the image, with a standard deviation below a predetermined threshold. This identified region is declared to be free of artifacts. In the next step, each pixel element, on the outer edges of the imaging sensor, starting from the initially identified region, is cleaned. Cleaning is achieved by testing each pixel in sequence and comparing its value with the two preceding clean neighbours in the respective row or column. If the tested pixel is determined not to have predetermined relationship with respect to these clean neighbours, it is replaced by a pixel value having a predetermined relationship with respect to the clean neighbours. In the last step, the remaining pixels are tested. If a pixel is found not to have a predetermined relationship with its neighbouring pixels, the pixel is replaced with the average value of the neighbouring pixels. 
     U.S. Pat. No. 6,118,848 to Simon et al. entitled “System and methods for the reduction and elimination of image artifacts in the calibration of X-ray imagers” directs to a method to reduce the representation of calibration markers present in an X-ray image. The representations of the calibration markers are reduced by replacing the pixels representing the calibration markers by pixels related to the pixels surrounding the representation of the calibration markers. The relationship between the surrounding pixels and the replaced pixels may be that of the average of the surrounding pixels or multiple regions averaging. 
     U.S. Pat. No. 6,314,310 to Ben-Haim et al., entitled “X-Ray Guided Surgical Location System with Extended Mapping Volume”, is directed to a method for displaying anatomical features of interest in the body of a patient acquired by one or more X-ray images, with a probe, inserted into the body of the patient. The probe includes sensing devices such as magnetic field responsive coils for determining six-dimensional position and orientation coordinates. During the surgery, as the probe is advanced into the body of the patient, signals generated by the coils on the probe are used to track the coordinates of the tool and to update accordingly, the display showing the image of the tool and the patient. Preferably, a new X-ray image is acquired from time to time. According to the publication to Ben-Haim et al, a surgeon is able to insert and manipulate the probe in the body of the patient under the visual guidance of an X-ray image of the body that includes continuously-updated representation of the tool. The X-ray images is acquired during the surgical procedure and may be updated as desired. 
     SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE 
     It is an object of the disclosed technique to provide a novel method and system for synchronizing a medical imaging system with a medical positioning system. 
     In accordance with the disclosed technique, there is thus provided a device for eliminating interference to an imaging detector caused by positioning radiation. A medical apparatus includes a medical imaging system and a medical position and navigation system (MPS). The medical imaging system includes an imaging transmitter, periodically emitting imaging radiation and an imaging detector. The medical position and navigation system (MPS) includes at least one MPS transmitter periodically transmitting MPS radiation and at least one MPS detector. The MPS radiation electromagnetically interferes with at least one mode of operation of the imaging detector. The device includes a synchronizer, coupled with the medical imaging system and with the medical position and navigation system. The synchronizer synchronizes the imaging detector and each the at least one MPS transmitter, so that neither of the at least one MPS transmitter transmits during the at least one mode of operation of the imaging detector. 
     In accordance with another embodiment of the disclosed technique, there is thus provided a combined imaging and positioning apparatus. The combine imaging a positioning apparatus includes a medical imaging system, a medical position and navigation system and a synchronizer. The synchronizer is coupled with the medical imaging system and with the medical position and navigation system. The medical imaging system obtains a representation of the anatomy of a portion of a body. The medical imaging system includes an imaging radiation transmitter for periodically transmitting imaging radiation and an imaging detector. The medical position and navigation system (MPS) includes at least one MPS transmitter for transmitting MPS radiation, the MPS radiation electromagnetically interferes with at least one mode of operation of the imaging detector. The medical position and navigation system (MPS) further includes and at least one MPS detector for detecting MPS radiation. The synchronizer, synchronizes the imaging detector and each the at least one MPS transmitter, so that neither of the at least one MPS transmitter transmits during the at least one mode of operation of the imaging detector. 
     In accordance with a further embodiment of the disclosed technique, there is thus provided a method for eliminating interference to an imaging detector caused by positioning radiation. A medical apparatus includes a medical imaging system and a medical position and navigation system (MPS). The medical imaging system includes an imaging transmitter and an imaging detector. The imaging transmitter periodically emits imaging radiation. The imaging detector periodically detects an image frame. The medical position and navigation system includes at least one MPS transmitter and at least one MPS detector. The MPS transmitter periodically transmits MPS radiation. The method includes the procedures of synchronizing the detection of image frames and the transmission of the MPS radiation, to be mutually exclusive in the time domain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
         FIG. 1  is a schematic illustration of a system, for navigating an object, such as a distal tip of a catheter, in conjunction with images of the anatomy of a portion of a body of a patient as detected by a medical imaging system, which is known in the art; 
         FIG. 2  is a schematic illustration of a system, for navigating an object such as a distal tip of a catheter in conjunction with images of the anatomy of a portion of a body of a patient as detected by a medical imaging system, constructed and operative in accordance with an embodiment of the disclosed technique; 
         FIG. 3  is a schematic illustration of a system, for navigating an object such as a distal tip of a catheter, in conjunction with images of the anatomy of a portion of a body of a patient, as detected by a medical imaging system, constructed and operative in accordance with another embodiment of the disclosed technique; 
         FIG. 4  is a schematic illustration of a timing diagram, in accordance with a further embodiment of the disclosed technique; 
         FIG. 5  is a schematic illustration of a timing diagram, in accordance with another embodiment of the disclosed technique; 
         FIG. 6  is a schematic illustration of a method for synchronizing a medical imaging system with a medical positioning system, operative in accordance with a further embodiment of the disclosed technique; 
         FIG. 7  is a schematic illustration of a method for synchronizing a medical imaging system with a medical positioning system, operative in accordance with another embodiment of the disclosed technique; 
         FIG. 8  is a schematic illustration of a method for synchronizing a medical imaging system with a medical positioning system, operative in accordance with a further embodiment of the disclosed technique; 
         FIG. 9  is a schematic illustration of a method for synchronizing a medical imaging system with a medical positioning system, operative in accordance with another embodiment of the disclosed technique. 
         FIG. 10  is a schematic illustration of a timing diagram, in accordance with a further embodiment of the disclosed technique; 
         FIG. 11  is a schematic illustration of a timing diagram, in accordance with another embodiment of the disclosed technique; 
         FIG. 12 , which is a schematic illustration of a method for synchronizing system the operation of a medical position system with a medical imaging system operative in accordance with a further embodiment of the disclosed technique; 
         FIG. 13 , which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique; 
         FIG. 14  which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with a further embodiment of the disclosed technique; and 
         FIG. 15  which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The disclosed technique overcomes the disadvantages of the prior art by providing a method and a system to reduce the interference in real time images, acquired by a medical imaging system, caused by a magnetic field, generated by positioning radiation transmitters of a medical positioning system (MPS). According to the disclosed technique, a synchronizer synchronizes the operation of the imaging radiation detector of the medical imaging system and the medical positioning radiation transmitters (i.e., at least one mode of operation of the imaging radiation detector and the operation of the positioning radiation transmitters are mutually exclusive in time). As a result of this synchronization, the positioning radiation transmitters do not transmit positioning radiation while imaging radiation detector acquires imaging radiation. (i.e., the operations of acquiring an image and transmitting positioning radiation are mutually exclusive in time). According to another embodiment of the disclosed technique, the position radiation transmitters do not transmit while the medical imaging system samples the acquired image frame from the imaging radiation detector (i.e., the operations of sampling an image frame and transmitting positioning radiation are mutually exclusive in time). During the image frame sampling period the medical imaging system samples the pixel values accumulated in the imaging radiation detector during the image acquisition period. 
     Additionally, the imaging radiation detector is electromagnetically shielded with metal plates to prevent the magnetic filed interference with the electronics thereof. Consequently, the interferences of the magnetic fields with the imaging radiation detector and the imaging radiation transmitter, is eliminated. Thus, the imaging system produces real time images, which does not exhibit visible flaws due to magnetic field interference caused by the proximity of the positioning radiation transmitter to the imaging radiation detector. 
     Reference is now made to  FIG. 2 , which is a schematic illustration of a system, generally referenced  100 , for navigating an object such as a distal tip of a catheter in conjunction with images of the anatomy of a portion of a body of a patient as detected by a medical imaging system, constructed and operative in accordance with an embodiment of the disclosed technique. System  100  includes a medical imaging system  118 , an MPS  124 , a catheter  106 , a synchronizer  126  and a table  104 . Medical imaging system  118  includes an imaging radiation transmitter  120 , an imaging radiation detector  116  and a display unit  122 . MPS  124  includes positioning radiation transmitters  110 ,  112  and  114  and a position radiation detector (not shown), operative for detecting magnetic fields, fitted on catheter  106 . Positioning radiation transmitters  110 ,  112  and  114  are, for example, three coils, positioned such that the axes, normal to the plane crated by one of the turns of the coils, are orthogonal. Catheter  106  includes a distal end  108 . Distal end  108  includes positioning radiation detectors, (e.g., a single axis coil or multiple axes coils). 
     Display unit  122  is coupled with medical imaging system  118 . Positioning radiation transmitters  110 ,  112  and  114 , and the position radiation detector (not shown) fitted on tip  108  of catheter  106  are coupled with MPS  124 . Synchronizer  126  is coupled to medical imaging system  118  and MPS  124 . 
     Catheter  106  is inserted to a patient  102 , subjected to a treatment, and navigated toward a region of interest (e.g., the cardiovascular system). Imaging radiation transmitter  120  transmits radiation that passes through patient  102 . Imaging radiation detector  116  detects an image frame. This detection includes two modes. The first mode is acquiring the imaging radiation and the second mode is sampling the acquired pixel values accumulated in the imaging radiation detector during the image acquisition period. This acquired radiation, detected by imaging radiation detector  116 , is a representation of the anatomy of a region of interest of patient  102  in an image coordinate system. An image representing the anatomy of the region of interest of patient  102  is formed on display unit  122 . This image includes catheter  106  and distal end  108 . Positioning radiation transmitters  110 ,  112  and  114  transmit magnetic fields which are mutually orthogonal, corresponding to an MPS coordinate system. The position detector at the distal end  18  detects the magnetic fields generated by positioning radiation transmitters  110 ,  112  and  114 . Synchronizer  126  enables positioning radiation transmitters  110 ,  112  and  114  to transmit when imaging radiation detector  116  does not acquire imaging radiation. Synchronizer  126  disables transmitters  110 ,  112  and  114  (i.e., at least from transmitting) when imaging radiation detector  116  acquires imaging radiation. According to another embodiment of the disclosed technique, synchronizer  126  enables positioning radiation transmitters  110 ,  112  and  114  to transmit when medical imaging system  118  does not sample the acquired image from image radiation detector  116 . Synchronizer  126  disables transmitters  110 ,  112  and  114  (i.e., at least from transmitting) when medical imaging system  118  samples the acquired image from image radiation detector  116 . 
     Reference is now made to  FIG. 3 , which is a schematic illustration of a system, generally referenced  150 , for navigating an object such as a distal tip of a catheter, in conjunction with images of the anatomy of a portion of a body of a patient, as detected by a medical imaging system, constructed and operative in accordance with a further embodiment of the disclosed technique. System  150  includes a MPS  152 , a medical imaging system  154 , a display unit  178  and a synchronizer  180 . MPS  152  includes a position detector  164 , positioning radiation transmitters  156 ,  158 ,  160  and positioning processor  162 . Each of position radiation transmitters  156 ,  158  and  160  may be a group of transmitters. These transmitters may transmit at mutually exclusive frequencies or mutually exclusive time periods. Position detector  164  includes positioning radiation detectors  166 ,  168  and  170 . Alternatively, position detector  164  may include a single position radiation detector. Medical imaging system  154  includes imaging radiation transmitter  172 , imaging radiation detector  176  and imaging processor  174 . 
     Synchronizer  180  and display unit  178  are coupled with imaging system  154  and with MPS  152 . Positioning processor  162  is coupled with position detector  164 , with positioning radiation transmitters  156 ,  158 , and  160 , with display unit  178  and with synchronizer  180 . Imaging processor  174  is coupled with imaging radiation detector  176 , with imaging radiation transmitter  178 , with display unit  178  and with synchronizer  180 . An object such as a catheter (not shown) is inserted to a patient (not shown) subjected to a treatment, and navigated toward a region of interest (e.g., the cardiovascular system). 
     Imaging radiation transmitter  172  emits radiation that passes through the patient. Imaging radiation detector  176  detects an image frame. This detection includes two modes of operation. The first mode is acquiring the imaging radiation and the second mode is sampling the acquired pixel values accumulated in the imaging radiation detector during the image acquisition period. This radiation, acquired by imaging radiation detector  176 , is a representation of the anatomy of a region of interest of the patient. Image detector  176  samples the acquired pixel values of the acquired imaging radiation. An image representing the anatomy of the region of interest of the patient is formed on display unit  178 . The image includes the catheter. Positioning radiation transmitters  156 ,  158  and  160  transmit magnetic fields which are mutually orthogonal, corresponding to an MPS coordinate system. Positioning detector  164 , detect the magnetic fields generated by positioning radiation transmitters  156 ,  158  and  160 . The detected signals are related to the position of the distal end of the catheter in relation to positioning radiation transmitters  156 ,  158 ,  160 . When the positioning radiation transmitters  156 ,  158 ,  160  are mounted on the imaging radiation detector  174 , the coordinates system, associated with the MPS, is registered with the coordinates system associated with imaging system. Synchronizer  178  enables positioning radiation transmitters  156 ,  158 , and  160  to transmit when imaging radiation detector  174  does not acquire imaging radiation. Synchronizer  178  disables transmitters  156 ,  158 , and  160  when imaging radiation detector  174  acquires imaging radiation. According to another embodiment of the disclosed technique, synchronizer  180  enables the positioning radiation transmitters  156 ,  158 , and  160  to transmit when medical imaging system  154  does not sample the acquired image. Synchronizer  180  disables transmitters  156 ,  158 , and  160  when medical imaging system samples the acquired image. 
     Consequently, the interferences, caused by the magnetic fields, with imaging radiation detector  176 , are eliminated. Thus, medical imaging system  154  produces an image, which does not exhibit visible flaws due to magnetic field interference caused by the proximity of positioning radiation transmitters  156 ,  158  and  160  to imaging radiation detector  176 . 
     Reference is now made to  FIG. 4  which is a schematic illustration of a timing diagram generally referenced  200 , in accordance with a further embodiment of the disclosed technique. Timing diagram  200  includes signals  202 ,  204 ,  206  and  208 . Signal  208  is the timing signal associated with the transmission of imaging radiation by imaging radiation transmitter  172  ( FIG. 3 ). Signals  202 ,  204  and  206  are the timing signals associated with the operation of positioning radiation transmitters  156 ,  158  and  160  ( FIG. 3 ) respectively. Transmitters  156 ,  158  and  160  ( FIG. 3 ) are operated sequentially so as to enable the detection of the position (and orientation) of an object, with respect to each axis of a reference coordinate frame, independently. Alternatively, positioning radiation transmitters  156 ,  158  and  160  may be operated concurrently but at different frequencies. 
     Time period  210  is the imaging radiation transmission period. During the imaging radiation transmission period the imaging radiation transmitter transmits imaging radiation. Time period  212  is the imaging radiation non-transmission period. During the imaging radiation non-transmission period the imaging radiation transmitter does not transmit imaging radiation. Time period  214  is the positioning radiation transmission period. During the positioning radiation transmission period the positioning radiation transmitters transmit positioning radiation. Time period  216  is the relative phase range. The relative phase range is the range in which the phase of either the positioning radiation transmission period or the position radiation transmission period may change without the two transmission periods overlapping. The relative phase is defined as the difference between the imaging radiation non-transmission period and the positioning radiation transmission period. 
     During time period  210 , imaging radiation detector  176  ( FIG. 3 ) acquires imaging radiation. However, during time period  210 , synchronizer  180  ( FIG. 3 ) at least disables positioning radiation transmitters  156 ,  158  and  160  ( FIG. 3 ) from transmitting. Consequently, the image obtained by imaging radiation detector  176  ( FIG. 3 ) does not exhibit visible flaws due to magnetic field interference. 
     According to another embodiment of the disclosed technique, MPS may employ more than three magnetic field transmitters. However, not all the magnetic field transmitters can be activated during the imaging radiation detector non-acquisition period. Thus, the synchronizer prevents the positioning radiation transmitters from transmitting during the period in which the imaging radiation detector acquires radiation, and continues after the imaging radiation detector stops acquiring radiation. 
     Reference is now made to  FIG. 5 , which is a schematic illustration of timing diagram generally referenced  220  in accordance with a further embodiment of the disclosed technique. In Timing diagram  220 , six positioning radiation transmitters are employed by the MPS. Timing diagram  220  includes signals  222 ,  224 ,  226 ,  228 ,  230 ,  232  and  234 . Signal  222 ,  224 ,  226 ,  228 ,  230  and  232  are the timing signals associated with the operation of the positioning radiation transmitters. Signal  234  is associated with the operation of the imaging radiation transmitter  172  ( FIG. 3 ). During time period  236  imaging radiation transmitter does not transmit imaging radiation. Thus, the positioning radiation transmitters can transmit. However, time period  236  is sufficient to operate only positioning radiation transmitters number 1, 2, 3 and 4. During time period  238 , imaging radiation transmitter transmits radiation and the synchronizer disables the positioning radiation transmitters from transmitting. However, after the imaging radiation transmitter stops transmitting radiation, the synchronizer enables positioning radiation transmitters to transmit, starting from positioning radiation transmitter number 5. 
     Reference is now made to  FIG. 6 , which is a schematic illustration of a method for synchronizing a medical imaging system with a MPS, operative in accordance with a further embodiment of the disclosed technique. In procedure  250 , the periodic imaging radiation acquisition is enabled. With reference to  FIG. 3 , synchronizer  180  enables periodic image acquisition and imaging radiation detector  176  acquires imaging radiation. 
     In procedure  252 , imaging radiation is periodically transmitted while imaging radiation acquisition is enabled. With reference to  FIG. 3 , image radiation transmitter  172  periodically transmits imaging radiation. After procedures  250  and  252 , the method proceeds to procedure  254 . 
     In procedure  254 , imaging radiation acquisition is disabled before enabling the positioning radiation transmission. With reference to  FIG. 3 , synchronizer  180  disables the imaging radiation transmission before enabling the positioning radiation transmission. 
     In procedure  256 , periodic positioning radiation transmission is enabled. With reference to  FIG. 3 , synchronizer  180  enables the periodic positioning radiation transmission. After procedure  256 , the method proceeds to procedure  260 . 
     In procedure  258 , an image frame is downloaded form the imaging radiation detector while the positioning radiation transmission is enabled. The image frame forms an image on the display unit. With reference to  FIG. 3 , imaging processor  174  downloads an image frame from imaging radiation detector  176 . 
     In procedure  260 , positioning radiation transmission is disabled before enabling imaging radiation acquisition. With reference to  FIG. 3 , synchronizer  180  disables the positioning radiation transmission before enabling the imaging radiation transmission. After procedure  260 , the method proceeds to procedures  250  and  252 . 
     According to another embodiment of the disclosed technique, two distinct (and may be different), preferably non-overlapping, periods, of the imaging acquisition and the positioning radiation, may overlap due to a drift in the relative phase between the two transmission periods. For example, with reference to  FIG. 4 , imaging radiation transmission period  210  may drift toward positioning radiation transmission period  212 . The relative phase drift may be larger than the relative phase range  216 . Thus an overlap between period  210  and period  212  will occur. The synchronizer delays the transmission of either the imaging radiation or the positioning radiation. 
     Reference is now made to  FIG. 7 , which is a schematic illustration of a method for synchronizing the operation of a MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique. In procedure  270 , imaging radiation is periodically transmitted and imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation and imaging radiation detector  176  periodically acquires imaging radiation. 
     In procedure  272 , positioning radiation is periodically transmitted while imaging radiation is acquired and while imaging radiation is periodically transmitted. The positioning radiation transmission period and the imaging radiation acquisition period are distinct and may be different. With reference to  FIG. 3 , positioning radiation transmitters  156 ,  158 , and  160  periodically transmit positioning radiation. After procedures  270  and  272 , the method proceeds to procedure  274 . 
     In procedure  272 , a potential overlap between the imaging radiation acquisition period and the positioning radiation transmission period is detected. This potential overlap is detected according to a change in the relative phase between the two periods. The relative phase is defined as the difference between the imaging radiation non-acquisition period and the positioning radiation transmission period. With reference to  FIG. 4 , the relative phase range  216  is the relative phase range in which the phase of either the imaging radiation acquisition period or the positioning radiation transmission period may change without the two transmission periods overlapping. When the combined relative phase drift of the imaging radiation acquisition period and the positioning radiation transmission period is larger than the relative phase range, then a potential overlap is detected and the method proceeds to procedure  276 . When the relative phase drift of the imaging radiation acquisition period and the positioning radiation transmission period is at most equal to the relative phase range, then no potential overlap is detected and the method proceeds to procedures  270  and  272 . With reference to  FIG. 3 , synchronizer  180  detects a potential overlap between the imaging radiation acquisition period and the positioning radiation transmission period. 
     In procedure  276 , the relative phase between the imaging radiation acquisition and the positioning radiation transmission is adjusted so that no overlap occurs. With reference to  FIG. 3 , synchronizer  180  adjusts the relative phase between the imaging radiation acquisition and the positioning radiation transmission. After procedure  278 , the method proceeds to procedure  270  and  272 . 
     According to a further embodiment of the disclosed technique, the synchronizer enables the transmission of the positioning radiation when the end of an imaging radiation acquisition period is detected. Reference is now made to  FIG. 8 , which is a schematic illustration of a method for synchronizing the operation of a MPS with a medical imaging system, operative in accordance with a further embodiment of the disclosed technique. In procedure  290 , the imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation detector  176  periodically acquires imaging radiation. 
     In procedure  290 , imaging radiation is periodically transmitted while imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation. After procedures  290  and  292 , the method proceeds to procedure  294 . 
     In procedure  294 , the end of an imaging radiation acquisition period is detected. With reference to  FIG. 3 , synchronizer  180  detects the end of the imaging radiation acquisition period. 
     In procedure  296 , periodic positioning radiation transmission is enabled. With reference to  FIG. 3 , synchronizer  180  enables the periodic positioning radiation transmission. After procedure  296 , the method proceeds to procedure  298 . 
     In procedure  298 , an image frame is downloaded form the imaging radiation detector while the position radiation transmission is enabled. The image frame forms an image on the display unit. With reference to  FIG. 3 , imaging processor  174  downloads an image frame from imaging radiation detector  176 . 
     In procedure  300 , positioning radiation transmission is disabled before the next imaging radiation acquisition period. With reference to  FIG. 3 , synchronizer  180  disables the positioning radiation transmission before the next imaging radiation acquisition period. After procedure  300 , the method proceeds to procedures  290  and  292 . 
     According to another embodiment of the disclosed technique, the synchronizer enables image acquisition when the positioning radiation transmission is disabled. Reference is now made to  FIG. 9 , which is a schematic illustration of a method for synchronizing the operation of a MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique. In procedure  310 , positioning radiation is transmitted periodically. With reference to  FIG. 3 , positioning radiation transmitters  156 ,  158  and  160  periodically transmit positioning radiation. After procedure  310 , the method proceeds to procedure  314 . 
     In procedure  312 , an image frame is downloaded form the imaging radiation detector while positioning radiation is transmitted. The image frame forms an image on the display unit. With reference to  FIG. 3 , imaging processor  174  downloads an image frame from imaging radiation detector  174 . 
     In procedure  314 , the end of a positioning radiation transmission period is detected. With reference to  FIG. 3 , synchronizer  180  detects the end of a positioning radiation transmission period. 
     In procedure  316 , periodic imaging radiation acquisition is enabled. With reference to  FIG. 3 , synchronizer  180  enables the periodic imaging radiation acquisition. After procedure  316 , the method proceeds to procedure  320 . 
     In procedure  318 , the imaging radiation is periodically transmitted while imaging radiation acquisition is enabled. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation. 
     In procedure  320 , imaging radiation acquisition is disabled before the start of the next positioning radiation transmission period. With reference to  FIG. 3 , synchronizer  180  disables the imaging radiation acquisition before the next positioning radiation transmission period. After procedure  320 , the method proceeds to procedures  310  and  312 . 
     Reference is now made to  FIG. 10  which is a schematic illustration of a timing diagram generally referenced  350 , in accordance with a further embodiment of the disclosed technique. Timing diagram  350  includes signals  352 ,  354 ,  356 ,  358  and  368 . Signal  358  is the timing signal associated with the image frame sampling. Signals  352 ,  354  and  356  are the timing signals associated with the operation of positioning radiation transmitters  156 ,  158  and  160  ( FIG. 3 ) respectively. Signal  368  is the timing signal associated with the transmission of imaging radiation by imaging radiation transmitter  172  ( FIG. 3 ) Transmitters  156 ,  158  and  160  ( FIG. 3 ) are operated sequentially so as to enable the detection of the position (and orientation) of an object, with respect to each axis of an MPS coordinate system, independently. Alternatively, positioning radiation transmitters  156 ,  158  and  160  may be operated concurrently but at different frequencies. Time period  360  is the image frame sampling period. During time period  360  the medical imaging system samples the pixel values accumulated in the imaging radiation detector during the image acquisition period. During time period  360  the medical imaging system does not transmit imaging radiation. Time period  362  is the imaging radiation transmission period. During the imaging radiation transmission period the medical imaging system does not sample the accumulated pixel values. Time period  364  is the positioning radiation transmission period. During period  364  the positioning radiation transmitters transmit positioning radiation. Time period  366  is the relative phase range. The relative phase range is the range in which the phase of either the image frame sampling period or the position radiation transmission period may change without the two transmission periods overlapping. The relative phase is defined as the difference between the image frame non-sampling period and the positioning radiation transmission period. 
     During time period  360 , medical imaging system  154  ( FIG. 3 ) samples an image frame. However, during time period  360 , synchronizer  180  ( FIG. 3 ) at least disables positioning radiation transmitters  156 ,  158  and  160  ( FIG. 3 ) from transmitting. Consequently, the image sampled by medical imaging system  154  ( FIG. 3 ) does not exhibit visible flaws due to magnetic field interference. 
     According to another embodiment of the disclosed technique, MPS may employ more than three magnetic field transmitters. However, not all the magnetic field transmitters can be activated during the image frame non-sampling period. Thus, the synchronizer prevents the positioning radiation transmitters from transmitting during the period in which the medical imaging system samples an image frame, and continues after the medical imaging system stops sampling an image frame. 
     Reference is now made to  FIG. 11 , which is a schematic illustration of timing diagram generally referenced  380  in accordance with another embodiment of the disclosed technique. In Timing diagram  380 , six positioning radiation transmitters are employed by the MPS. Timing diagram  380  includes signals  382 ,  384 ,  386 ,  388 ,  390 ,  392 ,  394  and  400 . Signal  382 ,  384 ,  386 ,  388 ,  390  and  392  are the timing signals associated with the operation of the positioning radiation transmitters. Signal  394  is associated with the image frame sampling. Signal  400  is the timing signal associated with the transmission of imaging radiation by imaging radiation transmitter  172  ( FIG. 3 ). 
     During time period  396 , medical imaging system transmits medical imaging radiation and does not sample an image frame. Thus, the positioning radiation transmitters can transmit. However, time period  396  is sufficient to operate only positioning radiation transmitters number 1, 2, 3 and 4. During time period  398  synchronizer disables the positioning radiation transmitters from transmitting. Furthermore, during time period  398 , the medical imaging system samples an image frame and does not transmit imaging radiation. However, after the sampling of the image frame stops, the synchronizer enables positioning radiation transmitters to transmit, starting from positioning radiation transmitter number 5. 
     As mentioned above, according to a further embodiment of the disclosed technique, the transmission radiation transmission and the acquired image sampling are synchronized. Reference is now made to  FIG. 12 , which is a schematic illustration of a method for synchronizing system the operation of a medical position system with a medical imaging system operative in accordance with a further embodiment of the disclosed technique. In procedure  420 , imaging radiation is periodically transmitted and imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation and imaging radiation detector  176  periodically acquires imaging radiation. After procedure  420 , the method proceeds to procedure  424 . In procedure  422 , position radiation is periodically transmitted. With reference to  FIG. 3 , position radiation transmitters  156 ,  158  and  160  periodically transmit position radiation. 
     In procedure  424 , the position radiation transmission is disabled before sampling an image frame from the imaging radiation detector. The position radiation detector may interfere with the image frame sampling, thereby corrupting the image. With reference to  FIG. 3 , synchronizer  180  disables the image frame sampling before enabling the positioning radiation transmission. 
     In procedure  426 , an image frame is sampled after each image acquisition period form the imaging radiation detector. The image frame forms an image on the display unit. With reference to  FIG. 3 , imaging detector  176  samples an image frame after each image acquisition period. 
     In procedure  428 , image frame sampling is disabled before enabling position radiation transmission. With reference to  FIG. 3 , synchronizer  180  disables the image frame sampling. After procedure  430  the method returns to procedure  422 . 
     According to another embodiment of the disclosed technique, synchronization between the position radiation transmission and the image frame sampling is achieved by detecting the relative phase between the position radiation transmission period and the image frame sampling period, and adjusting this relative phase when necessary. Reference is now made to  FIG. 13 , which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique. In procedure  450 , imaging radiation is periodically transmitted and imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation and imaging radiation detector  176  periodically acquires imaging radiation. After procedure  450 , the method proceeds to procedure  454 . In procedure  452 , positioning radiation is periodically transmitted while imaging radiation is acquired and while imaging radiation is periodically transmitted. With reference to  FIG. 3 , positioning radiation transmitters  156 ,  158 , and  160  periodically transmit positioning radiation. After procedure  454 , the method proceeds to procedure  458 . 
     In procedure  454 , an image frame is sampled from the imaging radiation detector after each position radiation acquisition period. With reference to  FIG. 3 , imaging detector  176  samples an image frame after each image acquisition period. 
     In procedure  456 , a potential overlap between the imaging radiation transmission period and the image frame sampling period is detected. This potential overlap is detected according to a change in the relative phase between the two periods. The relative phase is defined as the difference between the imaging radiation non-sampling period and the positioning radiation transmission period. With reference to  FIG. 4 , the relative phase range  216  is the relative phase range in which the phase of either the image frame sampling period or the positioning radiation transmission period may change without the two transmission periods overlapping. When the combined relative phase drift of the image frame sampling period and the positioning radiation transmission period is larger than the relative phase range, then a potential overlap is detected and the method proceeds to procedure  458 . When the relative phase drift of the image frame sampling period and the positioning radiation transmission period is at most equal to the relative phase range, then, no potential overlap is detected and the method proceeds to procedures  450  and  452 . With reference to  FIG. 3 , synchronizer  180  detects a potential overlap an image frame sampling period and the positioning radiation transmission period. 
     In procedure  458 , the relative phase between the image frame sampling period and the positioning radiation transmission period is adjusted so that no overlap occurs. With reference to  FIG. 3 , synchronizer  180  adjusts the relative phase between the image frame sampling period and the positioning radiation transmission period. After procedure  460 , the method proceeds to procedure  450  and  452 . 
     According to a further embodiment of the disclosed technique, synchronization is achieved by disabling the position radiation transmission when the end of an image acquisition period is detected. The end of the image acquisition period marks the start of the image frame sampling period. Reference is now made to  FIG. 14  which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with a further embodiment of the disclosed technique. In procedure  480 , imaging radiation is periodically transmitted and imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmits imaging radiation and imaging radiation detector  176  periodically acquires imaging radiation. After procedure  480 , the method proceeds to procedure  484 . 
     In procedure  482 , positioning radiation is periodically transmitted while imaging radiation is acquired and while imaging radiation is periodically transmitted. With reference to  FIG. 3 , positioning radiation transmitters  156 ,  158 , and  160  periodically transmit positioning radiation. After procedure  482 , the method proceeds to procedure  484 . 
     In procedure  484 , the end of the image acquisition period is detected. With reference to  FIG. 3 , synchronizer  180  detects the end of the imaging acquisition period. After procedure  484 , the method proceeds to procedures  486  and  488 . 
     In procedure  486 , the image frame is sampled from the imaging radiation detector. With reference to  FIG. 3 , imaging detector  176  samples the image frame after each image acquisition period. 
     In procedure  488 , the position radiation transmission is disabled while the image frame is sampled. With reference to  FIG. 3 , synchronizer  180  disables positioning radiation transmitters  156 ,  158  and  160 . 
     In procedure  490 , the image frame sampling is disabled before the start of the next position radiation transmission period. With reference to  FIG. 3 , synchronizer  180  disables image frame sampling before the start of the next position radiation transmission period. After procedure  490  the method returns to procedure  484   
     In accordance with another embodiment of the disclosed technique, synchronization is achieved by disabling the image frame sampling when the end of a position radiation transmission period is detected.  FIG. 15  which is a schematic illustration of a method for synchronizing the operation of an MPS with a medical imaging system, operative in accordance with another embodiment of the disclosed technique. In procedure  510 , imaging radiation is periodically transmitted and imaging radiation is periodically acquired. With reference to  FIG. 3 , imaging radiation transmitter  172  periodically transmit imaging radiation imaging radiation detector  176  periodically acquires imaging radiation. After procedure  510 , the method proceeds to procedure  514 . 
     In procedure  512 , positioning radiation is periodically transmitted while imaging radiation is acquired and while imaging radiation is periodically transmitted. With reference to  FIG. 3 , positioning radiation transmitters  156 ,  158 , and  160  periodically transmit positioning radiation. After procedure  5124 , the method proceeds to procedure  514 . 
     In procedure  516 , the end of the position radiation transmission period is detected. With reference to  FIG. 3 , synchronizer  180  detects the end of the imaging acquisition period. 
     In procedure  516 , the image frame is sampled from the imaging radiation detector. With reference to  FIG. 3 , imaging detector  176  samples the image frame after each image acquisition period. 
     In procedure  518 , image frame sampling is disabled before the start of the next position radiation transmission period. With reference to  FIG. 3 , synchronizer  180  disables image frame samples before the start of the next position radiation transmission period. After procedure  518  the method returns to procedure  512 . 
     It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.