Abstract:
A detection unit and a method for detecting an implanted medical device in an MRI environment employ a telemetry transmission from the implanted medical device.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to implantable medical devices and more particularly to detecting these devices in a magnetic resonance imaging (MRI) environment. 
     BACKGROUND 
     Many implantable medical devices (IMD&#39;s), for example, including pacemakers, cardioverter-defibrillators and neural stimulators, are operatively coupled to electrodes, which are joined to elongate lead wires that extend from the devices to a target site either on or within a body of a patient. The electrodes sense electrical signals from the patient, for example cardiac depolarization signals, which are used to diagnose the patient and, in many cases, may be used to guide or dictate therapy delivery. Having such an IMD may be a contraindication for MRI, due, at least in part, to the lead wires acting as antennae, which pick up radio-frequency (RF) energy transmitted during MRI; the RF energy can cause heating of the electrodes, which are coupled to the lead wires, and may introduce sensing artifact, causing erroneous cardiac event detection that can compromise therapy delivery during MRI. Thus, there is a need to detect if a patient has an IMD before allowing the patient to undergo MRI. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
         FIG. 1  is a schematic block diagram of a system, according to some embodiments of the present invention. 
         FIG. 2  is a schematic block diagram of a system, according to some alternate embodiments of the present invention. 
         FIG. 3  is a flow chart outlining some methods of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Constructions, materials, dimensions, and manufacturing processes suitable for making embodiments of the present are known to those of skill in the field of the invention. 
       FIG. 1  is a schematic block diagram of a system according to some embodiments of the present invention.  FIG. 1  illustrates an IMD  10  in the presence of an MRI system  100 . Although not shown as such, it should be appreciated that IMD  10  is implanted within a body of a patient who has been referred for diagnostic imaging, via MRI system  100 ; thus, apart from the methods and apparatus of the present invention, an MRI operator may not be aware of IMD  10 .  FIG. 1  further illustrates IMD  10  including a can or housing  13 , which encloses a battery and electronic components, and, coupled to housing  13 , a connector header  11 , which houses a telemetry antenna  12  and connections for electrical leads, which are not shown, but are understood to be components of IMD  10 . Some of the salient electronic components are shown schematically and include a telemetry unit  15  and a telemetry activation module  17 ; according to the illustrated embodiment, particular telemetry signals  19  of a prescribed frequency or frequencies are sent from unit  15  via antenna  12  when activation module  17  detects the presence of a static magnetic field of a strength associated with MRI. According to some embodiments activation module  17  includes a reed switch which closes in the presence of the static magnetic field in order to couple unit  15  to antenna  12 ; according to other embodiments, activation module  17  includes a Hall effect sensor that detects the static magnetic field to activate unit  15  for transmission of telemetry signals  19 . Those skilled in the art will appreciate that antenna  12  is shown schematically and is coupled, along with lead connectors of connector header  11 , via feedthroughs extending through housing  13  to the electronic components housed therein. 
     MRI system  100  is shown including a telemetry antenna  112  coupled to a telemetry receiver  121 , which is part of an IMD detection unit  120 ; detection unit  120  scans the frequency band for possible IMD transmissions and antenna  112  is tuned to receive the particular frequencies of transmission  19 . According to some embodiments, receiver  121  may include transmitter capability, which would allow detection unit  120  to send an activation signal, different from the static magnetic field of system  100  that activates transmission  19 .  FIG. 1  further illustrates detection unit  120  including a signal generator  123  coupled to receiver  121 ; according to the illustrated embodiment, signal generator  123  sends a signal, indicating the presence of IMD  10 , to a signaling element  150  and/or to a monitor  140  of system  100  via imaging unit  133 . According to some embodiments, element  150  provides a visible signal, for example a flashing light; according to alternate embodiments, element  150  provides an audible alarm. In some embodiments, IMD  10  may further transmit additional information, carried by transmission  19 , concerning IMD  10  to detection unit  120 . The received signal may pass through signal generator  123  and imaging unit  133  to monitor  140  for display, which may be useful, if MRI is still undertaken, to manage interactions between MRI and IMD  10 ; some examples of the additional information include, but are not limited to, information concerning the identity of the IMD type, the particular identity of IMD  10  (i.e. manufacturer and model number), special instructions for monitoring IMD  10 , and programmed parameters of IMD  10 . 
       FIG. 1  further illustrates detection unit  120  including a controller  125  coupled to receiver  121 . According to the illustrated embodiment, controller  125  is coupled to an MRI control unit  135  in order to send control signals to unit  135  that cause unit  135  to alter the function of MRI system  100  according to the presence of IMD  10  as detected by receiver  121 . According to some embodiments, MRI function may be altered by disabling a magnetic field generator  132  and an electromagnetic radiation source  131 , which basically prevents scanning of the patient having IMD  10 . According to an alternate embodiment, a low Specific Absorption Rate (SAR) scanning mode is activated by controller  125  to reduce an applied power of MRI system  100  and thereby prevent excessive heating of the electrodes via the electrical leads that would be coupled to IMD  10  and act as antennas. According to further embodiments, transmission  19  includes cardiac event signals from IMD  10 , and controller  125  activates a scanning procedure that is synchronized with cardiac events so that MRI induced signals received by the leads coupled to IMD  10  are not misconstrued by IMD  10  as cardiac events. 
     It should be noted that some embodiments of the present invention include an IMD detection unit, which is kept in an MRI environment but is not hardwired into the MRI system; one such embodiment is described in conjunction with  FIG. 2 .  FIG. 2  is a schematic block diagram of a system, according to some alternate embodiments of the present invention.  FIG. 2  illustrates IMD  10  in the presence of an MRI system  200  and an IMD detection unit  220 , which is similar to unit  120  illustrated in  FIG. 1  but is packaged independently of an MRI system, i.e. system  200 . According to some embodiments, detection unit  220  may be a handheld device equipped to detect the presence of IMD  10 , via telemetry transmission  19  picked up by antenna  112  and receiver  121 , as previously described.  FIG. 2  further illustrates detection unit  220  including a signal generator  223  coupled to receiver  121 , so that signal generator  223  may send a signal indicating the presence of IMD  10  to signaling element  150  and/or a monitor  240 ; types of signals, via element  150 , and additional information, for example, displayed on monitor  240 , are the same as those described in conjunction with  FIG. 1 . 
       FIG. 2  further illustrates detection unit  220  including a controller  225 , which communicates with MRI system  200  via a telemetry transmission  29 ; according to the illustrated embodiment, receiver  121  further includes transmission capability to send transmission  29  to antenna  212  coupled to telemetry receiver  221  of MRI system  200 . Controller  225  may thus send control signals to MRI control unit  135  that cause unit  135  to alter the function of MRI system  200  according to the presence of IMD  10  as previously described in conjunction with  FIG. 1 . It should be noted that, according to alternate embodiments, detection unit  220  does not include controller  225  and need not include both signaling element  150  and monitor  240 , either being sufficient to inform an operator of system  200  that IMD  10  is present. 
       FIG. 3  is a flow chart outlining some methods of the present invention.  FIG. 3  illustrates an initial step  21  in which telemetry transmission from an IMD is activated, for example, by a static magnetic field produced by an MRI system. According to some embodiments of the present invention, for example as illustrated in  FIG. 1 , a detection unit, hardwired into the MRI system, includes a telemetry receiver having an antenna tuned to the particular frequency assigned to the transmission, and, according to step  22 , the transmission is received by the receiver. According to alternate methods outlined in  FIG. 3 , once the transmission is received, either a control signal is sent (step  23 A) to automatically alter function of the MRI system due to the presence of the IMD, or an indicating signal is sent ( 23 B) to a signaling element, which lets an operator of the MRI system know of the presence of the IMD, or both signals are sent (step  23 C). Thus, a detection unit of the present invention may include one or both of signal generator  123  and controller  125  ( FIG. 1 ), either being sufficient acting alone to prevent an operation of an MRI system that is incompatible with the IMD which is detected. Although  FIG. 1  illustrates detection unit  120  hardwired into MRI system  100 , the invention is not so limited and alternate embodiments include detection units that communicate wirelessly with other units of system  100 . 
     In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.