Patent Publication Number: US-11660458-B2

Title: Method of detecting presence of implanted power transfer coil

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/841,904, filed Apr. 7, 2020. 
    
    
     FIELD 
     The present technology is generally related to detecting the presence of a power transfer coil implanted in a patient. 
     BACKGROUND 
     Referring to  FIG.  1   , an implantable LVAD system  10  has internal components (in the body of the patient) and external components. The LVAD system  10  may typically include an LVAD pump  12  an implanted controller (i-controller)  14  having an internal battery  16 , an implanted internal transcutaneous energy transfer system (TETS) coil (i-coil)  18 , an external TETS coil (e-coil)  20  and an external power transmitter  22  with a detachable battery  24 . In operation, power is supplied from the external power transmitter  22  to the i-controller  14  via of mutual coupling of the coils  18  and  20 , in order to charge i-controller  14  and to power the LVAD pump  12 . The coils  18  and  20  transfer power by mutual induction of electromagnetic energy over the air and through the body. The power supplied by the external power transmitter  22  may come from the detachable battery  24  or from a wall outlet, for example. 
     When the external coil, e-coil  20 , is aligned with the internal coil, i-coil  18 , and is close to the body, there is a high degree of power transfer efficiency. When the two coils are distant and/or unaligned, power transfer efficiency declines and heat generated in the coils may increase. Also, if there is a nearby foreign metal object, energy losses may occur transferring energy to the foreign metal object. Further, if the i-coil  18  is unconnected, it is undesirable to attempt energy transfer to the i-coil  18 . 
     SUMMARY 
     The techniques of this disclosure generally relate to detecting the presence of a power transfer coil implanted in a patient. 
     According to one aspect, a method is implemented by a medical implant system having an internal coil implanted within the body of a patient, the internal coil being capable of receiving power from an external coil outside the body, the external coil being in communication with external processing circuitry to execute steps of the method. The method includes periodically detecting a presence of the internal coil, the periodically detecting including monitoring change in a resonance frequency associated with the external coil. 
     According to this aspect, in some embodiments, when change in the resonance frequency indicates the presence of the internal coil, then determining connectivity of the internal coil, the determining including monitoring a rate at which the resonance frequency rises to a steady state value. In some embodiments, the method further includes detecting a presence of a metal object, the detecting the presence of the metal object including determining when the external coil is drawing increased power for a given drive current and monitoring for reception of power regulation packets from the internal coil. In some embodiments, the method further includes, when there is no reception of power regulation packets within a time interval, concluding that a metal object is present. In some embodiments, in some embodiments, the method further includes, when there is no reception of power regulation packets within a time interval, concluding that there is a fault in one or more internal components of the medical implant system. In some embodiments, the method includes sensing for acceleration of an external component of the medical implant system and when acceleration is detected, then adjusting a duty cycle of the periodically detecting. In some embodiments, the periodically detecting includes concluding that the implanted coil is present when the resonance frequency increases as the distance between an expected location of the internal coil and the location of the external coil decreases. In some embodiments, the determining connectivity includes concluding that the internal coil is connected to an internal load when the resonance frequency ramps up to the steady state value at a rate that falls below a rate threshold. 
     According to another aspect, a medical implant system is provided, the medical implant system having an internal coil implanted within the body of a patient, the internal coil being capable of receiving power from an external coil outside the body, the external coil being in communication with external processing circuitry. The external processing circuitry is configured to periodically detect the presence of the internal coil, the periodically detecting including monitoring change in a resonance frequency associated with the external coil. 
     According to this aspect, in some embodiments, when change in the resonance frequency indicates the presence of the internal coil, then the external processing circuitry is configured to determine connectivity of the internal coil, the determining including monitoring a rate at which the resonance frequency rises to a steady state value. In some embodiments, the external processing circuitry is further configured to detect a presence of a metal object, the detecting the presence of the metal object including determining when the external coil is drawing increased power for a given drive current and monitoring for reception of power regulation packets from the internal coil. In some embodiments, the external processing circuitry is further configured to, when there is no reception of power regulation packets within a time interval, conclude that a metal object is present. In some embodiments, the external processing circuitry is further configured to, when there is no reception of power regulation packets within a time interval, conclude that there is a fault in one or more internal components of the medical implant system. In some embodiments, the external processing circuitry is further configured to sense for acceleration of an external component of the medical implant system and when acceleration is detected, then adjusting a duty cycle of the periodically detecting. In some embodiments, the periodically detecting includes concluding that the implanted coil is present when the resonance frequency increases as the distance between an expected location of the internal coil and the location of the external coil decreases. In some embodiments, the determining connectivity includes concluding that the internal coil is connected to an internal load when the resonance frequency ramps up to the steady state value at a rate that falls below a rate threshold. 
     According to yet another aspect, an external device of a medical implant system is provided. The external device has an external coil and processing circuitry, the processing circuitry configured to monitor a resonance frequency associated with the external coil. When the resonance frequency changes as a distance between the external coil and an expected location of an internal coil, then the processing circuitry is configured to conclude that the internal coil has been detected. When the resonance frequency ramps up to a steady state value at a rate that falls below a rate threshold, then the processing circuitry is further configured to conclude that the internal coil is connected to an internal load. 
     According to this aspect, in some embodiments, the processing circuitry is further configured to monitor power drawn by the external coil and monitor for reception of power regulation packets. When the power drawn by the external coil increases for a given drive current and no power regulation packets have been received within a time interval, then the processing circuitry is configured to conclude that one of a metal object is present and a fault exists in an internal component of the medical implant system. In some embodiments, the processing circuitry is further configured to adjust a frequency of attempts to detect the internal coil. In some embodiments, the adjusting is based on an acceleration of the external device. 
     The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG.  1    is a block diagram of an LVAD implant system; 
         FIG.  2    is a block diagram of an LVAD implant system constructed according to principles set forth herein; 
         FIG.  3    is a more detailed block diagram of the processing circuitry of the LVAD implant system of  FIG.  2   ; 
         FIG.  4    is a flowchart of an exemplary process for detecting presence of an internal coil; 
         FIG.  5    is a flowchart of an exemplary process for detecting connectivity of an internal coil; 
         FIG.  6    is a flowchart of an exemplary process for detecting presence of a metal object; 
         FIG.  7    is a flowchart of an exemplary process for determining motion of an external device and adjusting a duty cycle of internal coil detection attempts; and 
         FIG.  8    is a flowchart of an exemplary process for detecting presence and connectivity of an internal coil. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments described herein are related to detecting the presence of a power transfer coil implanted in a patient.  FIG.  2    shows a block diagram of one example configuration of an LVAD system  26  having an internal component such as an internal controller (i-controller)  28  configured to perform functions related to detecting presence of a power transfer coil. The i-controller  28  may have processing circuitry  30  which may include a processor  32  and a memory  34 . The processor  32  may be configured to execute computer instructions stored in the memory  34 . Those instructions may include instructions to cause the processor to perform the algorithms described in more detail below. 
     Information from the i-controller  28  may be sent to be displayed on an external display  38  of an external device  40 , which may include a processor  42  and a memory  44  within processing circuitry  46 , the external power transmitter  25  and the detachable battery  24 , as well as the e-coil  20  in some embodiments. The memory  44  may be configured to store computer instructions to be executed by the processor  42  and may also be configured to store instructions for detection of presence of the i-coil  18  as well as other algorithms described below. Accordingly, the processor  42  may implement an internal coil presence detection algorithm (PDA)  48 , which is configured to detect the presence of the i-coil  18 . 
     Electrical communication of signals and power between the internal components of i-controller  28  may be via communication busses and individual electrical conductors not shown in  FIG.  2   . For example, a multi-conductor address bus and data bus may connect processor  32  with memory  34 . In some embodiments, an i-coil interface  19  associated with i-coil  18  may be included in the set of internal components making up the LVAD system  26 . One purpose of i-coil interface  19  may be to modulate the alternating current applied to the i-coil  18  with signals from the i-controller  28  to be transmitted from the i-coil  18  to the e-coil  20  and/or to demodulate signals to be received by the i-coil  18  from the e-coil  20 . In some embodiments, a purpose of the i-coil interface  19  is to provide conversion between the alternating current (AC) of the i-coil  18  and direct current (DC) to charge the battery  16 . Some or all functions of the i-coil interface  19  may be included in the i-controller  28  and/or the i-coil  18 . Similarly, electrical communication of signals and power between the internal components of external device  40  may be by communication busses and individual electrical conductors not shown in  FIG.  2   . For example, a multi-conductor address bus and data bus may connect processor  42  with memory  44 . In some embodiments, an e-coil interface  21  associated with e-coil  20  may be included in the set of external components making up the LVAD system  26 . One purpose of e-coil interface  21  may be to modulate the alternating current applied to the e-coil  20  with signals from the processing circuitry  46  to be transmitted from the e-coil  20  to the i-coil  18  and/or to demodulate signals received by the e-coil  20  from the i-coil  18 . 
     In some embodiments, the internal components of the LVAD system  26  may include monitoring and control circuitry  13 . A purpose of monitoring and control circuitry  13  may include monitoring speed and temperature, for example, of the LVAD pump  12 . Another purpose of the monitoring and control circuitry  13  may include controlling the speed of the LVAD pump  12 . In some embodiments, some or all of the monitoring and control circuitry  13  may be incorporated into the LVAD pump  12  and/or the i-controller  28 . In some embodiments, some or all of the functions performed by the monitoring and control circuitry  13  may be performed by the processing circuitry  30 . Thus, in some embodiments, the monitoring and control circuitry  13  may include one or more temperature sensors embedded in or on the LVAD pump  12 . Information obtained from and/or about the LVAD pump  12 , such as speed and temperature, may be sent to the external device  40  to be displayed by external display  38 . 
     The various internal components making up the LVAD system may be grouped into one or more separate housings. Similarly, the various external components making up the LVAD system may be grouped into one or more separate housings. Further, some of the components shown and described as being internal to the i-controller  28  may be instead, external to i-controller  28  in some embodiments. Similarly, some of the components shown and described as being internal to the external device  40  may be instead, external to external device  40  in some embodiments. Note further that some of the functions performed by processor  32  may be performed instead by processor  42 . 
     Note that transfer of information from the external device  40  to the internal memory  34 , and vice versa, may be by electrical conductor or by wireless radio frequency (RF) transmission (over the air and through the body). Accordingly, in some embodiments, the external device  40  includes an external radio interface  50  and the i-controller  28  includes an internal radio interface  52 . In some embodiments, the external radio interface  50  and the internal radio interface  52  are RF transceivers having both an RF receiver for receiving information wirelessly and an RF transmitter for transmitting information wirelessly. Such RF transceivers may be Bluetooth and/or Wi-Fi compliant, for example. 
     The external device  40  could be a patient&#39;s external device that has an external wireline interface  54  which provides an interface between the external device  40  and a clinician&#39;s device  56 . The clinician&#39;s device might, for example, have a USB port and wireline interface  54  might include a USB port, so that a USB cable may connect the two ports. The clinician&#39;s device  56  may read data from the external device  40  and write information and control signaling to the external device  40 , in some embodiments. In the alternative to a wireline connection, the wireline interface  54  could include or be replaced by a radio interface. 
     In some embodiments, the external power transmitter  25  may be in electrical communication with the processing circuitry  46 . 
     Note that although the internal components are shown to include an LVAD pump  12 , in some embodiments, one or more other internal devices that require electrical power are implemented instead of or in addition to the LVAD pump  12 . 
       FIG.  3    shows a more detailed view of the processing circuitry  30  of the i-controller  28  and the processing circuitry  46  of the external device  40 . In  FIG.  3   , some of the internal and external components of the implant system  26  are omitted for clarity. Also, a system load block  11  is shown connected to the i-coil  18 . The system load  11  may be or include the LVAD pump  12  or other implanted load device and may also include the load presented by other internal components, including the i-controller  28 . 
     In the processing circuitry  30  of the i-controller  28 , a voltage error detector  60  is configured to determine a difference between the voltage received at the i-coil  18  and a predetermined target voltage set by the processing circuitry  30 . This difference is a voltage error that may be modulated by the modulator  62  to be carried via a time-varying signal applied to the i-coil  18 . The i-coil transmits the voltage error-carrying signal to the external device  40  to inform the external device  40  of the voltage error so that the voltage applied to the e-coil  20  may be adjusted in a direction calculated to drive the voltage error toward zero. 
     The processing circuitry  30  may also include a threshold comparator  64  configured to compare the received voltage at the i-coil  18  to a voltage threshold to determine whether to send power regulation packets generated by the power regulation packet generator  66  to the external device. When the received voltage at the i-coil  18  exceeds the voltage threshold, power regulation packets are sent to the external device  40 . 
     In the processing circuitry  46  of the external device  40 , a pulse width modulation duty cycle controller  70  is configured to modulate or adjust the power delivered to the e-coil  20  by the external power transmitter  25 . A power monitor  72  monitors the power drawn by the e-coil  20  to determine if the e-coil  20  is drawing additional power for a given drive current, as this may be indicative of the presence of a metal object. A frequency monitor  74  monitors the resonance frequency of the e-coil  20  to determine the presence and connectivity of the i-coil  18 . Note that when reference is made herein to the resonance frequency of the e-coil  20 , it will be understood that this resonance frequency may be of a circuit including the e-coil  20  that may also include other circuit components such as capacitors. 
     A demodulator  76  demodulates the signal received by the e-coil  20 . The demodulated signal may include a voltage error value and/or power regulation packets generated by the power regulation packet generator  66 . A power regulation packet monitor  78  monitors the demodulated signal to detect the presence of power regulation packets. 
     The processing circuitry  46  may perform one or more algorithms described in more detail below with reference to  FIGS.  4 - 7   . The i-coil presence detection algorithm (PDA)  48  attempts to detect the presence of the i-coil  18 . The i-coil connectivity algorithm attempts to determine i-coil connectivity to protect diodes that prevent current overload to protect implanted components and the patient. The metal object detection algorithm  84  attempts to detect the presence of a metal object. The motion detection algorithm  86  attempts to detect whether the e-coil is in motion and to adjust a frequency of i-coil detection attempts depending on whether the e-coil is in motion. 
     Note that some or all of the blocks shown within the processing circuitry  46  may be performed within the external power transmitter  25  or in a different location within the external device  40 . 
       FIG.  4    is a flowchart of an exemplary process for detecting, by the external device  40 , the presence of the i-coil  18 . In Block S 10  of the process, the e-coil  20  is driven by the external power transmitter  25  at a low power and low duty cycle at a resonance frequency of the e-coil  20 . In Block S 12 , the resonance frequency of the e-coil  20  is monitored by the frequency monitor  74 . If, at Block S 14 , it is observed by the monitoring that the resonance frequency of the e-coil  20  increases as the e-coil  20  is moved closer to the body toward the expected location of the i-coil  18 , then at Block S 16 , the decision is made that the i-coil  18  is present. Otherwise, a decision is made at Block S 18  that the i-coil  18  is not present. Note that when the i-coil  18  is not present, the resonance frequency of the e-coil does not change when the e-coil  20  is moved closer to the general area where the i-coil  18  is expected to be. 
       FIG.  5    is a flowchart of an exemplary process for detecting, by the external device  40 , whether the i-coil  18  is connected to the system load  11 . This process may logically follow completion of the process of detecting the presence of the i-coil  18  shown in  FIG.  4   , in some embodiments. In Block S 20 , the rate at which the resonance frequency of the e-coil  20  increases to its steady state value is monitored by the frequency monitor  74 . If the resonance frequency ramps up to its steady state value slowly over time, as determined at Block S 22 , the decision is made that the i-coil  18  is connected to the system load  11  (Block S 24 ). In some embodiments, the rate of increase of the resonance frequency toward the steady state value is compared to a rate threshold and if the rate of increase is less than the rate threshold, the decision is made that the i-coil  18  is connected to the system load  11 . If instead, for example, the resonance frequency jumps quickly to its steady state value, then the decision is made that the i-coil  18  is not connected to the system load  11  (Block S 26 ). 
       FIG.  6    is flowchart of an exemplary process for detecting presence of a metal object. In Block S 28 , the power monitor  72  determines whether the e-coil  20  is drawing additional power for a given drive current (which is an indication of the possible presence of a metal object.) For example, the processing circuitry  46  may compare the power drawn by the e-coil  20  to a power threshold corresponding to the drive current applied to the e-coil  20 . If the e-coil  20  is drawing additional power for a given drive current, then, in Block S 30 , the power regulation packet monitor  78  monitors for reception of power regulation packets received from the power regulation packet generator  66 , via the i-coil  18 . These power regulation packets are generated via the power regulation packet generator  66  once the received voltage at the i-coil  18  exceeds a threshold, to confirm to the external device  40  that power is being received. If the power regulation packets are being received, at Block S 32 , then a decision is made at Block S 34  that the object that is present is the i-coil  18 , not a metal object. Otherwise, at Block S 136 , a decision is made that the object that is present is a metal object rather than the i-coil  18 , or there is a fault in the implanted system. 
       FIG.  7    is a flowchart of an exemplary process for detecting coil motion and adjusting power delivered to the i-coil  18 . In Block S 49 , an output of the accelerometer  88  is monitored to detect acceleration (indicative of motion) of the e-coil  20 . If the e-coil  20  is stationary (no acceleration), as determined at Block S 42 , then it may be assumed that that the e-coil  20  is not being held or worn. In this case, the duty cycle or frequency of attempts to detect the presence of the i-coil  18  may be reduced by the pulse width modulation (PWM) duty cycle controller  70  (Block S 44 ), or power used to detect the presence of the i-coil  18  may otherwise be reduced. If the e-coil  20  is not stationary (acceleration is detected), then the duty cycle of the i-coil detection attempts may be increased (Block S 46 ). 
     Note that some or all of the steps of the processes shown in  FIGS.  4 - 7    may be implemented by execution of software instructions by the processor  42  of the external device  40 . 
       FIG.  8    is a flowchart of an exemplary process for determining the presence and connectivity of an internal coil in a medical implant system. The process includes periodically detecting a presence of the internal coil, the periodically detecting including monitoring change in a resonance frequency associated with the external coil (Block S 48 ). The process also includes, when change in the resonance frequency indicates the presence of the internal coil, then determining connectivity of the internal coil, the determining including monitoring a rate at which the resonance frequency rises to a steady state value (Block S 50 ). 
     Thus, to conserve power, the e-coil  20  may be driven at low power and with a low duty cycle. The e-coil  20  may be driven at a resonance frequency, while monitoring the resonance frequency. If the i-coil  18  is not present, the driving frequency will be the tuned frequency of the e-coil  20 . If the i-coil  18  is present, the resonant frequency of the e-coil  20  increases as the distance between the coils decreases. By monitoring the resonance frequency of the e-coil  20 , presence or absence of the i-coil  18  can be detected. 
     Rate of change of the resonance frequency of the e-coil  20  may also be monitored to determine if the i-coil  18  is connected to the load  11 . If the i-coil  18  is not connected to the load  11 , the frequency will jump to the steady state value quickly. If the i-coil  18  is connected to the load  11 , the frequency will ramp up to a steady state value as the energy storage capacitors internal to the i-controller  28  battery  16  are charged up to the regulation voltage. If an unconnected i-coil  18  is detected, application of power to the e-coil  20  may be quickly stopped or lowered so that protection diodes are not overheated. By monitoring the rate at which the resonance frequency rises to its steady state value, whether the i-coil  18  is connected to the system load  11  can be detected. 
     The input power to the coil may be monitored to determine if there is a metal object present. When a metal object is present there will be eddy currents induced in the metal which will draw additional power to drive the e-coil  20  at a given drive current. Depending on the magnitude of the additional power, the duty cycle of the drive voltage used to detect the i-coil  18  may be reduced or the duration of a burst of the drive voltage may be reduced to reduce or minimize heating of the metal object and to reduce a drain on the external battery  24 . While driving the e-coil  20 , the power regulation packet monitor  78  monitors the signal received from demodulator  76 . The demodulator  76  demodulates the signal modulated onto the i-coil signal by the modulator  62 . If the signal modulated onto the i-coil signal contains power regulation packets, these power regulation packets will be sent to the e-coil  20 , once the received voltage at the i-coil  18  exceeds the voltage threshold. The power regulation packets serve to confirm to the external device  40  that power is being received via the i-coil  18 . Absence of these power regulation packets indicates that the power delivered by the e-coil  20  is being delivered to a metal object rather than to the i-coil  18 , and/or there is a fault in the implanted system. 
     To further save power, the accelerometer  88  may be used to detect when the e-coil  20  is being moved. When the e-coil  20  is being moved, the duty cycle of the i-coil detection attempts may be increased. If the e-coil  20  is not being worn, the output of the accelerometer  88  may be expected to be low. In such case, the frequency or duty cycle of the attempts to detect the i-coil  18  may be decreased. 
     It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device. 
     In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer). 
     Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     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 herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.