English:
[0001] This application claims priority from U.S. Provisional Patent Application 61/235,386, filed August 20, 2009, which is incorporated herein by reference.
[0002] The present invention relates to implantable medical devices, specifically, increasing the safety of such devices for use with Magnetic Resonance Imaging (MRI).
[0003] The widely used technique of Magnetic Resonance Imaging (MRI) can pose various risks for patients with implantable electronic devices such as cochlear implant systems, both to the patient and/or to the implant. For example, in implants with elongated electrodes, interactions with the induced RF pulses and switching gradient fields can lead to MRI-induced heating at electrode contacts which can be especially dangerous with longer implant electrodes such as in cardiac pacemakers, spinal cord stimulators, and deep brain stimulators. With cochlear implants, this potential risk may be somewhat lower because of the relatively short electrode. MRI-induced currents also can result in unintentional stimulation of the target neural tissue. At best, this may be just uncomfortable for the patient (e.g. with cochlear implants there can be unintentional auditory sensations during MRI). At worst, such unintentional stimulation may be potentially dangerous (e.g. with deep brain stimulators). The strength of MRI-induced effects depends on multiple factors such as electrode length, electrode contact size, MRI equipment, and MRI sequences used. The impedance, inductance and capacitance of the electrode circuit and the stimulator housing also have a significant influence on the strength of these effects.
[0004] The impedance within the electrode circuit is the sum of the electrode impedance, the wiring impedance, and the impedance of the electronic output circuit which typically consists of CMOS switches and transistors. The impedance of such semiconductors is relatively undefined when the implant has no power supply, such as when the external power supply components are removed for safety reasons before performing an MRI. Without a power supply, such semiconductors typically act as a diode to rectify signals picked up by the electrode circuit such as RF signal pulses during MRI. Such spurious signals (the Larmor frequency of a 1.5 Tesla MR scanner is 63.9 MHz) are only limited by the capacitance of the diode, typically on the order of 10 pF.
[0005] Currently, MRI-related heating of electrodes and elongated implant structures is avoided by having a prohibition against the use of MRI on patients having such implants. This may be either a complete prohibition against MRI, or a partial limit that permits only low-field MRI and/or low SAR values. Alternatively or in addition, electrode wire coiling may be used to improve safety with MRI.
[0006] Embodiments of the present invention are directed to a power supply arrangement for an implantable electronic system such as a cochlear implant system. An MRI power supply arrangement cooperates with an implantable power supply circuit to provide a high output impedance for implanted circuitry during magnetic resonance imaging (MRI).
[0007] In further specific embodiments, the MRI power supply arrangement may include an implantable MRI power supply circuit coupled to the implantable power supply circuit for providing a power supply voltage to the implanted circuitry during MRI.
[0008] In other specific embodiments, the MRI power supply arrangement may include an external MRI power supply circuit coupled to the implantable power supply circuit for providing a power supply voltage to the implanted circuitry during MRI. The external MRI power supply circuit may be battery powered or powered by RF pulses generated during MRI. There may also be a removable external holding magnet for cooperating with a corresponding implant magnet to establish a correct position of the external MRI power supply circuit with respect to the implantable power supply circuit.
[0009] Figure 1 shows components of an implantable MRI power supply circuit according to one embodiment which is coupled to the implantable power supply circuit for providing a power supply voltage to the implanted circuitry during MRI.
[0010] Figure 2 shows an embodiment of an external MRI power supply circuit which is powered by RF pulses generated during MRI.
[0011] Figure 3 shows an embodiment of an external MRI power supply circuit which is battery powered.
[0012] Figure 4 shows an embodiment of an external MRI power supply having a removable magnet and a headband.
[0013] Embodiments of the present invention are directed to a power supply arrangement for an implantable electronic system such as a cochlear implant system. An MRI power supply arrangement cooperates with an implantable power supply circuit to provide a high output impedance for implanted circuitry during magnetic resonance imaging (MRI). More specifically, the time- invariant magnetic fields that are present during MRI are exploited to generate a sufficient power supply for the implanted electronic circuits so that the semiconductor outputs are in a well-defined high- impedance state during the MRI. This results in an implantable system with improved MRI-safety with regard to RF-induced electrode heating and currents.
[0014] Many Active Implantable Medical Devices (AIMD's) are partially or fully implantable, and they include an implantable coil for transferring an electrical signal through the skin that provides power to one or more implanted electronic circuits (and which also typically includes a data component that is not relevant in the present discussion).
[0015] Figure 1 shows one approach based on an implantable MRI power supply arrangement that is coupled to the main implant power supply circuit which does not need an external coil to provide power to the implant during MRI. Normally, an externally generated RF electrical signal is received by implant receiver coil Lioi, which forms a resonant circuit with parallel capacitor Cioi. Schottky diode Dioi rectifies the RF signal present in the L101/C101 resonant circuit to develop the main implant supply voltage, which is filtered by output capacitor Cio2. Zener diode D102provides over-voltage protection. To this main power supply circuit is added a new implantable MRI power supply circuit in which MRI inductance L102has broad-band inductive coupling characteristics to sense the RF pulses from a wide range of MR scanner fields. MRI rectifier diode D103 develops the received pulses to generate an implant supply voltage during MRI which is sufficiently high to power the semiconductor outputs of the implant circuits into a well-defined high- impedance state during the MRI.
[0016] While embodiments based on an implantable MRI power supply circuit are useful for new implant systems, there are a large number of existing implant systems which are already in use without such a protective circuit built in. For such existing systems, an external MRI power supply is useful. Figure 2 shows one embodiment of an external MRI power supply circuit for use during MRI which is placed onto the skin over the implant circuit which converts the energy of the RF pulses into a signal which is transferred through the skin and which is suited to generate a sufficiently high supply voltage within the implant. The arrangement is powered by RF pulses generated during MRI: MRI inductance L201 senses RF pulses from the MRI scanner field, and MRI diode D201rectifies the pulses to generate an external electrical signal for inductive transmission through the skin by the external transmitter circuits to the implanted receiver coil. Zener diode D202provides over voltage protection. This MRI signal is developed by the implanted circuits to generate an implant supply voltage during the MRI which is sufficiently high to power the semiconductor outputs of the implant circuits into a well- defined high- impedance state during the MRI.
[0017] Figure 3 shows an embodiment of another external MRI power supply circuit for use during MRI which is battery powered and which contains an external coil that is placed on the skin over the implant circuit. The external battery powered coil generates a signal which is transferred through the skin and is suitable to generate a sufficiently high supply voltage within the implant to power the semiconductor outputs of the implant circuits into a well-defined high-impedance state during the MRI.
[0018] Figure 4 shows an embodiment of an external MRI transmitting coil 401 as in Figure 2 or Figure 3 for use during MRI which also includes a removable external holding magnet 402 and a headband 403. Prior to MRI, such an external transmitting coil 401 with the removable external holding magnet 402 attached would be placed over the implanted receiver coil to cooperate with a corresponding implant magnet to establish a correct position of the external MRI transmitting coil 401 with respect to the implantable power supply circuit. The head band 403 is then attached around the head to fix the external MRI transmitting coil 401 in the correct position, after which, the removable external holding magnet 402 can be removed, and the MRI can be performed.
[0019] The MRI electrical power signal that is inductively transferred to the implant for MRI supply voltage can be generated in any of several different ways. For example, specific embodiments could be based on use of a frequency converter (e.g. frequency divider or frequency multiplier). Alternatively or in addition, an external broadband receiver can be used to convert the MRI RF signal into a DC voltage (e.g. by rectifying and low-pass filtering) which can be used to drive an oscillator running at the frequency of the inductive link.
[0020] Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.

中文:
[0001]本申请要求2009年8月20日提交的美国临时专利申请61/235,386的优先权,在此并入其全部内容作为参考。
[0002]本发明涉及可植入医疗装置,具体地,涉及提高这些装置与磁共振成像(MRI)一起使用时的安全性。
[0003]广泛应用的磁共振成像(MRI)技术对于具有诸如耳蜗植入系统的可植入电子装置的患者,可能对患者和/或植入装置两者造成各种风险。例如,在具有细长电极的植入装置中,与感应RF脉冲和转换梯度场的相互作用会导致在电极触点处产生MRI感应加热,这对于诸如心脏起搏器、脊髓刺激器以及深脑刺激器中的较长的植入电极来说特别危险。对于耳蜗植入装置来说,这些潜在危险可能较低,因为其电极相对短。MRI感应电流还可导致目标神经组织的无意识刺激。在最好的情况下,这仅会使患者略微不适(例如具有耳蜗植入装置的患者会在MRI过程中产生无意识听觉)。在最坏的情况下,这种无意识刺激可能会产生潜在危险(例如对具有深脑刺激器的患者而言)。MRI感应效应的强度取决于多种因素,诸如电极长度、电极触点尺寸、MRI设备以及MRI的使用顺序。电极电路的阻抗、电感和电容以及刺激器外壳也对这些效应的强度产生重要影响。
[0004]电极电路中的阻抗是电极阻抗、布线阻抗以及通常由CMOS开关和晶体管构成的电子输出电路的阻抗之和。这些半导体的阻抗在植入装置没有电源时相对不确定,诸如当外部电源部件在执行MRI之前因安全原因而被移除时。没有电源,这些半导体通常起到二极管的作用,从而整流由电极电路拾取的信号,诸如在MRI过程中的RF信号脉冲。这些寄生信号(1.5特的回旋频率(larmor frequency),MR扫描器是63.9MHz)仅由二极管的电容限制,而该电容通常约为10pF的数量级。
[0005]当前,与MRI有关的电极和细长植入结构的加热可通过禁止对具有这些植入装置的患者使用MRI来避免。这可以是完全禁止MRI或仅允许使用低场MRI和/或低SAR值的部分限制。替代地或另外地,电极线圈可用于提高与MRI有关的安全性。
[0006]本发明的实施例涉及用于诸如耳蜗植入系统的可植入电子系统的电源布置。MRI电源布置与可植入电源电路协作,从而在磁共振成像(MRI)过程中为植入电路提供高输出阻抗。
[0007]在另外的特定实施例中,MRI电源布置可包括耦合至可植入电源电路的可植入MRI电源电路,其用于在MRI过程中将电源电压提供给植入电路。
[0008]在其他特定实施例中,MRI电源布置可包括耦合至可植入电源电路的外部MRI电源电路,其用于在MRI过程中将电源电压提供给植入电路。外部MRI电源电路可以是电池供电或由MRI过程中产生的RF脉冲供电。还可具有可拆卸外部保持磁铁,用于与相应的植入磁铁协作,从而相对于可植入电源电路建立外部MRI电源电路的校正位置。
[0009]图1示出根据一个实施例的可植入MRI电源电路的部件,其耦合至可植入电源电路,用于在MRI过程中将电源电压提供给植入电路。
[0010]图2示出由MRI过程中产生的RF脉冲供电的外部MRI电源电路的一个实施例。
[0011]图3示出由电池供电的外部MRI电源电路的一个实施例。
[0012]图4示出具有可拆卸的磁铁和头带的外部MRI电源的一个实施例。
[0013]本发明的实施例涉及用于诸如耳蜗植入系统的可植入电子系统的电源布置。MRI电源布置与可植入电源电路协作以在磁共振成像(MRI)过程中为植入电路提供高输出阻抗。更具体地,利用在MRI过程中存在的时不变磁场产生用于植入电子电路的足够的电源,以便半导体输出在MRI过程中处于良好设定的高阻抗状态。这致使可植入系统在RF感应电极加热和电流方面具有改善的MRI安全性。
[0014]许多有源可植入医疗装置(AIMD)是部分或全部可植入的,且它们包括通过皮肤传递电信号的可植入线圈,其将电能提供至一个或多个植入电子电路(且其通常还包括与本讨论无关的数据部件)。
[0015]图1示出一种方法,其基于耦合至主植入电源电路的可植入MRI电源布置,该主植入电源电路在MRI过程中不需要外部线圈来将电能提供给植入装置。一般来说,外部产生的RF电信号由植入接收线圈L101接收,其与并联的电容C101构成谐振电路。肖特基二极管D101整流L101/C101谐振电路中存在的RF信号以放大主植入电源电压,该主植入电源电压由输出电容C102滤波。齐纳二极管D102提供过压保护。为该主电源电路加入一种新的可植入MRI电源电路,其中MRI的电感L102具有宽带电感耦合特性,以从MR扫描器场的宽范围内感测RF脉冲。MRI整流二极管D103放大接收的脉冲以在MRI过程中产生植入电源电压,该植入电源电压足够高以使植入电路的半导体输出在MRI过程中进入良好限定的高阻抗状态。
[0016]虽然基于可植入MRI电源电路的实施例对于新的植入系统是有用的,但当前仍然有许多已经使用的已有植入系统,其中并未置入这种保护电路。对于上述已有系统来说,可使用外部MRI电源。图2示出在MRI过程中使用的外部MRI电源电路的一个实施例,该外部MRI电源电路放置在植入电路之上的皮肤上且将RF脉冲的能量转换成通过皮肤传递的信号,且该信号适于在植入装置中产生足够高的电源电压。由MRI过程中产生的RF脉冲供电的布置如下:MRI电感L201从MRI扫描器场感测RF脉冲,且MRI二极管D201整流该脉冲以产生用于从外部发射器电路通过皮肤感应传输至植入接收器线圈的外部电信号。齐纳二极管D202提供过压保护。该MRI信号由植入电路放大以在MRI过程中产生植入电源电压,该电源电压足够高以使植入电路的半导体输出在MRI过程中进入良好限定的高阻抗状态。
[0017]图3示出在MRI过程中使用的另一外部MRI电源电路的实施例,其是电池供电的并包括放置在植入电路之上的皮肤上的外部线圈。外部电池供电的线圈产生通过皮肤传递的信号,且该信号适于在植入装置中产生足够高的电源电压,以使植入电路的半导体输出在MRI过程中进入良好限定的高阻抗状态。
[0018]图4示出在MRI过程中使用的如图2或图3中的外部MRI发射线圈401的一个实施例,其还包括可拆卸外部保持磁铁402以及头带403。在MRI进行之前,这种附接有可拆卸外部保持磁铁402的外部发射线圈401将放置在植入接收线圈之上,从而与相应的植入磁铁协作以相对于可植入电源电路建立外部MRI发射线圈401的校正位置。头带403随后围绕头部附接以在校正位置上固定外部MRI发射线圈401,此后,可以卸下可拆卸外部保持磁铁402,且可以执行MRI。
[0019]用于MRI电源电压而感应地传递至植入装置的MRI电能信号可以任意若干不同方式产生。例如,特定实施例可以基于频率转换器(例如分频器或倍频器)的使用。替代地或另外地,外部宽带接收器可用于将MRI RF信号转换成DC电压(例如通过整流和低通滤波),该DC电压可用于驱动在感应链路的频率下运行的振荡器。
[0020]虽然已经公开的本发明的各种示例性实施例,但对于本领域技术人员来说显而易见的是在不脱离本发明的真正范围的情况下可对本发明进行各种改变和修改,从而实现本发明的某些优点。