Abstract:
Controlling the interaction between an external device and an implanted device, including a method of controlling interaction between an external device and an implanted device, the method including at least the steps of: establishing communications between the implanted device and the external device; the external device determining an identification of the implant and comparing the identification with identifications in a stored list; if the device matches one of said identifications, then using a corresponding set of operating parameters to interact with said implant; and otherwise, not interacting with said device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage application of PCT/AU2007/000142 entitled “IMPLANT ID RECOGNITION”, filed on Feb. 9, 2007, which claims priority from Australian Provisional Patent Application No. 2006900628, filed on Feb. 10, 2006, which are hereby incorporated by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to implantable medical devices, and more particularly, to recognition of implantable medical devices. 
     2. Related Art 
     Implantable hearing prostheses provide the benefit of hearing to individuals suffering from severe to profound sensorineural hearing loss. Sensorineural hearing loss is due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. An implantable hearing prosthesis essentially simulates the cochlear hair cells by delivering electrical stimulation to the auditory nerve fibers. This causes the brain to perceive a hearing sensation resembling the natural hearing sensation. 
     The present invention is particularly concerned with situations where a user, patient or recipient, “recipient” herein has an external processing device that communicates with an implanted device. For example, in a modern, conventional cochlear implant, an external speech processor transmits power and data to the implanted device via an inductive coil arrangement. The implanted device includes an electrode array to deliver the desired electrical stimuli to the cochlea of the recipient. 
     Once implanted, the implant system is typically adjusted to suit the specific needs of the recipient. As the dynamic range for electrical stimulation is relatively narrow and varies across recipients and electrodes, there is a need to individually tailor the characteristics of electrical stimulation for each recipient. This procedure, often referred to as “fitting,” “programming,” “mapping” (“mapping” herein) involves measuring and controlling the amount of electrical current delivered to the cochlea. Typically, a clinician, audiologist or other medical practitioner (generally and collectively referred to as “audiologist” herein) uses interactive software and computer hardware to create individualized programs, commands, data, settings, parameters, instructions, and/or other information (generally and collectively referred to as a “MAP” herein) that define the specific characteristics used to generate the electrical stimulation signals presented to the electrodes of the implanted electrode assembly. It is increasingly common for recipients to have a cochlear implant for each ear, which is commonly known as bilateral implantation. The advantages of bilateral implantation vary from recipient to recipient, and may include improved speech perception, and the ability to localize sounds. However, due to differences in the anatomy and physiology of recipients, and in the need to precisely place the electrode array, there will almost always be differences in the map between the left and right ears. The recipient will have two speech processor devices, each operating according to a different MAP. The speech processor devices are typically identical in appearance, and may inadvertently be swapped. This is a particular issue for very young and elderly recipients, as well as those with conditions such visual impairment. The use of the incorrect speech processor device will at best lead to reduced speech perception, as the incorrect MAP is applied, and potentially to pain for the recipient as excessive stimulation values are utilized for that ear. 
     SUMMARY 
     In a broad form, the present invention provides multiple sets of operating parameters (maps or the like) within each external device, each set being associated with an identified implant. Before the external device begins to transmit stimulation or other operational data to the implant, it determines the identity of the implant, and then uses the corresponding set. 
     According to one aspect, the present invention provides a method of controlling interaction between an external device and an implanted device, the method including at least the steps of: 
     establishing communications between the implanted device and the external device; 
     the external device determining an identification of the implant and comparing the identification with identifications in a stored list; 
     if the device matches one of said identifications, using a corresponding set of operating parameters to interact with said implant; and 
     otherwise, not interacting with said device. 
     According to another aspect, the present invention provides an external device adapted to interact with an implanted device, the external device being adapted to detect an identification from an implanted device, determine if the identification corresponds to one of a plurality of identifications, and if the identification does correspond, utilise a stored set of operating parameters corresponding to said identification. 
     According to another aspect, the present invention provides an external hearing device adapted to interact with an implanted device, the external device being able to be operatively positioned to interact with either a left ear or right ear implanted device, said external device including sensor means operatively adapted to detect whether the external device is positioned to interact with the left ear or the right ear implanted device, and in response to said sensor utilise a stored set of operating parameters corresponding to the left ear or the right ear implanted device. 
     The present invention accordingly provides an arrangement whereby, for the bilateral implantee, it does not matter which SP is selected for which ear—both can store the map for each ear, and deliver the correct stimulation instructions for the respective implant. If the implant is not identified, the SP will not operate. The invention can be applied in any form of implanted device where multiple external devices may be inadvertently associated with the wrong implanted device. 
     The invention is also applicable to implanted devices where the external device may only be periodically connected, for example, a totally implantable auditory prosthesis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described with reference to the accompanying figures, in which: 
         FIG. 1  illustrates schematically a bilateral implant situation; 
         FIG. 2  is a conceptual block diagram of the operation of one implementation of the present invention; 
         FIG. 3  is a flowchart illustrating the operation of the required software of one implementation; 
         FIG. 4  illustrates the general operation of a cochlear implant system; 
         FIG. 5  illustrates the operation of another implementation of the identification system; and 
         FIG. 6  is a graph illustrating how the characterisation of a predefined subset of parameters can be used to differentiate between two similar implants. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is capable of implementation in any desired type of implantable device which interacts with an external device. For example, the present invention may be used in conjunction with any acoustic or electrical auditory device, such as a middle ear implant, intracochlear array implant, brain stem implant, implanted acoustic device or any combination, for example combined electrical and acoustic stimulation. The external device may be continuously, intermittently or occasionally in communication with the implanted device. The present invention may also be used in non-auditory applications where a component is implanted and interacts with an external device. However, embodiments of the invention are described with reference to an embodiment in a cochlear implant system. 
       FIG. 1  illustrates conceptually a recipient  10  having an intracochlear device  11 ,  12  implanted in each ear  13 ,  14 , respectively. For each implant  11 ,  12 , a corresponding external device  17 ,  18  is required. The external device incorporates one or more microphones, batteries, processor and the necessary software to process sound signals and transmit them via coils  15 ,  16  to the implanted device. 
     A more detailed description of typical external and implant devices of a cochlear implant is provided in  FIG. 4 . It is noted that such devices are in widespread commercial use, and well understood by those skilled in the art, so that only a general overview of their structure and operation will be provided. Moreover, various structural variations and alternatives exist, as will be well known to those skilled in the art. 
       FIG. 4  illustrates an overview of the components of one form of implantable hearing prosthesis, a cochlear implant. The external component of the cochlear implant, generally indicated as  142 , includes a behind the ear (BTE) device  116 , designed to sit behind the pinna  122 . This houses the required electronics and software (not shown), and batteries to power the external component as well as transfer power to the implanted device  144 . BTE device  116  is connected via a lead  118  to the antenna transmitter coil  106 , which is generally disc shaped and includes housing  108  for the coil itself (not shown). A magnet  110  is provided to assist in correctly locating the antenna transmitter coil  106  relative to the implanted device, to optimize efficiency of power and data transfer. 
     The implanted component  144  includes receiver/stimulator unit  112  and electrode lead  130 . Receiver stimulator unit  112  includes a sealed electronics package  128 , and a coil  124  to receive the RF signals sent from transmitter coil  106 . There may also be a back transmission mechanism, to transfer telemetry data to the external device  142 . A magnet  140  provides assistance in alignment of the transmission coil  106 . Electrode lead  130  passes stimuli to the electrodes  134  for delivery within the cochlea  132 , so as to produce a neural response in auditory nerve  138 . 
     In operation, the electronics within the BTE device  116  convert sound detected by microphone(s)  120  into a coded signal. The external antenna coil  106  transmits the coded signals, together with power, to the receiver/stimulator unit  112  via a radio frequency (RF) link. 
     Once implanted, the parameters for stimulation are typically adjusted to suit the specific needs of the recipient. As the dynamic range for electrical stimulation is relatively narrow and varies across recipients and electrodes, there is a need to individually tailor the characteristics of electrical stimulation for each recipient. Audiology measurements may be used to establish the useful range for each electrode, and such parameters can be stored within the recipient&#39;s BTE device  116  for continual use. As noted, this procedure is often referred to as “mapping” and is the term commonly given to the process of measuring and controlling the amount of electrical current delivered to each electrode, as well as selecting which electrodes to stimulate corresponding to the respective sound signal. Other operational issues which may differ between ears include the speech processing strategy or parameters of that strategy, when to switch between different strategies, and other functions and parameters. Different “MAPS” may be applied in different situations/environments such as home, car, classroom, theatre etc, so each external device may store many maps. It will be appreciated that the present invention is applicable to the selection of all such functions and parameters as may be customizable for each patient or implant according to the particular requirements and options of the implant and external device in question. 
     Importantly for the present invention, the MAP for each implant will differ due to variations in the patient&#39;s anatomy and physiology, and in the precise placement of the electrode array, there will almost always be differences in the MAP between the left and right ears. 
       FIG. 2  illustrates one implementation of the present invention. Microphone(s)  120  receives ambient sound signals which are then processed by a digital signal processor (DSP)  31 . The signals are processed according to any one of the known speech processing strategies to produce a set of signals which are intended as the basis for stimulation. The signals are then converted into specific sets of stimuli for specific electrodes at specific times and for specific amplitudes. The set of MAPS (that is, the MAPS corresponding to different environments) for the appropriate implanted component  144  is required to perform this process. According to this implementation, multiple sets of MAPS are stored, each set of MAPS corresponding to a particular implant identifier. Embodiments of the implant identifier are described in further detail below. Module  33  selects the appropriate MAP, and other parameters as required, based on the implant ID identified by module  33 . Once the stimuli have been determined, the appropriate coded signals are transmitted via the bidirectional communications interface  34  to interface  44  of implanted component  144 . From the perspective of implanted component  144 , it is not necessary to change the mode of operation. The receiver/stimulator  41  receives the signal, converts it to a set of stimuli, for example using an optional digital signal processor (DSP)  42 , and sends the stimuli to electrodes  134 . 
     Implanted component  144  may contain a module to provide the require ID signal. This may be any arrangement capable of providing an appropriate ID signal which is not shared with other implants. It is ideally unique, but need not be. One option would be to send a specific electrical signal after power up or after detection that the external device is in operation. This type of ID is used in some commercially available devices. Any alternative form of implant identification can be employed with the present invention. 
     One alternative would be to provide some form of specific automatic identification of which side of the recipient&#39;s head an external device, such as a BTE device, has been placed. This could be done by the use of a proximity or thermal sensor such as is shown as reference  200  on  FIG. 4 . In the thermal case, the sensor will operatively either be placed near adjacent the user&#39;s head, or facing away, with a substantial difference in heat. This allows the appropriate left or right map to be selected. However, this does not prevent the recipient from using a completely wrong device, as may occur in a classroom situation. 
     Another alternative would be to provide a source localization algorithm on the microphone in external device  17 ,  18 . If the device is on the left ear, most sound will come from the right side and vice versa allowing determination of which ear the device has been placed and therefore allowing the appropriate selection of left or right map. 
     If no sensor is working and the implanted component is one that cannot transmit internal voltages, external device  17 ,  18  may still have MAPS for the left and right which the recipient  10  may select themselves, for example by pressing a selection button at start-up. 
     An approach suitable for use for an implant which has not been designed to produce a specific ID signal will be described with reference to  FIGS. 5 and 6 . The general approach is in principle applicable to any implant which is capable of sending the required parameters via a telemetry system to the external device. The principle of this approach is that each device has internal operating values that vary from device to device. The present example uses certain internal voltages which can be output using existing telemetry arrangements, and which as a statistical measure allow for accurate identification of particular implants. However, any suitable subset of internal parameters could be used as may be appropriate for a particular implant device. 
       FIG. 5  illustrates the statistical basis used. In any real system, manufacturing variations result in various parameters having a normally distributed range of values about a nominal value. The parameters are required to fall within minimum and maximum ranges to be acceptable from a quality perspective. However, some of these values are relatively constant over time, and are a specific value of that parameter for the particular implant. When a number of these parameters are considered separately, then if there is a sufficient overall match, the implant can be sufficiently identified. 
     The choice of the suitable subset of parameters for use in device identification will depend on device design and the normal variance of the parameters. Most active implantable devices have a range of internal parameters that may be suitable, such as regulated supply voltages, reference voltages and programmable currents. 
     For example, referring to  FIGS. 6A and 6B , the following parameters might be selected: 
     Parameter 1=Regulated analogue supply voltage (Vdda) 
     Parameter 2=Regulated digital supply voltage (Vddd) 
     Parameter 3=Reference voltage (Vref) 
     Parameter 4=Voltage measured across internal load for stimulus level A 1   
     Parameter 5=Voltage measured across internal load for stimulus level A 2 , where the value of the internal load resistor and the two current levels A 1  and A 2  will vary between implants. 
     Parameters 6 to 10=Parameters 1 to 5 but measured using a different voltage measurement range. The gains of the different measurement ranges will vary between implants, for example due to the non-linearity of the voltage amplifier in each implant. 
     Alternatively, other measurements such as the physiological properties of the ear, eg some aspect of the neural response with the implant or the impedance of the electrodes in the cochlea, can be used as parameters for use in device identification. 
       FIGS. 6A and 6B  show the value of various voltages, plotting the parameter value against the parameter. It can be seen that each implant has a specific signature which is different from other implants, so as to provide a specific identification of a particular implant. It is possible that another implant could have the set of parameter values, but this is sufficiently unlikely that that the practical risk of inadvertent connection may be disregarded. 
     One implant will now be described. For each implant (at the time of first surgery, or first fitting) the subset of parameters listed above is measured and stored as internal ID pattern. To improve the reliability of the measurement the parameters can be averaged, which also serves to minimize the statistical variance. 
     Every time the speech processor is placed on an implant the same subset of parameters is measured. The ID recognition test passes if and only if all of the parameters measured lie within, say T*sd of the value of that parameter in the internal ID pattern. The parameter T is a threshold that determines the trade-off between the sensitivity and specificity of the test: a large value of T means that we have a very low probability of wrongfully rejecting the correct implant (false negative rate), a small value of T means we have a low probability of wrongfully accepting the wrong implant (false positive rate). The parameter sd in the test criteria is the standard deviation of each parameter on repetitive measurement on the same implant, which is around 0.6 for the Freedom implant. Trials have indicated that T=3.25 provides acceptable false negative and false positive outcomes. It will be understood that for each type of implant, different parameters may be appropriate, and different values for T and standard deviation will need to be applied. The standard deviation may be different for different parameters. 
     It will be appreciated that this is a process which will differ for different external devices and a suitable set of identification parameters can be selected as has been described. 
     In practice, every time the speech processor is switched on stimulation should be halted until an implant is detected. Also, when a coil-off condition occurs for longer than 3 seconds, stimulation should halt until the implant is detected again. Before starting stimulation (at switch on, or after coil-off the test should pass first. 
     When an implant is (re)detected, the above mentioned parameters are measured using 50 averages. This dataset is labelled D(1) . . . D(n). The speech processor should check that for I=1 . . . n:
 
 R ( i )+ T*sd&lt;T ( i )&gt; R ( i )− T*sd  
 
     When the test passes, stimulation can start. If the test fails, it is repeated to rule out statistical errors. When after five (5) tests, the test still fails the speech processor should refrain from stimulating and give a helper message on the LCD display of the implant. 
     It may be desirable in some applications that the user be able to overrule the error and start stimulation by a specific button press combination to manually select the correct operating program for the implant. 
     It will be understood that a different process may be used to implement the invention if desired, and that alternative processes are likely for different external devices. 
       FIG. 3  is a flow chart illustrating the process which can be employed in the BTE device  116  software. It is noted that it would be possible to perform the ID process primarily from the implant itself, however, in general it is preferred to minimise the complexity and processing load for the implanted device. 
       FIG. 3  shows the step  50  by which the identifier is detected. This will obviously differ depending upon the identifier used. Once the identifier is located, at step  51 , the appropriate parameters and mode of operation will be selected, corresponding to the implant identified. It will be appreciated that the exact set of parameters will depend upon the type of implant, and apart from the map as such, may include other operating parameters, mode of stimulation, type of speech processing algorithm, and such other parameters as are desired. 
     It is preferred that the identification process occur as often as required to ensure safe operation. This may include, for example, at power on of the BTE device, or whenever communications between the implant and BTE are interrupted for more than some predetermined period, for example 3 seconds. In each case, the ID process should be completed before stimulation occurs. 
     Once the parameters are determined at step  51 , operation of the device can be initiated. At step  53 , operation can continue until conditions require the ID to be re-checked, as noted above. 
     It will be understood that the present invention may be applied to include more than two sets of operating parameters. For example, in a household where there are multiple implant users, all the SP devices could be loaded with the parameters for the implants of everyone in the house. This may be of particular benefit with small children. The present invention further provides flexibility for the user. If one SP device is not operating, for example due to low battery power, the remaining device can be used for the better ear. 
     Further features and advantages of the present invention may be found in International Application No. PCT/AU2007/000142 entitled “IMPLANT ID RECOGNITION”, filed on Feb. 9, 2007, which claims priority from Australian Provisional Patent Application No. 2006900628, filed on Feb. 10, 2006, which are hereby incorporated by reference. 
     It will be appreciated that any other suitable identification process can be used in accordance with the present invention. Variations and additions can be readily added as will be apparent to those skilled in the art.