WO2016191878A1

WO2016191878A1 - Ultrasound transducers as aids to implantation

Info

Publication number: WO2016191878A1
Application number: PCT/CA2016/050629
Authority: WO
Inventors: Thomas Gregory LANDRY
Original assignee: Nova Scotia Health Authority
Priority date: 2015-06-04
Filing date: 2016-06-03
Publication date: 2016-12-08

Abstract

Among other things, an implantable medical device is described that is equipped with one or more ultrasound transducers, positioned so as to provide spatial information for proper implantation. Methods of implantation and systems for guidance and verification of proper implantation are also described.

Description

ULTRASOUND TRANSDUCERS AS AIDS TO IMPLANTATION

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No.

62/170,724, filed June 4, 2015, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0001] Implantable medical devices have become increasingly important in the care and treatment of various diseases and conditions, be they simple orthopedic devices for internal fixation of bones or complex devices such as replacement heart valves, deep brain stimulators, and cochlear implants. Proper implantation of such medical devices is important for proper function. While many devices may be placed (however suboptimally) with reference to X-ray or other images of the site of implantation, some are particularly difficult to implant due to fragility / criticality of the surrounding tissue, difficulty of access to the site of implantation, and/or lack of structural information (e.g., due to anatomical features that mask the site from some images). Additionally, current methods of implantation that are performed under anesthesia lack feedback with respect to positioning within the site, other than inspection of those areas directly visible to the surgeon; fine positioning is limited to the accuracy of the available views or images.

[0002] These limitations are particularly worrisome in situations when a surgeon cannot visualize within the implanted tissue and most implant "blindly". For example, cochlear implants (CIs) are often positioned such that they are in close proximity to the modiolus, in order to maintain closeness with the spiral ganglion neurons of the auditory system. These implants are also often required to avoid contact with the basilar membrane, as contact could lead to damage, increase inflammatory response, and potentially severe reduction in residual hearing from that cochlea. Preservation of residual hearing is increasingly important, as CIs become more often a complementary treatment to hearing loss of a specific frequency range rather than complete profound hearing loss. In another example, deep brain stimulators (DBSIs) are implanted in particularly critical tissue, and it is extremely important that no major blood vessels are damaged during implantation. Current practice in DBSI implantation calls for a pre- or intraoperative computed tomography (CT) scan of the brain to be captured in order to map a patient's brain structures and blood vessels. The patient's head is then fixed to a stereotaxic frame and device is implanted using the CT map and frame reference points to insert along a predetermined

l path. While this method makes implantation possible, it relies upon continued integrity of the stereotaxic frame and is limited to the accuracy of the CT and frame reference points.

[0003] Previous efforts to improve fit in implantation have relied on advanced imaging techniques to provide better pictures of the site of implantation, but these techniques are still only an external guide to mapping the position of the implant during insertion; they do not provide feedback. To the extent feedback has been considered in implantation, it has been limited to contact sensing, which could itself to damage to tissue. As medical implants increase in complexity, there remains a need to develop implants that provide better implantation and feedback while minimizing damage to surrounding tissue.

SUMMARY

[0004] In general, in an aspect, an implantable medical device has aids to implantation in an implantation site having a tissue of interest, the aids including an ultrasound transducer positioned so as to face the tissue of interest. Implementations may include one or more of the following features. The site has a second tissue of interest and the aids further include a second ultrasound transducer positioned so as to face the second tissue of interest. The site has a several tissues of interest and the aids include several ultrasound transducers so arranged as to produce spatial information for each respective tissue of interest. The device is a cochlear implant. The device is a deep brain stimulator.

[0005] In general, in an aspect, a system for implantation of an implantable medical device has an implantable medical device as described above, electrical connections between the transducer(s) on that device and an integrated control unit. Implementations may include one or more of the following features. The integrated control unit is operatively coupled to a computer. The computer has a monitor with visual indicia of distance to the tissue of interest. The computer is capable of producing audible alerts when the transducer is closer than a predetermined distance from the tissue of interest. The integrated control unit has a field programmable gate array. The integrated control unit has a multiplexer.

[0006] In general, in an aspect, a method of implanting an implantable medical device in a living subject includes inserting the implantable medical device while actively coupled to a system having a monitor as described above and positioning the device according to the indicia.

[0007] In general, in an aspect, a method of implanting an implantable medical device in a living subject includes inserting the implantable medical device while actively coupled to the system having alerts as described above and positioning the device with lninimum eliciting of the alerts.

[0008] These and other features and aspects, and combinations of them, may be expressed as methods, systems, components, means and steps for performing functions, apparatus, articles of manufacture, compositions of matter, and in other ways.

[0009] Among other advantages, the implantable medical devices described herein are constructed so as to provide improved accuracy of positioning during implantation. The methods described herein improve the process of implantation in that enhanced feedback as to positioning is provided. Other advantages and features will become apparent from the following description and claims.

DESCRIPTION

[00010] FIG. 1 shows a perspective view (A) the front and (B) the back of an array of five ultrasound transducers for use with an implantable medical device.

[00011] FIG. 2 shows a partial cutaway perspective of the array of FIG. 1 embedded in silicone at the tip of a cochlear implant.

[00012] FIG. 3 shows the arrangement of important anatomical elements with respect to the array of FIG. 1 during insertion in two use cases, with possible visual feedback for each case.

[00013] FIG. 4 shows a block diagram for a system for guidance and/or verification of implantation.

[00014] FIG. 5 shows graphs of voltage vs time, with a dashed vertical line representing distance zero at left and the end of the trace representing distance 1 mm at right. From top to bottom these are: baseline, distance ~700 ran, distance ~500 urn, distance ~300 um, distance ~100 um. All distance graphs were produced by subtracting the baseline at top from the raw data, per the method described herein for reduction of ring noise.

[00015] FIGs. 6 through 10 depict various geometries of transducer arrays, with the shaded regions each representing the front of an ultrasound transducer.

[00016] FIG. 11 illustrates electrical paths for daisy chaining of a transducer array to electrodes of an implant.

[00017] Parts Legend

101 5-element array of ultrasound transducers 103 ultrasound transducer 1 , front of the array

105 ultrasound transducer 2

107 ultrasound transducer 3

109 ultrasound transducer 4

111 ultrasound transducer 5 (not shown)

113 electrical lead/connection for ultrasound transducer 1

115 electrical lead/connection for ultrasound transducer 2

117 electrical lead/connection for ultrasound transducer 3

119 electrical lead/connection for ultrasound transducer 4

121 electrical lead/connection for ultrasound transducer 5

123 non-conductive epoxy

125 ground lead/connection to back of transducers, ground wire

201 cochlear implant

203 silicone tip

205 implant electrodes

401 transducer array (attached or embedded in/on an implantable medical device)

403 ultrasound transducers of transducer array

405 multiplexer

407 ultrasound pulser-receiver

409 field programmable gate array (FPGA)

411 analysis and output computer

413 monitor

415 integrated control unit

417 electrical leads

419 ground lead/connection to back of transducers, ground wire

1301 ultrasound transducer, front face imaging array element 1

1302 ultrasound transducer, front face imaging array element 2

1303 electrical connection (depicted as shaded circle)

1305 wire from front face imaging array element 1

1307 electrical lead from implant electrode daisy chained to front face imaging array element 1

1311 implant electrode daisy chained to front face imaging array element 1 1313 implant electrode daisy chained to front face imaging array element 2

1315 non-daisy-chained implant electro des

1317 ground lead/connection to back of transducers, ground wire, common back face connection

[00018] Improved implantable medical devices, methods of implantation, and among other things, systems for guidance and/or verification of proper implantation are described herein. Devices equipped with ultrasound transducers are described that are capable of providing realtime echolocation information as to their position in space. Single element transducers obtain information about the material in a line directly in front of the transducer. This information is transmittable to a system equipped with visual, audio, or other output modalities appropriate to the environment. A surgeon, or any other person qualified to implant a given medical device, can receive this feedback from the system. The feedback can include an alert, for example, if the implant may be about to contact some tissue or structure that he/she is aiming to avoid contact with. The feedback can also include distance information to help direct the implant towards some tissue/structure he/she is aiming to contact or have a specific proximity to.

[00019] In one embodiment, an implantable medical device has an ultrasound transducer attached to its exterior, in a position that in the process of implantation would face an anatomical feature, the distance from which is important to detennine optimal implantation. In some embodiments, the transducer is embedded in silicone or some other carrier material to seal it from the biological environment. In some embodiments, the transducer is embedded in a silicone tip that would ordinarily be present in certain implantable medical devices. In one embodiment, an implantable medical device has an ultrasound transducer embedded near its exterior in a position that in the process of implantation would face an anatomical feature, the distance from which is important to determine optimal implantation. In some embodiments, the transducer is embedded in silicone or some other carrier material to seal it from the biological environment. In cases where attachment to a device's exterior is indicated, environmental isolation can be achieved by coating the transducer in parylene, for example. Whether attached or embedded, ultrasound signal to noise ratio for each transducer can be acoustically optimized by applying a coating as a matching layer, of such thickness as to match to a quarter wavelength of the predetennined ultrasound pulse frequency. This feature helps bridge the acoustic impedance mismatch between the piezoelectric substrate of the transducer and its local environment, which can be expected to be water-based in this application. In some embedded embodiments, the presence of the matching layer, if any, and/or the identity and thickness of the material for the matching layer will be selected based in part on the acoustic properties of the silicone.

[00020] One embodiment directed to cochlear implants depicted in FIGs. 1 and 2, an array 101 of 5 ultrasound transducers 103, 105, 107, 109, 111 are arranged in a "box" on a core of conductive epoxy, which forms the ground connection for all transducers via the ground lead 125. Individual elements are electrically isolated using non-conductive material such as epoxy 123. Electrical leads 113, 115, 117, 119, 121 are respectively attached to transducers 103, 105, 107, 109, 111, with each lead attached on its other end so as to provide independent power and input/output to each transducer. The array 101 is fixed to or within an implantable medical device, which in FIG. 2 is depicted as a cochlear implant 201 having the array 101 embedded in silicone that culminates in a tip 203.

[00021] In some embodiments, the ultrasound transducers used are less than about 250 square micrometers in size. In some embodiments, the ultrasound transducers used are less than about 1 square millimeters in size. In some embodiments, the ultrasound transducers used are less than about 5 square millimeters in size. In some embodiments, the ultrasound transducers used are less than about 10 square millimeters in size. The size of the ultrasound transducers used depends upon a number of factors, including the size of the implantable medical device, the space available at the site of implantation, and the resolution required during implantation. In some embodiments, multiple ultrasound transducers exist in/on the implantable medical device to provide spatial information from multiple positions. Given a sufficient number of single element ultrasound transducers, the positioning of the transducers can be used to create two- or three-dimensional images in the vicinity of the implantable medical device. See for example U.S. Patent Ser. No. 4,271,706, hereby incorporated by reference.

[00022] In some embodiments, ultrasound transducers are arranged into a polygon to provide several independent one-dimensional views with known spatial relationships. See FIGs. 1, 2, 6- 10 for examples of potential arrays of ultrasound transducers arranged in geometries appropriate to such views, including box, wedge, pyramid, and wheel geometries. Array geometries are not limited to what are depicted here and can have any number of individual elements, including wedge shapes with any number of elements, radial shapes with any number of elements (10 sides given in the example Figure), pyramidal shapes with any number of elements, and tetrahedral shapes with any number of elements. In some embodiments, the array geometry includes multiple elements facing in the same direction; in some embodiments, the array geometry uses only one element for each direction or polygon face. In some embodiments, the ultrasound transducers are fashioned in shapes other than the rectangular ones depicted herein, including circle, square, hexagon, etc. In some embodiments, the array only includes elements on the polygonal sides of interest, such as in the L-shape example Figure, which is two elements situated at a right angle to each other. Arrays can be mounted so as to face out from an implant at any arbitrary predetermined orientation w.r.t. the implant. In some embodiments, the array includes multiple geometries, such as a radial array and a forward-looking pyramidal array. In some embodiments, the array has only a single element, providing one-dimensional distance information for, e.g., the tip of an implant; such a possibility is demonstrated in Example 2 below. The designer can choose to implement any array geometry, number of elements, shape of each element, or orientation of each element w.r.t. the implant as seems best given the specific application, cost point, resolution required, complexity of implantation site, and other factors relevant to implantation of a medical device.

[00023] One possible design is the "box" array of FIGs. 1 and 2. FIG. 3 shows examples of how data from the 5 -element array could be displayed to person implanting the device for two use cases of a cochlear implant. On left, the elements are defined based on the direction within the cochlea that they project pulses (forward, medial, lateral, apical, basal). On middle and right, each use case is depicted on top in midmodiolar and longitudinal cross sections of the scala media (SM), scala tympani (ST), and scala vestibule (SV), with a corresponding output modality on bottom. Each transducer produces an echo corresponding to the distance from the tissue. In this embodiment, the output shows, with arrows on a distance scale, how far away the echoes are from each transducer.

[00024] In some embodiments, the implantable medical device is a cochlear implant. In some embodiments, the implantable medical device is an implantable deep brain stimulator. In some embodiments, the implantable medical device is an implantable pacemaker. In some embodiments, the implantable medical device is an implantable hearing aid. In some embodiments, the implantable medical device is a tinnitus masker. In some embodiments, the implantable medical device is an implantable defibrillator. In some embodiments, the implantable medical device is an auditory brainstem implant. In some embodiments, the implantable medical device is a brain stimulator for epilepsy. In some embodiments, the implantable medical device is an implantable cerebellar stimulator. In some embodiments, the implantable medical device is an implantable intracranial pressure monitor. In some embodiments, the implantable medical device is an implantable nerve stimulator. Diseases or conditions treated, diagnosed, and/or monitored by such implantable medical devices vary widely depending on the nature of each device. Applicable implantable medical devices of the invention may include any device classified in the U.S. Food and Drug Administration device class III in which the device classification contains the word "implant", "implanted", or "implantable"; see htt ://www. accessdata.fda. gov/scripts/ cdrli/cfdocs/cfpcd/classification. cfm for a database containing device classifications, applicable regulations and/or consensus standards for construction and/or testing of such devices, all of which are hereby incorporated by reference.

[00025] In some embodiments, implantation of an implantable medical device of the present invention generally proceeds by the methods currently used, except that feedback during implantation allows for enhanced confidence in positioning. It may be that for some such procedures, the feedback provided is sufficient to complete the procedure while reducing the invasiveness, by not requiring as large of an incision or by reducing the degree of tissue retraction needed for direct visualization. For example, cochlear implants are often positioned such that they are in close proximity to the modiolus, in order to maintain closeness with the spiral ganglion neurons of the auditory system. These implants are also often required to avoid contact with the basilar membrane, as contact could lead to damage, increase inflammatory response, and potentially severe reduction in residual hearing from that cochlea. In some CI embodiments, one or more ultrasound transducers are arranged in/on the implantable medical device such that it faces the modiolus when properly inserted, and/or one or more ultrasound transducers are arranged in/on the implantable medical device such that it faces the basilar membrane when properly inserted. In another example, deep brain stimulators are implanted in particularly critical tissue, and it is extremely important that no major blood vessels are damaged during implantation. Current practice in DBSI implantation calls for a pre- or intra-operative computed tomography scan of the brain to be captured in order to map a patient's brain structures and blood vessels. The patient's head is then fixed to a stereotaxic frame and device is implanted using the CT map and frame reference points to insert along a predetermined path. In some DBSI embodiments, one or more ultrasound transducers are arranged in/on the implantable medical device such that it faces the nearest blood vessel when properly inserted.

[00026] Systems for guidance and/or verification of proper implantation include an implantable medical device equipped with one or more ultrasound transducers, the transducer(s) being operatively coupled to a control unit that is capable of powering the transducers and transmitting the results to a computer for further analysis and display/alert. An embodiment of such a system is shown in FIG. 4. A transducer array 401 has one or more ultrasound transducers 403. Each transducer 403 is connected by an electrical lead 417 (grounded by wire 419) to a multiplexer 405, which is in turn connected to an ultrasound pulser/receiver 407. An FPGA 409 is capable of sending clock sync to an analysis and output computer 411 as well as triggering commands to the ultrasound pulser/receiver 407. In some embodiments, the FPGA 409 is configured to output trigger events at a pre-programmed interval consistent with the desired rate of data acquisition and speed of multiplexer switching. Upon receiving a trigger event from the FPGA 409, the pulser/receiver 407 forwards the trigger event to the multiplexer 405 to initiate a delayed switch event, and to the computer 411 to begin acquisition of data. The pulser/receiver 407 sends a pulse through the multiplexer 405 to pulse one of the ultrasound transducers 403, with the multiplexer 405 sending an indicator as to which transducer is pulsed to the computer 411. In some embodiments, after a predetermined data acquisition time has passed, the delayed multiplexer 405 switch event occurs, cycling to a new transducer awaiting the next trial. Each pulse propagates through tissue and echoes are received by each transducer as an ultrasound signal. The ultrasound pulser/receiver 407 by way of the multiplexer 405's signal path receives each ultrasound signal and outputs it to the computer 411, which is equipped with software and/or dedicated hardware to analyze each signal and display one or more indicia on a monitor 413, such as, for example, shown in FIG. 4. In some embodiments, the trigger event is interpreted by the multiplexer 405 to provide automatic cycling to the next transducer in sequence after a pre-programmed delay time, e.g., 0.5 ms. In some embodiments, the multiplexer 405, the ultrasound pulser/receiver 407, and the FPGA 409 are integrated into a single control unit 415. In some embodiments, the output includes color ranges (green, yellow, red) for each transducer in an effort to optimize positioning within the site of implantation. In some embodiments, the monitor has audio functionality to produce an audible alert if one or more of the transducers is judged too close to tissue within the site of implantation. In some embodiments, there is a visual alert if one or more of the transducers is judged too close to tissue within the site of implantation.

[00027] Whether a transducer is judged to be too close to tissue within the site of implantation depends on the specific site, the fragility of the tissue, the complexity of implantation, the fragility of the implant, and other factors relevant to implantation of a medical device. In some embodiments, warning begins when the implant is within 10 mm of the tissue. In some embodiments, warning begins when the implant is within 5 mm of the tissue. In some embodiments, warning begins when the implant is within 4 mm of the tissue. In some embodiments, warning begins when the implant is within 3 mm of the tissue. In some embodiments, warning begins when the implant is within 2 mm of the tissue. In some embodiments, warning begins when the implant is within 1 mm of the tissue. In some embodiments, warning begins when the implant is within 0.5 mm of the tissue. For example, in some embodiments for implantation of a cochlear implant, warning would begin when the implant tip is within 4 mm of the basilar membrane and increase in intensity once the implant tip is within 0.5 mm of the basilar membrane. In some embodiments, the increase in intensity is indicated by increase in volume, pitch, or speed of an aural alarm. For example, an alarm could be emitting brief beeps at a rate of 1/sec at 4.0 mm, increasing pro ortionally to 10/sec once the implant tip reaches 0.1 mm. In some embodiments, the increase in intensity is indicated by a change in color, brightness, flashing of text, or other visual indicia. In some embodiments, both aural and visual alarms are used.

[00028] In some embodiments, implantable medical devices of the present invention are constructed so as to make the transducer electrically inactive after implantation is complete. In some embodiments, implantable medical devices of the present invention are constructed so as to allow for periodic or episodic re-activation of the transducer. For example, in CI or DBSI devices, electrical leads are customarily available within the implantable medical device, which presents a signal path that can be utilized for activation of the transducer. In some embodiments, the ground wire for use with the transducer and implantation system (e.g., during implantation) may be separate from the ground wire used by the implantable medical device when in active use (post-implantation). In some embodiments for implantable medical devices that do not customarily include electrical leads, the electrical leads and ground wire for the transducer and implantation system may terminate in a plug at the exterior of the implantable medical device; during implantation, the plug can be mated to a corresponding connector and set of wires leading to the other parts of the implantation system, which can be removed post-implantation.

[00029] Ultrasound pulse generation and echo signal reception can be handled by

commercially available pulse/receivers, such as the 1 OE S-4 Pulser/Receiver (Daxsonics, Halifax, NS, Canada). In some embodiments, there is only one transducer in the array and a multiplexer is not needed. In some embodiments, trigger rate is set internally in the pulser on a pre-programmed rate, obviating the need for an FPGA. In some embodiments, the pulse rate is controlled by software in the computer generating a trigger event which is sent to the

pulser/receiver, obviating the need for an FPGA. In some embodiments, a multi-channel pulser/receiver is used, obviating the need for a multiplexer.

Software for analysis of the ultrasound signal may include analysis of time vs voltage for each transducer; for single element transducer systems, such software is available from, e.g., Daxsonics, and can be adapted to accept signal from multiple elements.

In some applications the site of implantation is small enough that echoes may return to the receiver before the initially generated pulse has decayed, thus potentially obscuring the signal. Software for analysis of the ultrasound signal may also include reduction of this "ring noise" as follows: a baseline pulse is recorded from a position with little to no reflection, and when performing measurements of interest, this baseline is subtracted in order to produce a cleaner signal for analysis. In some embodiments, the baseline is established at the beginning of each session. In some embodiments, a baseline representing the characteristic ring noise for each transducer is saved on the computer for application to subsequent pulses. In some embodiments, the saved baseline is also optimized for the tissue or surgical site to be analyzed. In some embodiments, the software enables a raw signal display. In some embodiments, the software enables the display of the calculated distance to tissue for each ultrasound signal with appropriate labeling for each transducer.

In some embodiments having a common back face or grounding lead, the front sides of each ultrasound transducer are attached (using conductive epoxy or welds, e.g.) to their own respective flexible electrical wires or leads, the other ends of which are then attached in an electrically operative manner to the rest of the system as described above (such as to a multiplexer). In some embodiments, such as that depicted in FIG. 11 : rather than follow an independent signal path, the front sides of each ultrasound transducer are attached to their own respective flexible electrical wires or leads, the other ends of which are then electrically coupled to the rest of the system by way of the existing implant electrodes. For example, in a system employing two ultrasound transducers 1301 and 1302, each has its own electrical connection and wire leading to a different respective connection at an implant electrode 1311 and 1313, each of which in turn has an electrical lead to attach to the implant power source and/or to the system as described above. In some embodiments, the implant electrodes are circular and the wires are attached on the inside; the common back face connection 1317 and electrical leads are depicted in FIG. 13 as dashed lines passing through the hollow space inside, so as to only touch each implant electrode at the relevant connection point. In some embodiments, the electrical leads are insulated by, e.g., silicone or Teflon coating.

[00030] Other design variations are possible.

[00031] Examples

[00032] Example 1

[00033] Construction of a box array embedded in a silicone tip of a cochlear implant [00034] A piece of bulk lead zirconate titanate (PZT) piezoelectric crystal was ground down to an appropriate thickness using a lapping machine. For PZT, a thickness of approximately 49 microns yields a resonant frequency of 45MHz, which proved to be appropriate for high axial resolution echo location. The lapped bulk substrate was then cut into small square elements of 250x250 microns using a dicing saw. The elements were arranged within a silicone mold of the desired box shape. The empty space between the elements (inside of the "box") was filled with conductive epoxy and a ground wire held by a micromanipulator arm was lowered into the epoxy. The array was placed on a hot plate at 80°C to cure, for approximately 8 hours. The array and ground lead were manually released from the mold. The front face of the elements and the space between elements were cleaned of residual conductive epoxy. Non-conductive epoxy (e.g., 301 epoxy mixed with 3 micron aluminum oxide power in a 1 :2 ratio by weight) was applied to the back of the array to cover the conductive epoxy, and was applied to the spaces between the elements to ensure electrical isolation. A thin wire strand was then attached to each element front face individually by conductive epoxy. Each strand was soldered to the inner lead of a coaxial cable, giving 5 individual coaxial cables. The coaxial shielding of all cables were then soldered together, and the array ground lead was soldered to this common shielding. SMA (SubMiniature version A coaxial RF) connectors were attached to each coaxial cable.

[00035] Example 2

[00036] Detecting bone reflections from within a cadaveric human cochlea [00037] A single element probe of 250 sq um, excited by 15V 45MHz pulse, was used to collect one-dimensional reflection data near a cadaveric human cochlear bone at approximately 200 um increments, in order to demonstrate that the implementation aid and associated system can indeed measure such distances from a relevant tissue type. See FIG. 5. As can be seen in the ring-noise corrected traces in the Figure, the echo distance becomes smaller as the distance between the probe and the cochlear bone decreases. The bottom trace is an example of how the signal appears at short distances. After it has been deconvolved from the ring noise, the signal is still apparent and usable for navigation at short distances. Data was collected at distance steps between these traces and ring noise corrections were applied to arrive at FIG. 5.

[00038] A system can be constructed that includes real-time ring noise correction and a monitor that continuously shows ring noise corrected data. Motion of the probe toward or away from the cochlear bone will result in a proportionate change in echo distance on the monitor.

Claims

CLAIMS:

1. An implantable medical device having aids to implantation in an implantation site having a tissue of interest, the aids comprising an ultrasound transducer positioned so as to face the tissue of interest.

2. The device of claim 1 in which the site has a second tissue of interest, the aids further comprising a second ultrasound transducer positioned so as to face the second tissue of interest.

3. The device of claim 1 in which the site has a plurality of tissues of interest and the aids comprise a plurality of ultrasound transducers so arranged as to produce spatial information for each respective tissue of interest.

4. The device of claim 1 in which the device is a cochlear implant.

5. The device of claim 1 in which the device is a deep brain stimulator.

6. A system for implantation of an implantable medical device, the system comprising the device of any of claims 1-5, electrical connections between the transducers and an integrated control unit, the unit being operatively coupled to a computer.

7. The system of claim 6 in which the computer has a monitor with visual indicia of distance to the tissue of interest.

8. The system of claim 6 in which the computer is capable of producing audible alerts when the transducer is closer than a predetermined distance from the tissue of interest.

9. The system of claim 6 in which the integrated control unit has a field programmable gate array.

10. The system of claim 6 in which the integrated control unit has a multiplexer.

11. A method of implanting an implantable medical device in a living subject, the method comprising inserting the implantable medical device while actively coupled to the system of claim 7 and positioning the device according to the indicia.

12. A method of implanting an implantable medical device in a living subject, the method comprising inserting the implantable medical device while actively coupled to the system of claim 8 and positioning the device with minimum eliciting of the alerts.