Patent Description:
Hearing loss, which may be due to many different causes, is generally of two types, conductive and/or sensorineural. Conductive hearing loss occurs when the normal mechanical pathways of the outer and/or middle ear are impeded, for example, by damage to the ossicular chain or ear canal. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain.

Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As such, individuals suffering from conductive hearing loss typically receive an auditory prosthesis that generates motion of the cochlea fluid. Such auditory prostheses include, for example, acoustic hearing aids, bone conduction devices, and direct acoustic stimulators.

In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Those suffering from some forms of sensorineural hearing loss are unable to derive suitable benefit from auditory prostheses that generate mechanical motion of the cochlea fluid. Such individuals can benefit from implantable auditory prostheses that stimulate nerve cells of the recipient's auditory system in other ways (e.g., electrical, optical and the like). Cochlear implants are often proposed when the sensorineural hearing loss is due to the absence or destruction of the cochlea hair cells, which transduce acoustic signals into nerve impulses. Auditory brainstem stimulators might also be proposed when a recipient experiences sensorineural hearing loss due to damage to the auditory nerve <CIT> relates to calculating electrode frequency allocation in a cochlear implant and discloses all of the features in the preamble of claim <NUM>.

Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:.

Presented herein are intra-operative techniques for setting the angular insertion depth of a stimulating assembly during implantation into a recipient's cochlea. In certain embodiments, the angular insertion depth is monitored in real-time during insertion of the stimulating assembly and advancement of the stimulating assembly is terminated when a selected angular insertion depth is achieved. In further embodiments, a linear insertion depth that corresponds to a selected angular insertion depth is intra-operatively calculated and advancement of the stimulating assembly is terminated when the calculated linear insertion depth is achieved.

<FIG> is perspective view of an exemplary cochlear implant <NUM> that may be implanted in a recipient using the angular insertion depth setting techniques in accordance with embodiments presented herein. The cochlear implant <NUM> includes an external component <NUM> and an internal/implantable component <NUM>. The external component <NUM> is directly or.

Stimulating assembly <NUM> extends through an opening in the cochlea <NUM> (e.g., cochleostomy <NUM>, the round window <NUM>, etc.) and has a proximal end connected to stimulator unit <NUM> via lead region <NUM> that extends through mastoid bone <NUM>. Lead region <NUM> couples the stimulating assembly <NUM> to implant body <NUM> and, more particularly, stimulator unit <NUM>.

An intra-cochlear stimulating assembly, such as stimulating assembly <NUM>, may be a perimodiolar stimulating assembly or a non-perimodiolar stimulating assembly. A perimodiolar stimulating assembly is a stimulating assembly that is configured to adopt a curved configuration during and/or after implantation into the recipient's cochlea so as to have at least the distal section positioned close to the wall of the recipient's modiolus (i.e., close to the modiolar wall). One type of non-perimodiolar stimulating assembly is a lateral stimulating assembly that is configured to be implanted so as to be positioned along the lateral wall of the recipient's scala tympani (i.e., the wall that is opposite the modiolar wall). Another type of non-perimodiolar stimulating assembly is a mid-scala stimulating assembly which assumes a mid-scala position during or following implantation (i.e., positioned approximately midway between the modiolar wall and the lateral wall).

In general, the sound processor in sound processing unit <NUM> is configured to execute sound processing and coding to convert a detected sound into a coded signal corresponding to electrical signals for delivery to the recipient. The coded signal generated by the sound processor is then sent to the stimulator unit <NUM> via the RF link between the external coil <NUM> and the internal coil <NUM>. The stimulator unit <NUM> includes one or more circuits that use the coded signals, received via the transceiver unit <NUM>, so as to output stimulation (stimulation current) via one or more stimulation channels that terminate in the intra-cochlear stimulating contacts <NUM>. As such, the stimulation is delivered to the recipient via the intra-cochlear stimulating contacts <NUM>. In this way, cochlear implant <NUM> stimulates the recipient's auditory nerve cells, bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity.

<FIG> is cross-sectional view of cochlea <NUM> illustrating stimulating assembly <NUM> partially implanted therein. <FIG> is a simplified top view of cochlea <NUM> illustrating stimulating assembly <NUM> partially implanted therein. Referring first to <FIG>, cochlea <NUM> is a conical spiral structure that comprises three parallel fluid-filled canals or ducts, collectively and generally referred to herein as canals <NUM>. Canals <NUM> comprise the tympanic canal <NUM>, also referred to as the scala tympani <NUM>, the vestibular canal <NUM>, also referred to as the scala vestibuli <NUM>, and the median canal <NUM>, also referred to as the scala media <NUM>. Cochlea <NUM> includes the modiolus <NUM> which is a conical shaped central region around which the cochlea canals <NUM> spiral. The modiolus <NUM> consists of spongy bone in which the cochlea nerve cells, sometimes referred to herein as the spiral ganglion cells, are situated. The cochlea canals <NUM> generally turn <NUM> times around the modiolus <NUM>.

To insert intra-cochlear stimulating assembly <NUM> into cochlea <NUM>, an opening (facial recess) is created through the recipient's mastoid bone <NUM> (<FIG>) to access the recipient's middle ear cavity <NUM> (<FIG>). The surgeon then creates an opening from the middle ear into the cochlea <NUM> through, for example, the round window, oval window, the promontory, etc. of the cochlea <NUM>. The surgeon then gently advances (pushes) the stimulating assembly <NUM> forward into the cochlea <NUM> until the stimulating assembly <NUM> achieves a final implanted position. As shown in <FIG> and <FIG>, the stimulating assembly <NUM> follows the helical shape of the cochlea <NUM>. That is, the stimulating assembly <NUM> spirals around the modiolus <NUM>.

In normal hearing, sound entering auricle <NUM> (<FIG> ) causes pressure changes in cochlea <NUM> that travel through the fluid-filled tympanic and vestibular canals <NUM>, <NUM>. The organ of Corti <NUM>, which is situated on basilar membrane <NUM> in scala media <NUM>, contains rows of hair cells (not shown) which protrude from its surface. Located above the hair cells is the tectoral membrane <NUM> which moves in response to pressure variations in the fluid-filled tympanic and vestibular canals <NUM>, <NUM>. Small relative movements of the layers of membrane <NUM> are sufficient to cause the hair cells to move, thereby causing the creation of a voltage pulse or action potential which travels along the associated nerve fibers that connect the hair cells with the auditory nerve <NUM>. Auditory nerve <NUM> relays the impulses to the auditory areas of the brain (not shown) for processing.

Typically, in cochlear implant recipients some portion of the cochlea <NUM> (e.g., the hair cells) is damaged such that the cochlea cannot transduce pressure changes into nerve impulses for relay to the brain. As such, the contacts <NUM> of the stimulating assembly <NUM> are used to directly stimulate the cells to create nerve impulses resulting in perception of a received sound. In the specific embodiments illustrated herein, stimulating assembly <NUM> comprises twenty-two (<NUM>) intra-cochlear contacts <NUM>(<NUM>) through <NUM>(<NUM>) that may deliver stimulation to the cochlea <NUM>. Contact <NUM>(<NUM>) is the most proximal/basal contact (i.e., the contact configured to be implanted closest to the basal end of the cochlea <NUM>), while intra-cochlear contact <NUM>(<NUM>) is the most distal/apical contact (i.e., located closed to the cochlea apex <NUM>). Due to the illustrative view, only a subset of the twenty-two (<NUM>) intra-cochlear contacts <NUM>(<NUM>) through <NUM>(<NUM>) are visible in <FIG>.

A reference contact (not shown in <FIG> and <FIG>) may also be provided. The reference contact is positioned outside of the recipient's cochlea <NUM> and, as such, is sometimes referred to as an extra-cochlear electrode (ECE).

As noted above, the contacts <NUM>(<NUM>)-<NUM>(<NUM>) deliver stimulation to the cochlea <NUM> to evoke a hearing percept. The effectiveness of the stimulation depends, at least in part, on the place along basilar membrane <NUM> where the stimulation is delivered. That is, the cochlea <NUM> has characteristically been referred to as being "tonotopically mapped" in that regions of the cochlea toward the basal end are more responsive to high frequency signals, while regions of cochlea <NUM> toward the apical end are more responsive to low frequency signals. These tonotopical properties of cochlea <NUM> are exploited in a cochlear implant by delivering stimulation within a predetermined frequency range to a region of the cochlea that is most sensitive to that particular frequency range. However, this stimulation relies on the particular contacts <NUM>(<NUM>)-<NUM>(<NUM>) having a final implanted positioned adjacent to a corresponding tonotopic region of the cochlea <NUM> (i.e., a region of the cochlea that is sensitive to the frequency of sound represented by the contact).

To achieve a correct final implanted position, the distal end/tip <NUM> of the stimulating assembly <NUM> should be placed at a correct angular position, sometimes referred to herein as a correct angular insertion depth. As used herein, the angular position or angular insertion depth of the stimulating assembly <NUM> refers to the angular rotation of the distal end <NUM> from the cochlea opening <NUM> (e.g., round window, cochleostomy, etc.) through which the stimulating assembly enters the cochlea. As such, the angular position/angular insertion depth may be expressed in terms of how many angular degrees (°) the distal end <NUM> has traveled within the cochlea <NUM> with respect to the cochlea opening <NUM>. For example, an angular insertion depth of one hundred and eighty (<NUM>) degrees indicates that the distal end <NUM> has traveled around half (<NUM>/<NUM>) of the first turn <NUM> of cochlea <NUM>. An angular insertion depth of three hundred and sixty (<NUM>) degrees indicates that the distal end <NUM> has traveled completely around the first turn <NUM>. Angular insertion depth, if achieved accurately, is a constant for all recipients that enables correct frequency alignment (i.e., positioning of the contacts <NUM>(<NUM>)-<NUM>(<NUM>) adjacent to a corresponding tonotopic region of the cochlea <NUM>.

However, a problem arises due to the fact the size of the cochlea may vary from recipient to recipient. These different cochlea sizes result in cochlea turns that have different radii, thereby resulting in different linear lengths to achieve an angular insertion depth. For example, an angular insertion of <NUM> degrees for one recipient may require a linear insertion depth of <NUM> millimeters (mm), while the same angular insertion depth of <NUM> degrees may require a linear insertion depth of <NUM> for a different recipient. The linear insertion depth of a stimulating assembly refers to the linear length of the stimulating assembly that is within the cochlea (i.e., has passed through the cochlea opening).

The cochlea <NUM> shown in <FIG> is defined so as to include a central axis <NUM> extending generally through the geometric center of the cochlea (e.g., through modiolus <NUM>). The cochlea <NUM> is further defined to include a plurality of different angular reference points with respect to the central axis <NUM>. In particular, a zero (<NUM>) degree angular reference point (<NUM>° point) <NUM> is a point within the scala tympani <NUM> that is located at or adjacent to the cochlea opening <NUM> through which the stimulating assembly <NUM> is inserted. A one hundred and eighty (<NUM>) degree angular reference point (<NUM>° point) <NUM> is a point within the scala tympani <NUM> that is diametrically opposite from the <NUM>° point <NUM> (i.e., <NUM>° point <NUM> is located on the opposite side of the modiolus <NUM> from <NUM>° point <NUM>). The <NUM>° point <NUM> and <NUM>° point <NUM> both lie within a reference plane <NUM> that passes through the central axis <NUM>. As noted above, the scala tympani <NUM> spirals around the modiolus <NUM>. As such, the <NUM>° point <NUM> is further "up" the cochlea spiral (i.e., at a different level within the reference plane <NUM>) than the <NUM>° point <NUM>.

<FIG> illustrates the distal end <NUM> of the stimulating assembly <NUM> positioned at the <NUM>° point <NUM>. The distal end <NUM> of the stimulating assembly <NUM> reaches the <NUM>° point <NUM> after the surgeon pushes the stimulating assembly <NUM> through the scala tympani <NUM> past the beginning <NUM> of the basal (first) turn <NUM>.

In <FIG>, the cochlea <NUM> also includes a two hundred and seventy (<NUM>) degree angular reference point (<NUM>° point) <NUM>, a three hundred and sixty (<NUM>) degree angular reference point (<NUM>° point) <NUM>, a four hundred (<NUM>) degree angular reference point (<NUM>° point) <NUM>, and a four hundred and fifty (<NUM>) degree angular reference point (<NUM>° point) <NUM>. The <NUM>° point <NUM> is located diametrically opposite the <NUM>° point <NUM> and lies within reference plane <NUM>. More specifically, the <NUM>° point <NUM> is located between the <NUM>° point <NUM> and the <NUM>° point <NUM>. However, since as noted above the scala tympani <NUM> spirals around the modiolus <NUM>, the <NUM>° point <NUM> is further up the cochlea spiral (i.e., at a different level within the reference plane <NUM>) than both the <NUM>° point <NUM> and the <NUM>° point <NUM>.

The <NUM>° point <NUM> is a point within scala tympani <NUM> located at an angular position midway between the <NUM>° point <NUM> and the <NUM>° point <NUM>. The <NUM>° point <NUM> is a point within the scala tympani <NUM> that is diametrically opposite from the <NUM>° point <NUM> (i.e., <NUM>° point <NUM> is located on the opposite side of the modiolus <NUM> from <NUM>° point <NUM>). The <NUM>° point <NUM> and the <NUM>° point <NUM> both lie within a reference plane <NUM> that passes through the central axis <NUM>. Since the scala tympani <NUM> spirals around the modiolus <NUM>, the <NUM>° point <NUM> is further up the cochlea spiral (i.e., at a different level within the reference plane <NUM>) than both the <NUM>° point <NUM>. The <NUM>° point <NUM> is a point within the scala tympani <NUM> that is located between the <NUM>° point <NUM> and the <NUM>° point <NUM> (i.e., a point <NUM> degrees after the <NUM>° point <NUM> and <NUM> degrees before the <NUM>° point <NUM>).

In <FIG>, specific angular reference points have been selected and shown merely for ease of description. It is to be appreciated that a number of other angular reference points may be defined and used in accordance with embodiments presented herein.

In conventional intra-cochlear stimulating assembly insertion techniques, the surgeon operates "blind. " That is, due to the nature of the access (through the facial recess and the middle ear cavity), the surgeon cannot actually see the stimulating assembly <NUM> once it passes into the cochlea <NUM>. Therefore, the surgeon is unaware of the actual location of the distal end <NUM> of the stimulating assembly <NUM>. Instead, a surgeon typically inserts the stimulating assembly until met with resistance (i.e., relies upon only touch/feel during the insertion). Certain conventional techniques may be based on the "average" cochlea size and do not account for recipient-specific variations in cochlea size. Other conventional techniques require pre-operative imaging of the cochlea. A technician or other user manually estimates the size of the recipient's cochlea based on the pre-operative image and the size estimate is used in an attempt to achieve the correct angular insertion depth of the distal end <NUM>. Conventional techniques that rely upon estimations of the cochlea size may result in incorrect positioning of the stimulating assembly <NUM> and thus misalignment of the contacts <NUM> with the corresponding frequency regions of the cochlea <NUM>.

As such, presented herein are techniques for intra-operative setting the angular insertion depth of a cochlear implant stimulating assembly. For ease of illustration, the intra-operative angular insertion depth determination techniques are primarily described herein with reference to implantation of stimulating assembly <NUM> into cochlea <NUM> as described with reference to <FIG>, <FIG>, and <FIG>.

<FIG> is a flowchart of a first intra-operative method <NUM> for setting the angular insertion depth of stimulating assembly <NUM>. <FIG> illustrates a real-time method that enables the determination of the current/present (i.e., actual) angular insertion depth of stimulation assembly <NUM> within cochlea <NUM>.

Method <NUM> begins at <NUM> where stimulating assembly <NUM> is at least partially inserted into cochlea <NUM>. At <NUM>, during insertion of the stimulating assembly into the cochlea, the impedance between different pairs of intra-cochlear contacts of the stimulating assembly <NUM> is measured and used to determine the angular insertion depth of the stimulating assembly.

In one embodiment, to measure the impedance between two intra-cochlear contacts, bipolar electrical stimulation (i.e., one or more bipolar current signals) is repeatedly delivered between a first intra-cochlear contact and a second intra-cochlear contact. After the delivery of each set of bipolar stimulation between the first and second intra-cochlear contacts, the impedance between the first and second contacts is measured (e.g., at the second intra-cochlear contact). The contact that delivers the current signals is sometimes referred to herein as the "stimulating" or "source" contact and the contact that sinks the current is sometimes referred to herein as the "return" contact. Additionally, the two contacts between which the stimulation is delivered are sometimes collectively referred to herein as a "stimulating pair. " The remaining contacts that are not part of the stimulating pair are disconnected from the system ground (i.e., are electrically "floating").

It is to be appreciated that impedance measurements are made between two points, thus the impedance may be "measured" at either of the two points (i.e., it is a relative measurement between those two points). However, merely for ease of illustration of certain embodiments presented herein, the return contact of the stimulating pair is sometimes referred to herein as a "measurement" contact.

In general, the impedance between two intra-cochlear contacts in a stimulating pair can be correlated to their physical proximity with one another and their location in the cochlea. The physically closer the contacts of the stimulating pair are to one another, the lower the impedance that will be measured between the contacts. At <NUM>, again while inserting the stimulating assembly <NUM>, the impedance-to-proximity relationship is used to evaluate the plurality of impedance measurements relative to one another to determine the relative proximity between the two or more intra-cochlear contacts and thus determine the real-time (current/present) angular insertion depth of the stimulating assembly <NUM>. As described further below, the method includes the selection one or more sets/pairs of intra-cochlear contacts for impedance measurement that have a relationship to one another that enables the angular insertion depth of the stimulating assembly <NUM> to be determined from the relative proximity of the one or more pairs of intra-cochlear contacts.

In certain embodiments of <FIG>, the two or more intra-cochlear contacts selected for impedance measurement comprise two specific (static contacts) that have a maximum physical separation when the angular insertion depth of the stimulating assembly <NUM> is <NUM>° (i.e., the distal end <NUM> of the stimulating assembly <NUM> is inserted to <NUM>° point <NUM>), and a minimum physical separation when the angular insertion depth of the stimulating assembly <NUM> is <NUM>° (i.e., the distal end <NUM> of the stimulating assembly <NUM> is inserted to <NUM>° point <NUM>). This relationship between contacts having a maximum and minimum separation arrangement at the specific <NUM>° and <NUM>° points is referred to herein as an angular proximity relationship.

Depending on, for example, the shape, size, length, etc. of a stimulating assembly, different contacts may have an angular proximity relationship. As such, different stimulating pairs of contacts may be used in accordance in different embodiments to determine the angular insertion depth of the stimulating assembly <NUM>. Therefore, in certain embodiments, the method includes determining and selecting the one or more pairs of intra-cochlea contacts that are believed to have a correct angular proximity relationship.

For example, in one illustrative embodiment, the most distal/apical contact <NUM>(<NUM>) and the most proximal/basal contact <NUM>(<NUM>) have an angular proximity relationship that enables the use of impedance measurements between these two contacts to determine the angular insertion of the stimulating assembly <NUM>. More specifically, <FIG> is a graph <NUM> that illustrates impedances measured between contacts <NUM>(<NUM>) and <NUM>(<NUM>) over a period of time during insertion of stimulating assembly <NUM>. The graph <NUM> has a vertical (Y) axis that represents the measured impedance and a horizontal (X) axis that represents the angular insertion depth of the stimulating assembly.

In <FIG>, bipolar stimulation is delivered between contact <NUM>(<NUM>) and contact <NUM>(<NUM>) and the impedance between the contacts is measured. This process is repeated over a period of time to produce a plurality of impedance measurements. These impedance measurements are plotted as an impedance curve <NUM>. As shown, the measurement of the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) begins at point <NUM> of the impedance curve <NUM>. The measurement of the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) may begin, for example, when contact <NUM>(<NUM>) enters the cochlea through opening <NUM> and may continue while the stimulating assembly <NUM> is inserted into the cochlea <NUM>. In general, the contacts <NUM>(<NUM>)-<NUM>(<NUM>) the stimulating assembly <NUM> to be determined from the relative proximity of the one or more pairs of intra-cochlear contacts.

In <FIG>, bipolar stimulation is delivered between contact <NUM>(<NUM>) and contact <NUM>(<NUM>) and the impedance between the contacts is measured. This process is repeated over a period of time to produce a plurality of impedance measurements. These impedance measurements are plotted as an impedance curve <NUM>. As shown, the measurement of the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) begins at point <NUM> of the impedance curve <NUM>. The measurement of the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) may begin, for example, when contact <NUM>(<NUM>) enters the cochlea through opening <NUM> and may continue while the stimulating assembly <NUM> is inserted into the cochlea <NUM>. In general, the contacts <NUM>(<NUM>)-<NUM>(<NUM>) experience a significant impedance change after entering into the cochlea <NUM> (e.g., due to immersion in the conductive perilymph). As such, the system can monitor the impedance at the contact <NUM>(<NUM>) to determine when the contact enters the cochlea <NUM>.

As noted above, <FIG> illustrates the measured impedance plotted against the angular insertion depth of the stimulating assembly <NUM>. The impedance rises from starting point <NUM> to a first peak/maximum at point <NUM>. The impedance subsequently falls to a minimum at point <NUM>, then again rises to second peak/maximum at point <NUM>. Because the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) is a maximum at point <NUM>, point <NUM> indicates that the stimulating assembly <NUM> has been inserted <NUM> degrees (i.e., the contacts <NUM>(<NUM>) and <NUM>(<NUM>) are at the maximum possible distance from one another within cochlea <NUM>). Stated differently, this first maximum point <NUM> indicates that the distal end <NUM> of stimulating assembly <NUM> has reached <NUM>° point <NUM> (<FIG>), while contact <NUM>(<NUM>) is relatively close to <NUM>° point <NUM> (<FIG>).

Similarly, because the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) is a minimum at point <NUM>, point <NUM> indicates that the stimulating assembly <NUM> has been inserted <NUM> degrees (i.e., the contacts <NUM>(<NUM>) and <NUM>(<NUM>) are at the minimum possible distance from one another within cochlea <NUM>). Stated differently, this minimum point <NUM> indicates that the distal end <NUM> of stimulating assembly <NUM> has reached <NUM>° point <NUM> ( <FIG> ), while contact <NUM>(<NUM>) is located within the basal region of cochlea <NUM> substantially close to <NUM>° point <NUM> (i.e., the contacts <NUM>(<NUM>) and <NUM>(<NUM>) are physically close together, but separated by a section of the modiolus <NUM>).

The second maximum <NUM> indicates a location of distal end <NUM> of stimulating assembly <NUM> at which the impedance between contacts <NUM>(<NUM>) and <NUM>(<NUM>) is a second maximum. That is, the stimulating assembly <NUM> has been inserted another <NUM> degrees from the minimum point <NUM> such that the stimulating assembly <NUM> is at an angular insertion depth of <NUM> degrees.

In summary, <FIG> illustrates <FIG> in which the impedance between two selected contacts is monitored and evaluated to determine the angular insertion depth of the stimulating assembly <NUM>. In <FIG>, the impedances between different pairs of contacts may be monitored and simultaneously evaluated to determine the angular insertion depth of stimulating assembly <NUM>. For example, <FIG> is a graph <NUM> illustrating a curve <NUM> of the impedance measured between contact <NUM>(<NUM>) and each of the contacts <NUM>(<NUM>) through <NUM>(<NUM>) during insertion of stimulating assembly <NUM>. The graph <NUM> has a vertical (Y) axis that represents the measured impedance and a horizontal (X) axis that represents contacts <NUM>(<NUM>) through <NUM>(<NUM>).

In contrast to graph <NUM> that illustrates the measured impedance values between two specific contacts over a period of time, graph <NUM> illustrates the impedance values measured between <NUM>(<NUM>) and each of a plurality of contacts <NUM>(<NUM>) through <NUM>(<NUM>) at a particular instant while the stimulating assembly <NUM> is at a specific location. The impedance curve <NUM> may be generated by sequentially delivering bipolar stimulation between stimulating contact <NUM>(<NUM>) and each of the return contacts <NUM>(<NUM>)-<NUM>(<NUM>), and measuring the impedance at each contact (i.e., sequentially changing the return contact for the bipolar stimulation measuring the impedance between the present return contact and the stimulating contact).

In the example of <FIG>, contact <NUM>(<NUM>) is located near the cochlea opening <NUM>. Maximum impedance, shown by point <NUM>, is measured at contact <NUM>(<NUM>). This maximum at contact <NUM>(<NUM>) indicates that the impedance measured between stimulating contact <NUM>(<NUM>) and <NUM>(<NUM>) is greater than the impedance measured between stimulating contact <NUM>(<NUM>) and each of the other return contacts <NUM>(<NUM>)-<NUM>(<NUM>) and <NUM>(<NUM>)-<NUM>(<NUM>). Therefore, at the instant location of stimulating assembly <NUM>, contact <NUM>(<NUM>) is farthest away from stimulating contact <NUM>(<NUM>). Additionally, minimum impedance, shown by point <NUM>, is measured at contact <NUM>(<NUM>). This minimum at contact <NUM>(<NUM>) indicates that the impedance measured between stimulating contact <NUM>(<NUM>) and <NUM>(<NUM>) is less than the impedance measured between stimulating contact <NUM>(<NUM>) and each of the other return contacts <NUM>(<NUM>)-<NUM>(<NUM>) and <NUM>(<NUM>)-<NUM>(<NUM>). Therefore, at the instant location of stimulating assembly <NUM>, contact <NUM>(<NUM>) is closest to stimulating contact <NUM>(<NUM>).

The measured impedance values and the corresponding relative proximities between the stimulating contact <NUM>(<NUM>) and the various return contacts can be utilized to determine the current angular insertion depth of the stimulating assembly <NUM>. For example, the locations of the maximum and minimum shown in <FIG> indicate that the stimulating assembly <NUM> has an angular insertion depth of approximately <NUM> degrees (i.e., distal end <NUM> has reached <NUM>° point <NUM>).

In accordance with <FIG>, <FIG>, and <FIG>, feedback may be generated that indicates to a surgeon or other user the real-time angular insertion depth of a stimulating assembly. For example, plots or graphs, such as those shown in <FIG> and <FIG>, may be generated and displayed to a surgeon. The surgeon could use the plots to determine the current angular insertion depth of the stimulating assembly. It is to be appreciated that the plots shown in <FIG> and <FIG> are merely illustrative and that other plots may be used.

Feedback in the form of a numerical/text display of the determined angular insertion depth may be provided to the surgeon. Audible, tactile, etc. feedback could be provided to a surgeon to indicate the real-time angular insertion depth of the stimulating assembly. For example, an audible beep or tone could be generated as the stimulating assembly reaches predetermined reference points (e.g., angular insertion depths of <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> degrees). The tones may change to indicate the current angular insertion depth (e.g., one beep at the first reference point, two beeps at the second reference point, and so on).

A two-dimensional (<NUM>-D) or three-dimensional (<NUM>-D) image of a cochlea may be displayed at a display screen. A corresponding <NUM>-D or <NUM>-D image of a stimulating assembly may also be displayed at the display screen. As a stimulating assembly is inserted into a recipient's cochlea, the location of the stimulating assembly shown on display screen may be corresponding updated so that the surgeon can visualize the real-time location of the stimulating assembly in the cochlea.

<FIG>, <FIG>, and <FIG> have also been described with reference to measurement of impedance between two or more intra-cochlear contacts of only a single (i.e., one) implanted stimulating assembly and the relative evaluation of the measured impedances to determine the angular insertion depth of that stimulating assembly. It is to be appreciated that embodiments presented herein may use other relative electrical measurements (e.g., voltage) in a similar manner as described above to determine the real-time angular insertion depth of a stimulating assembly.

In summary, <FIG>, <FIG>, and <FIG> illustrate techniques for determining the real-time angular insertion depth of the stimulating assembly. These techniques generate feedback to a surgeon that enables the surgeon to precisely place the stimulating assembly at a selected implanted position. The techniques may facilitate improved hearing performance and increase the preservation of residual hearing. These techniques also eliminate the need for pre or postoperative imaging and the need to use stimulating assemblies having different lengths for different recipients (e.g., conductive contact) configured to detect an impedance change that indicates the distal end <NUM> is adjacent to, or is in contact with, the wall of the cochlea <NUM> located at the distal end <NUM> of the basal region <NUM>. In another embodiment, the sensor <NUM> is a pressure sensor configured to detect when the distal end <NUM> contacts the wall of the cochlea <NUM> located at the distal end <NUM> of the basal region <NUM>. It is to be appreciated that the use of a separate sensor is merely illustrative. It is also to be appreciated that reference to the use of an impedance or pressure sensor is also illustrative and that other sensors may be used in alternative embodiments to detect when the distal end <NUM> of the stimulating assembly <NUM> reaches the distal end <NUM> of the basal region <NUM>.

When it is determined that the distal end <NUM> of the stimulating assembly <NUM> is positioned at the distal end of the basal region <NUM>, the length of the basal region <NUM> is measured. The length of the basal region <NUM> is measured to be the current/present linear insertion depth of the stimulating assembly <NUM>. As noted above, the stimulating assembly <NUM> is implanted in a substantially straight configuration and remains substantially straight until reaching the first turn <NUM> of the cochlea <NUM>. As such, the linear insertion depth of the stimulating assembly <NUM> (i.e., how far the stimulating assembly is inserted past the cochlea opening <NUM>) when the distal end <NUM> of the stimulating assembly <NUM> is positioned at the distal end of the basal region <NUM> corresponds to the length of the basal region.

In one embodiment, the linear insertion depth of the stimulating assembly <NUM> is calculated by determining the last contact <NUM> to enter the cochlea <NUM> through cochlea opening <NUM>. As noted above, the contacts <NUM> experience a significant impedance change after entering into the cochlea (e.g., due to immersion in the conductive perilymph). As such, the system can monitor the impedance at the contacts <NUM> and determine which contacts are inside the cochlea <NUM> and which contacts are outside of the cochlea. With pre-determined knowledge of the physical configuration of the stimulating assembly <NUM> (e.g., contact spacing, distance measurements between different portions of the stimulating assembly, etc.), the distance between the distal end <NUM> and the last contact to enter the cochlea <NUM> can be calculated as the linear insertion depth and thus the length of the basal region <NUM>.

It is to be appreciated that the above described method for calculating the insertion depth is illustrative and that other methods are possible. For example, in certain arrangements the stimulating assembly <NUM> includes markings (e.g., visual, tactile, etc.) that indicate a distance from the marking to the distal end <NUM>. In certain embodiments, these markings can be used to calculate the linear insertion depth of the stimulating assembly <NUM> when the distal end <NUM> of the stimulating assembly <NUM> is positioned at the distal end <NUM> of the basal region <NUM>.

The length of the basal region is referred to herein as being intra-operative measured as it is based on intra-operative operations. These operations produce an accurate measurement that is specific to the recipient's particular cochlea.

Returning to the example of <FIG>, at <NUM> the size of the cochlea is calculated from the measured length <NUM> of the basal region <NUM>. In particular, it has been shown that the length <NUM> of a recipient's basal region <NUM> is largely correlated to the largest distance <NUM> from the cochlea opening <NUM> to the lateral wall <NUM> of the cochlea <NUM>. In turn, the largest distance <NUM> from the cochlea opening <NUM> to the lateral wall <NUM> of the cochlea <NUM> can be used to calculate the size of the cochlea <NUM>.

As used herein, the calculation of the size of cochlea <NUM> may refer to a determination of all or one or more specific dimensions of the cochlea <NUM>. In one specific example, the determination of the size of the cochlea <NUM> refers to a determination of the linear length of the lateral wall <NUM> and/or the linear length of the modiolar wall <NUM> (<FIG> ) to reach a selected angular insertion depth. For example, the linear/path length (L) of the lateral wall <NUM> of the cochlea <NUM> to reach a selected angular insertion depth (θ ) may be given as shown below in Equation <NUM>: <MAT> where A is the largest distance <NUM> from the cochlea opening <NUM> to the lateral wall <NUM> of the cochlea <NUM>.

Assuming a lateral insertion (i.e., an insertion where the stimulating assembly <NUM> follows the lateral wall <NUM> of the cochlea <NUM>), the linear insertion depth of stimulating assembly <NUM> to reach the selected angular insertion depth (θ) is equal to the path length (L) calculated in Equation <NUM>, above. In a perimodiolar insertion (i.e., an insertion where the stimulating assembly <NUM> generally follows the modiolar wall <NUM>) or a mid-scala insertion (i.e., an where the stimulating assembly <NUM> is approximately midway between the lateral and modiolar walls), predetermined offsets from the path length (L) calculated in Equation <NUM> may be used to calculate the proper perimodiolar or mid-scala insertion depths. In alternative embodiments, additional equations may be utilized to directly calculate the perimodiolar or mid-scala insertion depths.

Feedback may be generated to the surgeon or other user that indicates the linear insertion depth of stimulating assembly <NUM> needed to reach a selected angular insertion depth. For example, feedback in the form of a numerical/text display of the determined linear insertion depth may be provided to the surgeon. In accordance with certain embodiments, the stimulating assembly <NUM> may include visual or tactile markers indicating different linear insertion depths (e.g., one marker every <NUM> mms). A surgeon could use these markers to insert the stimulating assembly <NUM> to the selected linear depth.

After measurement of the size of the recipient's cochlea, a surgeon may enter a selected angular insertion depth into a computing device executing the techniques of <FIG>. The computing device may then provide the surgeon with the linear insertion depth needed to position the stimulating assembly at the selected angular insertion depth. For example, a surgeon could enter an indication that the selected angular insertion depth is <NUM> degrees. The computing device could use the cochlea size measurement to determine that the proper linear insertion depth is <NUM>. The computing device could then inform the surgeon of the calculated linear insertion depth (e.g., output the text: "Insert to <NUM>").

<FIG> shows an improvement over conventional methods that require pre-operative imaging to manually estimate the largest distance <NUM> from the cochlea opening <NUM> to the lateral wall <NUM> of the cochlea <NUM>. Such estimates, although performed by trained technicians, may be subject to significant variability (e.g., different technicians may use different reference points, etc.). An incorrect pre-operative estimate may result in a failure to achieve a correct angular insertion depth.

<FIG> is a block diagram of an arrangement for implementation of the intra-operative angular insertion depth setting techniques. For ease of reference, <FIG> will be described with reference to the implantation of implantable component <NUM> of <FIG> into a recipient <NUM>.

In the example of <FIG>, the angular insertion depth setting functionality is implemented as part of computing device <NUM>. The computing device <NUM> comprises a plurality of interfaces/ports <NUM>(<NUM>)-<NUM>(N), a memory <NUM>, a processor <NUM>, a user interface <NUM>, a display device (e.g., screen) <NUM>, and an audio device (e.g., speaker) <NUM>. The memory <NUM> comprises measurement logic <NUM> and evaluation logic <NUM>.

The interfaces <NUM>(<NUM>)-<NUM>(N) may comprise, for example, any combination of network ports (e.g., Ethernet ports), wireless network interfaces, Universal Serial Bus (USB) ports, Institute of Electrical and Electronics Engineers (IEEE) <NUM> interfaces, PS/<NUM> ports, etc. In the example of <FIG>, interface <NUM>(<NUM>) is connected to an external coil <NUM> and/or an external device (not shown) in communication with the external coil. Interface <NUM>(<NUM>) may be configured to communicate with the external coil <NUM> (or other device) via a wired or wireless connection (e.g., telemetry, Bluetooth, etc.). The external <NUM> may be part of an external component of a cochlear implant.

Memory <NUM> may comprise read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical/tangible memory storage devices. The processor <NUM> is, for example, a microprocessor or microcontroller that executes instructions for the measurement logic <NUM> and evaluation logic <NUM>. Thus, in general, the memory <NUM> may comprise one or more tangible (non-transitory) computer readable storage media (e.g., a memory device) encoded with software comprising computer executable instructions and when the software is executed (by processor <NUM>) it is operable to perform the operations described herein. More specifically, in one embodiment, the measurement logic <NUM> may be executed by the processor <NUM> to generate signals/commands that cause stimulator unit <NUM> to: (<NUM>) generate bipolar stimulation, and (<NUM>) obtain electrical measurements at one or more contacts. Evaluation logic <NUM> may be executed by the processor <NUM> to evaluate the electrical measurements to determine the relative proximity of different contacts and determine the real-time insertion depth of the stimulating assembly <NUM> and generate appropriate feedback to the surgeon or other user.

In another embodiment, the measurement logic <NUM> may be executed by the processor <NUM> to determine when the distal end <NUM> of stimulating assembly <NUM> is located at the distal end of the basal region of the recipient's cochlea. The evaluation logic <NUM> may be executed by the processor <NUM> to: (<NUM>) calculate the length of the basal region recipient's cochlea, (<NUM>) determine a size of the recipient's cochlea, (<NUM>) determine a linear insertion depth for stimulating assembly <NUM> to achieve a selected angular insertion depth, and (<NUM>) generate appropriate feedback to the surgeon or other user.

The computing device <NUM> may be any of a number of different hardware platforms configured to perform the monitoring techniques presented herein. In one embodiment, the computing device <NUM> is a computer (e.g., laptop computer, desktop computer, etc.) present within the operating theatre. In another embodiment, the computing device <NUM> is an intra-operative remote assistant. In a further embodiment, the computing device <NUM> is an off-the-shelf device, such as a mobile phone or tablet device, to which the measurement logic <NUM> and evaluation logic <NUM> is downloaded as an application or program. In these various embodiments of <FIG> , both control of the measurements and the display/notification of evaluation results occur through the computing device <NUM>.

It is to be appreciated that this software implementation of <FIG> is merely illustrative, and that other implementations are possible. For example, in an alternative arrangement, measurement logic <NUM> and evaluation logic <NUM> may be implemented fully or partially as hardware elements, such as digital logic gates in one or more application-specific integrated circuits (ASICs).

<FIG> illustrates an example in which the monitoring functionality is part of an external computing device. In alternative arrangements, the monitoring functionality may be incorporated, for example, in an external or implantable component of a cochlear implant.

<FIG> is a flowchart of a method <NUM>. Method <NUM> begins at <NUM> where, during insertion of an elongate stimulating assembly comprising a plurality of longitudinally spaced contacts into a recipient's cochlea, one or more electrical measurements are performed. At <NUM>, based on the one or more electrical measurements, an insertion depth for the stimulating assembly is set.

Setting an insertion depth for the distal end of the stimulating assembly comprises determining a real-time angular insertion depth of the distal end of the stimulating assembly within the cochlea. More particularly, one or more bipolar impedance measurements may be performed between a first stimulating contact and one or more other contacts. The one or more bipolar impedance measurements may be evaluated relative to one another to determine physical proximity between the first stimulating contact and the one or more other contacts. The real-time angular insertion depth may be determined based on the physical proximity between the first stimulating contact and the one or more other contacts.

Setting an insertion depth for the distal end of the stimulating assembly comprises determining a linear insertion depth of the stimulating assembly that corresponds to a selected angular insertion depth of the stimulating assembly. More particularly, at least one electrical measurement is performed to measure a length of a basal region of the cochlea. Based on the measured length of the basal region, a size of the cochlea is calculated and the calculated size of the cochlea is used to determine the linear insertion depth of the stimulating assembly to obtain the selected angular insertion depth for the distal end of the stimulating assembly.

The above examples utilize different intra-cochlea impedance and/or voltage measurements to determine, for example, proximity between pairs of stimulating contacts or proximity of one or more stimulating contacts to the basal wall of a recipient's cochlea. These and other intra-cochlea measurements may make use of different frequencies so as to enhance the effectiveness of the measurements.

More specifically, it has been determined that different cochlea structures react differently to different frequencies of stimulation. For example, cochlea tissue (i.e., the cochlea structures) has an impedance which decreases as the frequency is raised to the power of about <NUM> to <NUM>. (i.e., its impedance decreases roughly as the square or cube root of the frequency). In the frequencies of interest to cochlear implants, perilymph is generally resistive (Ohmic) in nature, but tissue walls are capacitive in nature. Therefore, as the frequency of the stimulation increases, the impedance of the "capacitive" cells of the tissue decreases and the overall tissue impedance decreases.

This property of tissue is useful for systems that use impedance and voltage sensing measurements. In particular, impedance measured using high frequency stimulation is lower than impedance measured using low frequency stimulation. This means that the tissue appears more "transparent" to the stimulation (electrical current) at high frequencies, when compared to measurements made at low frequencies. Stated differently, in the case of a constant current stimulator, impedances/voltages measured at the end of short pulse widths (i.e., high frequency stimulation) are lower than impedances/voltages measured at the end of long pulse widths (i.e., low frequency stimulation).

For example, referring to the examples of <FIG>, <FIG>, and <FIG>, the angular insertion depth is monitored using dipoles created between stimulating contacts located near the distal tip of the stimulating assembly and stimulating contacts located near the proximal end of the stimulating assembly. The impedances/voltages measured from the dipoles are used to determine the angle of insertion of the stimulating assembly. In these examples, the stimulation passes through the modiolus of the recipient's cochlea, particularly when the stimulating assembly is inserted a full turn or more. If these measurements are performed at high frequencies (i.e., by measuring at the end of constant current pulses having a short pulse widths/time lengths), the dipole will be more easily sensed by the basal contacts than if low frequencies (i.e., by measuring at the end of constant current pulses having long pulse widths/time lengths) are used. Since it is desirable to sense the dipole with as large a signal as possible, the high frequency measurements would be advantageous.

In other examples, such as in <FIG> and <FIG>, the proximity of one or more stimulating contacts to, for example, a cochlea wall is determined. In these examples, it is desirable for the impedance of the tissue of the cochlea wall to appear as high as possible so that when a selected stimulating contact approaches the wall, the impedance increases substantially. A measurement system in this case would preferably use a low frequency (long pulse width) measurement as this would increase the impedance of the cochlea wall relative to that of the perilymph and, accordingly, accentuate the increase in impedance when the selected stimulating contact is closer to the wall.

Claim 1:
A system, comprising:
a cochlear implant (<NUM>) comprising:
an implantable stimulator unit (<NUM>), and
an elongate stimulating assembly (<NUM>) comprising a plurality of longitudinally spaced contacts (<NUM>) configured to be inserted into a recipient's cochlea (<NUM>); and
a processor (<NUM>),
characterized in that
the processor (<NUM>) is configured to:
during insertion of the stimulating assembly (<NUM>) into the cochlea (<NUM>),
perform one or more electrical measurements to determine a real-time angular position of the distal end (<NUM>) of the stimulating assembly (<NUM>) within the cochlea(<NUM>) based on an impedance-to-proximity relationship or a voltage-to-proximity relationship.