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Funding Information: We want to thank M.Sc. (Tech) Pekka Paavola for photo stacking technique photographing. We also want to thank Ph.D. Jukka Kuva (Geological Survey of Finland, Espoo, Finland) for collaboration with regard to micro-CT imaging. X-ray tomography was supported by the Academy of Finland via RAMI infrastructure project (#293109). Funding Information: This study has been funded by the Tauno Palva Foundation, the Helsinki University Hospital Research Fund and the Academy of Finland Grant 325509. Publisher Copyright: © 2023 Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License, permitting distribution and reproduction in any medium, provided the original work is properly cited. Despite advances in prosthesis materials, operating microscopes and surgical techniques during the last 50 years, long-lasting hearing improvement remains a challenge in ossicular chain reconstruction. Failures in the reconstruction are mainly due to inadequate length or shape of the prosthesis, or defects in the surgical procedure. 3D-printed middle ear prosthesis might offer a solution to individualize treatment and obtain better results. The aim of the study was to study the possibilities and limitations of 3D-printed middle ear prostheses. Design of the 3D-printed prosthesis was inspired by a commercial titanium partial ossicular replacement prosthesis. 3D models of different lengths (1.5–3.0 mm) were created with Solidworks 2019–2021 software. The prostheses were 3D-printed with vat photopolymerization using liquid photopolymer Clear V4. Accuracy and reproducibility of 3D printing were evaluated with micro-CT imaging. The acoustical performance of the prostheses was determined in cadaver temporal bones with laser Doppler vibrometry. In this paper, we present an outline of individualized middle ear prosthesis manufacturing. 3D printing accuracy was excellent when comparing dimensions of the 3D-printed prostheses and their 3D models. Reproducibility of 3D printing was good if the diameter of the prosthesis shaft was 0.6 mm. 3D-printed partial ossicular replacement prostheses were easy to manipulate during surgery even though they were a bit stiffer and less flexible than conventional titanium prostheses. Their acoustical performance was similar to that of a commercial titanium partial ossicular replacement prosthesis. It is possible to 3D print functional individualized middle ear prostheses made of liquid photopolymer with good accuracy and reproducibility. These prostheses are currently suitable for otosurgical training. Further research is needed to explore their usability in a clinical setting. In the future, 3D printing of individualized middle ear prostheses may provide better audiological outcomes for patients.

Objective: The objective of this study was to investigate the localization ability of bilateral cochlear implant (BiCI) users for virtual sound sources produced over a limited loudspeaker arrangement. Design: Ten BiCI users and 10 normal-hearing subjects participated in listening tests in which amplitude- and time-panned virtual sound sources were produced over a limited loudspeaker setup with varying azimuth angles. Three stimuli were utilized: speech, band-passed pink noise between 20 Hz and 1 kHz, and band-passed pink noise between 1 kHz and 8 kHz. The data were collected via a two-alternative forced-choice procedure and used to calculate the minimum audible angle (MAA) of each subject, which was subsequently compared to the results of previous studies in which real sound sources were employed. Result The median MAAs of the amplitude-panned speech, low-frequency pink noise, and high-frequency pink noise stimuli for the BiCI group were calculated to be 20 degrees, 38 degrees, and 12 degrees, respectively. For the time-panned stimuli, the MAAs of the BiCI group for all three stimuli were calculated to be close to the upper limit of the listening test. Conclusions: The computed MAAs of the BiCI group for amplitude-panned speech were marginally larger than BiCI users' previously reported MAAs for real sound sources, whereas their computed MAAs for the time-panned stimuli were significantly larger. Subsequent statistical analysis indicated a statistically significant difference in the performances of the BiCI group in localizing the amplitude-panned sources and the time-panned sources. It follows that time-panning over limited loudspeaker arrangements may not be a useful clinical tool, whereas amplitude-panning utilizing such a setup may be further explored as such. Additionally, a comparison with the patient demographics indicated correlations between the results and the patients' age at time of diagnoses and the time passed between date of diagnosis and their implant surgeries.

Failure in the structural maintenance of the hair cell stereocilia bundle and ribbon synapse causes hearing loss. Here, we have studied how ER stress elicits hair cell pathology, using mouse models with inactivation of Manf (mesencephalic astrocytederived neurotrophic factor), encoding an ER-homeostasispromoting protein. From hearing onset, Manf deficiency caused disarray of the outer hair cell stereocilia bundle and reduced cochlear sound amplification capability throughout the tonotopic axis. In high-frequency outer hair cells, the pathology ended in molecular changes in the stereocilia taper region and in strong stereocilia fusion. In high-frequency inner hair cells, Manf deficiency degraded ribbon synapses. The altered phenotype strongly depended on the mouse genetic background. Altogether, the failure in the ER homeostasis maintenance induced early-onset stereociliopathy and synaptopathy and accelerated the effect of genetic causes driving age-related hearing loss. Correspondingly, MANF mutation in a human patient induced severe sensorineural hearing loss from a young age onward. Thus, we present MANF as a novel protein and ER stress as a mechanism that regulate auditory hair cell maintenance in both mice and humans.

Publisher Copyright: © 2021, The Author(s). Background: Gelsolin amyloidosis (AGel amyloidosis) is a hereditary form of systemic amyloidosis featuring ophthalmological, neurological and cutaneous symptoms. Previous studies based mainly on patients’ self-reporting have indicated that hearing impairment might also be related to the disease, considering the progressive cranial neuropathy characteristic for AGel amyloidosis. In order to deepen the knowledge of possible AGel amyloidosis-related hearing problems, a clinical study consisting of the Speech, Spatial and Qualities of Hearing Scale (SSQ) questionnaire, clinical examination, automated pure-tone audiometry and a speech-in-noise test was designed. Results: Of the total 46 patients included in the study, eighteen (39%) had self-reported hearing loss. The mean scores in the SSQ were 8.2, 8.3 and 8.6 for the Speech, Spatial and Qualities subscales, respectively. In audiometry, the mean pure tone average (PTA) was 17.1 (SD 12.2) and 17.1 (SD 12.3) dB HL for the right and left ears, respectively, with no difference to gender- and age-matched, otologically normal reference values. The average speech reception threshold in noise (SRT) was − 8.2 (SD 1.5) and − 8.0 (SD 1.7) dB SNR for the right and left ears, respectively, which did not differ from a control group with a comparable range in PTA thresholds. Conclusion: Although a significant proportion of AGel amyloidosis patients experience subjective difficulties in hearing there seems to be no peripheral or central hearing impairment at least in patients up to the age of 60 years.

Sisäkorvaistutehoito sopii sekä synnynnäisen vaikea-asteisen kuulovian että etenevän kuulovian hoidoksi. Istutteella voidaan saavuttaa hyvä puheentunnistuskyky vaikea-asteisessa kuulonalenemassa. Hoito on osoitettu kustannusvaikuttavaksi kaikissa ikäryhmissä. Nuorimmat potilaat ovat olleet 8–10 kuukauden ja vanhimmat yli 80 vuoden ikäisiä. Vanhusväestössä on paljon vaikea-asteisesta kuuloviasta kärsiviä potilaita, jotka hyötyisivät istutehoidosta. Heitä tulisi ohjata nykyistä aktiivisemmin leikkausarvioon.

Väestön ikääntyessä kuulonalenemien esiintyvyys ja tarve vaikuttavaan kuulonkuntoutukseen kasvavat. Hyvän yleiskäsityksen kuulosta antavat äänieriön hiljaisuudessa tehtävät perustutkimukset, äänesaudiometria ja puheaudiometria. Ne eivät kuitenkaan välttämättä kuvasta kuulonaleneman aiheuttamaa haittaa hälyisissä tilanteissa. Uuden suomenkielisen hälylausetestin avulla voidaan tutkia aiempaa paremmin aikuisten kuntoutuspotilaiden kuulonvaraista selviämistä arjessa. Suomenkielisen lasten hälypuhetestin validointi on meneillään.

English summary

The effect of the sound incidence angle on loudness was investigated for fifteen listeners who matched the loudness of sounds coming from five different incidence angles in the horizontal plane to that of the same sound with frontal incidence. The stimuli were presented via binaural synthesis by using head-related transfer functions measured for an artificial head. The results, which exhibited marked individual differences, show that loudness depends on the direction from which a sound reaches the listener. The average results suggest a relatively simple rule for combining the two signals at the ears of an artificial head for binaural loudness predictions.

Udgivelsesdato: Maj 2006 The effect of sound incidence angle on loudness was investigated using real sound sources positioned in an anechoic chamber. Eight normal-hearing listeners produced loudness matches between a frontal reference location and seven sources placed at other directions, both in the horizontal and median planes. Matches were obtained via a two-interval, adaptive forced-choice (2AFC) procedure for three center frequencies (0.4, 1 and 5 kHz) and two overall levels (45 and 65 dB SPL). The results showed that loudness is not constant over sound incidence angles, with directional sensitivity varying over a range of up to 10 dB, exhibiting considerable frequency dependence, but only minor effects of overall level. The pattern of results varied substantially between subjects, but was largely accounted for by variations in individual head-related transfer functions. Modeling of binaural loudness based on the at-ear signals favored a sound-power summation model, according to which the maximum binaural gain is only 3dB, over competing models based on larger gains, or on the summation of monaural loudness indices.

In an earlier study (1), the loudness of directional sounds presented in an anechoic chamber was investigated by having listeners make loudness matches to a frontal reference source. The listeners' individual head-related transfer functions (HRTFs) were also measured, in an attempt to model the binaural loudness summation of the at-ear signals. Even though the effects of HRTFs were taken into account, considerable individual differences in the binaural summation of loudness remained. In order to create conditions in which the directional at-ear changes were identical for all participants, the present experiment employed 'generic' HRTFs to create directional sounds via binaural synthesis. When inspecting the results of the listening tests, however, large individual differences were still evident, as in the earlier study. The generality of this finding was further corroborated by running an independent, inexperienced sample of ten participants exclusively being exposed to the present generic HRTFs. Despite the individual differences, the average results suggest a relatively simple rule for combining the binaural input when carrying out acoustical measurements using an artificial head. That is particularly useful when attempting to predict loudness for dichotic listening situations, as they typically result from real sound sources positioned in space.

Loudness, the perceived intensity of sound, is a fundamental attribute in psychoacoustics. An immense body of literature on loudness has been accumulated, and based on the reported findings, models for predicting loudness from monophonic, acoustical measurements of sound pressure have been developed. The research and modeling of loudness have mainly been concerned with the temporal and spectral aspects of sounds, while the spatial aspects have mostly been overlooked.This PhD thesis investigates the spatial aspects of loudness perception, namely, how does the direction from which a sound reaches the listener affect its perceived loudness. The results obtained in a series of listening experiments show that loudness depends considerably on direction for a variety of sound stimuli. Furthermore,these directional dependencies could be largely accounted for by determining binaural at-ear exposures, individually for each listener. The results of the thesis were used for developing a binaural loudness model. This model is applicable to acoustical measurements made with artificial heads, commonly used in a variety of applications, ranging from the assessment of noise annoyance to evaluating product soundquality and the fidelity of multichannel sound reproduction systems.

Even though there is a vast body of literature on spatial hearing, little is known on how the location of a sound source affects its loudness. The pertinent research on head-related transfer functions(HRTFs) primarily deals with issues of localization and spatial discriminability. The literature on binaural loudness summation, on the other hand, focuses on a highly artificial paradigm according to which unnatural combinations of sound pressure levels(such as monotic-diotic comparisons) are presented to listeners via headphones. In order to reconcile these two approaches, we recently started a series of experiments determining the effect of sound incidence angle on loudness[1,2,3,4]. The basic experiment to be reported on here was conducted in an anechoic chamber, in which loudspeakers were mounted to present sounds from a number of directions both in the horizontal, and median planes. The subject’s task was to produce a loudness match to a frontal reference location, and matches were obtained via a two-interval adaptive forced-choice procedure. Narrow-band noises were used, in order to investigate the frequency-specific effects of direction on loudness. Furthermore, individual HRTFs were measured for each incidence angle, in order to relate the changes in actual at-ear exposure to the observed changes in loudness as a function of sound incidence. Combining the listening-test data with the physical measurements, an attempt was made to model the binaural summation underlying the directional loudness matches.

The effect of incidence angle on loudness was investigated for wideband and reverberant sounds. In an adaptive procedure, five listeners matched the loudness of a sound coming from five incidence angles in the horizontal plane to that of the same sound with frontal incidence. The stimuli were presented to the listeners via individual binaural synthesis. The results confirm that loudness depends on sound incidence angle, as it does for narrow-band, anechoic sounds. The directional effects, however, were attenuated with the wideband and reverberant stimuli used in the present investigation.

The effect of sound incidence angle on loudness is investigated in this study using binaural synthesis. Individual head-related transfer functions (HRTFs) and headphone equalization are used to present narrow-band noises from different directions to listeners. Their task is to match the loudness of these stimuli in an adaptive procedure to a reference noise in front of the listeners. The results are compared to an earlier investigation with the same experimental design in a real sound field. Based on the results the role of the individual HRTFs in loudness judgments is inspected, and finally, binaural loudness summation of signals presented to the two ears is examined.

Cochlear implant (CI) enables verbal communication for patients with severeto-profound hearing impairment. With a CI, the hearing sensation is produced by stimulating the cochlear nerve (CN) with an intracochlear electrode array. The desired location of the electrode array is in the scala tympani (ST). The ST is surrounded by structures with poor conductivity. Thus, the current injected into an intracochlear electrode conducts along the ST, leading to a wide spread of the intracochlear electrical field (EF). In addition to the ability to stimulate the CN, CIs are equipped with versatile telemetry measurements. The spread of the intracochlear EF can be measured with the monopolar transimpedance matrix (TIMmp). For this measurement, current is injected into one electrode contact at a time, and the resulting potential difference is measured between every intracochlear electrode and the extracochlear reference electrode. The potential difference is further divided by the stimulating current, resulting in impedance according to Ohm’s law (𝑍 = 𝑈/𝐼). Every intracochlear is sequentially stimulated, resulting in a n × n matrix, where n is the number of electrode contacts in the electrode array. Depending on the implant manufacturer and the model of the electrode array, the number of intracochlear electrode contacts is 12–22. The responsiveness of the CN to electrical stimulation can be measured via the electrically evoked compound action potential (eCAP). The smallest current required to elicit a measurable neural response from the CN is called the eCAP threshold. The extent of neural activation can be estimated with the spread of excitation (SOE) measurement. Inner ear dimensions and the location of the electrode array affect these measurements. Therefore, these measurements may be used to estimate the intracochlear placement and note the successful insertion of the electrode array. Also, these measurements may be utilized in more individualized CI rehabilitation in the future. In Study I, the relationship between the intracochlear EF (TIMmp) and the extent of neural activation (SOE) was investigated. In addition, the effect of the cochlea diameter on these measurements was evaluated. The intraoperative TIMmp and SOE were measured for patients implanted with the Cochlear Nucleus CI522 or CI622 implant with the Slim Straight (SS) electrode array (Cochlear Ltd, Sydney, Australia). The SS electrode array consists of 22 separate electrodes. The measurements were conducted from electrodes 6, 11, and 19 that represent the basal, middle, and apical parts of the electrode array, respectively. The cochlea diameter was measured from the preoperative computed tomography (CT) images. For every measured electrode contact, the widths where the maximum amplitude of TIMmp and SOE halves were determined using an automated algorithm. These 50 % widths of TIMmp and SOE correlated between each other, indicating that intracochlear EF partially determines the extent of neural activation. Also, both of these measurements were inversely correlated with the cochlea diameter, which suggests that in larger cochlea, the electrical stimulation and the resulting neural activation is more local than it is in smaller cochleae. In Study II, the relationship between the intraoperative TIMmp and eCAP threshold was examined. These measurements were recorded intraoperatively from patients implanted with the Cochlear Nucleus CI522 or CI622 implant with the SS electrode array. The measurements were recorded from all 22 intracochlear electrodes to estimate the behavior of the measurements along the entire electrode array. The intracochlear EFs with a high peak were also wide. Further, when an electrode generates an EF with a high peak or a wide spread, the current required to elicit a neural response is lower at the corresponding electrode. These results indicate that the responsiveness of the CN to electrical stimulation is also dependent on the physical environment of the electrode array. In Study III, the effect of the inner ear dimensions on the responsiveness of the CN to electrical stimulation was evaluated. The patients were younger than two years and implanted with the Cochlear Nucleus CI522 or CI622 implant with the SS electrode array. The eCAP thresholds were measured intraoperatively from all 22 electrode contacts of the electrode array. The CN exits the cochlea through the bony cochlear nerve canal (BCNC) to the internal auditory canal. Therefore, in this study, the key inner ear dimensions were chosen to be the diameters of the cochlea and the BCNC as well as the crosssectional areas of the internal auditory canal and the CN. The anatomical dimensions were measured from preoperative CT and magnetic resonance images. The BCNCs were wider in larger cochleae. Also, thick CNs were found from internal auditory canals with large cross-sectional areas. The current required to elicit a measurable neural response was higher in larger cochleae and BCNC. As the diameters of the cochlea and BCNC correlated, the latter relationship between the eCAP thresholds and BCNC may be explained by the correlation between the cochlea and the eCAP thresholds. In Study IV, the effect of the scala dimensions and the distance between the scalar medial wall and the electrode (electrode-to-medial wall distance, EMWD) on the intracochlear EF measurements were assessed. Also, the usefulness of the electrical measurements for estimating the intracochlear electrode contact location was investigated. The experiment was conducted using six temporal bones, which were implanted sequentially with the Cochlear SS, Contour Advance and Slim Modiolar electrode arrays. After the implantation, the TIMmp and bipolar TIM (TIMbp) measurements and imaging with a cone-beam CT (CBCT) were conducted simultaneously. From the CBCT images, the scalar cross-sectional areas (SA) at the location of each electrode and EMWD were measured. In those cochleae with larger SA, the EF peak values were lower. The EFs generated by electrodes located in the vicinity of the scalar medial wall decayed with a steeper slope than did the EFs generated in more lateral positions. This finding indicates that when the electrode is located more proximally to the medial scalar wall, the electrical stimulation may become more focused. TIMbp correlated with both the SA and the EMWD. As the SA generally narrows from the basal to the apical direction and each electrode array has a typical intracochlear position, these measurements may be useful when assessing the successful implantation of the electrode array without imaging. These results suggest that the excitability of the CN depends on the dimensions and the physical properties, such as the dimensions and the conductivity, of the cochlea. Also, the EF measurements may be used to estimate the intracochlear location of the electrode array. In the future, the EF measurements may reduce the need for intra- and postoperative imaging. Sisäkorvaistute (SI) mahdollistaa vaikeasta kuulonalenemasta kärsivälle potilaalle kuulonvaraisen kommunikaation. Kuuloaistimus tuotetaan ärsyttämällä kuulohermoa suoraan elektrodiketjulla, jonka tavoiteltu sijainti on scala tympani (ST). Sitä ympäröivien rakenteiden heikon sähkönjohtavuuden vuoksi elektrodikontaktille syötetty virta johtuu ensisijaisesti ST:a pitkin, johtaen laajaan intrakokleariseen sähkökenttään. Stimuloivien ominaisuuksien lisäksi SI:ssa on valmiudet monipuolisiin sähköfysiologisiin mittauksiin. Intrakoklearista sähkökenttää voidaan mitata esimerkiksi monopolaarisella transimpedanssimatriisilla (TIMmp). Mittauksessa sähkövirtaa johdetaan yhdelle elektrodikontaktille kerrallaan, ja jännite-ero jokaisen intrakokleaarisen elektrodin ja ekstrakokleaarisen referenssielektrodin välillä mitataan. Mitattu jännite-ero jaetaan stimulaatioon käytetyllä sähkövirralla, jolloin Ohmin lain mukaisesti saadaan yksiköksi impedanssi (Z= U/I). Kun mittauksessa stimuloidaan jokaista intrakokleaarista elektrodia yksi kerrallaan, on lopputuloksena n × n matriisi, jossa n on elektrodikontaktien määrä elektrodiketjussa. Istutevalmistajasta ja -mallista riippuen elektrodikontaktien lukumäärä on 12–22. Fysiologisia mittauksia ovat kuulohermon ärtyvyyden herkkyyttä arvioiva kuulohermovastemittaus (electrically evoked compound action potential, eCAP) ja ärtyvyyden laajuutta mittaava hermoaktivaation laajuustutkimus (spread of excitation, SOE). Pienintä virtaa, joka tuottaa mitattavan vasteen kuulohermosta kutsutaan hermovastekynnykseksi (eCAP-kynnys). Elektrodin intrakokleaarinen sijainti ja sisäkorvan rakenteiden koko vaikuttavat edellä mainittuihin mittauksiin. Sähköfysiologisia mittauksia voidaan mahdollisesti tulevaisuudessa hyödyntää yksilöllisen istutekuntoutuksen suunnittelussa sekä elektrodin sijainnin ja onnistuneen implantoinnin arvioinnissa. Ensimmäisessä osatyössä tutkittiin intrakokleaarisen sähkökentän (TIMmp) ja kuulohermon aktivaation laajuuden (SOE) välistä yhteyttä. Lisäksi arvioitiin koklean koon vaikutusta kyseisiin mittauksiin. Mittaukset tehtiin Slim Straight (SS) -elektrodiketjun sisältävän Cochlear Nucleus CI522- tai CI622 -istutteen (Cochlear Ltd, Sydney, Australia) saaneille potilaille SI-leikkauksen yhteydessä. Kyseisessä elektrodiketjussa on 22 elektrodia ja mittaukset tehtiin elektrodeilta 6, 11 ja 19, jotka edustavat elektrodiketjun tyvi-, keski- ja kärkiosia. Koklean koko mitattiin leikkausta edeltäneestä tietokonetomografiakuvasta (TT). Jokaiselle mitatulle elektrodikontaktille määritettiin automatisoidulla algoritmilla TIMmp- ja SOE-leveydet, joissa näiden mittausten huippuarvot puolittuvat. Nämä TIMmp- ja SOE-puoliintumisleveydet olivat keskenään verrannollisia viitaten, että intrakokleaarisen sähkökentän laajuus määrittää osittain kuulohermon aktivaation laajuuden. Molemmat puoliintumisleveydet olivat kapeampia suuremmissa kokleoissa, mikä voi tarkoittaa paikallisempaa intrakokleaarista sähkökenttää ja kuulohermon aktivaatiota. Toisessa osatyössä tutkittiin leikkauksen aikana mitatun intrakokleaaristen sähkökentän huippuarvon ja leveyden yhteyttä hermovastekynnykseen. TIMmp ja hermovastekynnykset mitattiin leikkauksen aikana potilailta, jotka saivat Cochlear Nucleus CI522- tai CI622 -istutteen, joka sisältää SS elektrodiketjun. Mittaukset tehtiin kaikilta 22 elektrodikontakteilta. Intrakokleaariset sähkökentät, joilla oli korkeat huippuarvot, olivat myös leveitä. Kun stimuloiva elektrodi tuottaa korkeahuippuisen tai leveän sähkökentän, kyseisellä elektrodikontaktilla tarvittava virta kuulohermovasteen saamiseksi on pieni. Löydös osoittaa, että kuulohermon ärtyvyyteen sähköiselle stimulaatiolle vaikuttaa sen kunnon lisäksi myös elektrodiketjun fyysinen ympäristö. Kolmannessa osatyössä tarkasteltiin keskeisten sisäkorvan rakenteiden kokoja ja niiden vaikutusta kuulohermon ärtyvyyteen. Hermovastekynnykset mitattiin SI-leikkauksen aikana alle 2-vuotialta lapsilta, joille asetettiin Cochlear Nucleus CI522- tai CI622 -istute, joka sisältää SS-elektrodiketjun. Kuulohermon kulkee ulos kokleasta koklean proksimaaliosassa sijaitsevan modioluksen luisen kuulohermon kanavan (MLK) kautta kuulohermon kanavaan. Siksi tutkimuksessa keskeisiksi arvioidut anatomiset mitat olivat koklean ja MLK:n halkaisijat sekä kuulohermon kanavan että kuulohermon poikkipinta-alat. Anatomiset mittaukset tehtiin leikkausta edeltäneistä TT- ja magneettikuvista. Suuremmissa kokleoissa oli leveämmät MLK:t. Lisäksi kuulohermot olivat paksumpia poikkipinta-alaltaan suuremmissa kuulohermon kanavissa. Suurista kokleoista ja kokleoista, joissa oli leveä MLK, vaadittiin enemmän virtaa mitattavan hermovasteen tuottamiseksi. Koska koklean ja MLK:n halkaisijat olivat verrannollisia keskenään, jälkimmäinen löydös eCAP kynnyksen ja MLK:n välillä selittynee koklean ja hermovastekynnysten välisellä yhteydellä. Neljännessä osatyössä tutkittiin koklean kanavan poikkipinta-alan sekä elektrodin ja scala tympanin mediaaliseinän välisen etäisyyden vaikutusta intrakokleariseen sähkökenttään. Lisäksi arviointiin kyseisten mittausten käyttökelpoisuutta elektrodin intrakokleaarisen sijainnin arvioinnissa. Kuusi kadaaveritemporaaliluuta implantoitiin Cochlear SS, Contour Advance ja Slim Modiolar elektrodiketjuilla. Implantoiduille kadaaveritemporaaliluille tehtiin samanaikaiset kartiokeila-TT-kuvaus sekä TIMmp ja bipolaari-TIM (TIMbp) -mittaukset. Kartiokeila-TT-kuvista mitattiin scalan kanavan poikkipinta-ala jokaisen elektrodin kohdalla. Lisäksi kuvista mitattiin jokaisen elektrodin etäisyys scalan mediaaliseinämästä. Kokleoissa, joiden kanavien poikkipinta-alat olivat suurempia, sähkökenttään huippuarvot TIMmp:lla arvioituna olivat pienempiä. Sähkökenttään heikkenemisnopeus oli puolestaan riippuvainen elektrodin ja scalan mediaaliseinämän välisestä etäisyydestä. Kun elektrodi oli lähempänä scalan mediaaliseinämää, oli sähkökentän heikkenemisen kulmakerroin suurempi. Löydös viittaa siihen, että elektrodin ollessa scalan mediaaliseinämän läheisyydessä, sähköinen stimulaatio voi olla paikallisempaa kuin lateraalisimmissa sijainneissa. TIMbp korreloi sekä koklean poikkipinta-alan että elektrodin ja scalan mediaaliseinämän välisen etäisyyden kanssa. Koska koklean poikkipinta-ala kapenee tyvestä kärkeä kohti ja jokaisella elektrodiketjulla on tyypillinen asento koklean sisällä, voidaan kyseisiä mittauksia mahdollisesti käyttää elektrodiketjun onnistuneen implantoinnin arvioinnissa ilman kuvantamistutkimuksia. Tulosten perusteella kuulohermon ärtyvyyteen ja ärtyvyyden laajuuteen vaikuttavat koklean fyysiset ominaisuudet, kuten koko ja sähkönjohtavuuteen vaikuttavat seikat. SI:n sähköisiä mittauksia voidaan käyttää hyödyksi elektrodiketjun sijainnin arvioinnissa, joka voi vähentää leikkauksen aikaisen tai sen jälkeisen kuvantamisen tarvetta tulevaisuudessa.