ARTFit-A Quick and Reliable Tool for Performing Initial Fittings in Users of MED-EL Cochlear Implants.

This study assessed the safety and performance of ARTFit, a new tool embedded in MAESTRO, the cochlear implant (CI) system software by MED-EL GmbH (Innsbruck, Austria). ARTFit automatically measures thresholds of the electrically evoked compound action potential (ECAP) to produce initial 'maps' (ECAPMAPs), i.e., configuration settings of the audio processor that the audiologist switches to live mode and adjusts for comfortable loudness (LiveECAPMAPs). Twenty-three adult and ten pediatric users of MED-EL CIs participated. The LiveECAPMAPs were compared to behavioral maps (LiveBurstMAPs) and to the participants' everyday clinical maps (ClinMAPs). Four evaluation measures were considered: average deviations of the maximum comfortable loudness (MCL) levels of the LiveECAPMAPs and the LiveBurstMAPs from the MCLs of the ClinMAPs; correlations between the MCLs of the LiveECAPMAPs (MCLecap) and the LiveBurstMAPs (MCLburst) with the MCLs of the ClinMAPs (MCLclin); fitting durations; and speech reception thresholds (SRTs). All evaluation measures were analyzed separately in the adult and pediatric subgroups. For all evaluation measures, the deviations of the LiveECAPMAPs from the ClinMAPs were not larger than those of the LiveBurstMAPs from the ClinMAPs. The Pearson correlation between the MCLecap and the MCLclin across all channels was r2 = 0.732 (p < 0.001) in the adult and r2 = 0.616 (p < 0.001) in the pediatric subgroups. The mean fitting duration in minutes for the LiveECAPMAPs was significantly shorter than for that of the LiveBurstMAPs in both subgroups: adults took 5.70 (range 1.90-11.98) vs. 9.27 (6.83-14.72) min; children took 3.03 (1.97-4.22) vs. 7.35 (3.95-12.77). SRTs measured with the LiveECAPMAPs were non-inferior to those measured with the ClinMAPs and not statistically different to the SRTs measured with the LiveBurstMAPs. ARTFit is a safe, quick, and reliable tool for audiologists to produce ECAP-based initial fitting maps in adults and young children who are not able to provide subjective feedback.

Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting.

Cochlear Implants (CIs) are medical implantable devices that can restore the sense of hearing in people with profound hearing loss. Clinical trials assessing speech intelligibility in CI users have found large intersubject variability. One possibility to explain the variability is the individual differences in the interface created between electrodes of the CI and the auditory nerve. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose in mind, we developed a parametric model that can be adapted to each CI user based on landmarks from individual cone beam computed tomography (CBCT) scans of the cochlea before and after implantation. The conductivity values of each cochlea compartment as well as the weighting factors of different grounding modes have also been parameterized. Simulations were performed modeling the cochlea and electrode positions of 12 CI users. Three models were compared with different levels of detail: a homogeneous model (HM), a non-patient-specific model (NPSM), and a patient-specific model (PSM). The model simulations were compared with voltage distribution measurements obtained from the backward telemetry of the 12 CI users. Results show that the PSM produces the lowest error when predicting individual voltage distributions. Given a patient-specific geometry and electrode positions, we show an example on how to optimize the parameters of the model and how to couple it to an auditory nerve model. The model here presented may help to understand speech performance variability and support the development of new sound coding strategies for CIs.

Intratympanic Iodine Contrast Injection Diffuses Across the Round Window Membrane Allowing for Perilymphatic CT Volume Acquisition Imaging.

HYPOTHESIS: Whether the round window membrane (RWM) is permeable to iodine-based contrast agents (IBCA) is unknown; therefore, our goal was to determine if IBCAs could diffuse through the RWM using CT volume acquisition imaging. INTRODUCTION: Imaging of hydrops in the living human ear has attracted recent interest. Intratympanic (IT) injection has shown gadolinium's ability to diffuse through the RWM, enhancing the perilymphatic space. METHODS: Four unfixed human cadaver temporal bones underwent intratympanic IBCA injection using three sequentially studied methods. The first method was direct IT injection. The second method used direct RWM visualization via tympanomeatal flap for IBCA-soaked absorbable gelatin pledget placement. In the third method, the middle ear was filled with contrast after flap elevation. Volume acquisition CT images were obtained immediately postexposure, and at 1-, 6-, and 24-hour intervals. Postprocessing was accomplished using color ramping and subtraction imaging. RESULTS: After the third method, positive RWM and perilymphatic enhancement were observed with endolymph sparing. Gray scale and color ramp multiplanar reconstructions displayed increased signal within the cochlea compared with precontrast imaging. The cochlea was measured for attenuation differences compared with pure water, revealing a preinjection average of -1,103 HU and a postinjection average of 338 HU. Subtraction imaging shows enhancement remaining within the cochlear space, Eustachian tube, middle ear epithelial lining, and mastoid. CONCLUSION: Iohexol iodine contrast is able to diffuse across the RWM. Volume acquisition CT imaging was able to detect perilymphatic enhancement at 0.5-mm slice thickness. The clinical application of IBCA IT injection seems promising but requires further safety studies.

Deeper Cochlear Implant Electrode Insertion Angle Improves Detection of Musical Sound Quality Deterioration Related to Bass Frequency Removal.

BACKGROUND: Cochlear implant (CI) electrode arrays typically do not reach the most apical regions of the cochlea that intrinsically encode low frequencies. This may contribute to diminished implant-mediated musical sound quality perception. The objective of this study was to assess the effect of varying degrees of apical cochlear stimulation (measured by angular insertion depth) on musical sound quality discrimination. HYPOTHESIS: Increased apical cochlear stimulation will improve low-frequency perception and musical sound quality discrimination. METHODS: Standard (31.5 mm, n = 17) and medium (24 mm, n = 8) array Med-EL CI users, and normal hearing (NH) listeners (n = 16) participated. Imaging confirmed angular insertion depth. Participants completed a musical discrimination task in which they listened to a real-world musical stimulus (labeled reference) and provided sound quality ratings to versions of the reference, which included a hidden reference and test stimuli with increasing amounts of low-frequency removal. Scores for each CI users were calculated on the basis of how much their ratings differed from NH listeners for each stimulus version. RESULTS: Medium array and standard users had significantly different insertion depths (389.4 ± 64.5 and 583.9 ± 78.5 degrees, respectively; p <  .001). A significant Pearson's correlation was observed between angular insertion depth and the hidden reference scores (p < 0.05). CONCLUSION: CI users with greater apical stimulation made sound quality discriminations that more closely resembled those of NH controls for stimuli that contained low frequencies (< 200 Hz of information). These findings suggest that increased apical cochlear stimulation improves musical low-frequency perception, which may provide a more satisfactory music listening experience for CI users.

Stimulating on multiple electrodes can improve temporal pitch perception.

OBJECTIVE: The objective of this study was to test if stimulating multiple electrodes can improve temporal pitch ranking performance at low and high stimulation rates. DESIGN: Temporal pitch cues are usually based on modifying the stimulation rate of the implant and thereby provide a continuum of pitches on a single electrode up to approximately 300 Hz. STUDY SAMPLE: Ten cochlear implant subjects were asked to pitch rank stimuli presented with direct electrical stimulation. The pulses were applied on one, three, six, or eleven electrodes. In one of the conditions the current amplitude of each pulse was randomly varied between 0 and 100%. Their frequency ranged from 100 up to 500 pps. RESULTS: Listeners showed the previously reported performance pattern in most conditions with very good performance at the lowest standard rates and deteriorating performance to near chance level at the highest rate tested. Performance with eleven electrodes was significantly better than performance with one electrode at 500 pps. CONCLUSION: Stimulating on multiple electrodes can improve temporal pitch perception.

Perception of polyphony with cochlear implants for 2 and 3 simultaneous pitches.

HYPOTHESIS: It was hypothesized that cochlear implant (CI) subjects would be able to correctly identify 1, 2, and 3 simultaneous pitches through direct electrical stimulation. We further hypothesized that the location on the implant array and the fundamental frequency of the pitches would have an impact on the performance. BACKGROUND: "They gave me back speech but not music" is a sentence commonly heard by CI subjects. One of the reasons is that in music, multiple streams are frequently played at the same time, which is an essential feature of harmony. Current CI speech processors do not allow CI users to perceive such complex polyphonic sounds. METHODS: In the present study, the authors assessed the ability of CI subjects to perceive simultaneous modulation frequencies based on direct electrical stimulation. Ten CI subjects were asked to identify 1, 2, and 3 simultaneous pitches applied on different electrodes using sinusoidal amplitude modulation. All stimuli were loudness balanced before the actual identification task. RESULTS: Subjects were able to identify 1, 2, and 3 simultaneous pitches. The further the distance between the 2 electrodes, the better was the performance in the 2-pitch condition. The distance between the modulation frequencies had a significant effect on the performance in the 2-and 3-pitch condition. CONCLUSION: Subjects are able to identify complex polyphonic stimuli based on the number of active electrodes. The additional polyphonic rate pitch cue improves performance in some conditions.

Experimental assessment of polyphonic tones with cochlear implants.

HYPOTHESIS: We hypothesized that cochlear implant (CI) users are able to discriminate tones consisting of 1 and 2 modulation frequencies when the stimuli are applied through direct electrical stimulation. BACKGROUND: Music perception is a very challenging task for CI users. In music, multiple tones often occur simultaneously, an essential feature of harmony. Proper encoding of simultaneous tones is crucial to musical perception and appreciation. With current implant processing strategies, CI users are severely impaired in the perception of pitch and polyphony. METHODS: The ability of CI users to identify the number of simultaneous tones was assessed. Stimuli were applied with direct electrical stimulation. Stimuli with 1 modulation frequency were applied on a basal, a middle, and an apical electrode to determine if there was an effect of cochlear region. Stimuli with 2 modulation frequencies were applied on combinations of an apical electrode together with a basal or a middle electrode. Additionally, 2 modulations frequencies were presented at the same time on an apical electrode only. RESULTS: Results demonstrate that subjects were generally able to identify the number of modulation frequencies in the presented stimuli. Performance for 1 modulation frequency stimuli was significantly above chance level on all 3 electrodes tested. Performance was best on the apical and the middle electrode, followed by the basal electrode. Subjects were also able to identify 2 modulation frequencies significantly above chance level on all 3 combinations tested. Performance was best on combination apical-basal followed by apical-middle. Performance was worst when 2 modulation frequencies were applied on an apical electrode only, but it was still significantly above chance level. CONCLUSION: If sound processing strategies were to use concurrent modulation frequencies on multiple or single electrodes, then possibly polyphonic tones would be better perceived by CI users yielding better music and language perception.

Perception of pure tones and iterated rippled noise for normal hearing and cochlear implant users.

Cochlear Implant (CI) users typically perform poorly on musical tasks, especially those based on pitch ranking and melody recognition. It was hypothesized that CI users would demonstrate deterioration in performance for a pitch ranking and a melody recognition task presented with iterated rippled noise (IRN) in comparison to pure tones (PT). In Addition, it was hypothesized that normal hearing (NH) listeners would show fewer differences in performance between IRN and PT for these two tasks. In this study, the ability of CI users and NH subjects to rank pitches and to identify melodies created with IRN and PT was assessed in free field in a sound-isolated room. CI subjects scored significantly above chance level with PT stimuli in both tasks. With IRN stimuli their performance was around chance level. NH subjects scored significantly above chance level in both tasks and with all stimuli. NH subjects performed significantly better than CI subjects in both tasks. These results illustrate the difficulties of CI subjects to rank pitches and to identify melodies.

Multislice computed tomography in the diagnosis of superior canal dehiscence: how much error, and how to minimize it?

HYPOTHESIS: Multi-slice computed tomography (MSCT) overestimates the size of superior semicircular canal dehiscences (SSCDs) and also can misinterpret thin bone over the superior semicircular canal as dehiscent. A threshold of the radiodensity of the bone over the superior semicircular canal may exist that could optimize prediction of an actual SSCD. BACKGROUND: The gold standard for diagnosis of SSCD is MSCT, but there is a higher prevalence of SSCD based on MSCT compared with histologic studies. Overestimation of SSCD can lead to inappropriate diagnosis and treatment. METHODS: We correlated radiographic and surgical findings in SSCD to determine if MSCT overestimated the size of SSCD and if a threshold radiodensity could be defined, below which actual dehiscence could best be predicted. Participants were 34 humans with SSCD confirmed at surgery. MSCT scans were acquired axially with 0.5-mm collimation and a small field of view (24 cm). Dehiscence sizes measured from radial reconstructions were compared with measurements made during surgery. RESULTS: There were significant differences between radiographic and actual length and width, indicating that MSCT tends to overestimate the size of SSCD. Receiver operating characteristic analysis found a threshold in Hounsfield units that optimized the prediction of dehiscence. CONCLUSION: Computed tomographic imaging alone can be misleading for diagnosis of SSCD. It can overestimate the size of the dehiscence, and it can falsely detect dehiscences. Clinical symptoms and other signs must be clearly indicative before surgery, and MSCT cannot be used exclusively for the diagnosis of SSCD.

Cone-beam volumetric tomography for applications in the temporal bone.

HYPOTHESIS: Cone beam volumetric tomography (CBVT) has better spatial resolution compared with multi slice computed tomography (MSCT) in temporal bone imaging for superior canal dehiscence (SCD). BACKGROUND: Imaging of SCD has traditionally used MSCT, but the ability to resolve thin bone next to low-radiodensity brain and inner ear fluids at the interface of the superior canal (SC) with the middle cranial fossa can be adversely affected by partial volume averaging, errors in registration of successive slices, and other factors. CBVT may offer advantages in these regards and may have better spatial resolution for this application. METHODS: Five cadaveric temporal bones were scanned using both CBVT and MSCT. The information content at the interface of the SC and the middle cranial fossa was measured for each method using spatial differential transformations. The ability of each method to resolve progressively smaller interfaces between bone and fluid was measured by creating a spatial grating model from a human temporal bone. RESULTS: The information content and spatial resolution were superior for CBVT compared with MSCT. CONCLUSION: The gold standard for diagnosis of SCD has been MSCT, but CBVT may offer improvements in information content and spatial resolution at the interface of the SC and the middle cranial fossa.