Reinhold Schatzer

Ultrasound-Guided Versus Computed Tomography-Controlled Facet Joint Injections in the Lumbar Spine: A Prospective Randomized Clinical Trial

Background and Objectives: Facet joint injections are widely used for alleviation of back pain. Injections are preferentially performed as fluoroscopy or computed tomography (CT)-controlled interventions. Ultrasound provides real-time monitoring, does not produce ionizing radiation, and is broadly available. Methods: We studied feasibility, accuracy, time-savings, radiation doses, and pain relief of ultrasound-guided facet joint injections versus CT-controlled interventions in a prospective randomized clinical trial. Forty adult patients with chronic low back pain were consecutively enrolled and evenly assigned to an ultrasound or a CT- group. Results: Eighteen subjects from the group randomized to ultrasound were judged to be feasible for this type of approach. In 16 of them the facet joints were clearly visible and all of the associated facet joint injections were performed correctly. The duration of procedure and radiation dose was 14.3 ± 6.6 minutes and 14.2 ± 11.7 mGy˙cm in the ultrasound group, and 22.3 ± 6.3 minutes and 364.4 ± 213.7 mGy˙cm in the CT group. Both groups showed a benefit from facet joint injections. Conclusions: The ultrasound approach to the facet joints in the lumbar spine is feasible with minimal risks in a large majority of patients and results in a significant reduction of procedure duration and radiation dose.

Multicenter U.S. bilateral MED-EL cochlear implantation study: Speech perception over the first year of use

Objective: Binaural hearing has been shown to support better speech perception in normal-hearing listeners than can be achieved with monaural stimulus presentation, particularly under noisy listening conditions. The purpose of this study was to evaluate whether bilateral electrical stimulation could confer similar benefits for cochlear implant listeners. Design: A total of 26 postlingually deafened adult patients with short duration of deafness were implanted at five centers and followed up for 1 yr. Subjects received MED-EL COMBI 40+ devices bilaterally; in all but one case, implantation was performed in a single-stage surgery. Speech perception testing included CNC words in quiet and CUNY sentences in noise. Target speech was presented at the midline (0 degrees), and masking noise, when present, was presented at one of three simulated source locations along the azimuth (−90, 0, and +90 degrees). Results: Benefits of bilateral electrical stimulation were observed under conditions in which the speech and masker were spatially coincident and conditions in which they were spatially separated. Both the “head shadow” and “summation” effects were evident from the outset. Benefits consistent with “binaural squelch” were not reliably observed until 1 yr after implantation. Conclusions: These results support a growing consensus that bilateral implantation provides functional benefits beyond those of unilateral implantation. Longitudinal data suggest that some aspects of binaural processing continue to develop up to 1 yr after implantation. The squelch effect, often reported as absent or rare in previous studies of bilateral cochlear implantation, was present for most subjects at the 1 yr measurement interval.

Two new directions in speech processor design for cochlear implants.

Two new approaches to the design of speech processors for cochlear implants are described. The first aims to represent “fine structure” or “fine frequency” information in a way that it can be perceived and used by patients, and the second aims to provide a closer mimicking than was previously possible of the signal processing that occurs in the normal cochlea.

Ultrasound-guided periradicular injections in the middle to lower cervical spine : An imaging study of a new approach

Background and Objectives The objective of this study was to show the efficacy of ultrasound in facilitating the performance of a simulated cervical periradicular injection in cadavers. Methods A total of 40 ultrasound-guided examinations at 4 levels (C3 to C7) were performed on 4 embalmed cadavers. The cervical spinal nerves were located with ultrasound. First, the transverse process of each level was taken as a sonoanatomic landmark. The most lateral aspect of the transverse process of the seventh cervical vertebra was then established as the reference point. Ipsilateral distances (A, B, C, and D) between this point and each one of the transverse processes of the cervical spine up to the third vertebra were then computed. Subsequently, coronal computed tomography (CT) scans were taken to verify these distances. In a second part, a spinal needle was advanced under ultrasound guidance to the spinal nerves C5 to C8 on both sides of one cadaver. The exact placement of the needle tips was checked by CT. Results The transverse processes were identified in all cadavers. In 5 attempts, a depiction of the spinal nerves was not possible. Ultrasound and CT provided the same mean measurements of 1.1 cm, 2.1 cm, 3.1 cm, and 4.1 cm for distances A, B, C, and D, respectively. All 8 needle tips were placed within 5 mm dorsal to the spinal nerve and less than 5 mm away from the posterior tubercle of each levels transverse process, as also verified by CT. Conclusions This preclinical study suggests that ultrasound is a useful guiding tool for periradicular injections in the cervical spine.

Ultrasound-guided and CT-navigation-assisted periradicular and facet joint injections in the lumbar and cervical spine: a new teaching tool to recognize the sonoanatomic pattern.

Background and Objectives The aim of this study is to provide a teaching tool to facilitate the acquirement of periradicular and facet-joint infiltration techniques in the cervical and lumbar spine. Methods On 3 fresh cadavers, a computed tomography (CT) of the lumbar and cervical region was obtained. By use of a dedicated image navigation and reconstruction system, sonographic images were generated and fused with the collected CT data set. Results The sonoanatomy can be instantly compared with the correlating CT-images. This new bimodal method allows for simultaneous views of CT and ultrasound images. Multiplanar imaging of ultrasound-guided infiltrations is facilitated. Conclusions This teaching tool provides immediate CT-verification of sonographically identified structures and helps in the identification of bony landmarks, which are necessary for facet-joint and periradicular injections.

Temporal fine structure in cochlear implants: Preliminary speech perception results in Cantonese-speaking implant users

Abstract Conclusion: Acute comparisons between continuous interleaved sampling (CIS) and a temporal fine structure (TFS) coding strategy in Cantonese-speaking cochlear implant (CI) users did not reveal any significant differences in speech perception. Performance with the unfamiliar TFS coding strategy was on a par with CIS. Benefits of extended fine structure use observed in other studies should be investigated for tonal languages. Objectives: CIS-based stimulation strategies lack an explicit representation of fine structure, which is crucial for tonal language speech perception. The aim of this study was to assess speech recognition with a TFS coding strategy in Cantonese-speaking CI users with no prior fine structure experience. Methods: The fine structure coding strategy encodes TFS on a few apical channels, while the remaining more basal channels carry CIS stimuli. Twelve MED-EL implantees and long-term CIS users participated in a study comparing recognition for Cantonese lexical tones and CHINT sentences between CIS and fine structure stimulation. Results: Mean tone identification scores in 12 subjects were 59.2% with CIS and 59.2% with fine structure stimulation using 4 TFS channels, mean scores of CHINT sentences in 8 subjects were 54.2% with CIS and 55.9% with TFS stimulation. Differences between the two strategies were not significant for any speech test. Two additional versions of TFS strategy and pulse rates were tested in six subjects. No significant differences between strategies were found.

Frequency-place map for electrical stimulation in cochlear implants: Change over time

The relationship between the place of electrical stimulation from a cochlear implant and the corresponding perceived pitch remains uncertain. Previous studies have estimated what the pitch corresponding to a particular location should be. However, perceptual verification is difficult because a subject needs both a cochlear implant and sufficient residual hearing to reliably compare electric and acoustic pitches. Additional complications can arise from the possibility that the pitch corresponding to an electrode may change as the auditory system adapts to a sound processor. In the following experiment, five subjects with normal or near-to-normal hearing in one ear and a cochlear implant with a long electrode array in the other ear were studied. Pitch matches were made between single electrode pulse trains and acoustic tones before activation of the speech processor to gain an estimate of the pitch provided by electrical stimulation at a given insertion angle without the influence of exposure to a sound processor. The pitch matches were repeated after 1, 3, 6, and 12 months of experience with the sound processor to evaluate the effect of adaptation over time. Pre-activation pitch matches were lower than would be estimated by a spiral ganglion pitch map. Deviations were largest for stimulation below 240° degrees and smallest above 480°. With experience, pitch matches shifted towards the frequency-to-electrode allocation. However, no statistically significant pitch shifts were observed over time. The likely explanation for the lack of pitch change is that the frequency-to-electrode allocations for the long electrode arrays were already similar to the pre-activation pitch matches. Minimal place pitch shifts over time suggest a minimal amount of perceptual remapping needed for the integration of electric and acoustic stimuli, which may contribute to shorter times to asymptotic performance.

A Binaural Cochlear Implant Sound Coding Strategy Inspired by the Contralateral Medial Olivocochlear Reflex.

Objectives: In natural hearing, cochlear mechanical compression is dynamically adjusted via the efferent medial olivocochlear reflex (MOCR). These adjustments probably help understanding speech in noisy environments and are not available to the users of current cochlear implants (CIs). The aims of the present study are to: (1) present a binaural CI sound processing strategy inspired by the control of cochlear compression provided by the contralateral MOCR in natural hearing; and (2) assess the benefits of the new strategy for understanding speech presented in competition with steady noise with a speech-like spectrum in various spatial configurations of the speech and noise sources. Design: Pairs of CI sound processors (one per ear) were constructed to mimic or not mimic the effects of the contralateral MOCR on compression. For the nonmimicking condition (standard strategy or STD), the two processors in a pair functioned similarly to standard clinical processors (i.e., with fixed back-end compression and independently of each other). When configured to mimic the effects of the MOCR (MOC strategy), the two processors communicated with each other and the amount of back-end compression in a given frequency channel of each processor in the pair decreased/increased dynamically (so that output levels dropped/increased) with increases/decreases in the output energy from the corresponding frequency channel in the contralateral processor. Speech reception thresholds in speech-shaped noise were measured for 3 bilateral CI users and 2 single-sided deaf unilateral CI users. Thresholds were compared for the STD and MOC strategies in unilateral and bilateral listening conditions and for three spatial configurations of the speech and noise sources in simulated free-field conditions: speech and noise sources colocated in front of the listener, speech on the left ear with noise in front of the listener, and speech on the left ear with noise on the right ear. In both bilateral and unilateral listening, the electrical stimulus delivered to the test ear(s) was always calculated as if the listeners were wearing bilateral processors. Results: In both unilateral and bilateral listening conditions, mean speech reception thresholds were comparable with the two strategies for colocated speech and noise sources, but were at least 2 dB lower (better) with the MOC than with the STD strategy for spatially separated speech and noise sources. In unilateral listening conditions, mean thresholds improved with increasing the spatial separation between the speech and noise sources regardless of the strategy but the improvement was significantly greater with the MOC strategy. In bilateral listening conditions, thresholds improved significantly with increasing the speech-noise spatial separation only with the MOC strategy. Conclusions: The MOC strategy (1) significantly improved the intelligibility of speech presented in competition with a spatially separated noise source, both in unilateral and bilateral listening conditions; (2) produced significant spatial release from masking in bilateral listening conditions, something that did not occur with fixed compression; and (3) enhanced spatial release from masking in unilateral listening conditions. The MOC strategy as implemented here, or a modified version of it, may be usefully applied in CIs and in hearing aids.

Simultaneous Intracochlear Stimulation Based on Channel Interaction Compensation: Analysis and First Results

A simultaneous paradigm for electric stimulation of the acoustic nerve based on a monopolar electrode configuration and sign-correlated pulses is presented. Simultaneous pulse amplitudes are determined by taking into account parameters of spatial channel interaction. The computation of simultaneous amplitudes requires the solution of linear systems of equations in an iterative procedure. The computation amount can be reduced significantly, if the spatial impulse responses in individual electrodes can be approximated by two exponentially decaying branches with decay constants alpha toward apex and beta toward base. Generally, the associated inverse of the channel interaction matrix is tridiagonal. Preliminary vowel and consonant identification tests with four cochlear implant patients have been conducted for sequential and simultaneous processor settings. For equal overall pulse repetition rates, comparable speech perception scores were obtained, when the decay constants alpha and beta were set accordingly. Theoretically, the pulse rate of an N-channel system can be increased up to a factor of N as compared to the standard sequential paradigm, and pulses with technically reasonable phase durations can be utilized.

Roles of the Contralateral Efferent Reflex in Hearing Demonstrated with Cochlear Implants

Our two ears do not function as fixed and independent sound receptors; their functioning is coupled and dynamically adjusted via the contralateral medial olivocochlear efferent reflex (MOCR). The MOCR possibly facilitates speech recognition in noisy environments. Such a role, however, is yet to be demonstrated because selective deactivation of the reflex during natural acoustic listening has not been possible for human subjects up until now. Here, we propose that this and other roles of the MOCR may be elucidated using the unique stimulus controls provided by cochlear implants (CIs). Pairs of sound processors were constructed to mimic or not mimic the effects of the contralateral MOCR with CIs. For the non-mimicking condition (STD strategy), the two processors in a pair functioned independently of each other. When configured to mimic the effects of the MOCR (MOC strategy), however, the two processors communicated with each other and the amount of compression in a given frequency channel of each processor in the pair decreased with increases in the output energy from the contralateral processor. The analysis of output signals from the STD and MOC strategies suggests that in natural binaural listening, the MOCR possibly causes a small reduction of audibility but enhances frequency-specific inter-aural level differences and the segregation of spatially non-overlapping sound sources. The proposed MOC strategy could improve the performance of CI and hearing-aid users.