Thomas G. Landry

The Effect of Piston Diameter in Stapedotomy for Otosclerosis : A Temporal Bone Model

Hypothesis: The use of larger-diameter pistons in stapedotomy leads to better hearing outcomes compared with the use of smaller-diameter pistons. There is an interaction between stapes piston diameter and fenestration diameter. Background: Otosclerosis can be treated surgically by removing part of the stapes and bypassing the stapes footplate with a prosthesis. Available piston shaft diameters range between 0.3 and 0.8 mm. There has been a tendency toward the use of smaller-diameter pistons, because of a suspected decreased risk of cochlear trauma and subsequent sensorineural hearing loss (SNHL) with smaller pistons. However, mathematical models, temporal bone studies, and clinical studies suggest that the use of larger-diameter pistons is associated with better hearing outcomes. Methods: Three fresh-frozen, non-pathologic temporal bones were harvested from human cadaveric donors. Acoustic stimuli in the form of pure tones from 250 to 8000 Hz were generated at 110 dB sound pressure level. A total of 16 frequencies in a 1/3-octave series were used. Stapes and round window velocities in response to the acoustic stimuli were measured at multiple equally spaced points covering the stapes footplate and round window using a scanning laser Doppler interferometry system. Eight sets of measurements were performed in each temporal bone: 1) normal condition (mobile stapes), 2) stapes fixation and stapedotomy followed by insertion of 3) a 0.4-mm-diameter piston in a 0.5-mm-diameter fenestration, 4) a 0.4-mm-diameter piston in a 0.7-mm-diameter fenestration, 5) a 0.4-mm-diameter piston in a 0.9-mm-diameter fenestration, 6) a 0.6-mm-diameter piston in a 0.7-mm-diameter fenestration, 7) a 0.6-mm-diameter piston in a 0.9-mm-diameter fenestration, and 8) a 0.8-mm-diameter piston in a 0.9-mm-diameter fenestration. Results: At midrange frequencies, between 500 and 4000 Hz, round window velocities increased by 2 to 3 dB when using a 0.6-mm-diameter piston compared with a 0.4-mm-diameter piston. Using a 0.8-mm-diameter piston led to a further increase in round window velocities by 2 to 4 dB. Conclusion: Our results suggest a modest effect of piston diameter on hearing results following stapedotomy.

Effect of round window reinforcement on hearing : A temporal bone study with clinical implications for surgical reinforcement of the round window

Hypothesis: Round window reinforcement leads to conductive hearing loss. Background: The round window is stiffened surgically as therapy for various conditions, including perilymphatic fistula and superior semicircular canal dehiscence. Round window reinforcement reduces symptoms in these patients. However, it also reduces fluid displacement in the cochlea and might therefore increase conductive hearing loss. Methods: Perichondrium was applied to the round window membrane in nine fresh-frozen, nonpathologic temporal bones. In four temporal bones cartilage was applied subsequently. Acoustic stimuli in the form of frequency sweeps from 250 to 8000 Hz were generated at 110 dB sound pressure level. A total of 16 frequencies in a 1/3-octave series were used. Stapes velocities in response to the acoustic stimuli were measured at equally spaced multiple points covering the stapes footplate using a scanning laser Doppler interferometry system. Measurements were made at baseline, after applying perichondrium, and after applying cartilage. Results: At frequencies up to 1000 Hz perichondrium reinforcement decreased stapes velocities by 1.5 to 2.9 dB compared with no reinforcement (p value = 0.003). Reinforcement with cartilage led to a further deterioration of stapes velocities by 2.6 to 4.2 dB at frequencies up to 1000 Hz (p value = 0.050). The higher frequencies were not affected by perichondrium reinforcement (p value = 0.774) or cartilage reinforcement (p value = 0.644). Conclusion: Our results seem to suggest a modest, clinically negligible effect of reinforcement with perichondrium. Placing cartilage on the round window resulted in a graded effect on stapes velocities in keeping with the increased stiffness of cartilage compared with perichondrium. Even so, the effect was relatively small.

Real-time imaging of in-vitro human middle ear using high frequency ultrasound

Imaging techniques currently used in the clinic to inspect ears in patients are generally limited to views terminating at the tympanic membrane (TM) surface. For imaging past the TM, methods such as computed tomography are typically used, but in addition to disadvantages such as being costly, time consuming, and causing radiation exposure, these often do not provide sufficient resolution of the middle ear structures of interest. This study presents an investigation into the capability of high frequency ultrasound to image the middle ear with high resolution in real-time, as well as measure vibrations of TM and middle ear structures in response to sound stimuli. In unfixed cadaver ears, the TM, ossicles, and ossicular support tissues were all readily identifiable, with capabilities demonstrated for real-time imaging and video capture, and vibrometry of middle ear structures. Based on these results, we conclude that high frequency ultrasonography is a relatively simple and minimally invasive technology with great potential to provide clinicians with new tools for diagnosing and monitoring middle ear pathologies.

In vivo measurement of basilar membrane vibration in the unopened chinchilla cochlea using high frequency ultrasound

The basilar membrane and organ of Corti in the cochlea are essential for sound detection and frequency discrimination in normal hearing. There are currently no methods used for real-time high resolution clinical imaging or vibrometry of these structures. The ability to perform such imaging could aid in the diagnosis of some pathologies and advance understanding of the causes. It is demonstrated that high frequency ultrasound can be used to measure basilar membrane vibrations through the round window of chinchilla cochleas in vivo. The basic vibration characteristics of the basilar membrane agree with previous studies that used other methods, although as expected, the sensitivity of ultrasound was not as high as optical methods. At the best frequency for the recording location, the average vibration velocity amplitude was about 4 mm/s/Pa with stimulus intensity of 50 dB sound pressure level. The displacement noise floor was about 0.4 nm with 256 trial averages (5.12 ms per trial). Although vibration signals were observed, which likely originated from the organ of Corti, the spatial resolution was not adequate to resolve any of the sub-structures. Improvements to the ultrasound probe design may improve resolution and allow the responses of these different structures to be better discriminated.

High Frequency Ex Vivo Ultrasound Imaging of the Middle Ear to Show Simulated Ossicular Pathology.

Hypothesis: To illustrate the ability of high frequency ultrasound (HFUS) using a transducer array to demonstrate a variety of simulated clinical scenarios involving the ossicular chain. Background: HFUS (>20 MHz) is a relatively new area of ultrasonic imaging that provides an order of magnitude better image resolution than the conventional low-frequency systems. HFUS may be a real-time imaging system that could be used in the clinic and would complement computed tomography (CT) and magnetic resonance imaging (MRI) to enhance the decision-making process for patients with middle ear pathology. Methods: Using a commercially available HFUS scanner, we imaged a variety of simulated clinical scenarios to demonstrate the ability of HFUS to image middle ear pathology. Results: We were able to clearly demonstrate real-time visualization of ossicular pathology in human temporal bones, whereas there are some limitations in the current technique to be addressed before it is used in vivo. Conclusion: HFUS allows excellent visualization of middle ear anatomy and pathology through an intact tympanic membrane (TM), and these experiments go some way towards giving the otologist access to high resolution, real-time imaging of the middle ear in the clinic.

Real-time intracochlear imaging of automated cochlear implant insertions in whole decalcified cadaver cochleas using ultrasound

Objectives: This study aimed to determine the feasibility of combining high-frequency ultrasound imaging, automated insertion, and force sensing to yield more information about cochlear implant insertion dynamics. Methods: An apparatus was developed combining these aspects along with software to control implant and imaging probe positions. Decalcified unfixed human cochleas were implanted at various speeds, insertion sites, and implant models while imaging near the implant tip throughout insertion and recording force data from the cochlea mounting stage. Ultrasound video data were also captured. Results: The basilar membrane (BM) was frequently penetrated by the implant in either the mid-basal or lower middle turn. Measurements were also performed of apical BM motion in response to upstream implant movement at varying insertion speeds. Increasing insertion speed resulted in greater BM displacement. Discussion: Multiple insertions per cochlea increase the volume of data per specimen while also reducing variability due to differences between cochleas. However, to image inside the cochlea with ultrasound, the bone had to be decalcified, which likely had a significant effect upon the response of tissue to contact by the implant. As calcified bone strongly reflects ultrasound, we also found ultrasound imaging to be an excellent method for easily assessing bone decalcification progress. Conclusion: This technique may be very useful for some studies, although the confounding effects of bone decalcification may make results of other studies too difficult to generalize. The approach could be adapted to other real-time imaging modalities, such as optical coherence tomography.

A low-cost 10 mm diameter histotripsy transducer for tissue ablation guided by a co-registered high-frequency endoscopic phased array

In this work, we present the development of a low-cost, 10 mm diameter histotripsy transducer with co-registered imaging using a 45 MHZ, 64-element phased array. The construction of 10 mm diameter transducer consisting of a 45% volume fraction composite, aluminum lens, and quarter-wavelength parylene matching layer is outlined. Steady-state peak-to-peak pressure ranges from 3.0 to 10.6 MPa as drive voltage ranges from 15 V to 50 V. The beam profile of the transducer was measured using a hydrophone, where the radial 3 dB width was found to be 0.176 mm while the 3 dB length in the axial direction was found to be 1.109 mm for a 20 cycle pulse. Co-registered imaging and ablation results for chinchilla neural tissue are shown.

No effect of prolonged pulsed high frequency ultrasound imaging of the basilar membrane on cochlear function or hair cell survival found in an initial study

&NA; Miniature high frequency ultrasound devices show promise as tools for clinical middle ear and basal cochlea imaging and vibrometry. However, before clinical use it is important to verify that the ultrasound exposure does not damage the cochlea. In this initial study, electrophysiological responses of the cochlea were measured for a range of stimulus frequencies in both ears of anesthetized chinchillas, before and after exposing the organ of Corti region of one ear to pulsed focused ultrasound for 30 min. Measurements were again taken after an 11 day survival period. Cochlear tissue was examined with a confocal microscope for signs of damage to the cochlear hair cells. No significant change in response thresholds due to exposure was found, and no signs of ultrasound‐induced tissue damage were observed, although one animal (out of ten) did have a region of extensive tissue damage in the exposed cochlea. However, after further analysis this was concluded to be not likely a result of the ultrasound exposure. HighlightsHigh frequency ultrasound has promise for clinical imaging of middle and inner ears.Chinchilla cochleas were exposed to pulsed ultrasound to assess its safety.Cochlear responses were measured before, just after, and 11 days after exposure.Organ of Corti hair cells and peripheral neural fibers were confocal imaged.The results indicate that the ultrasound exposure was not harmful to the cochlea.

Real-time swept-source Doppler optical coherence tomography for middle ear diagnostics

Transtympanic middle ear imaging is a very promising application of optical coherence tomography (OCT). We present progress on the development of a real-time swept-source OCT imaging system with Doppler vibrography for in-clinic functional imaging in live patients.