High-Frequency Ultrasound Imaging of the Auditory System

Abstract

Current technology used to diagnose hearing disorders is limited. This is mostly due to the fact that the auditory structures are very small and not easily accessible with existing imaging technologies. The objective of this dissertation was to investigate the potential of high-frequency ultrasound as a tool for exploring the anatomy of the auditory system. Three studies were conducted in order to demonstrate the feasibility of high-frequency ultrasound as a diagnostic technology for hearing disorders. In the first study, an in-house developed 50 MHz annular array-based ultrasound system was used to provide ex-vivo images of auditory structures in cadaveric temporal bones. It was shown that the spatial resolution was sufficient to visualize a high level of detail of the ossicular bones of the middle ear as well as intra-cochlear structures of the inner ear. In the second study, a 50 MHz 1.26? pitch phased array ultrasound transducer was designed for imaging intra-cochlear structures through the round window membrane. As this element pitch results in large grating lobe artifacts, novel transmit beamforming techniques were developed to suppress grating lobes resulting from this large-pitch array. Theoretical techniques using the impulse-response simulation method and experimental verification using high-frequency linear array ultrasound system (Vevo 2100, VisualSonics, Canada) showed that these techniques were able to suppress grating lobe levels up to 40 dB. In the third study, a needle mounted 45 MHz single-element ultrasound probe was fabricated in order to measure the vibrations of intra-cochlear structures on human cadavers. Basilar membrane velocimetry measurements were successfully performed using pulsed-wave Doppler ultrasound in the frequency range between 100 Hz-2 KHz. The measured velocity of the basilar membrane and the round window membrane showed that the middle ear resonance frequency near 1 KHz was present over multiple temporal bones. This is the first work that has explored the human auditory system with high resolution ultrasonic visualization and Doppler velocimetry.