New Imaging Modalities in Otology.

Despite steady improvements in cross-sectional imaging of the ear, current technologies still have limitations in terms of resolution, diagnosis, functional assessment and safety. In this chapter, state-of-the-art imaging techniques in current clinical practice are presented including cone-beam computerized tomography, non-echo planar imaging magnetic resonance imaging, imaging for labyrinthine hydrops and imaging of the central auditory pathways. Potential future imaging modalities are also presented, including optical coherence tomography (OCT) and high-frequency ultrasound (HFUS) of the ear. These experimental modalities offer new opportunities for the assessment of ear structure and function. For example, middle ear structures can be visualized through the tympanic membrane, basilar membrane vibrations can be assessed through the round window and the passage of cochlear implants can be assessed in decalcified cochlear. Functional assessment of the middle ear using Doppler techniques are also discussed, including measurement of tympanic membrane and middle ear vibration amplitudes, visualization of dynamic changes, such as tensor tympani movements and movement of the tympanic membrane with breathing. These new modalities currently have limitations that preclude mainstream clinical use. For example, OCT is limited by the optical scattering of the thickened tympanic membrane and HFUS needs a coupling medium such as gel or fluid from the transducer to the imaged structure although it can visualize through thicker tissues. Nevertheless, further development of these novel techniques may provide an enhanced ability to assess the ear in conjunction with current technologies.

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.