Читать книгу Advances in Hearing Rehabilitation - Группа авторов - Страница 21

Ultrasound imaging is a low-cost, real-time modality used widely throughout many areas of medicine. Conventional ultrasound technology operates by sending an acoustic stimulus at a frequency between 1 and 10 MHz into tissue and forming images from the reflections from tissue structures. High-frequency ultrasound (HFUS) operates in the same way, but at frequencies in the 20–100 MHz range. The higher frequency allows for improved axial and lateral resolutions of the order of 10’s of microns compared to 100’s of microns for conventional ultrasound, but at the expense of lower penetration in soft tissues (i.e., 10–15 mm at 50 MHz) due to increased absorption and scattering [17–21]. HFUS is a promising technology for use in the auditory system where it can provide better resolution than MRI or CT of middle ear and inner ear structures [18, 20, 21]. It also offers the potential of being able to measure the vibration of structures in both the middle and inner ears [18, 20], which could be an important new source of diagnostic information. Imaging requires a fluid acoustic coupling such as gel or liquid and this requires that the middle ear is filled with saline (unless there is already serous fluid present). Ultrasound imaging of the cochlea is possible through the round window with a drop of fluid or gel providing coupling [18]. Ultrasound is minimally attenuated by soft tissues, such as the tympanic membrane, round window folds or cholesteatoma or by middle ear effusion. While the need for direct acoustic coupling makes high-frequency ultrasound (HIFUS) imaging more invasive than some other modalities, it may have some application for specific disorders of the middle ear and offers great promise for intracochlear imaging.

Fig. 8. 3-D reconstructions of the micro-CT images: Semi-transparent 3-D models of human cochlea with inserted cochlear implant electrode (Advanced Bionics Hi-Focus II electrode with 16 contacts). Side view (a). View from above (b).