New HRCT-based measurement of the human outer ear canal as a basis for acoustical methods

As the form and size of the external auditory canal determine its transmitting function and hence the sound pressure in front of the eardrum, it is important to understand its anatomy in order to develop, optimize, and compare acoustical methods.

High-resolution computed tomography (HRCT) data were measured retrospectively for 100 patients who had received a cochlear implant. In order to visualize the anatomy of the auditory canal, its length, radius, and the angle at which it runs were determined for the patients’ right and left ears. The canal’s volume was calculated, and a radius function was created.

The determined length of the auditory canal averaged 23.6 mm for the right ear and 23.5 mm for the left ear. The calculated auditory canal volume (Vtotal) was 0.7 ml for the right ear and 0.69 ml for the left ear. The auditory canal was found to be significantly longer in men than in women, and the volume greater.

The values obtained can be employed to develop a method that represents the shape of the auditory canal as accurately as possible to allow the best possible outcomes for hearing aid fitting.