Optimization of TACT imaging protocols for in situ visualization of cochlear electrode arrays in cat temporal bones

To explore the effect of the number of two-dimensional (2D) images and x-ray projection angles on the resolution of reconstructed three-dimensional (3D) volumes of intracochlear electrode arrays in cadaveric cat temporal bones using Tuned Aperture Computed Tomography (TACT).

Multiple 2D radiographs (basis images (BI)) of implanted cadaveric cat temporal bones were acquired using a range of projection angles, and imported into the TACT workbench. 3D volumes were reconstructed using varying numbers of BIs. Contrast resolution in the image was determined by comparing the contrast ratio (using maximum and minimum grayscale values) in specified anatomic areas of interest.

Systematically increasing the number of BIs used in the reconstruction process resulted in a systematic increase in contrast resolution. Likewise, increasing the range of effective projection angles, as also the number of such angles used in the TACT computation also increased the contrast resolution of the resulting images.

Precise determination of the location of cochlear implant electrodes in situ is critical to understanding the factors influencing efficacy of electrical stimulation of the deaf ear. Renderings generated with the TACT algorithm produce 3D images permitting visualization of implant electrode features and anatomic details with resolution sufficient to accurately localize electrode contacts within scala tympani. The quality of resulting images, evaluated as a function of image contrast, improved with a larger number of BIs in the reconstruction. Wider projection angles also improved image detail in addition to generating thinner slices. Any loss in contrast was compensated for by the number of BIs. TACT can thus be optimized to provide useful data to help characterize the location of intracochlear electrode arrays.