This study aimed to develop a technique for calculating cochlear length and determining cochlear implant electrode position using cone-beam computed tomography (CBCT) scans. The researchers examined CBCT scans of 100 subjects who received cochlear implants with either straight or contour electrode arrays. They calculated cochlear length based on the number of electrodes inserted at 360 degrees. For straight arrays, cochlear length ranged from 27.44 to 35.91 mm. For contour arrays, length ranged from 17.8 to 22.24 mm. The study concluded that CBCT can be used to precisely map electrode position to the cochlear's tonotopic map, which may improve outcomes for cochlear implantation.

1. Use of ConeBeam Computed Tomography to determine
cochlear length and implant array positioning
Fadwa Alnafjan 1,2,3, A.Prof Melville Da Cruz 3, A.Prof Catherine McMahon 1,2
1 The HEARing Cooperative Research Centre, ² Macquarie University, Linguistics Department & ³ Westmead Hospital, Department of Otolaryngology
Abstract
A validated technique to calculate cochlear length
and cochlear implant electrode position using pre-
and post-implantation Computed Tomography (CT)
has previously been reported. However, CT
exposures subjects to high levels of radiation twice
(once per scan). More recently, Cone Beam
Computed Tomography (CBCT) has been used for
cochlear implantees, exposing them to lower
radiation, but providing similarly high quality images.
The aim of this study was to develop a technique to
calculate the length of the cochlea within individuals
and, from this, to determine whether the distribution
of the length was normal.
Study Design
100 temporal bone CBCT images of in vivo subjects
implanted with Cochlear straight or contour arrays
by one surgeon.
Main Outcome Measure
Main Outcome Measure: CBCT images were
examined by two independent examiners who
calculated the length of the cochlea based on the
number of electrodes inserted at 360°.
Results
The length of the organ of Corti based on the
position of the straight array within the cochlea was
27.44 to 35.91 mm (mean = 32.24 mm). The length
of the spiral ganglion based on the position of the
contour array within the cochlea ranged from 17.8 to
22.24 mm (mean = 19.43 mm).
Conclusion
Using an evidence-based paradigm, we have
developed a novel method of calculating cochlear
length that can be used with CBCT. This enables a
more precise mapping of the electrode position to
the tonotopic map, which may result in improved
outcomes of cochlear implantation.
creating sound value www.hearingcrc.org
Cone-beam computed tomography (CBCT) image of an implanted
electrode array (Slim Straight Electrode) showing the three
landmarks needed to measure the cochlear length; (i) bony lip of
round window (RW), (ii) modiolus, and (iii) most apical electrode
(#22). These are used to estimate the number of electrodes inserted
at 360 degrees (solid line) and the length between this point and the
bony lip of the RW (dashed line).
The distribution of cochlear length for 77 ears with a
straight array (CI422 and CI522). The dashed curve
shows a normal distribution.
The distribution of cochlear length for 23 ears with a
contour array (CI24RE and CI512). The dashed curve
shows a normal distribution.