Imaging cochlear implantation with round window insertion in human temporal bones and cochlear morphological variation using high-resolution cone beam CT

Figures & data

Figure 1. Electrode array types.

Table I. Technical specifications of the electrode types.

Factor	Standard array	Experimental array with 36 contacts	Flex28
Active stimulation length	26.4 mm	28	23.1
Number of contacts	24 (12 pairs)	36 (one line of contacts)	19 (7 pairs and 5 in a single line)
Contact separation	2.4 mm	0.8 mm	2.1 mm
Diameter at basal end	1.3 mm	1.3	0.8
Dimensions at apical end	0.5 mm	0.5	Oval-shaped (0.48/0.36)
Number of operations	3	1	2

Figure 2. Measurement of full insertion depth of the electrode. A standard electrode array with the measures (mm) is shown in (A). On the cone-beam computed tomography (CBCT) image (B), three contacts (C10–C12) were outside the round window (RW) and the intracochlear measures started from the RW.

Table II. Image quality demonstrated by average levels of five evaluators using a rating system from 5 to 1 in descending order.

Landmarks	Levels
Cochlea	3.8
Osseous spiral lamina	3.4
Modiolus	3.9
Stapes	4.5
Round window niche	4.3
Oval window	4.4

Level: 5, very good delineation of structures and excellent quality; 4, clear delineation of structures and good image quality; 3, anatomic structures still fully assessable in all parts and acceptable image quality; 2, structures identified but no details assessable and results in insufficient image quality; 1, anatomic structures not identifiable due to poor image quality.

Figure 3. Fine cochlear structures demonstrated by cone-beam computed tomography (CBCT). All specified landmarks were clearly identified in all six temporal bones (TB). BW, bony wall; Cont, contours of cochlear implant; Mod, modiolus; OSL, osseous spiral lamina.

Figure 4. Critical cochlear assessments on cone-beam computed tomography (CBCT) images. ‘A’ value (A), cochlear height (B), insertion depth for the first 360° insertion angle (C), and distance between the electrode contacts and the modiolus (D) are demonstrated (in mm). Ap, apex; Cont, contours of cochlear implant; Fund, fundus; LW, lateral wall; Mod, modiolus; RWM, round window membrane.

Figure 5. Correlations between ‘A’ value and cochlear implant electrode array insertion parameters measured on cone-beam computed tomography (CBCT) images. Good correlations appeared between A value and cochlear height shown (A), and between A value and insertion depth for the first 360° insertion angle (B). Sample 2 was removed.

Table III. Insertion angle and insertion depth of the electrode arrays with number of contact pairs outside the cochlea.

Sample no./electrode type	Insertion depth for first 360° insertion angle (mm)	Full insertion depth of electrode (mm)	Insertion angle for full insertion depth of electrode (°)	No. of contact pairs extracochlear
1/Standard	18.8	20.4	414	3
2/36 channel	18.6	18.6	340	13*
3/FLEX28	19.8	21	520	1
4/FLEX28	19.9	21	429	1
5/Standard	21.2	20.4	367	3
6/Standard	18.2	20.4	468	2

*One line of contacts.

Figure 6. 3D reconstruction of cone-beam computed tomography (CBCT) images showing spatial correlation between the electrode contacts and the osseous cochlear modiolus.