Cone-beam CT versus Multidetector CT in Postoperative Cochlear Implant Imaging: Evaluation of Image Quality and Radiation Dose

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FIG 1.
Coronal oblique (cochlear view with thick MPR = 5 mm) CBCT image showing the measurement of the angle of insertion between the deepest electrode and the reference line joining the insertion point (round window/cochleostomy center) (a) and the center of a circle formed by the 3 most apical electrodes (b). The insertion angle = 360°- (c). The cochlear lateral wall is also well-visualized in this thick MPR coronal view (white arrows).
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FIG 2.
CBCT group. A, Midmodiolar view (cochlea) shows the modiolus (white arrow), the perfectly visualized cochlear lateral wall (black arrow), and the scalar translocation from ST to SV at the pars ascendens (dashed arrow). B, Axial view (cochlea) shows good visualization of single electrode contacts, C, Sagittal oblique view shows good visualization of the facial nerve canal wall (arrow). D, In the MDCT group, the midmodiolar view (cochlea) shows the modiolus (white arrow), nonvisualized cochlear lateral wall (artifacts) (black arrow), and the difficult scalar localization of the electrode (mostly ST). E, Axial view (cochlea) shows difficult identification of single electrode contacts and the osseous spiral lamina. F, Sagittal oblique view shows difficult identification of the facial nerve canal wall (arrow). ST indicates scala tympani; SV, scala vestibuli.

Table 1:

Different electrodes with intercontact distancing

Electrodes	Intercontact Distancing (mm)	CBCT Group (n = 32)	MDCT Group (n = 19)
Widely spaced contacts
FLEX28^a	2.1	3	0
FLEX-Synchrony-Medium^a	1.9	2	2
HiRes MIDSCALA^{^b}	0.975	3	1
CI422*^{^c}	0.85–0.95	1	0
Narrowly spaced contacts
CI24RE-CA^{^c}	Nonuniform 0.4–0.8	9	0
CI512-CA^{^c}	Nonuniform 0.4–0.8	3	0
CI532-CA^{^c}	0.6	11	1
CI24RE-ST^{^c}	0.75	0	15

Note:—CA indicates contour advance; ST, straight electrode.
a MED-EL.
↵b Advanced Bionics.
↵c Cochlear.
All distances were obtained from the portfolios of the electrodes (* except for CI422 cited from Bennink et al.²⁹)

Table 2:

Qualitative image scoring results for fine anatomic structures and metallic artifacts

Scale Points	CBCT Group (n = 32)	MDCT Group (n = 19)	P Value
Cochlear inner wall
Not visualized (0)	1 (3%)	0 (0%)	>.99
Barely visualized (1)	3 (9%)	2 (10.5%)
Well-visualized (2)	6 (19%)	3 (15.8%)
Perfectly visualized (3)	22 (69%)	14 (73.7%)
Cochlear lateral wall
Not visualized (0)	0 (0%)	1 (5%)	.001
Barely visualized (1)	0 (0%)	0 (0%)
Well-visualized-(2)	2 (6%)	8 (42%)
Perfectly visualized (3)	30 (94%)	10 (53%)
Modiolus
Not visualized (0)	0 (0%)	0 (0%)	.37
Barely visualized (1)	2 (6%)	0 (0%)
Well-visualized (2)	5 (16%)	1 (5%)
Perfectly visualized (3)	25 (78%)	18 (95%)
Osseous spiral, lamina
Not visualized (0)	18 (56%)	19 (100%)	.002
Barely visualized (1)	10 (31%)	0 (0%)
Well -visualized (2)	4 (13%)	0 (0%)
Perfectly visualized (3)	0 (0%)	0 (0%)
Mastoid facial, canal wall
Not visualized (0)	4 (13%)	4 (21%)	.07
Barely visualized (1)	10 (31%)	6 (32%)
Well-visualized (2)	9 (28%)	9 (47%)
Perfectly visualized (3)	9 (28%)	0 (0%)
Metallic artifacts
Very strong artifact (0)	0 (0%)	0 (0%)	<.001
Strong artifacts (1)	6 (18.8%)	14 (74%)
Moderate artifacts (2)	22 (68.8%)	5 (26%)
Weak artifacts (3)	4 (12.5%)	0 (0%)

Table 3:

Qualitative image scoring results for electrode evaluation

Scale Points	CBCT Group (n = 32)	MDCT Group (n = 19)	P Value
Electrode scalar position
Not visualized (0)	0 (0%)	0 (0%)	.046
Barely visualized (1)	4 (13%)	3 (16%)
Well-visualized (2)	3 (9%)	7 (37%)
Perfectly visualized (3)	25 (78%)	9 (47%)
Single electrode contact visibility
Not visualized (0)	1 (3%)	10 (52.6%)	<.001
Barely visualized (1)	13 (41%)	6 (31.6%)
Well-visualized (2)	11 (34%)	0 (0%)
Perfectly visualized (3)	7 (22%)	3 (15.8%)
Insertion angle of electrode
Not measurable (0)	0 (0%)	0 (0%)	>.99
Measurable (1)	32 (100%)	19 (100%)
	Mean, 437.7° [SD, 120.8°]	Mean, 329.4° [SD, 80°]