Influence of CT Radiation Dose and Field-of-View on Automatic Morphometry for Cochlear Implant Planning

In cochlear implantation (CI), precise preoperative cochlear duct length (CDL) and angular insertion depth (AID) measurements are pivotal for individualized electrode carrier selection, since recipients benefit from sufficient cochlear coverage of the electrode carrier, enabling electric stimulation of all crucial frequency bands. Since the quality of temporal bone CT largely depends on acquisition and reconstruction settings and is limited by the technical capabilities of the CT scanner, this study aims to assess how radiation dose and reconstruction field-of-view (FOV) affect automatic cochlear morphometry and electrode contact determination in conventional multislice CT.

Twenty fresh-frozen human petrous bone specimens were examined at three radiation dose levels (40, 20, and 10 mGy) using a multislice CT scanner. Each dataset was reconstructed with three different FOV settings (250, 125, and 50 mm). Preoperative CDL and AID measurements were performed with dedicated otological planning software. Maxed-out dose images (250 mGy) served as standard of reference for comparing the morphometric results.

Regardless of the selected combination of dose level and FOV, significant CDL or AID measurement differences were neither ascertained among the individual groups, nor in comparison to the reference scans (all p ≥ 0.05). Likewise, the simulation of all stimulable frequency bandwidths showed no dependency on radiation dose or FOV settings (all p ≥ 0.05).

The assessment of cochlear morphometry with conventional multislice CT imaging before CI surgery allowed a radiation dose reduction up to 75% without compromising the accuracy of software-based cochlear analysis. Notably, automatic CDL and AID measurements for surgical planning did not benefit from a smaller reconstruction FOV.