Influence of Image Quality on Semi-Automatic 3D Reconstructions of the Lateral Skull Base for Cochlear Implantation Frank Heckel1,2, Stephan Zidowitz1, Thomas Neumuth2, Mary Tittmann3, Markus Pirlich3, Mathias Hofer3 1 Fraunhofer Institute for Medical Image Computing MEVIS, Bremen, Germany 2 Innovation Center Computer Assisted Surgery, Leipzig, Germany 3 Leipzig University Hospital, Department of ENT-Surgery, Leipzig, Germany

Introduction Complex Ear Anatomy Ossicles Ossicels = Gehörknöchelchen Semicircular canals = Bogengänge Cochlea = Hörschnecke Tympanic cavity = Paukenhöhle Corda tympani = „Zugennerv“ Facial nerve Corda tympani Round window

Introduction Real Situs

Introduction Image Data and 3D Reconstruction

Is the quality of the CT images sufficient for surgery planning? Introduction Research Questions Is the quality of the CT images sufficient for surgery planning? Does bad image quality influence the quality of semi-automatic 3D reconstructions (accuracy and reproducibility)?

Material and Methods Study: Segmentation Quality* CT data from 12 patients Acquired at University Hospital Leipzig Resolution: 0.19 x 0.19 x 0.19mm – 0.393 x 0.393 x 0.393mm Reference segmentation for each structure in each image by an experienced ENT surgeon in cooperation with an experienced neuroradiologist Each image was processed by 2-4 physicians Segmentation quality was measured by Jaccard index Average = measure for accuracy Maximum difference = measure for reproducibility We used only a subset of the data of the study by Prilich et al. * Pirlich et al., European Archives of Oto-Rhino-Laryngology, 2016, available online 09/16

Material and Methods Wizard-Based Semi-Automatic 3D Reconstruction* * Franz et al., BVM 2014

Material and Methods Study: Image Quality Annotation of each image by an experienced ENT surgeon

Results Image Quality

Results Accuracy Ossicels = Gehörknöchelchen Semicircular canals = Bogengänge Cochlea = Hörschnecke Tympanic cavity = Paukenhöhle Corda tympani = „Zugennerv“ AC = acoustic canal, OS = ossicles, TC = tympanic cavity, NF = facial nerve, NC = chorda tympani, RW = round window, CO = cochlea, vestibule, inner ear canal, SC = semicircular canal

Results Reproducibility Ossicels = Gehörknöchelchen Semicircular canals = Bogengänge Cochlea = Hörschnecke Tympanic cavity = Paukenhöhle Corda tympani = „Zugennerv“ AC = acoustic canal, OS = ossicles, TC = tympanic cavity, NF = facial nerve, NC = chorda tympani, RW = round window, CO = cochlea, vestibule, inner ear canal, SC = semicircular canal

Conclusion Image quality is not always sufficient (resolution and SNR) Even though the data has been acquired at a University Hospital Suboptimal image quality seems to (negatively) influence reconstruction quality (accuracy and reproducibility) – at least for some structures Limitations of the study: Small number of CT images from only one site Jaccard index as only indicator for reconstruction quality Image quality has only been rated by one ENT surgeon Low reproducibility of absolute grading studies

Thank You frank.heckel@mevis.fraunhofer.de