Virtual rendering techniques in otologic imaging.

Virtual postprocessing techniques combine the advantages of condensing the large amounts of data provided by high-resolution (HR) cross-sectional imag ing modalities with those of three-dimensional (3D) imaging. The techniques and indications for virtual representations in imaging of the middle ear ( ME), internal ear (IE), and cerebellopontine angle (CPA) are presented toge ther with practical examples. Material and methods: HR data sets acquired b y computed tomography (CT) and magnetic resonance imaging (MRI) in patients with ME, IE, and CPA pathologies were transferred to a workstation via an internal network to generate endo- or extraluminal 3D views by means of the volume rendering technique (VRT). The source data were acquired using scan ners and imaging protocols with the highest resolution available at present : a multislice spiral CT (MSCT) with a slice thickness of 0.5 mm and a reco nstruction increment of 0.2 mm and a 3D CISS sequence with a slice thicknes s of 0.5 mm for MRI. Results: Virtual endoscopy was superior to cross-secti onal images for assessing ME pathologies like dysplasia, postoperative chan ges, and destructive bone processes with extensive soft-tissue involvement; fibrous obliterations of the internal ear and labyrinthine dysplasia were depicted with a superior image quality on 3D renderings compared to convent ional reconstruction techniques. Virtual endoscopy of the CPA and external acoustic meatus (EAM) was helpful in detecting and visualizing neurovascula r conflicts and in assigning small intrameatal tumors to components of the acousticofacial bundle. A common feature of all applications was that the l arge numbers of source images could be reduced to a few 3D reconstructions for documentation and optimized communication of the findings between the r adiologist and otologist. Conclusion: Virtual rendering makes an important contribution towards establishing, presenting, and documenting the findings when certain otologic pathologies have to be assessed. It can be used for routine imaging and allows for more efficient handling of the large amounts of imaging data generated by high-resolution cross-sectional imaging modal ities.