Computed tomography data based rapid prototyping model of the temporal bone before cochlear implant surgery

Rapid prototyping (RP) technique allows automatic fabrication of 3D model parts. This method was applied to make a temporal bone model before cochlear implant surgery. A helical CT scan is used to acquire high resolution data from the middle and the inner ear of the patient. From the scanning data bone structures and soft tissues can be separated because their different grayscale pixel values. By using a guided image processing tool the desired parts of the anatomy can be extracted and 3D data created. The segmented data are processed to the form suitable for creating a high accuracy RP model. The RP model is made in the stereolithography (SLA) process by means of a computer guided HeCd laser beam inducing polymerisation of acrylic solution as it passes layer by layer over the surface of the polymer solution. In this prototype model the anatomy of the temporal bone can be clearly visualised, including, e.g., mastoid cells, tympanic cavity, bony canal of facial nerve, and round and oval windows. The inner ear spaces including vestibule, semicircular canals and cochlear turn are also shaped. The transparent acrylic material allows bonelike mechanical handling. The RP model can be dissected and used in individual surgical planning and simulation prior to cochlear implantation.