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Graham Treece


ENGINEERING TRIPOS PART IIA

Module 3G4 - Medical Imaging and 3D Computer Graphics

Titanium cranioplasty


In this work, medical imaging, computer graphics, surface interpolation and computer-controlled milling are used to create titanium cranial implants at Christchurch Hospital, New Zealand.

Researchers: Jonathan Carr, Richard Fright and Rick Beatson, now with Applied Research Associates NZ Ltd .

Skull with defect

Ray-tracing is used to depict bone surfaces within a stack of CT data slices.

A user graphically identifies a defect in the skull by highlighting the sound bone surrounding the defect

Defect and prosthesis support



incomplete depth-map interpolated depth-map

Radial basis function (RBF) approximation is used to fit a surface to the incomplete depth-map corresponding to the rendered view of the defect. The surface of the skull is smoothly interpolated across the defect. The thin-plate spline basis is chosen in this application.

CNC mill

A computer numerical controlled (CNC) mill produces a model of the defect and a mold in the shape of the interpolated surface.

Flat titanium plate is pressed into the mold in a hydraulic press.

Plate and press
Plate in mold

The finished annodised plate fits the mold.

The perimeter holes in the plate are for the mounting screws and the central holes allow fluid to circulate. Perforations give the plate a limited amount of adjustment in theatre.

Finished plate and mold
Plate fitted in operation

The plate is fixed in place with titanium screws.


Author: Jonathan Carr.
© 2005 Cambridge University Engineering Dept and Graham Treece .
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