Orthopedic Application of microCT

Orthopedic application of microCT

In orthopedic research into screw implants in bone, it is often the goal to examine osteointegration, that is, the status of bone immediately surrounding the implant. MicroCT can provide 3D image data of the implant and surrounding bone to facilitate such peri-implant analysis.

Frequently the implant is metallic, which poses a challenge to microCT imaging, since artefacts are created surrounding the metal due to its high x-ray absorption and consequent extreme beam hardening. The new SkyScan2211 multiscale nanoCT has an X-ray applied voltages up to 190 kV allowing artefact-free analysis of the bone immediately adjacent to the implant surface.

For this, the reference level function in CTAn can help simplify the selection of the cross-section height range in the Z axis, relative to your selected landmark.

In short, a VOI mask is created based on the binary of the metal implant. This binary is filled and dilated to create an ROI surface at a constant distance from the metal surface, set by the pixel value of the dilation. (Some dilation is always needed since the gradient of attenuation from the highly dense metal extends a few pixels away from the implant surface.) This dilated mask allows direct measurement of the bone implant contact (BIC). Running this analysis in 2D restricts the analysis to the sides of the implant in contact with skeletal tissue.

Extending the “BIC” concept into the third dimension is straightforward. You can create a 3D annular (ring) VOI around the implant within which peri-implant bone can be analyzed in full 3D, giving much richer information than BIC alone. Analysis by BIC and annular VOI can be extended further from the implant surface in successive steps.

Bruker microCT News

With around 60 abstracts submitted for the microCT User Meeting we already thank all the authors for their contribution! As a reminder, the deadline for registration is April 3. We look forward to welcome you all to Bruges.
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Accurate analysis of bone around the implant

The first step is adjustment in DataViewer of the 3D orientation of the scan dataset, such that the implant's long axis is orthogonal to the crossection's XY plane.

A new dataset is saved in which the image data is realigned as just described and restricted in size to only the necessary volume around the implant at the chosen site of analysis. The VOI selection process then moves to the CT-Analyser (CTAn) program, where a segment along the implant relative to a landmark such as the level of insertion into the bone is selected.

3D models
Surface rendered models of the implant screw (blue) and surrounding bone (gold) at a precisely controlled distance from the implant surface – Bone implant contact (BIC) taken to the 3rd dimension.
cross section implant
Small part of a cross section through the implant, the annular ROI and the bone formation inside the ROI.