Department of Metallurgy and Materials Engineering Materials Performance and Non-Destructive Testing Optimization and validation of micro-CT for the characterization of non-bone porous materials Kerckhofs Greet, Schrooten J., Van Cleynenbreugel T., Lomov SV., Wevers M. Katholieke Universiteit Leuven

-2- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Introduction Complex bone fractures Reconstruction Regeneration Ti bone scaffolds HA bone scaffolds Polymer bone scaffolds

-3- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Introduction Bone scaffolds design: pore size between 40 en 200µm, mechanical properties (stress and strain), biocompatibility, etc. For quantifying the microstructure and the mechanical properties of bone scaffolds in a non-destructive way = high throughput screening of the design Micro-CT

-4- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Introduction Current problems with micro-CT: - Acquisition parameters by ‘trial and error’ - No quantitative validation criteria for non-bone porous materials - No protocol for image processing and analysis Experimental protocol for the optimisation and validation of micro-CT

-5- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Overview Materials Optimisation of micro-CT Validation of micro-CT Work in progress

-6- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Materials Metal bone scaffolds Ceramic bone scaffolds Polymeric bone scaffolds

-7- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Overview Materials Optimisation of micro-CT Validation of micro-CT Work in progress

-8- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Optimisation of the acquisition: µCT simulator Micro-CT device Voltage? Current? Filter? Optimal images???? µCT-simulator Detector Sample material Source Objectively determined, ‘optimal’ acquisition parameters Optimal images!!!!

-9- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Spectrum Skyscan 1172 – 50kV

-10- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Overview Materials Optimisation of micro-CT Validation of micro-CT Work in progress

-11- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Full scaffold Philips HOMX 161 X-ray system with AEA Tomohawk CT-software Full scaffold micro-CT dataset Sliced parts Slicing Image registration, binarization and overlay Optical image Validation: micro-CT vs. optical light microscopy Interpolated micro-CT image Micro-CT image interpolation Physical slicing angle Micro-CT scanning angle ≠ Micro-CT image dataset Overlay image

-12- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Experimental protocol Interpolation of the micro-CT image  Finding the corresponding micro-CT image in the dataset

-13- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Full scaffold Philips HOMX 161 X-ray system with AEA Tomohawk CT-software Full scaffold micro-CT dataset Sliced parts Slicing Image registration, binarization and overlay Optical image Validation: micro-CT vs. optical light microscopy Interpolated micro-CT image Micro-CT image interpolation Physical slicing angle Micro-CT scanning angle ≠ Micro-CT image dataset Overlay image

-14- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Automatic image registration (F. Maes - KULeuven) Result = overlapping binarized images Overlap = total green / (total blue + green) Micro-CT mismatch = total red / (total blue + green) Optical mismatch = total blue / (total blue + green) Matching Optical Micro-CT image Optical image Micro-CT Overlap

-15- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Thresholding method Overlap and mismatch: influence of threshold Too high threshold Too low threshold

-16- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Thresholding method Overlap and mismatch: influence of threshold Best threshold 89.6 % overlap 45.1 % micro-CT mismatch 10.4 % optical mismatch Reference threshold

-17- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Results for Ti bone scaffolds 36 optical and their corresponding, interpolated micro-CT images Optimal threshold = 112

-18- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Results for Ti bone scaffolds 36 optical and their corresponding, interpolated micro-CT images 82.7 ± 4.54 % mean overlap 43.8 ± 9.63 % micro-CT mismatch 17.3 ± 4.39 % optical mismatch AND… … influence of the threshold is significant!!!!!!! Limits of the micro-CT device Limited field of view Large sample dimensions Complex structure of the sample Material of the sample +

-19- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Results for Ti bone scaffolds Influence of the threshold on the surface fraction (2D) Linear model predicts an increase of 2.6 % for a decrease of 5 % in threshold!!!

-20- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Overview Materials Optimisation of micro-CT Validation of micro-CT Work in progress

-21- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Work in progress Pixel size = 13.2 µmPixel size = 3.7 µm Optical light microscopy Micro-CT High-resolution micro-CT

-22- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Work in progress Physical measurements Micro-CT measurements Changing resolution Changing threshold He pycnometry Hg porosimetry Structural analysis Optical light microscopy Binning on the detector Binning of the reconstructed images Changing magnification Cfr. Validation protocol Different device Pore size distribution % open and closed porosity

-23- Department of Metallurgy and Materials EngineeringMicro-CT symposium – 31st May 2007 Materials Performance and Non-Destructive Testing Thank you for your attention!!!