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Computed Tomography: CT-Empowered Material Research and In-Vivo Testing

June 4, 2012
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CT-scanner grades up titanium implant research at the NRC.

Pictured is the cross-section of a carbon fiber showing layer delamination, similar to a CT scan of other materials, such as titanium foam. Source: Nikon Metrology


Industrial material researchers at the National Research Council Canada (NRC) investigate titanium foam plugs that have been implanted into rabbits. After six weeks, they operate an industrial CT-scanner to visualize bone ingrowth into the porous titanium foam implants. Fast reconstruction of volumetric images enables the researchers to accurately trace where and to what extent bone structure has penetrated into the porous implant. Micro CT-technology allows the researchers to study–in 3-D, with increased speed, depth and precision–the behavior of the porous material, and is a major step for-ward for material development when compared to destructive and time-consuming 2-D imaging technologies.

In general, the development of implants is a 3-step process: developing innovative implant material, in-vitro biocompatibility and in-vivo animal testing for implant prototypes validation, and testing implants in human beings. NRC extensively uses the industrial CT scanner both for implant-related material research and invivo testing purposes.

Titanium foam is a material that is particularly suited for implants because it combines biocompatibility, good surface roughness and high strength. Its ramified porous structure provides sufficient room for bone ingrowth. Industrial material researchers use the CT scanner–equipped with 225kV x-ray micro-focus source and 2000x2000pixel flat panel–to closely monitor the processing steps of titanium foam. Reconstructed CT-volumes of the structure before and after the sintering step enable researchers to verify pore size distribution, the presence of defects, and evaluate the dimensional stability of the titanium foam.

Developing Stronger Implants with a Longer Life

The 4 mm cylindrical titanium foam plugs were implanted in a rabbit femur at the Department of Orthopedic Surgery, McGill University Health Center, and after 6 weeks, the implants were extracted and encapsulated into a mounting resin. At this point, the focus of CT scanning shifts from material re-search to histology. To obtain long implant life, new bone structure should relatively easily expand into the pores of the titanium foam structure. This ensures solid implant locking and optimum load transfer between bone and implant.

CT-scanning visualizes the entire internal structure of the implant without damaging the specimens. High-resolution X-ray images generate accurate 3D digital volumes that serve as input for very detailed statistical investigations. In this regard, the pore surface occupied by bone tissue is of major interest. More detailed information includes the minimum/maximum pore size that contains bone. All this in-formation can be retrieved efficiently using CT-scanning.

Better Research Through CT Visualization Technology

CT-scanning at highest resolution involves dazzling datasets and massive data processing. Data acquisition of the implant takes about 5 hours, while processing the data for 8GB volume reconstruction requires one additional hour. This is achieved using a stand-alone system. More powerful processing hardware and software installed at NRC reduces data processing to only 5 minutes.

On average, it takes about one working day to take the measurement, process the data, and perform initial observation. This compares favorably to the traditional destructive 2-D visualization approach that consists of cutting and polishing the sample in order to observe the structure using light transmission or scanning electron microscope. NDT

Specifications

  • Detailed volumetric imaging of porous implant foam structure
  • CT scanner applied both for material research and histology
  • Graphic data drives statistical investigation of foam pore size and bone ingrowth
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