Micro-computed tomography (µCT) is an imaging technique that uses X-rays to produce cross-sectional images of an object, which can be reconstructed to create a three-dimensional model. It allows for non-destructive quantitative analysis of the density, geometry and microarchitecture of mineralized or high-density material, particularly bone and biomaterials stained with contrast chemicals. The reason the technique is called micro-computed tomography is that the pixels are in the micrometer range; much smaller than conventional clinical computed tomography (CT) scanners. However, with an increase in resolution comes a decrease in the field of view that can be imaged. This means that µCT can only be performed on small specimens such as human biopsies or animal bones.
We perform µCT scanning using two Scanco µCT40 scanners (Figure A). The Scanco µCT40 can obtain resolutions as low as 6 μm and can contain specimens up to 36 mm in diameter and 80 mm in length. The setup uses a cone-beam system for scanning and the X-ray source and detector remain stationary while the specimen is rotated.
A wide variety of results can be produced including:
- Trabecular bone analysis
- Cortical bone analysis
- 2D and 3D images
- Finite element analysis
Additional information on the specifications of our system can be found on the Scanco website.
If you are interested in our µCT services or collaborating, please contact Ara Nazarian. If possible, please fill out and include the CAOS µCT Requisition form. This form requests project details as well as contact and specimen information.
CT-based Structural Rigidity Analysis
We have developed and validated a technique called Computed Tomography-based Structural Rigidity Analysis (CTRA) in a series of ex-vivo and in-vivo experiments to monitor fracture risk associated with local (skeletal metastasis, fracture healing) and systemic (osteoporosis, osteomalacia) skeletal pathologies.
The axial (EA), bending (EI) and torsional (GJ) rigidities for each bone are calculated on each transaxial CT image through the bone using CTRA (Figure B). For each trans-axial image, EA, EI and GJ are calculated by summing the modulus-weighted area of each pixel within the bone contour by the position of the pixel relative to the centroid of the bone cross-section. The cross-section through the affected bone with the largest reduction in rigidity is considered the weakest link and is assumed to govern the failure behavior of the entire bone.
The density (ρ) of each pixel corresponding to bone is calculated from the CT images, using a hydroxyapatite calibration phantom to convert CT Hounsfield units to bone mineral density. The modulus of elasticity for trabecular bone is derived:
and the modulus for cortical bone was derived:
where the transition from trabecular bone to cortical bone was assumed to occur at an apparent density of 1.1 g.cm³. EA (axial rigidity) and EI (bending rigidity) were calculated using:
where x = distance to neutral axis, da = pixel area, X = coordinate of the modulus weighted centroid, which is also assumed to be the location of the neutral bending axis of the bone.
EA provides a measure of the bone's resistance to uniaxial loads; EI provides a measure of the bone's resistance to bending moments, and GJ provides a measure of the bone's resistance to torsional moments.
Please review relevant human and animal-based publications on this project below.
If you are interested in our CTRA analysis services or collaborating, please contact Ara Nazarian.
Although imaging is often used as a surrogate to evaluate bone fragility, direct measurements of mechanical strength are undoubtedly the gold standard for providing information about the mechanical integrity of bone. Destructive testing of a specimen provides a load-deformation curve that can provide many useful extrinsic properties, such as stiffness, ultimate strength, and displacement-to-failure. Alternatively, the load-deformation curve can be converted into a stress-strain curve that can provide intrinsic properties such as Young's modulus.
At our facility, we have access to a range of load frames that are capable of testing a wide range of specimens in various standard loading configurations. The smallest are handled by Synergie 200 (MTS Systems, Eden Prairie, MN) or Bose ElectroForce 3230 (Bose Corporation, Eden Prairie, MN). Larger specimens are tested on an Instron 8511 MTS (Instron, Norwood, MA). For the very largest specimens (such as human and bovine), we use an Interlaken Model 1331 (Interlaken Technology Corporation, Chaska, MN). These various systems can be outfitted with jigs to perform compression, tensile, bending, or torsional tests as required.
If you are interested in our µCT services or collaborating, please contact Ara Nazarian. Please fill out and include the CAOS Mechanical Testing Requisition form. This form requests project details as well as contact and specimen information.