Micro-computed tomography
Mechanical testing
Microindentation
High resolution peripheral computed tomography

Micro-computed Tomography

Micro-computed tomography (microCT) is an imaging technique that uses x-rays to produce cross-sectional images of an object that 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 microCT can only be performed on small specimens such as human biopsies or animal bones.

In the Bouxsein Lab, we perform microCT scanning using two Scanco uCT40 scanners. The Scanco uCT40 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. Four computers are available to perform analysis. A wide variety of results can be produced and many analyses are available, including:

• Trabecular bone analysis
• Cortical bone analysis
• 2D & 3D images
• Finite element analysis

Details regarding use of μCT for analysis of rodent specimens can be found in the recent guidelines authored by Dr. Bouxsein and colleagues. PDF

Additional information on the specifications of our system can be found on the Scanco website.

If you are interested requesting microCT services or collaborating, please contact Mary Bouxsein or Leeann Louis. If possible, please fill out and include the CAOS MicroCT Requisition form and the Sample Assignments form, which are found below. These forms request contact information, project details and specimen information.

We are also able to prepare your specimens if it is helpful to you. This includes dissection, removal of requested bones, and preservation of bones. We typically use the femur, tibia and/or lumbar vertebrae for scanning and analysis, but we are able to remove and scan any bones at your request. We are able to work with specimens that are frozen, or fixed in ethanol or formalin.

CAOS-MicroCT Requisition Form

Sample Assignments

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Mechanical Testing

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. Destructively testing a specimen to failure 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 loadframes that are capable of testing a wide range of specimens in various standard loading configurations. The smallest are handled by Synergie 100 (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 - i.e. 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.

Link to high speed testing of saw-bones femur in sideways fall configuration: VIDEO

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Microindentation — Reference Point Indentation

As part of our assessment of tissue properties, we perform microindentation using a novel reference point indentation device developed by ActiveLife Scientific. Reference Point Indentation enables assessment of bone material properties without requiring special surface preparation. As such, the measurement can be performed not only on excised bone specimens, but also in vivo.

This is made possible due to the unique design, where the outer reference probe shields the inner test probe from surrounding soft tissues. At the same time, it establishes a reference point at the site of indentation for measuring displacement. This allows accurate indentation measurements on a variety of bone surfaces. Furthermore, the device conducts cyclic testing, designed to reflect the bone’s resistance to fracture at the tissue level.

We are performing indentation measurements in rodent models, as well as primate and human cadaveric specimens. For accurate and reliable measurements, specimens must be stored fresh or frozen. Fixation in ethanol or formalin will alter the tissue properties. If you are interested in having indentation measurements performed on your bone specimens, contact Leeann Louis.

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High resolution peripheral computed tomography (hr-pQCT)

In collaboration with the Bone Density Center at Massachusetts General Hospital, we are assessing bone microarchitecture in vivo in patients using high-resolution peripheral computed tomography (hr-pQCT, XtremeCT, Scanco Medical AG). This device allows assessment of volumetric bone density and microarchitecture of the distal radius and distal tibia. Images are acquired using a voxel size of 82 μm, with scan times of only a few minutes. For further information contact Dr. Bouxsein.

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