Question

High-resolution peripheral quantitative computed tomography

1. How does this technique work and what does it measure?
2. What equipment is required for this technique?
3. How is the experiment/measurement performed?
4. What do the typical results look like? (you may want to include images here)  

Answer 1

Ans 1: High-resolution peripheral quantitative computed tomography is a newly developed in vivo clinical imaging modality. It can assess the 3D microstructure of cortical and trabecular bone at the distal radius and tibia and is suitable as an input for microstructural finite element analysis to evaluate bone’s mechanical competence.

Ans 2:

High-resolution peripheral quantitative computed tomography is an imaging technique that uses computerized processing of X-ray attenuation for the acquisition of sectional images. From the slices, it is possible to produce a three-dimensional (3D) high-quality model. The improved resolution of 3D images provided by this new device coupled with computer-based finite element analysis modeling provides estimates of functional properties of the material.

Ans 3:

Initially, a two-dimensional X-ray scan, is obtained to determine a precise region for the three dimensional measurement.

Each site includes 110 computerized tomography slices, totaling an extension of 9.02mm along the axial axis of the bone.

The acquisition of these images takes about 3 min.

After the acquisition of images, the system automatically performs an initial evaluation that consists of two processes:

(1) processing of digital data in sectional images

(2) construction of a 3D model

The first contour is characterized by the outer envelope of the radius, which is then used to define the full compartment. The software is provided with a semiautomatic contouring algorithm.

After obtaining this contour, the next necessary step is to determine the inner contour delineating cortical from trabecular bone, with the goal of obtaining isolated data relating to each of the compartments. This procedure automatically creates the different compartments based on image processing.

A series of tests to determine the main bone parameters used in the literature follows.1 Thus, mathematical algorithms are required that allow such calculations.

Ans 4:

The two mechanical properties of the bone under study are estimated, considering that no histofunctional study of bone tissue is being carried out:

• The first of them is the Young’s modulus, a measure of the ability of a material to return to its original shape after removal of a stress force, thus indicating the tissue’s elasticity. This measure is valid only in the range of forces in which the elastic deformation occurs, namely, when there is neither microrupture nor change in bone structure, enabling it to return to its original form.

• The second mechanical property is a measure of the Poisson effect, which is the tendency of a material to become thinner when it is stretched at a given axis. In other words, when a material is pulled, it increases it size in the axis of traction, and decreases its size in the other two axes.

In response to the tensile force applied, the elasticity of the material will tend to bring it to its original shape. This trend can be understood as a force that will shrink the material in the direction of its stretching and will increase it in the other directions. The Poisson ratio is a ratio between the first and second forces.