Basic principles of computed tomography (CT)
Micro-CT scan reconstruction of Pocillopora coral. Specimen courtesy of Alex Ball, Natural History Museum.
The CT process involves several steps:
- Scanning
- Reconstruction
- Visualisation
- Data collection
Micro- and nano-CT scanners produce 2D representations of a slice of an object based on material density, measured by X-ray transmissions.
The resulting slice is made up of 3D pixels, known as ‘voxels’. Each voxel is assigned a CT (grey) value derived from a linear attenuation coefficient that relates to the density of the materials being scanned.
Since a CT scan is a mathematical representation of an object rather than a true image, it is suited to quantitative analysis of structure and geometry.
Scan resolution
The resolution of a scan is largely determined by the size of the voxels. It is in the order of:
- 3-125μm for micro-CT
- 0.2-2μm for nano-CT