An algorithm is a computer compatible equation. Computed tomographic algorithms reconstruct a function from its projections. A very large number of measurements are processed with complex mathematical operations to compute cross-sectional images.

X-rays contain a range of energies (polychromatic photons), the higher energies pass through the patient, the lower energies are absorbed or scattered by the body. Ideally, the x-ray beam should be monochromatic or composed of photons having the same energy. Strong filtration of the beam results in more uniformity. The more uniform the beam, the more accurate the attenuation values or CT numbers are for the scanned anatomical region.
There are two types of filtration utilized in CT:
Inherent tube filtration and filters made of aluminum or Teflon are utilized to shape the beam intensity by filtering out the undesirable x-rays with low energy. Filtration of the x-ray beam is usually done by the manufacturer prior to installation. The half value layer provides information about the energy characteristics of the x-ray beam. Too much filtration produces a loss of contrast in the x-ray image.
A mathematical filter such as a bone or soft tissue algorithm is included into the CT reconstruction process to enhance resolution of a particular anatomical region of interest.

A logarithm is the exponent to which the base must be raised to produce a given number.
Logarithms are used to express dynamic processes, also in diagnostic imaging processes.



See also Algorithm, Integral, and Differential.

The pitch factor is a selectable CT parameter. The definition depending on the IEC standards is the ratio of the table speed per rotation and the total collimation.
The choice of pitch factor is determined on practical considerations and on the availability of the computed tomography algorithms and parameters for image reconstruction.

See Pitch.

Reconstruction is the mathematical process by which the displayed image is produced from the raw data.
Used equipment and data processing methods to reconstruct CT images:
See also Zoom Reconstruction, Reconstruction Matrix and Multiplanar Reconstruction.