(Å* or A*) A unit used to measure the wavelength of x-rays.
Definition: 0.1 nanometer or 10^-10 meter or 100 picometer.

The calibration factor helps to convert between the measured value of a parameter and the actual value of that parameter in a system.
This normalization is necessary in cases where detectors and sensors do not directly sample a parameter, for example the radiation energy is measured by a detector that produces an electrical pulse whose total charge is proportional to the supplied radiation.

The gantry aperture is the opening through which the table with the patient moves for the examination. Typical diameters of the gantry range from 50 to 85 cm. The gantry aperture diameters between 70 and 85 cm are useful for biopsy procedures and obese patients. Larger gantry apertures allow for easier handling of the biopsy equipment.
The scanning field of view in which the CT data are acquired is smaller than the gantry aperture diameter.

Same as micrometer (µm), one millionth of a meter.

See Meter.

(A or amp) The SI base unit of electric current.
Definition: Two parallel conductors, infinitely long and having negligible cross section should be placed 1 meter apart in a perfect vacuum. One ampere is the current that creates between them a force of 0.2 µN (micronewton) per meter of length.
One ampere represents a current flow of 1 coulomb of charge per second.
One ampere of current results from a potential distribution of 1 volt per ohm of resistance, or from a power production rate of 1 watt per volt of potential.
The unit is known informally as the amp, but A is its official symbol and is named for the French physicist André-Marie Ampère.
See also System International.