Different stages of testing drugs in humans, from first application in humans through limited and broad clinical tests, to postmarketing studies. Preclinical trials are the testing in animals.

(p) The pitch (in computed tomography) is the ratio of the patient table increment to the total nominal beam width for the CT scan. The pitch factor relates the volume coverage speed to the thinnest sections that can be reconstructed. In spiral CT, dose is always inversely proportional to pitch.
Among the different manufacturers, there are various definitions of pitch depending on whether a single-detector (single-slice) or multi-detector (multi-slice) CT scanner is used.

Radiation shielding is the process of limiting the penetration of radiation into the environment, by blocking with a barrier made of impermeable material. This protective barrier is usually formed of a material with high density, for example lead that absorbs the radiation.
Radiation sources are self-shielded with absorbing material incorporated into the equipment, adjacent to the source to reduce stray radiation to the surrounding area below dose limits.
Rooms with x-ray or other radiation equipment are additionally shielded with lead-lined walls to reduce the radiation exposure to humans within the facility. The amount of shielding required to protect against different kinds of radiation depends on how much energy they have. The shielding calculations are based on the half value layer of the primary radiation beam. Sufficient half value layers of shielding are calculated to reduce the radiation exposure outside the room to reasonable levels.
Personal shielding requirements depending on the type of radiation:
See also Radiation Safety.

Radiographic noise is a fluctuation in optical density on radiographic or mammographic images, often as a result of low radiation dose.

See also Electronic Noise.

(TLD) A thermoluminescent dosimeter contains a crystalline material (lithium fluoride, phosphor) for measuring radiation dose. TLDs are usually small crystals measuring 3 mm square by 1 mm thickness. Additional filters (absorbers) help to characterize the types of the impinging radiation. When heated, TLD crystals that have been exposed to ionizing radiation give off light proportional to the received energy.