A metric unit of temperature.
Definition: One degree is 1/273.16 of the difference between the triple point of water (at exactly 0.01°C) and absolute zero.
The triple point of water is the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states. Absolute zero is the temperature at which all molecular motion discontinues.
The Celsius temperature scale is named for the Swedish astronomer and physicist Anders Celsius (1701-1744), who used a similar scale.

See also Kelvin, Fahrenheit.

(COR) The center of rotation is the rotation or system axis in SPECT systems.

(CPU) The central processing unit is the main microprocessor unit in a computer. To increase processing power, parallel working CPUs are in use today.

The cerebral blood pool can be imaged with single photon emission computed tomography (SPECT) and positron emission computer tomography (PET) techniques. The used radiopharmaceuticals are technetium-99m labeled red blood cells (RCBs) for SPECT and O-15 labeled water for PET imaging. Measured can be cerebral blood volume, brain perfusion and cerebral metabolism.

See Cerebral Metabolic Imaging, Fluorodeoxyglucose, Regional Cerebral Blood Flow, Coincidence Detection, Annihilation Coincidence Detection and Cyclotron.

Cerebral metabolic imaging can be accomplished with positron emission computer tomography (PET), magnetic resonance spectroscopy, and functional magnetic resonance imaging.
PET uses positron-emitting radioisotopes of elements with short half-live such as fluorine-18, oxygen-15, nitrogen-13, and carbon-11 as tracers to image and to measure the cerebral metabolism.