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.

A chelate is a heterocyclic chemical compound whose molecules consist of a metal ion attached by coordinate bonds to at least two nonmetal ions. The parent organic compound is known as a chelating agent - for example, DTPA (diethylenetriaminepentaacetic acid) used in contrast agents. Chelates are used in analytical chemistry, in agriculture as carriers of essential trace metals, in water softening, and to remove an excess of iron, which may build up to toxic levels in the body. Metalloproteins may influence the performance of enzymes or provide a mechanism for the storage of iron in the spleen and plasma of the human body.
Paramagnetic metal ions such as gadolinium improve the MRI signal, but the toxicity of these uncomplexed metal ions makes the use of a chelate to bind the metal ion essential. The chelated metal ion could be safely excreted.

Chemical shift depends on the nucleus and its environment and is defined as nuclear shielding / applied magnetic field. Nuclei are shielded by a small magnetic field caused by circulating electrons, termed nuclear shielding. The strength of the shield depends on the different molecular environment in that the nucleus is embedded. Nuclear shielding is the difference between the magnetic field at the nucleus and the applied magnetic field.
Chemical shift is measured in parts per million (ppm) of the resonance frequency relative to another or a standard resonance frequency.
The major part of the MR signal comes from hydrogen protons; lipid protons contribute a minor part. The chemical shift between water and fat nuclei is about 3.5 ppm (~220 Hz; 1.5T). Through this difference in resonance frequency between water and fat protons at the same location, a misregistration (dislocation) by the Fourier Transformation take place, when converting MR signals from frequency to spatial domain. This effect is called chemical shift artifact or chemical shift misregistration artifact.

Quick Overview
Please note that there are different common names for this artifact.

During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.

For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.

See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.

An iron-based contrast agent with large molecular size, which prevents diffusion into body tissues and will be developed for MR imaging of the liver (taken up by macrophages), tumor microvasculature and microvessel permeability. The blood half live of the particles with 11-20 nm diameter is 3-4 hours.
At this time the development of Clariscanâ„¢ is discontinued.

See also NC100150 Injection and Ultrasmall Superparamagnetic Iron Oxide.