Table 2.

List of technical terms

Chemical shift	Resonance frequency of a nucleus in relation to the frequency of a standard chemical compound. See Shielding.
Hydrogen bond	Electrostatic force between molecules in which hydrogen is bound to an electronegative atom, e.g. oxygen. The charge of these molecules is polarized and therefore the negative end of the molecule attracts to the positive end of a similar molecule.
Brownian motion	Rapid, irregular movement.
Shielding	The effect of an electron cloud on the resonance frequency of an atom. In an external magnetic field the electron cloud induces an opposing magnetic field which reduces the local magnetic field of the atom leading to reduced resonance frequency (and greater chemical shift). The higher the electron density the stronger the shielding is.
RF-spoiled gradient echo sequence	Magnetic resonance imaging sequence in which echo is produced using a bipolar gradient and a phase of the radiofrequency pulses is systematically incremented in order to reduce coherence artifacts and repetition time.
Gyromagnetic ratio	The ratio of the magnetic momentum in a particle or system to its angular momentum.
Magnetic susceptibility	The ratio of the magnetization of a material and an external magnetic field. A measure of how much a material will become magnetized in a magnetic field.
Dipole-dipole interaction, Dipolar interaction	Interaction between two magnetic dipoles. Most important mechanism responsible for relaxation of the magnetization in biological tissues
Larmor frequency	The rate of precession of the magnetic moment of the proton around the external magnetic field.
Variable flip angle gradient echo sequence	Magnetic resonance imaging sequence in which echo is produced using a bipolar gradient and sequence is repeated with variable flip angles.
B1 inhomogenity	Non-uniform excitation of the atoms resulting in faulty flip angles within the object.
Transverse relaxation time, spin-spin relaxation time, T2 relaxation time	Time constant for decay of transverse magnetization after radiofrequency pulse.
Turbo-spin echo readout	Magnetic resonance imaging technique in which the phase-encoding gradient is changed between echoes and therefore multiple lines of k-space (i.e., phase-encoding steps) can be acquired within a given repetition time which may reduce imaging time significantly.
Diffusion gradient	A strong pulsed gradient that is used as pairs in order to cause a signal loss from moving spins.
Paramagnetic	A material including oxygen and metal ions and having a small positive susceptibility. Decreases relaxation times.
Shear modulus	The ratio of shear stress to the shear strain.
Scattering cross-section	A quantity which is proportional to the rate of radiation–target interaction.
Echogenicity	The ability of a material to return an echo in ultrasound examinations.
Cathode	A negative electrode from which electrons are emitted toward a positive electrode, anode.
Compton scattering	A phenomenon in which a photon strikes an electron and scatters. The direction and energy of the photon are changed.
Radiolength	Wavelength. In a periodic wave, the length of one complete wave pattern, i.e. the distance from any point to the corresponding point on the next repetition of the wave shape.
brightness temperature	Brightness temperature or radiance temperature is the temperature of a black body in thermal equilibrium with its surroundings, in order to duplicate the observed intensity of a gray body object at a frequency
Lossy body	A medium in which a significant amount of the energy of a propagating electromagnetic wave is absorbed per unit distance traveled by the wave.
Piezoelectric sensor	A device that measures pressure by piezoelectric effect. An electric charge is created when pressure is applied to a piezoelectric material.
Thermoelastic expansion	Volume expansion due to temperature rise.
Isothermal compressibility	Measure of relative volume change as a response to pressure change.