HRCT :

High-resolution computed tomography; usually applied to pulmonary imaging.

   Inhomogeneity :

The slight variation in uniformity of static magnetic field expressed in parts per million (ppm) as a fractional deviation from the average value of the field.

   Inversion recovery(IR) :

A basic pulse sequence which inverts the magnetization and measures the recovery rate as the nuclei return to equilibrium. This rate of recovery is dependent on the T1 relaxation rate.

   Inversion time (TI) :

The time from the centre of the first investion pulse (180°) to the beginning of the second (90°) excitation pulse in an MR sequence.

   Ionizing radiation :

Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become charged or ionized. Examples are gamma rays and neutrons.

   K-space :

The space which is filled with information (termed “raw data matrix”) and undergoes a Fourier transform to form the MR image. The points at the centre of this data matrix represent low spatial frequencies (which give gross signal levels i.e. contrast in the MR image). Increasing the offset from the centre corresponds to higher spatial frequencies (edge detection i.e. image sharpness). By manipulating K-space faster sequences can be implemented as in fast (or turbo) Imaging.

   Magic angle artefact :

In joint imaging if a tendon is orientated at a certain angle (55°) to the static main magnetic field, the tendon appears brighter on T1- and proton density (intermediate)- weighted images but normal low signal on T2-weighted images. This artefactual increase in signal within the tendon is termed the magic angle effect and can be potentially confused with pathology. This effect is due to the highly ordered structure of tendons, which are composed of type I collagen. This ordered structure restricts the motion and orientation of water protons, with consequent reduction in the dipolar interaction and thus an increase in signal.

   Magnetic moment :

A measure of the magnitude and direction (vector quantity) of the magnetic properties of an object or particle that cause it to align with the static main field and creates its own local magnetic field.