Echo time (TE) The between the mid point of the excitation pulse and the rephasing of the protons.
Echogenic Describes a structure that produces echoes.
Flip angle (FA) Refers to the angle of rotation of the net magnetization vector (NMV or M) produced by an RF pulse. Flip angles are measured relative from the longitudinal (z) axis of the main magnetic field (βo). For example, a 90-degree FA rotates the NMV from the longitudinal plane (Mz) into the transverse plane (Mxy).
Gradient echo A pulse sequence consisting of a FA (≤90-degree) excitation pulse and a gradient reversal.
Hyperechoic An increase in echoes (more echogenic) within a structure.
Hypoechoic A decrease in echoes (less echogenic) within a structure.
Inversion recovery A pulse sequence such as STIR or FLAIR that consists of an initial 180-degree pulse to invert the net magnetization followed by 90-degree and 180-degree pulses to generate a spin echo signal.
Inversion time (TI) The time between the initial 180-degree RF pulse and the subsequent 90-degree excitation pulse. Used in IR pulse sequences such as STIR and FLAIR.
Isoechoic Describes two structures having the same acoustic echogenicity.
Multislice/multidetector CT A CT scanner capable of acquiring more than one slice simultaneously per revolution of the x-ray tube. The number of slices acquired is dependent on the number of detector rows.
Proton (Spin) density—weighted A pulse sequence using a long TR and short TE value to demonstrate the concentration of hydrogen protons; the higher the concentration of hydrogen protons, the higher (brighter) the signal.
Repetition time (TR) The time between the beginning of one excitation pulse in a pulse sequence to the next excitation pulse in the same pulse sequence.
Spin echo A pulse sequence consisting of a 90-degree excitation pulse followed by a 180-degree rephasing pulse.
Spiral CT A method of scanning with continuous rotation of the x-ray tube and simultaneous continuous translation of the patient in the z-direction.
T1-weighted A pulse sequence using a short TR and short TE value to demonstrate the differences of tissues T1 relaxation. This sequence is commonly used to demonstrate the anatomy.
T2*-weighted (T-two-star) The gradient echo version of a T2-weighted spin echo pulse sequence. This pulse sequence is faster than a spin echo pulse sequence. T2* images are composed of spin-spin relaxation and inhomogeneities of the magnetic field. Image contrast in gradient echo pulse sequence depends on T2*.
T2-weighted A spin echo pulse sequence using a long TR and long TE value to demonstrate the differences between tissues with different T2 (spin-spin) relaxation times. This sequence is commonly used to identify pathology.
Windowing The process of adjusting the window center (density) and window width ...