Trigonometric functions are mathematical functions of an angle. There are six basic trigonometric functions (Sine (sin), Cosine (cos), Tangent (tan), Cotangent (cot), Secant (sec), Cosecant (cosec)), commonly defined as ratios of two sides of a right triangle. Used in MRI for Cartesian sampling, to describe radio frequency signals, etc.

(UTSE) The ultrashort turbo spin echo (TSE / FSE) sequence is a technique with extremely short echo spacing, resulting in shorter scan times. This is an advantage in areas where motion is a problem, for example dynamic or abdominal imaging. The shorter scan time and echo spacing are achieved by using a higher TSE factor and an increased data sampling rate.
Disadvantages are the decrease in SNR (caused through the increase of the bandwidth) and artifacts if minimum echo spacing is used (incomplete dephasing of the 180° pulse FID).

See also Fast Spin Echo.

The ensemble of raw data points collected during the signal readout. For example, during Cartesian sampling, normally used to refer to data collected with a fixed value of the phase encoding gradient. Also referred to as one line of k-space. In projection reconstruction, the line is radial oriented, while in spiral imaging, it is a spiral.

A wrap around artifact (also called backfolding artifact or aliasing artifact) is produced by inadequate sampling or digitization. Wrap around artifacts result from digitizing fewer than two samples per period in a periodic function. Aliasing can occur in MR imaging whenever the scanned area extends beyond the field of view. These areas extending beyond the field of view boundaries are aliased back into the image to appear at artifactual locations.

Quick Overview

Zipper artifacts appear as dashed lines. There are various causes for this MRI artifact.
Most of zipper artifacts result from inhomogeneities of the magnetic field caused by interferences with radio frequency from various sources ('your radio is working in the scanner room means your shielding is not working'). Software and equipment problems can also cause zipper lines in both directions.

Scanning room door during the acquisition of images is closed, shielding is working, and all disturbing devices are removed?

See also Room Shielding, Active Shielding, Radio Frequency Shielding.