(SCT) The total scan time is the time required to collect all data needed to generate the programmed images. The scan time is related to the used pulse sequence and dependent on the assemble of parameters like e.g., repetition time (TR), Matrix, number of signal averages (NSA), TSE- or EPI factor and flip angle.
For example, the total scan time for a standard spin echo or gradient echo sequence is number of repetitions x the scan time per repetition (means the product of repetition time (TR), number of phase encoding steps, and NSA).

See also Number of Excitations, Turbo Spin Echo Turbo Factor, Echo Planar Imaging Factor, Flip Angle and Image Acquisition Time.

See also acronyms for 'scan time parameters' from different manufacturers.

The respiratory phase can be used to control imaging either by only acquiring the image data during a particular portion of the respiratory cycle (which increases image acquisition time) or by adjusting the sequence of image data collection according to the phase of the respiratory cycle in such a way as to minimize motion-induced artifacts in the reconstructed image.

See also Respiratory Ordered Phase Encoding.

Imaging techniques in which NMR signals are gathered from the whole object volume to be imaged at once, with appropriate encoding pulse RF and gradient sequences to encode positions of the spins. Many sequential plane imaging techniques can be generalized to volume imaging, at least in principle. Advantages include potential improvement in signal to noise ratio by including signal from the whole volume at once; disadvantages include a bigger computational task for image reconstruction and longer image acquisition times (although the entire volume can be imaged from the one set of data). Also called simultaneous volume imaging.

(SE) The most common pulse sequence used in MR imaging is based of the detection of a spin or Hahn echo. It uses 90° radio frequency pulses to excite the magnetization and one or more 180° pulses to refocus the spins to generate signal echoes named spin echoes (SE).
In the pulse sequence timing diagram, the simplest form of a spin echo sequence is illustrated.
The 90° excitation pulse rotates the longitudinal magnetization (Mz) into the xy-plane and the dephasing of the transverse magnetization (Mxy) starts.
The following application of a 180° refocusing pulse (rotates the magnetization in the x-plane) generates signal echoes. The purpose of the 180° pulse is to rephase the spins, causing them to regain coherence and thereby to recover transverse magnetization, producing a spin echo.
The recovery of the z-magnetization occurs with the T1 relaxation time and typically at a much slower rate than the T2-decay, because in general T1 is greater than T2 for living tissues and is in the range of 100-2000 ms.
The SE pulse sequence was devised in the early days of NMR days by Carr and Purcell and exists now in many forms: the multi echo pulse sequence using single or multislice acquisition, the fast spin echo (FSE/TSE) pulse sequence, echo planar imaging (EPI) pulse sequence and the gradient and spin echo (GRASE) pulse sequence;; all are basically spin echo sequences.
In the simplest form of SE imaging, the pulse sequence has to be repeated as many times as the image has lines.
Contrast values:
PD weighted: Short TE (20 ms) and long TR.
T1 weighted: Short TE (10-20 ms) and short TR (300-600 ms)
T2 weighted: Long TE (greater than 60 ms) and long TR (greater than 1600 ms)
With spin echo imaging no T2* occurs, caused by the 180° refocusing pulse. For this reason, spin echo sequences are more robust against e.g., susceptibility artifacts than gradient echo sequences.

See also Pulse Sequence Timing Diagram to find a description of the components.