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.

Often used to indicate an image where most of the contrast between tissues or tissue states is due to differences in tissue T2 created typically by using longer TE and TR times.
This term may be misleading in that the potentially important effects of tissue density differences and the range of tissue T2 values are often ignored.
Choosing the machine parameters such that TR greater than T1 (typically greater than 2 000 ms) and TE less than T2 (typically greater than 100 ms) and noting that (1-exp(-TR/T1) = 1 for TR/T1 much greater than 1, will reduce Eq. 1 to the expression
Mxy = Mxy0exp(-TE/T2)
which is dependent on T2 only, hence the term T2 weighting. Therefore T2 weighted image contrast state is approached by imaging with a TR long compared to tissue T1 (to reduce T1 contribution to image contrast) and a TE between the longest and shortest tissue T2s of interest. A TR greater than 3 times the longest T1 is required for the T1 effect to be less than 5%. Due to the wide range of T1 and T2 and tissue density values that can be found in the body, an image that is T2 weighted for some tissues may not be so for others.
See also T2 Time.
Lesions with short T2 are (dark in T2 weighted sequences):
acute haemorrhage (deoxyHb)
haemosiderin
physiologic iron (basal ganglia, etc.)
mucinous lesions.

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.

California-based research and development company. Alliance has several patents regarding 'microbubble' compositions such as Imagent® that are intended to enhance ultrasound imaging and Imagent GI as a gastrointestinal MRI contrast agent. Another product is Oxygent™, a synthetic 'blood substitute'.

MRI Contrast Agents:

• Imagent GI

(ASSET) ASSET is a parallel imaging technique of the SENSE type (image domain reconstruction).
Each coil element is sensitivity encoded and the covered spatial zone is mapped. By reducing the field of view in the phase encoding gradient direction the scan time decreases, but this images of each coil element contain foldover artifacts. The sensitivity profiles of the elements are used to calculate unfolded images.

See also Sensitivity Encoding, Generalized Autocalibrating Partially Parallel Acquisition.