(MP-GRE / MPRAGE / MP-RAGE) A fast 3D gradient echo pulse sequence using a magnetization preparation pulse like TurboFLASH. Only one segment or partition of a 3D data record is obtained per inversion preparation pulse. After the acquisition, for all rows a delay time (TD) is used to prevent saturation effects.
MPRAGE is designed for rapid acquisition with T1 weighted dominance. Fast gradient echoes are characterized by their rapid sampling time, high signal intensity and image contrast while approaching steady state (the echo is collected during the time when tissues are experiencing T1 relaxation). The rapid speed of the acquisition makes it an excellent alternative to breath-hold abdominal imaging, neuro, dynamic bolus, MR angiography and cardiac imaging.

See Gradient Echo Sequence.

(RE MRI) There are several approaches to speeding up the MRI data acquisition process by repeating the excitation by RF pulses in times short compared to T1, typically using small flip angles and gradient echo refocusing. When TR is also on the order of or shorter than T2, the repeated RF pulses will tend to refocus transverse magnetization remaining from prior excitations, setting up a condition of steady state free precession, and a dependence of signal strength (and image contrast) on both T1 and T2.
This can be modified in various ways, particularly:
1) to spoil the tendency to build up a steady state by reducing coherence between excitations, e.g. by variation of the phase or timing of consecutive RF pulses or of the strength of spoiler gradient pulses, thus increasing the relative dependence of signal strength on T1 or
2) acquire the signal when it is refocusing immediately prior to the next RF pulse, thus increasing the relative dependence of signal strength on T2.

See also Ultrafast Gradient Echo Sequence.

(3D MRA) The 3D angiography technique can be applied to focus on fast flowing (arterial) blood and to visualize small tortuous vessels. 3D TOF images are less sensitive to turbulent flow artifacts. The advantage of this approach is that the signal, acquired from the entire volume has an increased signal to noise ratio. Slices are defined by a second phase encoded axis, which divides the volume into 'partitions'. 3D TOF MRA is acquired with 3D FT slabs or multiple overlapping thin 3D FT slabs (MOTSA) depending on the coverage required and the range of flow-velocities under examination.
Such 3D techniques can provide equal spatial resolution along all three axes, i.e. be 'isotropic', or the partition thickness can be greater or less than the in plane spatial resolution in which case can be said to be 'anisotropic'. The circle of Willis, anatomy as well as its fast arterial flow, lends itself well to both 3D TOF and 2D or 3D phase contrast angiography.

(DE prep) See Driven Equilibrium.

Diamagnetism occurs only by a substance in the presence of an externally applied magnetic field. Diamagnetic contrast agents are complexes in which the metal ion (e.g., Zn, Bi and Ca) is diamagnetic.
Potential diamagnetic materials in gastrointestinal MRI:
A suspension of clay minerals (Kaopectate with kaolin, a common over the counter drug) can be used as a negative oral contrast agent caused by the diamagnetic properties. By using this preparation as a gastrointestinal contrast agent e.g., in pancreas MRI or MRCP, the absence of signal is clearly visible in the stomach and duodenum. Barium sulfate commonly used as an X-ray contrast agent has also been tested for use in abdominal imaging. The diamagnetic properties of the barium particles are caused by a susceptibility effect around them, the resulting signal loss is strengthening by a replacement of water protons with barium.

See also Diamagnetism.