An agent currently in Phase III clinical trials that selectively targets diseased cells because they have increased rates of metabolism. Once inside the diseased cell, motexafin gadolinium may work to disrupt its energy production and the ability to repair itself. This biolocalization can be confirmed because the compound can be seen via MRI. Motexafin gadolinium accumulates in diseased cells with repeat doses and remains in the cells for days.
Motexafin gadolinium is being investigated in clinical trials, in combination chemotherapy and with radiation therapy for the treatment of several types of cancer.

Quick Overview
Please note that there are different common names for this artifact.

Patient motion is the largest physiological effect that causes artifacts, often resulting from involuntary movements (e.g. respiration, cardiac motion and blood flow, eye movements and swallowing) and minor subject movements.
Movement of the object being imaged during the sequence results in inconsistencies in phase and amplitude, which lead to blurring and ghosting. The nature of the artifact depends on the timing of the motion with respect to the acquisition. Causes of motion artifacts can also be mechanical vibrations, cryogen boiling, large iron objects moving in the fringe field (e.g. an elevator), loose connections anywhere, pulse timing variations, as well as sample motion. These artifacts appear in the phase encoding direction, independent of the direction of the motion.

Motion artifacts can be flipped 90° by swapping the phase//frequency encoding directions.
The artifacts can be reduced by using breath holding, cardiac synchronization or respiratory compensation techniques: triggering, gating, retrospective triggering or phase encoding artifact reduction. Flow effects can be reduced by using gradient moment nulling of the first order of flow, gradient moment rephasing or flow compensation, depending of the MRI system.
Peristaltic motion can be reduced with the intravenous injection of an anti-spasmodic (e.g. Buscopan).
By using multiple averages, respiratory motion can be reduced in the same way that multiple averages increase the signal to noise ratio. Noticeable motion averaging is seen when four averages are obtained, six averages are often as good as respiratory compensation techniques and higher averages will continue to improve image quality.
In some cases will help a presaturation of the anatomy that was generating the motion.

See also Phase Encoded Motion Artifact.

(MAST) See Gradient Motion Rephasing and Motion Artifact.

Pulse sequences, designed to be insensitive to flow, e.g. at every even echo, a spin echo sequence is not flow sensitive. Velocity compensation is achieved by using gradients, which are either symmetrical around a 180° pulse and switched on twice as is the case for motion compensated spin echo pulse sequences, or two antisymmetrical gradient lobes without 180° pulse, which is the way to produce a velocity compensated gradient echo pulse sequence.
The signal of the second echo (and all other even echoes) is independent of the velocity of the object. Thus, velocity-based motion effects stemming from the entire voxel or from spins within a voxel (intravoxel incoherent motion) are suppressed with such pulse sequences.
If higher order motion is relevant, as it may be in turbulent jets across valves, acceleration and jerk effects can also be compensated for by the use of appropriate combinations of gradient- and radio frequency pulses.
With the increasingly stronger gradients, echo times in MR systems can be shortened to the point at which effects other than velocity effects hardly ever become relevant.

Many MR imaging techniques using Motion Probing Gradients (MPG's) such as Spin Echo (SE), Stimulated Echo (STE), Rapid Acquisition with Relaxation Enhancement (RARE), Turbo-SE, and SE-EPI (Echo Planar Imaging for Spin echo acquisition), Spiral imaging, and Projection reconstruction including PROPELLER are applicable to DWI. In diffusion weighted imaging, 2 MPG's are required. The MPG's are put symmetrically into both sides of a 180° or 90° RF pulse to change the direction of the magnetized spin in the X-Y plane for spin echo or stimulated echo acquisition.