A strategy for incrementing the position of the k-space trajectory of an echo planar imaging (EPI) pulse sequence.
Echo planar imaging (EPI) uses a constant gradient amplitude in one direction. This, combined with an oscillating gradient system in the frequency encoding direction, produces a zigzag trajectory in k-space. In the blipped phase encoding variant of EPI, the k-space position in the phase encoded direction is incremented by gradient 'blips' of the appropriate area. These, when timed to occur during the reversals of the read-out gradient, produce a rectilinear path in k-space.
The artifacts in an EPI image can arise from both hardware and sample imperfections. These are most easily understandable from examination of the k-space trajectory involved, which is either a zigzag form (when using a constant phase encoding gradient) or a rastered zigzag (when the phase encoding is performed with small gradients at the end of each scan line, so-called 'blipped' EPI).

Name for the phase encoding top of the EPI sequence.

Phenomenological (classical) equations of motion for the macroscopic magnetization vector. They include the effects of precession about the magnetic field (static and RF) and the T1 and T2 relaxation times.

The brain tissue is provided with a tight endothelial layer on vessels that acts as a filter for substances that reach the brain through the blood stream. This filter is called the blood brain barrier.
The blood brain barrier is responsible for the absence of contrast agent enhancement in normal brain tissue after administration of the iodinated or paramagnetic contrast media used in brain MRI and computed tomography (CT) diagnostic. The absence of contrast uptake in normal tissue provides the basis for differentiation from pathological brain tissue, which is conversely characterized by a disruption of the blood brain barrier.

See also Contrast Enhanced MRI, MRI Safety, Adverse Reaction.

MR imaging techniques capable to provide maps of cerebral activity. All these techniques are based on indirect assessment of local cerebral haemodynamics that have been demonstrated to be closely related to cerebral activity.
Two kinds of techniques have been developed: