The gradient slew rate is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative. Which is the amplitude divided by the rise time in msec. Measured in mT/m/msec or T/m/sec. The shorter the rise time, the faster the gradients and therefore echo spacing. Gradients with a shorter echo spacing will have a better resolution and more slices per TR.

(ADC) A diffusion coefficient to differentiate T2 shine through effects or artifacts from real ischemic lesions. In the human brain, water diffusion is a three-dimensional process that is not truly random because the diffusional motion of water is impeded by natural barriers. These barriers are cell membranes, myelin sheaths, white matter fiber tracts, and protein molecules.
The apparent water diffusion coefficients can be calculated by acquiring two or more images with a different gradient duration and amplitude (b-values). The contrast in the ADC map depends on the spatially distributed diffusion coefficient of the acquired tissues and does not contain T1 and T2* values.
The increased sensitivity of diffusion-weighted MRI in detecting acute ischemia is thought to be the result of the water shift intracellularly restricting motion of water protons (cytotoxic edema), whereas the conventional T2 weighted images show signal alteration mostly as a result of vasogenic edema.
The reduced ADC value also could be the result of decreased temperature in the nonperfused tissues, loss of brain pulsations leading to a decrease in apparent proton motion, increased tissue osmolality associated with ischemia, or a combination of these factors. The lower ADC measurements seen with early ischemia, have not been fully established, however, a lower apparent ADC is a sensitive indicator of early ischemic brain at a stage when ischemic tissue remains potentially salvageable.

See also Diffusion Weighted Imaging and Diffusion Tensor Tractography.

From Siemens Medical Systems;

FDA cleared and CE Mark 2011.
The Biograph mMR has a fully-integrated design for simultaneous PET/MRI imaging. The dedicated hardware includes solid-state, avalanche photodiode PET detector and adapted, PET-compatible MR coils.
The possibility of truly simultaneous operation allows the acquisition of several magnetic resonance imaging (MRI) sequences during the positron emission tomography (PET) scan, without increasing the examination time.
See also Hybrid Imaging.

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).

Quick Overview

Pulsatile cerebro spinal fluid flow produces ghost artifacts that are superimposed in the image.

Flow compensation should be used to reduce these artifacts. This applies an additional gradient to eliminate phase differences for both stationary and moving spins at the echo time. At TE no phase differences is measured. If flow compensation is applied and there are still flow artifacts, cardiac triggering is an additional option to reduce these artifacts.
See also Motion Artifact.