The second is the SI unit of time.
Definition: The length of time taken for 9192631770 periods of vibration of the caesium-133 atom to occur.

Contrast enhanced GRE sequences provide T2 contrast but have a relatively poor SNR. Repetitive RF pulses with small flip angles together with appropriate gradient profiles lead to the superposition of two resonance signals.
The first signal is due to the free induction decay FID observed after the first and all ensuing RF excitations.
The second is a resonance signal obtained as a result of a spin echo generated by the second and all addicted RF-pulses.
Hence it is absent after the first excitation, it is a result of the free induction decay of the second to last RF-excitation and has a TE, which is almost 2TR. For this echo to occur the gradients have to be completely symmetrical relative to the half time between two RF-pulses, a condition that makes it difficult to integrate this pulse sequence into a multiple slice imaging technique. The second signal not only contains echo contributions from free induction decay, but obviously weakened by T2-decay. Since the echo is generated by a RF-pulse, it is truly T2 rather than T2* weighted. Correspondingly it is also less sensitive to susceptibility changes and field inhomogeneities.
Companies use different acronyms to describe certain techniques.
Different terms (see also acronyms) for these gradient echo pulse sequences:
CE-FAST Contrast Enhanced Fourier Acquired Steady State,
CE-FFE Contrast Enhanced Fast Field Echo,
CE-GRE Contrast Enhanced Gradient-Echo,
DE-FGR Driven Equilibrium FGR,
FADE FASE Acquisition Double Echo,
PSIF Reverse Fast Imaging with Steady State Precession,
SSFP Steady State Free Precession,
T2 FFE Contrast Enhanced Fast Field Echo (T2 weighted).
In this context, 'contrast enhanced' refers to the pulse sequence, it does not mean enhancement with a contrast agent.

A RF coil, often a transmit receive coil with a number of wires running along the z-direction, arranged to give a cosine current variation around the circumference of the coil, which looks like a bird cage. The bird cage coil works on a different principle to conventionally tuned local and surround coils in that it behaves like a tuned transmission line with one complete cycle of standing wave around the circumference. The frequency supply is generated by an oscillator, which is modulated to form a shaped pulse by a product detector controlled by the waveform generator. The signal must be amplified to 1000's of watts. This can be done using either solid state electronics, valves or a combination of both.
The bird cage coil design provides the best field homogeneity of all RF imaging coils.
One advantage is that it is simple to produce an exceedingly uniform B1 radio frequency field over most of the coil's volume, with the result of images with a high degree of uniformity.
A second advantage is that nodes with zero voltage occur 90° away from the driven part of the coil, thus facilitating the introduction of a second signal in quadrature, which produces a circularly polarized radio frequency field.
This type of volume coil is used for brain (head) MRI, or MR imaging of joints, such as the wrist or knees.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'

Flow phenomena are intrinsic processes in the human body. Organs like the heart, the brain or the kidneys need large amounts of blood and the blood flow varies depending on their degree of activity. Magnetic resonance imaging has a high sensitivity to flow and offers accurate, reproducible, and noninvasive methods for the quantification of flow. MRI flow measurements yield information of blood supply of of various vessels and tissues as well as cerebro spinal fluid movement.
Flow can be measured and visualized with different pulse sequences (e.g. phase contrast sequence, cine sequence, time of flight angiography) or contrast enhanced MRI methods (e.g. perfusion imaging, arterial spin labeling).
The blood volume per time (flow) is measured in: cm3/s or ml/min. The blood flow-velocity decreases gradually dependent on the vessel diameter, from approximately 50 cm per second in arteries with a diameter of around 6 mm like the carotids, to 0.3 cm per second in the small arterioles.

Different flow types in human body:
See also Flow Effects, Flow Artifact, Flow Quantification, Flow Related Enhancement, Flow Encoding, Flow Void, Cerebro Spinal Fluid Pulsation Artifact, Cardiovascular Imaging and Cardiac MRI.

(N) The SI unit of force.
Definition: 1 newton will accelerate a mass of 1 kilogram at the rate of 1 meter per second per second.
The relationship between force (F), mass (m), and acceleration (a) is expressed by the formula F = ma.
The newton is named for Isaac Newton (1642-1727), the British mathematician, physicist, and natural philosopher.