A number of spins affected by the same magnetic field.

The spins flow with the blood through a slice and experience a RF pulse. If they flow out of the slice by the time the signal is recorded (because the repetition time (TR) is asynchronous with the pulsatile flow), the flowing blood produces intravascular signal void by 'time of flight' effects, turbulent dephasing and first echo dephasing. The liquid flow occasionally produces an intravascular high signal intensity due to flow related enhancement, even echo rephasing and diastolic pseudogating.

See also Flow Artifact and Flow Effects.

(I) Property of all nuclei related to the largest measurable component of the nuclear angular momentum. Non-zero values of nuclear angular momentum are quantized (fixed) as integral or half-integral multiples of (h/2p), where h is Planck's constant. The number of possible energy levels for a given nucleus in a fixed magnetic field is equal to 2I + 1. Similarly, an unpaired electron has a spin of 1/2 and two possible energy levels.

NMR spectral lines may consist of groups of lines called multiplets. This multiplet structure is caused by interactions between nuclei that split the NMR energy levels and result in the observation of multiple allowed transitions separated by an amount of energy related to J, the spin spin coupling constant. These interactions are called spin spin coupling.

(T2) The return of the transverse magnetization to its equilibrium value, zero.