Glossary Terms  Home

N

Net Magnetization (M)

The sum of the magnetic moments of all spins within a spin system.

Neurological Convention

The practice of displaying images of the brain so that the left and right sides of the image correspond to the same sides of the brain, as if one were behind the subject.

Normalization

The transformation of MRI data from an individual subject to match the spatial properties of a standardized image, such as an averaged brain derived from a sample of many individuals.

 Nuclear Induction

The initial term for nuclear magnetic resonance effects, as labeled by bloch and colleagues.

Nuclear Magnetic Resonance (NMR)

 The measurable changes in magnetic properties of atomic nuclei induced by the application of an oscillating magnetic field at the resonant frequency of the nuclei.

Nuisance Factors

Model factors that are associated with known sources of variability that are not related to the experimental analyses. 

Null Hypothesis

The proposition that the experimental manipulation will have no effect upon the experimental data.  Most statistical analyses evaluate the probability that the null hypothesis is true, i.e., that the observed data reflect chance processes.

Nutation

The spiraling change in the precession angle of the net magnetization during an excitation pulse.

Nyquist Frequency

The highest frequency that can be identified in a digitally sampled signal; it is defined as one-half of the sampling rate.