The T1 time constant, which determines the rate at which excited protons return to equilibrium within the lattice. The longitudinal relaxation time is a measure of the time taken for spinning protons to realign with the external magnetic field. The magnetization will grow after excitation from zero to a value of about 63% of its final value in a time of T1.

See also T1 Time.

(LUT) A lookup table is a data structure, usually an array. In MRI for example the intensity values are mapped to the related image pixels.

Usual shape of the lines in a NMR spectrum, characterized by a central peak with long tails; proportional to 1/[(1/T2)2 + (f - fo)2], where f is frequency and fo is the frequency of the peak (i.e., central resonance frequency). A Lorentzian function is the Fourier transformation of a decaying exponential.

A mathematical function used for signal fitting (filtering) of raw data. Other commonly used line shapes are the Gaussian line shape or the super-Lorentzian line shape.

(LASE) See Gradient Echo Sequence and Spin Echo Sequence.