(1) Impregnation of one substance by another to the greatest possible extent. (2) Neutralization, as of an acid by an alkali. (3) That concentration of a dissolved substance that cannot be exceeded. (4) In optics, see saturated color. (5) Filling of all available sites on an enzyme molecule by its substrate, or on a hemoglobin molecule by oxygen (symbol SO2) or carbon monoxide (symbol SCO). (6) In MRI, a temporary state in which there is no net magnetization of the spins; can be induced with special radiofrequency pulses. Saturated tissues emit no signal when sampled; partially saturated tissues do, however, emit a weak signal.saturation pulse. [L. saturatio, fr. saturo, to fill, fr. satis, enough]