Nuclear magnetic resonance of tissue 23Na. II. Theoretical line shape.

The theoretical line-shape function of the nuclear magnetic resonance (NMR) signal of (23)Na in biological tissue (and other unoriented systems) was obtained under the following conditions: (I) there occur two states of (23)Na in the system, (II) the exchange of (23)Na between the two states is rapid (but not too rapid), (III) in the absence of exchange, the (23)Na in one state is characterized by a single transverse relaxation time T(2) and a single Larmor frequency, and (IV) in the absence of exchange, the (23)Na in the other state possesses (a) two different values of T(2) and/or (b) more than one Larmor frequencies in the first order perturbation effect. The theoretical signal obtained consists of two Lorentzian components, which are centered at the same frequency, but characterized by different T(2). Only the narrower component, comprising 40% of the total intensity, is visible, when the fast T(2) is sufficiently short. The theoretical line-shape function of (23)Na signal was also calculated for oriented systems in which the above conditions are fulfilled.