Nuclear magnetic resonance: a gray scale model for head images.

The gray scale of nuclear magnetic resonance (NMR) head images is explained in terms of tissue and machine parameters. Tissue parameters considered here include the spin-lattice relaxation time, the spin-spin relaxation time, and the proton density. Machine parameters include the pulse sequence (saturation recovery, inversion recovery, or spin echo), the repetition time, and the delay time. The ability of the operator to alter the NMR gray scale predictably is examined by computer simulation. The simulation computes NMR pixel values for a selected combination of tissue and machine parameters. The computed values are compared with those extracted from clinical NMR images. The agreement between simulation and clinical pixel values implies that the operator can use the machine parameters to alter the NMR gray scale, and thereby control contrast, appropriate to the diagnostic requirements. The extent to which the NMR gray scale can be predictably controlled is illustrated through graphs, simulated contrast displays, and representative NMR images.