reversal of the magnetization by adiabatisch fast and nonlinear passage in the magnetic kernresonanz.

摘要

A method for the complete inversion of magnetization by adiabatic fast passage during an NMR experiment on a sample having a selected nuclear specie with a Larmor frequency omega 0. A radio-frequency magnetic field is generated with an amplitude B1 and an instantaneous frequency omega (t) which is non-linearly swept, as a function of time, from a minimum frequency omega 1 substantially at a maximum offset frequency DELTA omega below the Larmor frequency omega 0, through the Larmor frequency, to a maximum frequency omega h substantially at the maximum offset frequency DELTA omega above the Larmor frequency. The non-linearly swept, monotonic RF signal is applied to the sample-being-investigated for a sweep time interval sufficient to invert the magnetization of the selected nuclear specie. The preferred sweep is a tangential function: omega (t)= omega 0+/- gamma B1 tan (arcsin ( omega st)), (A) or omega (t)= omega 0+/- gamma B1 tan ( omega st) where omega s= alpha gamma B1, gamma is the gyromagnetic ratio of the selected nuclear specie and 0 alpha /=1.