Lorenz Mitschang | PubMed Health

PubMed2005

An adjustable adiabatic pulse for selective population inversion.

A new adiabatic inversion pulse and its design principles are presented. An analytical expression in the pulse length, inversion bandwidth, inversion efficiency, peak RF amplitude, and width of the transition region is derived and validated. Accordingly, the pulse shape can be adapted to achieve a specified inversion performance. Adjusted for broadband application, population can be inverted band selectively, rather independently of spatial RF field inhomogeneities, and with significantly reduced peak RF amplitude in comparison with the well-known hyperbolic secant adiabatic pulse.

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PubMed2004

Design of a constant adiabaticity pulse for selective population inversion.

A new adiabatic pulse for population inversion and the principles of its design are presented. The pulse shape is characterized by the combination of two constraints. (i) Adiabatic following of the central isochromat of the spectral region of interest occurs with constant, possibly small adiabaticity parameter; thereby, the center isochromat gets most efficiently inverted. (ii) Frequency and amplitude modulations obey the principle of offset-independent adiabaticity; thus, the inversion dynamics of the center isochromat is extended over the desired bandwidth. Selective population inversion can be achieved rather independently of spatial radio frequency field inhomogeneities and with significantly reduced peak RF amplitude in comparison with the well-known sech/tanh adiabatic pulse.

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