| 摘要 |
A method of NMR spectroscopy or tomography, wherein a sequence of temporarily offset radio frequency pulses is applied onto a spin ensemble, is characterized in that after a sequence of pulses with flip angles alpha1 . . . alphan (with alpha1 . . . alphan>=0°) and phases phi1 . . . phin between which spins are dephased by phi1 . . . phin, a central refocusing pulse is applied as (n+1)th pulse, followed by a pulse sequence which is mirror-symmetrical to the central refocusing pulse, wherein the flip angles alphan+2 . . . alpha2n+1 and phases phin+2 . . . phi2n+1 of the pulses have, in comparison with the mirror-symmetrical pulses with alphan . . . alpha1 and phin . . . phi1, negative sign with respect to amplitude and phase and the dephasings phin+2 . . . phi2n+1 which are also mirror-symmetrical to the central refocusing pulse in the sequence are equal to the respective mirror-symmetrical dephasings phin . . . phi1 such that at the end of the pulse sequence, an output magnetization MA(Mx,My,Mz) of the spin ensemble is refocused with respect to the central refocusing pulse through application of rotation corresponding to the symmetrical relationinto a final magnetization MR=(-Mx,My,-Mz) (=hyperecho formation). In this fashion, even after application of refocusing pulses of any flip angles, the occurring signal losses can be cancelled and the complete signal amplitude can be regained with respect to dephasing through chemical shift, susceptibility and field inhomogeneity.
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