Patent ID: 6456071
Filing Date: 2002-09-24
Classification: G01R

Abstract:
A method of nuclear magnetic resonance spectroscopy or nuclear magnetic tomography comprising the steps of:applying a hyper-echo sequence of radio frequency pulses to a spin ensemble in a manner that for at least 2n+1 consecutive pulses within the sequence, n being greater than one and the pulses having flip angles &agr;1 . . . &agr;2n+1 and phases &PHgr;1 . . . &PHgr;2n+1, and wherein spins are respectively dephased by &phgr;1 . . . &phgr;2n between successive pulses; using a central (=(n+1)st) pulse as a refocusing pulse with a preferred flip angle of 180Â° and phase &PHgr;0. placing corresponding pulses symmetrically around the central (=(n+1)st) refocusing pulse, such that for the i-th pulse with i between 1 and n the following relations hold: the flip angle &agr;(n+1)âˆ’i of the (n+1âˆ’i)th pulse is equal to the negative flip angle of the corresponding (n+1+i)th pulse: &agr;(nâˆ’1)âˆ’i=&agr;(n+1)+i â€ƒand the phase of the (n+1âˆ’i)th pulse is equal to the negative phase of the corresponding (n+1+i)th pulse with respect to the phase of the central refocusing pulse: &PHgr;(n+1)âˆ’i=&PHgr;0âˆ’&PHgr;(n+1)âˆ’i using dephasing intervals following the i-th pulse, which are symmetrical around the central and (n+1)st refocusing pulse according to the relation: &phgr;(n+1)âˆ’i=&phgr;n+1, â€ƒsuch that at the end of a pulse sequence, where the phase of the central refocusing pulse is chosen to be aligned along My, the vector describing the initial magnetization MA(Mx,My,Mz) of the spin ensemble will appear to be rotated to MR(âˆ’Mx,My, âˆ’Mz) by 180Â° around the axis of the radio frequency field of the central refocusing pulse (=hyper-echo formation),: MR(âˆ’Mx,My, âˆ’Mz)=Roty(180Â°)*MA(Mx,My,Mz).