Bir-4-si rf pulses, use therefor and method of creating the...

Details Bir-4-si rf pulses, use therefor and method of creating the... Bir-4-si rf pulses, use therefor and method of creating the...

G - Physics

01

R

G01R 33/54 (2006.01) G01R 33/48 (2006.01)

Patent

CA 2313059

Adiabatic RF pulses are very useful in MRI when precise flip angles are needed. Unfortunately, adiabatic pulses suffer from a long application time and a high SAR. A new concept to modify the usual adiabatic pulse into a "pseudo-adiabatic" pulse having a shorter application time and lower SAR is introduced. For example, a BIR-4 of 32 ms of application time and a relative SAR of 20 will be transformed into a BIR-4-S1 of 1 ms and relative SAR of 1. The new pulse obtained stays insensitive for a large B1 range but loses its slice selectivity to become a 3D pulse. Experimental results are presented to illustrate the sensitivity to B1 and B0.

Les impulsions RF adiabatiques sont des plus utiles en IRM pour ce qui est des angles de bascule. Le temps d'application de ces impulsions est toutefois très long, et le SAR est élevé. Un nouveau concept est proposé pour modifier l'impulsion adiabatique en une impulsion pseudo-adiabatique dont le temps d'application est plus court et le SAR plus bas. Par exemple, un BIR-4 avec un temps d'application de 32 ms et un SAR de 20 sera transformé en un BIR-4-S1 de 1 ms et un SAR relatif de 1. La nouvelle impulsion ainsi obtenue demeure insensible dans le cas d'un vaste intervalle B1, mais elle perd sa sélectivité de tranches pour devenir une impulsion 3D. Des résultats expérimentaux sont présentés pour illustrer la sensibilité à B1 et B0.

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