Numerically optimized RF-refocusing pulses in localized MR proton spectroscopy.
The slice selection properties of three different soft refocusing-pulses (sinc-pulse, Hanning filtered sinc-pulse, and the numerically optimized reburp-pulse) within a standard double spin-echo sequence for localized proton spectroscopy were examined and compared. The slice profiles were measured acquiring two-dimensional images of the selected volumes of interest (VOI) appending a gradient-echo imaging part at the end of the spectroscopic part of the sequence. A comparison of the reached signal strength with the different pulses using the same voxel size (same Full Width Half Maximum, FWHM) was performed by in vitro and in vivo measurements. Additionally theoretical calculations using the Schrödinger equation for spin 1/2 particles in combination with a phase averaging method that takes into account the magnetic field spoiling and selection gradients of the spectroscopy sequence were performed. Calculated and measured slice profiles did well correspond. The numerically optimized reburp-pulse showed significant better slice selection and phase behaviour properties compared to the sinc-pulses. Further, a signal gain of about 20% was measured using the reburp-pulse, which was in good agreement with the calculated signal gain of 23%.
Department of Neuroradiology, University of Tübingen, Germany.
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D000293:Adolescent; D001921:Brain / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male