SNR improvement in NMR microscopy using DEFT

Abstract

This paper examines the use of a driven equilibrium Fourier transform (DEFT) pulse sequence for improving the signal per unit time and hence image resolution in NMR microscopy. DEFT vs partial saturation (PS) is modeled and it is shown that DEFT is most useful in physiologic materials provided short TE values (TE ⪡ T 2) and short TR values (TR < T 1) are used. Under these conditions, DEFT can yield up to a fourfold signal increase compared to PS. It is shown that DEFT can provide spin density and T 1/ T 2-ratio-weighted images. DEFT is also shown to have SNR advantages as T 1 increases—an important consideration at higher magnetic fields. Experimental data that verify the theoretical predictions and the functioning of a DEFT pulse sequence to produce high-quality 2D spin-warp images of a phantom are presented. Studies performed on small animals demonstrate the utility of the DEFT sequence in MR microscopy by providing increased SNR and new contrast mechanisms over limited fields of view.