Using T1 as a direct detection dimension in two-dimensional time-domain NMR experiments using CWFP regime

Abstract

The transverse relaxation time (T₂), measured with Carr-Purcell-Meiboom-Gill (CPMG) sequence, has been widely used to obtain the direct dimension data in two-dimension time domain NMR (2D TD-NMR). In this paper we are demonstrating that Continuous Wave Free Precession sequence, with low flip angle (CWFP-T₁), can be an alternative to CPMG as direct detection dimension. CWFP-T₁ is a fast single shot sequence, like CPMG, and yields an exponential signal governed predominantly by the longitudinal (T₁) relaxation time. To obtain the correlations between T₁ and T₂ (T₁-T₂ maps) we are proposing the use of CPMG-CWFP-T₁ pulse sequence. In this sequence CPMG encodes T₂ information (indirect dimension) that modulates the CWFP-T₁ (direct dimension) signal amplitudes. CPMG-CWFP-T₁ experiments were compared with classical 2D sequences such as Saturation-Recovery-CPMG (SR-CPMG) and Inversion-Recovery-CPMG (IR-CPMG) sequence and yields similar results in phantom sample. The experimental time for the 2D sequences, using single scan, shows that SR-CPMG ≤ CPMG-CWFP-T₁ < IR-CPMG. Experimental and simulated results demonstrated that 2D-CPMG-CWFP-T₁ maps have higher resolution in T₁ dimension than the techniques that uses CPMG as direct dimension. CPMG-CWFP-T₁ sequence was also applied to study beef samples, and 2D maps showed higher resolution in the two fat signals than the classical IR-CPMG method.

Keywords: 2D TD-NMR pulse sequence; 2D-Laplace transform; CPMG-CWFP-T(1); T(1)-T(2) maps.