On resonance phase alternated CWFP sequences for rapid and simultaneous measurement of relaxation times

T-1 and T-2 relaxation times have been frequently used as probes for physical-chemical properties in several time-domain NMR applications (TD-NMR) such as food, polymers and petroleum industries. T2 measurements are usually achieved using the traditional Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence because it is a fast and robust method. On the other hand, the traditional methods for determining T-1 i.e., inversion and saturation recovery, are time-consuming, driving several authors to develop rapid 1D and 2D methods to obtain T-1 and T-2 or T-1/T-2 ratio. However, these methods usually require sophisticated processing and/or high signal to noise ratio (SNR). This led us to develop simple methods for rapid and simultaneous determination of T-1 and T-2 using Continuous Wave Free Precession (CWFP) and Carr-Purcell Continuous Wave Free Precession (CP-CWFP) pulse sequences. Nevertheless, a drawback of these sequences is that they require specific adjustment of the frequency offset or the time interval between pulses (T-p). in this paper we present an alternative form of these sequences, named CWFPx-x, CP-CWFPx-x, where a train of pi/2 pulses with phases alternated by pi enable performing the experiments on-resonance and independently of T-p when T-p < T-2*. Moreover, a CPMG type sequence with pi/2 refocusing pulses shows similar results to CP-CWFP when the pulses are alternated between y and y axis, CPMG(90y-y). In these approaches, the relaxation times are determined using the magnitude of the signals after the first pulse vertical bar M-0 vertical bar and in the steady-state vertical bar M-ss vertical bar, as well as the exponential time constant T* to reach the steady-state regime, as in conventional CWFP. CP-CWFP, shows the highest dynamic range to measure T* among CWFP sequences and, therefore, is the best technique to measure T-1 and T2 since it is less susceptible to SNR and can be performed for any T-1/T-2 ratio. (C) 2015 Elsevier Inc. All rights reserved.