title: On resonance phase alternated CWFP sequences for rapid and simultaneous measurement of relaxation times.
abstract: T1 and T2 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 T1, i.e., inversion and saturation recovery, are time-consuming, driving several authors to develop rapid 1D and 2D methods to obtain T1 and T2 or T1/T2 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 T1 and T2 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 (Tp). In this paper we present an alternative form of these sequences, named CWFPx-x, CP-CWFPx-x, where a train of π/2 pulses with phases alternated by π enable performing the experiments on-resonance and independently of Tp, when Tp<T2(∗). Moreover, a CPMG type sequence with π/2 refocusing pulses shows similar results to CP-CWFP when the pulses are alternated between y and -y axis, CPMG90y-y. In these approaches, the relaxation times are determined using the magnitude of the signals after the first pulse |M0| and in the steady-state |Mss|, as well as the exponential time constant T(∗) to reach the steady-state regime, as in conventional CWFP. CP-CWFPx-x shows the highest dynamic range to measure T(∗) among CWFP sequences and, therefore, is the best technique to measure T1 and T2 since it is less susceptible to SNR and can be performed for any T1/T2 ratio.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, São Carlos, SP 13566-590, Brazil; Embrapa Instrumentação, Rua XV de Novembro, 1452, São Carlos, SP 13560-970, Brazil.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Monaretto
authors.affiliation: Embrapa Instrumentação, Rua XV de Novembro, 1452, São Carlos, SP 13560-970, Brazil.
authors.forename: Fabiana Diuk
authors.initials: FD
authors.lastname: Andrade
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, São Carlos, SP 13566-590, Brazil.
authors.forename: Tiago Bueno
authors.initials: TB
authors.lastname: Moraes
authors.affiliation: Schlumberger Brazil Research and Geoengineering Center, Rua Paulo Emídio Barbosa, 485, Quadra 7B, Rio de Janeiro, RJ 21941-907, Brazil.
authors.forename: Andre Alves
authors.initials: AA
authors.lastname: Souza
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, São Carlos, SP 13566-590, Brazil.
authors.forename: Eduardo Ribeiro
authors.initials: ER
authors.lastname: deAzevedo
authors.affiliation: Embrapa Instrumentação, Rua XV de Novembro, 1452, São Carlos, SP 13560-970, Brazil. Electronic address: luiz.colnago@embrapa.br.
authors.forename: Luiz Alberto
authors.initials: LA
authors.lastname: Colnago
keywords: CP-CWFP; CWFP; Phase alternation; SSFP; TD-NMR