Saturation-recovery pulse sequence

Spin-Lattice Relaxation. In order to determine whether each resonance line comprises a single component, we first measured the spin-lattice relaxation time Tic by the pulse sequence developed by Torchia [53] or by the standard saturation-recovery pulse sequence. The Tic values thus obtained were 2560,263 and 1.7 s for resonance line I and 0.37 s for line II. As reported by several investigators, the line at 33 ppm is associated with three different Tic values [ 17,54,55]. This means that this line is contributed to by three components with different molecular mobilities. However, since each component was represented by a single Lorentzian line shape at 33 ppm, they are all assignable to methylene groups in the orthorhombic crystalline form or in the trans-trans conformation. The component with a Tic of s can be assigned to methylene groups with a some-... 

The inversion and saturation recovery pulse sequences are used for measurement of the T relaxation time and for partial suppression of signals in samples with distributions of T relaxation times. These pulse sequences can be employed for contrast enhancement in imaging (cf. Section 7.2.1). 

T, Measurements. Ti values for the mobile domain carbons were measured using a (l80 -t-90 -T) inversion recovery pulse sequence (77) with continuous proton saturation. The optimum 180 pulse width was determined prior to each set of measurements. The time between pulse sequences was 2 s at 21 kG and 3 s at 47 kG. Measurements were generally made for 10-12 values of t which ranged from 0.005 s to T. Both integrated peak intensities and peak heights were used for the analysis of each T) data set equivalent results were obtained in both cases. 

Spectral resolution enhancement can be achieved by partial relaxation, which capitalizes on the different relaxation times, T, of the protons in a molecule (324). The partial relaxation experiment usually employs the inversion recovery pulse sequence [180°- r-90°-acquisition] (390), though progressive saturation (106) can also be employed. 

A number of pulse-sequence methods are available for measurement of Ti values, and those most commonly used are the methods of saturation recovery (s.r.F.t.),69,70 progressive saturation (p.s.F.t.),71 inversion recovery (i.r.F.t.),72 and the Freeman-Hill modification of in-... 

Fig. 2.2.8 Pulse sequences for measurement of Ti relaxation times by (a) saturation recovery and (b) inversion recovery. The effect of the pulse sequences is illustrated in terms of the vector model of the nuclear magnetization and by graphs showing the evolution of the longitudinal magnetization M, as a function of ti.

Fig. 7.1.3 [Blii2] NMR-timescale of molecular motion and filter transfer functions of pulse sequences which can be utilized for selecting magnetization according to the timescale of molecular motion. The concept of transfer functions provides an approximative description of the filters. A more detailed description needs to take into account magnetic-field dependences and spectral densities of motion. The transfer functions shown for the saturation recovery and the stimulated-echo filter apply in the fast motion regime.

Fig. 7.2.1 Pulse sequences for T and related magnetization filters, typical evolution curves of filtered magnetization components, and schematic filter transfer functions applicable in the slow motion regime. Note that the axes of correlation times start at Tc = Wo (a) Saturation recovery filter, (b) Inversion recovery filter, (c) Stimulated echo filter.

Fig. 7.2.22 [Gutl] Pulse sequences for combined determination of T and T2 in inhomogeneous Bo fields, (a) Steady-state inversion recovery filter [Sezl). (b) Steady-state saturation recovery filter [Gutl]. (c) Train of echoes measured by sequence (b) which shows the magnetization build-up with T] and the decay with Ti of unfilled, cross-linked SBR.

CW experiments (sometimes called stationary or steady state ) are ones in which either no modulations are used, or they are so low in frequency that no spectral complications ensue. (This is only approximately the case if 100 kHz field modulation is employed. This frequency gives rise to modulation sidebands and, under saturating conditions, rapid passage effects.) Time-domain ESR involves monitoring the spin system response as a function of time. Pulse ESR can be divided into two broad categories the response of spin systems to sequences of microwave pulses (spin echo) and the response of spin systems to step changes in resonance conditions (saturation recovery). 

Pulse or time domain ESR can be divided into two categories the transient response of spin systems to abrupt or step changes in resonant condition and the transient response to sequence of pulses [20]. The step response, as in saturation recovery, is used commonly to measure T, and the pulse response, as in 90-180° spin echo, to measure Tj. 

Fig. 20.1. Timing diagrams of the NMR pulse sequences (a) C pulse saturation transfer (PST)/magic-angle spinning (MAS) and (b) " C inversion recovery (IR) combined with PST/MAS. DD dipolar decoupling FID free induction decay tt/2 and rr rf pulses t recovery time and n and m number of repeating units.

Figure Bl.14.6. Tj-maps of a sandstone reservoir core which was soaked in brine, (a), (b) and (c), (d) represent two different positions in the core. For -contrast a saturation pulse train was applied before a standard spin-echo imaging pulse sequence. A full Tj-relaxation recovery curve for each voxel was obtained by incrementing the delay between pulse train and imaging sequence. Mq- ((a) and (c)) and Tj-maps ((b) and... 

Double pulse sequences (inversion and saturation recovery)... 

---