Readout gradient

Figure Bl.14.1. Spin warp spin-echo imaging pulse sequence. A spin echo is refocused by a non-selective 180° pulse. A slice is selected perpendicular to the z-direction. To frequency-encode the v-coordinate the echo SE is acquired in the presence of the readout gradient. Phase-encoding of the > -dimension is achieved by incrementmg the gradient pulse G...

Figure Bl.14.2. Gradient-recalled echo pulse sequence. The echo is generated by deliberately dephasing and refocusing transverse magnetization with the readout gradient. A slice is selected in the z-direction and v- and y-dimension are frequency and phase encoded, respectively.

Plasma and urine samples were profiled using a suitable HPLC system under specific conditions (gradient, column). Readout was done off-line by fraction collection of the HPLC ran followed by liquid scintillation counting. Biotransformation profiles were prepared by plotting the base-line corrected radioactivity against time-after-injection. 

FIGURE 14.2 Pulse sequence for a two-dimensional NMR image in the xy plane, with slice selection along z. The value of the phase-encode gradient Gx is altered in successive repetitions, as indicated. The rf pulses are frequency selective and define the slice while gradient Gz is applied. Within one value of Gx there may be several repetitions with different values of frequency to obtain data from multiple slices. Data are acquired from the spin echo while the readout gradient Gy is applied. 

FIGURE 14.3 Pulse sequence for echo-planar imaging. Slice selection is carried out as in Fig. 14.2. The readout gradient Gy is rapidly switched in direction in synchrony with application of a pulsed phase-encode gradient G as indicated. Data are acquired while Gy is turned on but Gx is off. 

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