Imaging spin warp

Spin-warp imaging denotes the most common form of Fourier imaging with data acquisition in Cartesian k-space coordinates [Edel]. Instead of a variable evolution time t for phase encoding, the gradient amplitude is stepped during t in order to halt phase evolution from spin interactions other than with the applied space-encoding gradient. 

Given these prerequisites, a 2D spin-warp imaging sequence is set up in five steps. These are illustrated in Fig. 6.2.1(a)-(e) [Wehl], The indices assigned to the gradients... 

Typical flip angles are in the order of 15° for the slice-selective excitation pulses. The intensity of the FID after such a pulse corresponds to 25% (sin 15°) of the intensity after a 90° pulse. However, more than 96% (cos 15°) of the longitudinal magnetization are preserved, enabling fast repetition rates. The method can be employed in combination with the backprojection imaging scheme and with spin-warp imaging by phase encoding of spatial information. 

Hti. 7.2.10 Susceptibility contrast in commercial EPDM samples, (a) 2D projection acquireil by spin-warp imaging, (b) 2D projection acquired by gradient-echo imaging. The images were measured at a temperature of 363 K. Adapted from BIUR with permission from Hiithig Gmbh. 

Spin-warp imaging Edelstein et al., Phys. Med. Biol. 25 751... 

Figure 2 Spin warp imaging. (A) Sequence structure used in spin-warp imaging (again the slice selection component is shown as a block). The data acquisition gradient is fixed throughout the procedure the phase encoding gradient is stepped uniformly from one extreme to the other, hence the difference from one excitation to the next. (B) The /c-space average resulting from the spin-warp sequence.

Potato Freeze-drying Spin warp imaging... 

Edelstein, W. A., Hutchinson, J. M. S., Johnson, G., and Redpath, T. (1980). Spin-warp imaging and applications to human whole-body imaging. Phys. Med. Biol. 25,751-756. 

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