Crusher gradient

In Figures 2 and 3 are shown the GAMMA C++ code for a simulated spin-echo pulse sequence using ideal RF pulses and a simulated PRESS pulse sequence that accounts for a non-ideal RF pulse envelope, crusher gradients and spatially varying RF refocusing due to resonance group chemical shift offset and... 

Usually the rf pulses applied in an imaging sequence are not perfect. The pulses may differ in shape, phase, and amplitude from the required values. As a result, unwanted transverse magnetization may arise which leads to erroneous signals. This is so, in particular, for the 180° refocusing pulse of the Hahn echo. These transverse magnetization components can be dephased by application of homogeneity-spoil or crusher gradient pulses. 

Fig. 10. WEX filter combined with WATERGATE suppression. The first irtl pulse in the WEX filter is selective to the water, the second is nonselective and the third can be either hard or, as shown, selective on the NH protons. t defines the mixing period. The grey gradient pulses are used for coherence selection, the mottled gradient pulse is a crusher gradient and the two gradient pulses for the WATERGATE subiuiit are coloured black. Ideally three orthogonal Sections would be used for the different gradient pulses.

Figure 3 GAMMA C++ code to implement a PRESS pulse sequence simulation that accounts for the use of real RF pulses and the application of gradient crushers around refocusing pulses.

Rail-mounted mobile crushers can suitably be used in cases where the direction of travel is well defined in advance (Fig. 26c). Thanks to the low rolling resistance, drive power requirements for travel are low, and wear on the travel machinery is light. Against this there is the disadvantage that gradients of only about 1 in 40 can be overcome, while maneouvrability is limited and moving the plant to a fresh... 

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