RF pulse phase and spoiler gradients

[faq_user]

I am simulating basic sequences for NMR using ideal RF pulses. Spinach documentation is quite well written however I am not sure if I uderstood these two concepts correctly:

1) Phase for RF pulses:

Example - 90 degree excitation pulse:
rho=step(spin_system,cosd(phase)*Lx+sind(phase)*Ly,parameters.rho_eq,pi/2);

If I want to use phase of 180 degrees, then phase = 180. This gives me expected results, however
I am not sure if this is the correct way how to change phases for RF pulses.

2) Spoiler gradient:

Example:
rho=evolution(spin_system,L+grad_1_amp,[],rho,grad_duration, 1,'final');

where grad_1_amp is the gradient amplitude and grad_duration is its duration. The goal here is to simulate a spoiler gradient. This implementation definitely changes the spins but not in a way that I expect. For example if I place two identical spoilers around a refocusing pulse in the spin echo sequence, the amplitude and phases are off.

There is always a possibiIity that I might do something wrong, but confirmation or correction of these two examples from your end would be greatly appreciated. My background is in vivo NMR (MRS) and not pure NMR.

Thank you very much for your input and help.

[kuprov]

Item 1 is correct. Spoiler gradients are a more subtle matter.

If you are running in the NMR mode (i.e. with no explicit spatial grid) then using homospoil.m function would simply obliterate all transverse magnetisation analytically:

http://spindynamics.org/wiki/index.php? ... omospoil.m

If you are using the imaging context with an explicit spatial grid (by the looks if it, you do), make sure that you have enough points in the spatial grid to actually digitise your gradient spiral. This may need thousands of points! We have an example in Figures 1 and 2 of this paper:

https://advances.sciencemag.org/content/5/7/eaaw8962