Your crusher gradients are to dephase transverse magnetization created by your inversion pulse.  A perfect inversion pulse or a simulation that does not account for the transverse magnetization would not be affected by the crusher gradients.  

Your crusher gradients would have no effect along the Z-axis of the Larmor frame.

An easy model is to think of the crusher gradients as being rotations about the Z axis for transverse magnetization.    The reason the crushers work is that you can apply a total of 2PI of phase dispersal across a voxel so that all phase adds to 0 for the affected (transverse) magnetization in that volume element.

Thus to avoid destroying your refocused transverse magnetization a balance crusher must be ahead of the refocusing pulse.

Does this make this issue any clearer?  Good luck.

PS .. You can take a look at Gerry Matson's code - MatPulse at the following URL

http://radiology.ucsf.edu/cind/education/software/matpulse

Hi,

yes, the crushers have no effect on the transverse magnetisation if you place a one crusher before and after the refocusing pulse - given they are of similar strength. If you include molecular diffusion you will get an additional damping of the signal - which is used to measure ADCs in NMR.

By looking at your MATLAB code it seems to me that the offset term is not implemented correctly. I was just loading a 90˚ hard pulse of 1ms and saw that it gives perfect excitation for +- 10 kHz which cannot be true. Maybe check again, how the offset term is implemented, it should lead to a nutation angle for off-resonant excitation.

Also, I can recommend this paper here for selective refocusing pulses:

http://www.ncbi.nlm.nih.gov/pubmed/22975241

Best regards,

Franz

Dear Dr. Morris,

Thanks a lot for proving useful insight.

I would try to incorporate the crusher pair and let you know if there is any problem.

Regarding the tool "MatPulse", I requested the software (using the same link that you provided) almost 3 weeks back and did not get any response. Else, this would have been the easiest way for me.

Regards,

Dushyant

Dear Dr. Schilling,

Thanks for responding.

I would double check my code. 

Also I would go through the paper that you referred.

Regards,

Dushyant