sLASER has 5 pulses. Is the ‘best’ phase cycle 4^5=1024 steps, or is it important to cycle the adiabatic pulses in pairs, giving a 64-step phase cycle?
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Nice. I came here to ask a question about sLASER phase cycles and I found this from 3 years ago.
Hi Richard,
Sorry to hear that no one replied in years. Let me participate in the discussion 
I think, PC=1024 is a ‘best’ scheme only in theory. In practice I can’t imagine having sufficient stability over 1024 averages.
Having PC=64 is sufficient not because it is important to cycle adiabatic pulses in pairs, but because we can cycle them in pairs: phase imperfections caused by the first AFP are well eliminated by symmetrical second AFP, meaning that we don’t need separate cycling here.
Excellent point - thanks. What about not phase imperfections but 90-like edge behavior - presumably that is not addressed well with the “by-pairs” cycling? If 64 is good without being perfect (and I fully buy the argument over what level of stability it is reasonable to expect in vivo), what do people run in practice? What options are available in the product and major WIP sequences? (Also, do you know the (pulse-by-pulse) phase cycle being run in the CMRR sequences)?
As far as I remember, dealing with the edge imperfections is more about spoilers. Probably that the reason why the spoilers are stronger in sLASER comparing to PRESS (at least in the Philips product sequence). In Siemens CMRR eja you can change spoilers any way you want: durations and amplitudes, and achieve large areas. CMRR dkd, I believe, allows the same.
Regarding practical informaton on PC: in Philips product sLASER we use only PC=4 because we are interested in MRSI rather then single voxel, and going to NSA > 4 is not possible. Single voxel was awful even with maximal PC available (32 I believe), and the patch for the universal sLASER sequence we never received.
In Siemens CMMR eja we just use PC = ‘Auto’ (other option is ‘None’) and we don’t know the real values. Surprisingy, at Siemens with XA60 software we barely see any stimulated echos in our measurements. If they are present, they are close to the water signal at ~4.5 ppm (both 3T Prisma and 7T Terra when the spoiling is sufficient). So, we didn’t have to investigate on this topic.
Would be interesing to read other user’s replies.