Using MRIGradients for spiral pulseq sequence

[aTrotier]

Hi,
After playing around with the package and finding that most of the issues are due to some conversion problem from raw -> acq (pulseq split the ADC in 28):

for p in eachindex(raw.profiles)
  raw.profiles[p].traj = Float32.(traj[:,:,p])
  raw.profiles[p].head.trajectory_dimensions=2
  # issue with reverse
  raw.profiles[p].head.read_dir = (0.0,0.0,0.0)
end
raw.params["trajectory"] = "custom"
raw.params["encodedSize"] = (64,64)
raw.params["fov"] = (256,256,3)

# convert to acq
acq = AcquisitionData(raw)
acq.fov = (256,256,3)
acq.traj[1].circular = false #Removing circular window
acq.traj[1].numSamplingPerProfile = size(acq.kdata[1],1) #correct the issue with 28
acq.traj[1].numProfiles = 1 #correct the issue with 28
acq.traj[1].times = 0:raw.profiles[1].head.sample_time_us:raw.profiles[1].head.sample_time_us*(size(acq.kdata[1],1)-1)

The results seems okish except for the first points :

Do you also observe the fluctuation at the start in your experiments ?

By the way, I am not really familiar with spiral imaging and images are pretty bad :
Phantom with the spiral pulseq example https://pulseq.github.io/writeSpiral.html :

Brain with my own spiral implementation where dt is small (10us like the gradient raster time and I have a few starting points equal to 0 for Self-gating (should I remove the SG points from trajectory before applying girf ?):

Maybe gradient intensity is too high and I have a FOV/2, or it is only an issue with the B0 / spatial resolution...
Any thoughts ?

[alexjaffray]

@aTrotier It was great seeing you at ESMRMB! I've started looking at this again recently. Did you manage to solve this issue?

[aTrotier]

Yes it was nice.

I was not able to make it work but I gave up pretty fast because it was not really needed by any of our project.

The main issue here was also that I was not sure my sequence was working as expected. I don't remember if at that time I was simulated the results with Koma.

When the bruker pulseq interpreter will be working it will surely be the first thing that I want to work on.

Edit : for the initial fluctuation I think I have to zero fill the data a little bit on both side maybe ?
Or it is really something small in term of amplitude and won't affect the reconstruction ?