Slice thickness not working properly?

[777Beta]

Hi,

I'm confused about how slice selection is implemented in MRiLab. I tried an experiment like this: loaded built-in PSD_SPGR3D sequence. Slice thickness was 88mm. Examined sequence details in SeqDesignPanel: RF pulse: duration 0.3ms, TBP = 4. GzSS: same duration, amplitude = 10^-4 T/m. This RF pulse and SS gradient combination actually produced slice thickness of ~3m and can be confirmed with rfDesignPanel. Furthermore, if I changed slice thickness RF pulse and GzSS parameters did not change. Could you please provide some insights on this?

Thanks much!

[leoliuf]

Thank you for your feedback. In this current version v1.3, most of the default sequences assume a whole body excitation, which doesn't use the slab selection gradient. If there is a slab selection gradient (e.g., GzSelective) in the pulse waveform, the whole body excitation is also implemented with a default gradient value that can produce a very thick slab.

To produce an actual slab excitation matching the RF design, you can simply modify the GzSelective.m

....
% GzAmp=p.GzAmp;
bw = Pulse_TBP / (t2End-t2Start); % Pulse_TBP here is the pulse time-bandwidth product, which is pulse type specific
GzAmp = bw / ((VObj.Gyro/(2*pi)) * VCtl.FOVSlice); % slice-select gradient amplitude
....

I didn't implement this in v1.3 because I am working on a newer version with a wide range of 2D and 3D sequences which will have a more advanced and accurate excitation profile for sequence simulation.

Thanks.