I have a question regarding the --acqp file to run eddy in FSL.

On the webpage, it says that if we know the phase encoding direction (A>P), echo spacing (0.8) and EPI factor (128), we can then create the --acqp file and calculate its last number as 0.8*0.001*127 = 0.102.

I don't understand what this last number represents and why we should multiply the echo spacing (0.8) by 0.001 and 127 (i assume this last number is the EPI factor - 1?).

what we want is the time between acquiring the centre of the first echo and acquiring the centre of the last echo. The 0.001 is to convert the echo-spacing of 0.8ms to 0.0008s. The 128-1 is because there are 127 “echo spacings” between the 128 echoes.

Hope that helps.

Jesper

I would be very grateful if someone could explain this to me!

Thank you so much!

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