RF and echo time definition

[aelster]

Dear MrPaul,

Great question! I've never given that much thought before and am not sure there is any official definition of exactly where TE should start.

I quickly scanned through a number of papers with diagrams showing hard (rectangular) pulses and can't find any where TE began at the end of the pulse. All the papers I found measured TE from the middle of the rectangle. Because hard pulses tend to be relatively short in duration the difference is minimal.

I think that the unwritten rule is that for any symmetric RF pulse (sinc, rectangle, or otherwise), the middle of the pulse in the time domain should be chosen as the start of the TE interval.

Asymmetric pulses (e.g., truncated sinc, SLR, and various adiabatic pulses) are more tricky. Looking again through diagrams in the literature it seems the overwhelming majority of authors use the peak of the pulse in the time domain as the starting point for TE. If anyone else has better information, please chime in!