Clarification/Confusion Regarding Repetition Time in typical fMRI study



I am a new comer to fMRI/NeuroScience, so my apologies if this question is too basic.

I understand that repetition time(TR) is the time between successive RF pulses, for measuring the fMRI signal.Also there are TrialOnSet Times, at which we show the subject some stimulus.

Can someone suggest about:

how TrialOnSet Times and repetition time(TR) are related. For example for the dataset dataset, Trail onsets starts from 6+ second and their repetition time is 2 s. Does that mean we record first fMRI Image/volume at 0s, or at 2 s.


Onset times are relative to the beginning of the first volume of the corresponding imaging file (.nii). In other words recording of the imaging data starts at 0s.


I need to know when we finish acquiring the first volume. is it at 0s or 2s? You said recording of the imaging data starts at 0s. Does that mean if TR is 2s we finish acquiring the first image at 2s?


Correct. It’s also true for every image - not only the first. In other words RepetitionTime tells you what is the interval between the beginning of acqusition of each volume.


Thanks ChrisGorgolewski.