Meaning (and order of magnitude) of TR for structural vs functional images

neuroimaging
#1

Hello,

I understood TR as the time necessary to scan an entire volume, i.e. the acquisition duration for all the slices that make up a volume, regardless of whether anatomical or functional.

But while TR for fMRI is typically in the order of seconds, TR for structural images seems to be in the order of ms. Is it the case that TR then represents not the time between consecutive volumes but between consecutive slices? If so, then is it correct to say the volume acquisition time for structural images is the TR multiplied by the number of slices?

Thank you for any help!
–Francesco

#2

Hi, Francesco
This is related to MRI physics. Make a long story short. The meaning of TR in different MRI sequences are different. Most fMRI data use epi sequences and structural data use some 3D sequences (e.g., MPRage in Simense). They are not directly related.
Also, I would not assume the TR is the time to acquire a slice in structural data as many T1/T2 data use 3D sequences, which involve complex excitation regimes. You can do a simple math. A typical MPRage T1 scan takes ~5-6 mins. If you use TR in ms to multiply the number of slices, you should not get the total time of acquisition.

Ruyuan

2 Likes
#3

Thank you Ruyuan, this is helpful!