fMRI tutorial slides
<p>Jan 01, 2013 01:40 PM
 
in pdf form (exapnd this out to full width to see detail)
 
FOV = field of view;FOV =  200 mm/ 64 matrix = 3.12 mm voxel .
 
single shot TE = 30 ms
 
TR repetition time:
 
time btwn RF pulses:  how much mag is allowed to recover before it is knocked over again;
 
waiting for very long TRs  (5 seconds +)  allows for max  SNR.
 
need many images (to separate signal from physio noise) to see differences btwn conditions
therefore, TR times need to be shorter;
 
fMRI  can be performed with a TR as short as 100 ms.
 
bottom line:  use a TR as short as u can.
 
for TRs of 1-2 sec, a flip angle of around 60 to 70 degr is optimal.
 
separate slices in EPI are squeezed into a TR interval..
 
so far...  only image brain regionsof interest (to minimize # of slices acquired)
 
in genl  TRs  btwn 1 and 2 secs are not too bad...
 
TE = echo time  optimum is shorter at high field (say 30 ms at 3T)
 
high bandwidth means faster data acquisition and more slices can be gotten with less T2 blurring;
 
sampling at 128 kHz / 64 matrix means  2000 Hz per pixel.
 
matrix size impacts everything
incr matrix size  decr voxel dize and thus SNR
 
 
 
 
 
 
 
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