hi leina and others,
i will try to answer these for you. i don't pretend to know as much as peter or robert but i think i understood their mails. and maybe they could use the spare time they gain if i answer.
> Hi SPMer,hi Peter,hi Robert:
> I also have some questions in my mind:
> 1,In Peter's mail,*You want to make sure that TR > 3T2, *is it a slip
> ?sholud be *TR > 3T1*
that was not a slip. when you repeatedly excite the same slice you have to make sure that the transverse magnetization has completely died out. or as a rule of thumb you should wait about 3*T2.
> 2, In Peter's reply,*This sets a minimum TR ~ 300 ms*. but in
> robert'smail,he told me *Since you are only acquiring a single
> slice you can go
> quite short, 250ms or 500ms. *can someone explain to me more details?
i don't think there is a disagreement here. the 300ms quote by peter is within the range (250-500ms) given by robert.
> 3,I know that TR relate to slice number. In Robert's mail, he
> said:*Typicallyan echo planar (and spiral) acquisition per slice
> is on order 20-45 ms, *Did
> he mean that the TR will increase 40-45ms/ one slice when we keep
> otherparamter fixed?
yes. actually, i think what he meant was that the EPI readout train will take 40-45ms to acquire. so each slice will take you that long.
> can someone give me more info about the
> relation between the
> TR and slice number in EPI squence?
do you mean the number of slices? the number of slices is TR/(ES*ETL*PF)
here ES is the echo spacing. in other words ES the time it will take you to read a single line in k-space during an EPI readout train. ES will depend on
- how fast your gradients are
- how strong your gradeitns are
- whether you sample k-space points during the ramp up-down time
- your bandwith
ETL is the echo train length. basically your frequency encoding matrix. i assume it will be 64 or 128 for an fmri acquisition
PF represents partial fourier method. that is you may not actually read the entire line but only about 75 (or some people only read 50% and a few extra points.
or if we take the number which robert quoted it will take you TR/45ms
i hope this helped.
good luck,
zoltan
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