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Leina, You should look at your experimental design and let that drive your choice of TR in part. If you have an event related design where the duration of the stimulus is short then you may opt for a shorter TR. Since you are only acquiring a single slice you can go quite short, 250ms or 500ms. But I would actually advise taking a few more slices, very few studies now days get just a single slice, and in fact usually the reason to get a single slice is driven by a desire to acquire them very rapidly. Typically an echo planar (and spiral) acquisition per slice is on order 20-45 ms. If you don't need to acquire quickly then get move coverage. The coverage is especially good for any realignment and coregistrations etc. In much of cognitive neuroscience literature experiments typically have a TR or 2 or 3 seconds (state of the art now days) which 30-40 slices. You should match you flip angle according to the TR. Short TR, less of a flip, as Peter has indicated. -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Robert C. Welsh, PhD Research Investigator Department of Radiology University of Michigan (734) - 764 - 2412 (fax) [log in to unmask] >>> LeiNa Hua <[log in to unmask]> 11/03/05 8:35 PM >>> Hi SPMer,hi Peter: When we want to aquire single slice,How should we choose the TR? It also need TR ~3-4T1? Thanks Leina On 11/3/05, Kingsley, Peter <[log in to unmask]> wrote: > > It depends how long. With 90-degree pulses, "average" SNR per unit time is > best when TR/T1 ~ 1.25, so you certainly don't want to use TR < 1.25*T1unless you use a lower flip angle. At > 1.5 T, T1 is ~700 ms for white matter and ~1200 ms for gray matter, and > these numbers increase by 10-20% at 3 T. Therefore, for gray matter, TR > should be at least 1.5 s at 1.5 T and 2 s at 3 T. Beyond 4-6 seconds, you > will not gain much SNR because you are already ~3-4x T1 for gray matter, and > therefore almost fully relaxed. A longer TR allows more slices, but I see no > advantage in setting TR much longer than needed, so TR usually is chosen to > be between 1.5 s and 5 s. > > ----- > Peter B. Kingsley, MRI Physicist [log in to unmask] > Department of Radiology / MRI > North Shore University Hospital > 300 Community Drive, Manhasset, NY 11030, USA > Tel (516) 562-2842 Fax (516) 562-3561 > > > ------------------------------ > *From:* SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] *On > Behalf Of *chin wei > *Sent:* Thursday, November 03, 2005 6:01 AM > *To:* [log in to unmask] > *Subject:* [SPM] about TR > > hi all; > Who can tell me what is the advantages and disadvantages of a long TR > time in EPI scan? > thanks in advance > > _____________________________________________________________________ > > The information contained in this electronic e-mail transmission > > and any attachments are intended only for the use of the individual > > or entity to whom or to which it is addressed, and may contain > > information that is privileged, confidential and exempt from > > disclosure under applicable law. If the reader of this communication > > is not the intended recipient, or the employee or agent responsible > > for delivering this communication to the intended recipient, you > > are hereby notified that any dissemination, distribution, copying > > or disclosure of this communication and any attachment is strictly > > prohibited. If you have received this transmission in error, please > > notify the sender immediately by telephone and electronic mail, > > and delete the original communication and any attachment from any > > computer, server or other electronic recording or storage device > > or medium. Receipt by anyone other than the intended recipient is > > not a waiver of any attorney-client, physician-patient or other > > privilege. Thank you. > > ********************************************************** Electronic Mail is not secure, may not be read every day, and should not be used for urgent or sensitive issues.