JISCMail - SPM Archives

Hi Jonathan,
Glad to get your reply.
That is OK. I just want to figure out which definition is right.

I still have some more question to ask, and hope you can help!

First, actually, I agree with your comment that it is in a more sense that TA is the beginning of the first slice to the *end* of the last slice. But why SPM defines TA as (TR - TR/N)? Is that convenient for some calculations?

Second, as Nani Abdul Manan pointed out in the list:

From this SPM list I found 2 equation that can be use to calculate the microtime onset.

fMRI_T0 = fMRI_T* (TA/TR) (1/2)
fMRI_T0 = (fMRI_T /TR)(TR - TA/2)

What is more, I found one more comment on the Microtime onset calculation:

A common approach, especially if slice timing correction is implemented, is to set the microtime resolution to the number of slices, and the microtime onset to the middle slice. (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=SPM;70bf5c7f.0904)

So, in your opinion, which one is the most appropriate way to use.
In my opinion, this equation【fMRI_T0 = fMRI_T* (TA/TR) (1/2)】makes sense. I think it can be deprived as below:
   fMRI_T x
   ________ = ________ ===> x = fMRI_T*TA/TR ===> then the middle point of x is 【fMRI_T0 = fMRI_T* (TA/TR) (1/2)】
   TR      TA

Expecting for you answers.
Thanks!

So for the case of this post, TA=2.4-2.4/46

On Sun, Sep 11, 2011 at 10:43 AM, Jonathan Peelle <[log in to unmask]> wrote:
>
> Dear Senhua Zhu,
>
> I apologize for causing confusion on this—I was not being very precise in my use of TR and TA. You are correct that in SPM, TA = TR - TR/N, and so is not equal to the TR, even in continuous scanning.
>
> The difference is that in SPM, the TA refers to the time between the beginning of the first slice to the beginning of the last slice (as you have in your slide). However, I meant it in a more everyday sense of the beginning of the first slice to the *end* of the last slice—that is, how long, from beginning to end, it takes to acquire a full volume.
>
> The distinction I was trying to make was between continuous scanning (where there is no delay between volume acquisitions) and sparse scanning, where there is a delay of up to many seconds inserted.
>
> I hope that clears things up for you!
>
> Best regards,
> Jonathan
>
> --
> Dr. Jonathan Peelle
> Department of Neurology
> University of Pennsylvania
> 3 West Gates
> 3400 Spruce Street
> Philadelphia, PA 19104
> USA
> http://jonathanpeelle.net/
>
>
>
> On Sep 10, 2011, at 2:02 PM, cliff wrote:
>
> > After reviewing your comments here, now I am confusing about the definition of TR and TA.
> >
> > As the definition of TA in SPM, 【TA = TR - TR/N, where TA is the time between the onset of the ﬁrst and
> > last slice of one volume, and the TR is the time between the onset of the ﬁrst slice of one volume
> > and the ﬁrst slice of next volume】
> >
> > but according what you said, if there is no interscan delay time, then TA= TR (If the "Acquisition time" mentioned in this post is exact the same as the TA I mentioned here )
>
>
>
>