If the task you wish to study really demands a very long block time, of several minutes, you could consider Arterial Spin labelling fMRI instead of BOLD. See Wang et al, Magn Reson Med. 2003 May;49(5):796-802. In general, for typical cognitive neurology paradigms with short blocks of 20-30 s, ASL-fMRI is less efficient, and has poorer spatial and temporal resolution.
James Rowe
>Hi Manish,
>I think that 3-4 mins could be quite a lot of time for a block in fMRI. I think that you can have stimuli between 0 secs. (instant stimulus, but you have to leave time afterwards before the next stimulus and to be able to measure the baseline because the blood takes 2/3 secs.to arrive...) and 30/60 secs. I think that the BOLD signal can't be stable for a long time so... the minimum is clear and I'm sure that for 20/30 secs.the signal is stable. I can't say for more than that!
>Good Luck
>Juan J.
>______________________________________________
>Juan J. Lull - jualulno_at_upvnet.upv.es
>[MI - Medical Imaging Area]
>BET - Bioengineering, Electronics and Telemedicine Group
>UPV - Politechnical University of Valencia - Spain
>______________________________________________
> ----- Original Message -----
> From: Manish Dalwani
> To: [log in to unmask]
> Sent: Thursday, July 29, 2004 11:33 PM
> Subject: [SPM] Question about block design?
>
>
> Hi SPM Community!
>
> My question is in a block design is there a set rule/recommendation that the activation task should have a maximum duration of lets say x secs. Would it be ok if I have a design which has an activation task of 3-4 mins followed by a baseline task of similar duration? Is that too long a duration for a block design?
>
> Thank you for your help!
>
> Manish Dalwani
> Professional Research Associate
> Dept. of Pschiatry
> UCHSC
>
>
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