Thank Torben for quickly reply.
The data was acquired from GE signa 1.5T MRI scanner, which limits
the total images in a sequence not more than 512.
If I change NEX=4 to NEX=1, with slice=16 (covering the brain), I can
only get 32 volumes (16 slice_per_volume x 32 volume = 512 images).
The total scan time will be 32*2=64 seconds (TR=2) and be too short to
conduct my olfactory stimulation.
On Mon, Sep 6, 2010 at 10:07 PM, Torben Ellegaard Lund
<[log in to unmask]> wrote:
> Dear Kit
>
> With 32 volumes in 256s, the TR you have to give SPM is 8s (corresponding to 2s times 4 NEX). Slice timing is unlikely to work in general, at for such a long TR in particular. Your paradigm on the other hand is really nice and fast (which is normally good), but in your case it may actually be to fast for the changes to be caught by you long TR. When these facts are combined with a total of just 32 volumes in total acquired on a 1.5 T scanner I would be surprised if you will see any effect at all. You really should repeat the experiment using a bit different parameters. Changing NEX=4 to NEX=1 and use the time to acquire more volumes (?=phase) e.g. 128 would be a reasonable start. If you then decide to do slice-timing TA is the time from the beginning of the acquisition of the first slice until the beginning of the aquisition of the last slice.
>
>
> Best
> Torben
>
>
>
> Den 06/09/2010 kl. 14.50 skrev Kit Chen:
>
>> Hi, all.
>>
>> The stimulating pattern in my bold fMRI experiment was block design.
>> The baseline duration was 16 seconds and task duration was 16s, too.
>>
>> Acquistion parameter are: TR=2s, TE=60ms, NEX=4, phase=32, slice=16,
>> slice thickness=7, GE 1.5T scanner.
>>
>> Total scan time is 256 seconds and 512 dicom images were acquired.
>>
>> I used dcm2nii of MRIcorN(http://www.mricro.com) to automatically
>> convert there 512 dicom files to 32 3D NIfTI hdr/img files.
>>
>> When I launched SPM8 to process and analyze these 32 volumes, I'm
>> obstructed at the Slice Timing.
>>
>> What can I set the TR and TA values?
>>
>> Thanks in advance.
>
>
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