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Dear Moreno Moreno,

I think you will have to write some elaborate slice timing correction algorithm, to create new volumes as if they were acquired with equal TR. After that you could do normal SPM analyses. To my knowledge there are too many computations relying on constant acquisition time per volume (design matrix creation with temporal basis functions, temporal autocorrelation, high-pass filtering, to name a few).

Perhaps you can adapt the current source code doing slice time correction to suit your needs? Or perhaps someone else already did this for you? Doesnt sound like rocket science, simply interpolate linearly between subsequent volumes taking into account the time they really were acquired.

And with TR, do you mean time to acquire a volume? That is not strictly the same (for 3DEPI TR can be around 30 ms, and 1 volume is recorded in 1.5sec). For 2DEPI TR is the same as acquisition time/volume.

Good luck,

Bas


On 04/20/2011 05:47 PM, moreno moreno wrote:
[log in to unmask]" type="cite"> 
Dear SPM experts,
 
I have got a problem about fMRI with the cardiac trigger. 
I mean that using the trigger, the TR becomes depending on the heart beats, and so if the heart starts to beat faster or slower , then there is a variable TR that is not constant in time. 
I would like to know if there is an option in SPM (version 8 or 5) that allowes me to use a variable TR. I don't know what to do. Thank you ! 

Regards

Moreno






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Dr. S.F.W. Neggers
Division of Brain Research
Rudolf Magnus Institute for Neuroscience
Utrecht University Medical Center
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