And if you increased your voxel size from 3x3x3mm to 30x30x30mm then you could reduce your scantime by a factor of (10x10x10)^2= 1000000 so instead of scanning for 10 minutes you would only need to scan for 600microseconds.
Best
Torben
P.S. This mail was written on April 1st!
Getting serious: Could it be that your paradigm is not strong enough to give rise to any BOLD activity, this can happen!
Den 01/04/2011 kl. 19.57 skrev Meera Paleja:
> Yes- this makes sense. I suspect it's probably noise from the lower SNR that's the issue. Thanks Michael!
>
> Meera
> ________________________________________
> From: Michael Erb [[log in to unmask]]
> Sent: Thursday, March 31, 2011 3:55 PM
> To: Meera Paleja
> Cc: [log in to unmask]
> Subject: Re: [SPM] "dalmation" pattern in data
>
> Dear Meera,
>
> your data look very noisy! You mentioned, that was a high-resolution
> fMRI experiment, what is your actual voxel size? Remember that reducing
> voxel size from 3x3x3 to 1.5x1.5x1.5 reduces the volume by 2x2x2=8. To
> compensate this in term of SNR, you have to increase the measurement
> time by 8x8=64. So instead of measuring 10 min you have to measure 10h
> to get the same SNR!
>
> Regards,
> Michael.
>
> Am 31.03.2011 19:20, schrieb Meera Paleja:
>> Hi Alexander,
>>
>> I've attached the screenshot. This is what I'm seeing for single participants. I haven't done a group analysis yet since I only have 5 people in my sample so far. Does this effect normally disappear when I've done a 2nd level analysis?
>>
>> Meera
>> ________________________________________
>> From: Alexander Hammers [[log in to unmask]]
>> Sent: Wednesday, March 30, 2011 4:50 PM
>> To: Meera Paleja
>> Cc: [log in to unmask]
>> Subject: Re: [SPM] "dalmation" pattern in data
>>
>> Dear Meera,
>>
>>
>> I may have missed the screenshot. What you describe sounds like what happens with very few degrees of freedom - unlikely to be a problem with fMRI, but how many did you have?
>>
>> ATB,
>>
>> Alexander
>>
>>
>> -----------------------------
>> Alexander Hammers, MD PhD
>
> --
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> Dr. Michael Erb
> Sektion f. experimentelle Kernspinresonanz des ZNS
> Abteilung Neuroradiologie, Universitaetsklinikum
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