sparse temporal sampling

[Matt Davis <Matt.Davis@xxxxxxxxxxxxxxxxx>]

Hi Theresa

Here's a few suggestions for analysis of sparse fMRI data. I don't know of
a single methods paper that explains everything. You might to read a paper
like Hall et al (1999, Human Brain Mapping).
Most of the preprocessing and analysis steps are as usual for fMRI data. A
few points of difference between sparse and standard fMRI analysis are as
follows:

1. Don't perform slice acquisition time correction. Given the 15s delay
between scans, interpolation between successive scans is ineffective and
will damage your data.

2. At the analysis stage, I often use an FIR basis set of duration 15
seconds (equivalent to your scan repetition rate), with a single time bin.
This models the data as a box-car covering the single scan  following each
condition. This is a simpler model to set up than the typical haemodynamic
response model, but usually effective for sparse data.

3. If you do want to use an HRF model - for instance, if you have
differences in the timing of trials within your silent period - then you
also need to take care over the specification of SPM.xBF.T and SPM.xBF.T0
in your model.

4. You need to take care in specifying the low-pass filter and AR(1)
parameters in your model. I often turn these off entirely since my goal is
to do second level, group analyses rather than computing single subject
statistics. The reason for concern is that scan-to-scan auto-correlation
is greatly reduced with a long TR design, and the slow changes in
activation between conditions are at a much lower frequency in sparse
designs.

Good luck!

Matt



On 15/07/2011 05:06, "AUDITORY automatic digest system"
<LISTSERV@xxxxxxxxxxxxxxx> wrote:
>
>Date:    Thu, 14 Jul 2011 13:44:23 -0700
>From:    theresa veltri <theresaveltri@xxxxxxxxxxx>
>Subject: sparse temporal sampling
>
>Hi, I am currently starting some fMRI analysis in SPM8. Unfortunately I
>am 
>unsure how to account for the sparse temporal sampling design that was
>used.
>For example, each trial was 15s, but TR is only 4s. Does anyone have expe
>rience with specifying such parameters in SPM? Does anyone have any
>referen=
>ces the could suggest? any help would be appreciated.
>Best,
>
>Theresa Veltri
>MSc in Cognitive and Computational Neuroscience
>University of Sheffield, UK