Hi,
There are various ways to check for artefacts in your time series
data. Probably the most powerful is to use ICA to identify, and
optionally remove the artefacts - see FEAT and MELODIC manuals for
more on this.
Cheers, Steve.
On 26 Mar 2009, at 18:09, Lara Foland wrote:
> Hello,
>
> Many thanks for your reply.
>
> I am actually concerned about outliers in the timeseries used to
> compute %
> signal change. Is there any easy way to (1) check whether outliers
> exist, and
> (2) remove them?
>
> Thanks again,
> Lara
>
> On Wed, 25 Mar 2009 13:15:00 +0000, Steve Smith
> <[log in to unmask]> wrote:
>
>> Hi,
>>
>> On 24 Mar 2009, at 19:39, Lara Foland wrote:
>>
>>> Hello,
>>>
>>> I'm using featquery to extract % signal change from each of my
>>> subjects using
>>> anatomical ROIs and a cope image. I have two questions:
>>>
>>> 1. Some of my subjects are showing a negative percent signal change.
>>> I am
>>> concerned that outliers may be causing this (atleast in part). Is
>>> there any
>>> easy way to check whether this may be the case?
>>
>> Do you mean outlier values within the ROI or outlier subjects? If you
>> mean the former then you could just use alternative measures from the
>> Featquery output results table, such as median.
>>
>>>
>>> 2. If I apply a threshold of "0", does this mean that, foreach
>>> timepoint where
>>> % signal change is calculated to be negative, the % signal change is
>>> set
>>> to "0"?
>>
>> I think so, yes.
>>
>> Cheers.
>>
>>
>>>
>>> many thanks in advance for the help!
>>> Lara
>>>
>>
>>
>> --------------------------------------------------------------------------
> -
>> Stephen M. Smith, Professor of Biomedical Engineering
>> Associate Director, Oxford University FMRIB Centre
>>
>> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>> +44 (0) 1865 222726 (fax 222717)
>> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
>> --------------------------------------------------------------------------
> -
>
---------------------------------------------------------------------------
Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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