Natalie,
The subtraction data from an ASL sequence is only semi-quantatiative measure of cerebral perfusion and therefore can have variable baseline values from run to run. Calculation of perfusion maps is usually performed by fitting the data to a model. This model needs several additional parameters such as M0, T1 of the blood, etc to calculate the perfusion values in ml/100gm/min.
Hope this clarifies your situation
pk
________________________________________
From: FSL - FMRIB's Software Library [[log in to unmask]] On Behalf Of Natalie Paul [[log in to unmask]]
Sent: Wednesday, October 13, 2010 7:10 AM
To: [log in to unmask]
Subject: Re: [FSL] ASL ROI analysis
Hello,
We have collected a baseline scan (run 6) in addition to our task
scans (runs 7, 9, 11, and 13). If we subtract our Task ASL - baseline
ASL, can we do that to get a quantitative value?
Thank you,
Natalie
On Wed, Oct 13, 2010 at 3:12 AM, Stephen Smith <[log in to unmask]> wrote:
>
>
> ----------
>
> From: FSL - FMRIB's Software Library on behalf of Stephen
> Smith[SMTP:[log in to unmask]]
> Sent: Wednesday, October 13, 2010 3:12:49 AM
>
> To: [log in to unmask]
> Subject: Re: [FSL] ASL ROI analysis
> Auto forwarded by a Rule
> Hi, just as with BOLD data, FEAT leaves the mean signal in the data, and
> the overall (4D) mean is rescaled to be 10000. The units of signal change
> are therefore either in these scaled units, or in % signal change if that
> option has been selected in Featquery. I'm not quite sure what you mean by
> quantitative in this context, as ASL-timeseries data is in general not
> quantitative without further quantification of the baseline flow level.
> Cheers.
>
>
>
> On 11 Oct 2010, at 14:23, Natalie Paul wrote:
>
> We did an analysis on our ASL data using FSL feat following the web
> instructions. We then conducted an ROI analysis using featquery on the
> perfusion EV (the interaction of control-tag EV with the bold EV). My
> question is, what unit is used for the mean signal perfusion signal of the
> ROI? Also, is there a way to get quantitative perfusion measurement from the
> ROI analysis?
>
> Thank you,
>
> Natalie Paul
>
>
>
> ---------------------------------------------------------------------------
> 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
> ---------------------------------------------------------------------------
>
>
>
>
--
Natalie Paul
Post-Baccalaureate Fellow
Duke-UNC Brain Imaging and Analysis Center
2424 Erwin Road, Suite 501
Durham, NC 27705
727.542.2587
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