Hi everyone,
Just to answer Sean's question about newborns, judging from some of the
data we acquired in GOS, the FA values do tend to be a lot lower. But
it's not just due to the absence of myelin - Christian Beaulieu showed
that you get quite a lot of anisotropy even in unmyelinated nerves. It's
also that there's a lot more water around - the ADC is much higher than
in adult brain. So I'm not sure we can compare the newborn brain with
this one.
Back to the main problem: I'm really surprised about the lack of
contrast in the DWIs. Given the expected 3-fold loss in average ADC
(according to a couple of papers), the b=4500 should give an image
vaguely similar to what you would see in-vivo at b=1500. Have you
measured the ADC using these images? What's the signal intensity ratio
between the b=0 and the DWIs? My guess is it should be around a third if
you want to get a reliable measure of the ADC (Derek?). And if it isn't,
then either you're not getting the b-values you wanted, or the ADC
really is very different. Might help to explain the lack of DW contrast
though.
And as Chris says, there's also the effect of temperature to consider:
the couple of papers that I'm aware of both did their imaging at room
temperature. If the imaging was done at a much lower temperature -
straight out of the fridge, say - then the ADC is going to be a lot
lower again.
Best of luck!
Donald.
On Mon, 2005-10-31 at 10:55 +0000, Sean Deoni wrote:
> Hi guys,
>
>
> Somewhat related to your question Tim, i.e. would it be possible in
> the case of myelin break-down? Do you get normal FA values in maturing
> brain? Really not familiar with the literature with regards to DTI in
> 0-2 year old infants, but that might be the same situation as you have
> here, with little or no myelin.
>
>
> SD
>
> ----------
>
> "They keep creating new ways to celebrate mediocrity." Mr. Incredible
>
>
> Sean Deoni
>
> Centre for Neuroimaging Sciences
>
> Institute of Psychiatry, King's College London
>
>
> +44 020 7919 3069
>
> [log in to unmask]
>
>
>
>
--
Jacques-Donald Tournier (PhD)
Brain Research Institute
Neurosciences Building
ARMC Banksia Street
Melbourne, Australia
Tel: +61 3 9496 4169
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