Dear John,
I run DTI with ASSET (factor 2) regularly at 14m5, and everything is
satisfactory.
(BTW, what is stopping you from upgrading to 14m5, or 15x?)
We did OK at 12m5, though...
(We haven't gone to 15x cos we've heard not good things about fMRI, and
because we're doing a huge serial study and the last thing we want to do
is change things when I've got them working.)
One wise tip I was given about GE ASSET is that it's not as good as SENSE
from Philips. Having read the GE code, I sensed the need for the GE
engineers to get this stuff out of the factory ASAP.
In particular, make sure your ASSET ***CALIBRATION*** scans have a slice
thickness of 1cm. I know this sounds very 1980s, but the algorithms need a
decent amount of SNR to work their magic. The GE protocols using ASSET
calibration scans with slice thicknessses of less than this are probably
only suitable for abdominal imaging. This one change has made ASSET
scanning very reliable for us in human neuro DTI.
BTW, we love ASSET, as it reduces distortions and lets us run with a
shorter TE for better SNR and more coverage; it's all gravy, so it's worth
trying to get it right.
If you need more suggestions, please ask.
Best wishes,
Mark
> Dear all,
>
> I've been having problems with our DTI acquisition on our 3T GE Signa HD
> (v 12m5), any advice would be much appreciated.
>
> There are two issues:
>
> We run asset with our DTI acquisition. Running this in neonates (1month
> and 4months old) using the 8 channel head coil produced images with severe
> signal dropout in the centre of the FOV. Contacted GE about this and they
> came back with the suggestion of manually pre-scanning to adjust the Gain,
> as they felt the initial default Gain setting would be too high and
> suboptimal. A full manual prescan did seem to improve things but we still
> got repeat images (ghosting) which looked worse than one might expect from
> a typical EPI-diffusion scan.
>
> The second issue we had most recently occurred in an adult scan. Again
> running DTI with asset. On the resultant images we got severe parallel
> strips anterior to posterior across the image. This was on all slices and
> was replicated on repeat scanning. The artefact also switched orientation
> as we switched the Freq encode direction. One of my colleagues felt this
> was perhaps an issue with asset. We ran the DTI without asset and it
> looked much much better.
>
> I am now wondering whether there is anything to be gained from trying to
> resolve the problem we see with asset, we don't appear to save time on the
> acquisition and obviously the image quality is poor.
> I know the Asset FOV has to be bigger than the planned DTI acquisition and
> this was the case in these situations but is there something else I am
> missing, maybe our Asset FOV is still not big enough?
>
> If anyone has any advice/experience about Asset and DTI and in particular
> neonatal DTI acquisitions I'd be happy to chat on or off this list.
>
> Many Thanks
> John McLean
> [log in to unmask]
>
>
>
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