Markus,
On Sunday 05 April 2009 23:46:15 Markus Gschwind wrote:
> Hi Martin!
>
> Your PACS is giving you a strange format!
>
>
> Do you think this should be verified?
>
> Nevertheless, in this branch of problem solving I would make sure that the
>
> > image dataset does not include the trace-weighted images, which Philips
> > calculates if their diffusion encoding scheme is used. This image volume
> > is usually appended at the end of dataset I you can easily identify it,
> > because
> > it looks like diffusion weighted but lacks any WM orientation dependent
> > contrast.
>
> I got 1860 DICOM files.
> After conversion, they end up in 31 volumes of 60 slices. The first volume
> is the b=0.
> So far I cannot see a tracer Image.
I see. Philips doesn't have 30 direction encoding scheme. They have 6, 15, and
32. That could mean that you have a custom encoding scheme, which could be
Jones30. Philips does not have an electrostatic scheme, as far as I know. I
would still look at the last volume to really make sure that you see any WM
contrast. As far as I know from the Philips sequence code, the trace weighted
image could still be calculated even for non-Philips scheme. My guess is it
is not there, but just to rule it out.
>
> However... I had a detailed look at the dicoms with DICOMWORKS:
> I was wrong: The acquisition was not on an Achieva, but on a Philips Intera
> 1.5 T.
This may change the situation a bit. Could you please check the scanner
software version in the dicom header. It is in the tag: 0018, 1020
We will also need to retrieve the image angulations from the dicom header
which is stored in the private tags:
2005, 1071
2005, 1072
2005, 1073
Can you find these tags in your DICOM images?
> This could explain the difference in intensity, could it?
Not really. As Matt says, there can be several reasons for image intensity
scaling and as far as you have sufficient SNR and the scaling is the same
across the DTI volumes, you should be fine.
> And I attributed the screenshot wrongly: The scaled image 1:120 is the
> Philips 1.5T and the scaled image 1:900 is the Trio.
>
> Thanks for the bvecs link, I will try it tomorrow.
You should be able to use the link even with custom encoding scheme, if I
remember correctly.
Best,
Martin
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