[Insight-users] Error reading images with negative values

[Xin Guan]

Hi Kajetan,

You were right. I did find that the range is not from - 16686 (MRIcro
histogram came up with this value, not sure why). Looking through the data I
see that its actually [-1000, 3000]. However, reading directly from DICOM
series, I still got [0, 4094], but reading Analyze file (converted by
MRIcro) gave the correct value.

What is HU scale? Maybe I should use this information to render the images.

Thanks a lot, that's very helpful.

- xin

On 8/14/06, Kajetan Berlinger <kaje at kaje.info> wrote:
>
> Hi Xin,
>
> On Monday 14 August 2006 08:05, Xin Guan wrote:
> > Hi,
> >
> > I'm using ITK image IO to read images. MRI images are okay, but CT
> images
> > -- no matter it's DICOM or converted Analyze files -- always gave some
> > weird images. The actual pixel value range is  -16330 to 3000, but the
> > loaded image has a range of 0 to 4094.
>
> A range from -16330 to 3000 ist not possible, as the intensity value of a
> CT
> voxel  is represented by 12 bit. That is from 0 to 4095 or with respect to
> the HU scale -1023 to 3072.
> How do you come to this -16330 to 3000 value range?
> Is there perhaps a pixel padding value defined?
> This value is stored in DicomTag (0028,0120).
> If the image is non-rectangular, this value marks pixels used to pad to
> rectangular format.
>
> > It seems that part of the negative
> > values were simply negated to positive. The error remains the same
> > regardless of the pixel type specified -- signed short or float.
> >
> > I followed ITK example DicomSeriesReadSeriesWrite and Image2 (
> > itk::ImageFileReader).
> >
> > I'd appreciate any help on this. Thanks in advance.
> >
> > - xin
>
> cu
> kaj
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://public.kitware.com/pipermail/insight-users/attachments/20060815/a5eda962/attachment.htm