[vtkusers] Hounsfield Units : strange result (Volume rendering)

[Frederic Perez]

Hello BELHADJ wassim,

a region growing algorithm (probably using ITK) starting from the corners of
your data to get rid of the "unwanted air" might prove useful to tackle your
problem.

Regards,

Frederic Perez

On Tue, Feb 17, 2009 at 9:45 AM, <wassim_belhadj at topnet.tn> wrote:

> Hi,
>
> Thank you for your reply.
>
> According to Hounsfield Units, the pixel values that form the air is
> between -1000 <--------> -995.
>
> I want to display ONLY the lungs (not skin ...) so I set my function
> transfer like this:
>
> opacityFun->AddPoint(-3024,      0.0);
> opacityFun->AddPoint(-878.674,   0.0);
> opacityFun->AddPoint(-864.466,   1.0);
> opacityFun->AddPoint(-594.524,   1.0);
> opacityFun->AddPoint(-395.62,    1.0);
> opacityFun->AddPoint(3071,       0.0);
>
> Hounsfield Units for lungs are   -950 <--------> -550
>
> I Attached a NEW screenshot that illustrates the problem.
>
> I vary the values of the transfer function but no result.I did not manage
> to remove the part that surrounds the lungs.
>
> Best regards,
> BELHADJ wassim
>
>
>
>
>
> On Tue, 17 Feb 2009 18:06:18 +1100, Kevin Osborn <planck at netspeed.com.au>
> wrote:
> > Don't forget air surrounds the patient. What your image shows is the
> > air/skin interface, not the skin itself. As the lung is mostly air, your
> > Hounsfield range between -600 and -400 not only gives lung but also
> > includes air around the patient.
> >
> >
> > wassim_belhadj at topnet.tn wrote:
> >> Hi,
> >>
> >> I'am using VTK/VTKEdge and QT4 for volume rendering.
> >>
> >> I 'am using a CT Datasets of a young person ( 35  years old)
> >>
> >> I'm trying to define values of pixel that define lungs.
> >>
> >> I assigned opacity to each pixel by checking its intensity value  with
> >> Hounsfield Units values.
> >>
> >> Bone         +400 -----------> +1000
> >>
> >> Soft tissue  +40 -----------> +80
> >>
> >> Fat          -80 -----------> -100
> >>
> >> Lung         -400 -----------> -600
> >>
> >>
> >> I got a strange result !!  The volume obtained contains the lungs and
> >> skin
> >>
> >>
> >> According Hounsfield Units, the pixel values that form the skin and
> lungs
> >> are not in the same interval.
> >>
> >> I varied the opacity values to eliminate the skin that surrounds the
> >> lungs
> >> but I have not succeeded.
> >>
> >> Attached a screenshot that illustrates the problem.
> >>
> >> Can someone help me ?
> >>
> >> Best Regards,
> >> BEHADJ wassim
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