[vtkusers] about volume rendering in medicine.

[Lisa Avila]

Hello,

This is not an easy issue - the transfer function maps scalar value to 
opacity, and if you map a range of values to 0 opacity that "structure" 
will become invisible in your volume rendered image. The issue is then 
truly understanding the scalar values in your data set, and creating a 
transfer function that shows what you want to see. The transfer function is 
essentially a very simple segmentation of the data - you must perform that 
segmentation carefully.

This is the same issue that can arise when viewing an image with window and 
level - you can set these values in such a way that you have lost 
structures into region that are entirely black or white according to your 
window and level settings. The typical solution here is to set a default 
that shows everything, and let the user interactively adjust this.

Lisa



At 03:21 PM 2/9/2004, J. Zhou wrote:
>Thank you very much for your useful information.
>
>About volume rendering, I want to know how to make sure that the user 
>really gets the right
>object information what he wants to see. What makes user understand 
>whether he has
>gotten the right object information in volume rendering? And another 
>critical problem is how
>to make sure that the user does not miss the object information he wants 
>to see based on
>current settings (e.g. transfer functions) during volume rendering.
>
>Thank you!
>
>J. Zhou
>
>
> >
> > This is unfortunately true.
> > Radiologist only use slice images for diagnosis.
> >
> > It is probably the consequence of two facts:
> >
> > 1) Radiologist do not get training on images generated
> >      by volume renderting.
> >
> > 2) There are no stablished standards on the sort of
> >     transfer functions and visualization parameters
> >     that should be used for diagnostic of a particular
> >     disorder in a specific image modality.
> >
> >
> > It also leads to the circular dependency problem that:
> > because radiologist only look at slices, imaging protocols
> > tend to acquire slices with high in-plane resolution and
> > large inter-slice spacing, making those images unusable
> > for computer assisted image processing. It is not uncommon
> > to find voxel sizes with anisotropies of 1:10. Most image
> > segmentation and registration algorithms will have a hard
> > time producing something useful out of such images.
> >
> > Probably medical organizations such as RSNA should
> > make an effort for establishing standards for visualization
> > of 3D medical images, and provide training on how to take
> > advantages these modern visualization techniques on the
> > daily clinical practice.
> >
> > Otherwise most of the techological advances of 3D imaging
> > will keep being wasted before it gets to benefit the health care
> > offered to patients.
> >
> > Curiously,
> > it is more common to find surgeons using 3D rendering
> > images for image-guided surgery.
> >
> >
> >
> >      Luis
> >
> >
> >
> > .............
> >
> > Antoine ROSSET wrote:
> >
> > >>hi, vtk users,
> > >>
> > >>If there are some medical related guys here, it is possible for them to
> > >>answer my question. My question is more radiologist specific question. I
> > >>am doing volume rendering. I want to know what is the task of a 
> radiologist
> > >>in general for analyzing CT slices. How do they do this analysis based on
> > >>2D CT slices?(where can I find this kind of information?) Is it 
> possible for
> > >>volume rendering to detect all the structures of interest based on 
> the slice
> > >>information?
> > >>
> > >>
> > >
> > >For image interpretation, radiologists always look at the axial CT images,
> > >and sometimes use MPR images if slice thickness is less than 3mm. No
> > >radiologists would never give a diagnostic by simply looking at a 3D
> > >reconstruction like volume rendering, MIP, ... Volume rendering and 
> MIP are
> > >'nice' images to show to clinicians, but they are not 'diagnostic' images.
> > >
> > >
> > >
> >
> >
> >
> >
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