[Insight-users] RE: ShapeDetection

[Lydia Ng]

Hi Christina,

The ShapeDetection program is not very sophisticated in
that it only uses image gradient information to generate
an edge potential map. Ideally, the edge potential map is
zero at an "edge" and one in homogenous areas.

A fastmarching algorithm is used to grow out
a contour from a seed point. The rate of expansion of the 
contour is determined by the values in the edge potential map. 

I think the algorithm is working well for CT 
because the edges are nice and strong.
I am not familiar with MR images of the liver, but if there are
high gradient textures within the liver then these might 
interfere with the expansion of the contour.

The other issue is that the computed edge potential map
is far from ideal. For example, if the boundary gradient isn't
strong, the associated edge potential will be
some non-zero value and the contour will eventually leak 
across the boundary as time goes on.

What kind of output are you getting when you look
at it at various time crossing thresholds?

I guess you can also try some preprocessing with something
like anisotropic diffusion to get rid of some of the texture
and enhance the boundaries.

- Lydia

> -----Original Message-----
> From: Christina Lee [mailto:dreamie222 at yahoo.com]
> Sent: Wednesday, February 27, 2002 2:30 PM
> To: Lydia Ng
> Subject: ShapeDetection
> 
> 
> 
> Hi Lydia,
> 
> How are you? 
> I've been running the ShapeDetection program on some
> MR images (to segment out the liver) & I haven't had
> any luck. The program worked pretty well for the CT
> data but not for the MR data - I wonder if it's
> because the MR images are more textured. Any comments
> or suggestions?
>      
> Hope to hear from you soon.
> 
> Thanks,
> 
> Christina
> 
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Greetings - Send FREE e-cards for every occasion!
> http://greetings.yahoo.com
>