[Insight-users] Measuring tumor diameter

[Steve M. Robbins]

Hi Andriy,

This sounds like an interesting problem.  My initial reaction is that
a computational geometry approach could help, but I'm not sure I
understand what you are trying to measure.


On Thu, Dec 11, 2008 at 09:56:18AM -0500, Andriy Fedorov wrote:

> The approach I am currently considering is this:
> 
> 1) go through the axial slices, find the one with the largest area
> 2) extract that slice contour

This makes it seem like you have reduced the problem to 2D only.  Is
that desirable, or is that done due to convention (e.g. radiologists
traditionally look at stacks of 2D slices)?


> 3) go through all possible combinations of the contour points, find
> the pair of most distant points, and take this as a diameter

Here you are measuring using the normal Euclidean distance?  For
example, an "L" shape would have the two most distant points be the
end of the two legs and the diameter would join them to form a
right-angle triangle?


> 4) follow the line between the points in the previous step, and
> subtract the parts of the line that are outside the contour (this is
> how the tumor measurements are actually taken). This may change the
> measured diameter.

I don't understand "subtract the parts of the line outside the contour".
In my "L" shape example, almost the entire line is outside; does that
mean you would say its diameter is zero?


> 5) repeat steps 3 and 4 until the maximum is found after taking into
> account diameter parts outside the countour

Again, I'm not sure what this means.  

Naively, I might expect that you want to measure a longest distance
through the shape.  In the "L" example, this would be the sum of the
two legs.  However, elsewhere in the thread this notion (the "longest
geodesic") was proposed and rejected.

I googled a bit but did not find any precise explanation of how to
measure a "tumour diameter".  Can you explain a bit?

Thanks,
-Steve

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