[Insight-users] Measuring tumor diameter

[Andriy Fedorov]

On Sun, Dec 21, 2008 at 11:20 AM, Steve M. Robbins <steve at sumost.ca> 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)?
>

Based on my discussion with a neurosurgeon, they usually look at 2D
slices in AP/LR/IS directions, but also they may also look at oblique
slices.

To understand maximum diameter, as I understand it, imagine the
contour of the tumor segmented in a 2d slice. Then take a set of
segments connecting all possible combinations of the contour points.
For each segment, subtract the subsegment which is outside tumor
contour (this will happen only for concave shapes). The updated this
way length of the longest segment will be the maximum diameter.

I assume, one can take all combinations of surface points in 3d,
instead of looking at a slice with the largest area, but this will be
very time-consuming to walk along the segments connecting all possible
pairs of points. I simplify the problem to develop an initial
solution.

>> 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?
>

An "L" shape will have the maximum diameter equal to the length of the
longer leg. With the diameter you suggest most of it will belong to
the outside of the shape.

>> 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?
>

The diameter defined this way will indeed be almost 0. This will not
be the maximum diameter though.

>> 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.

The diameter by definition should be measured along a line, you cannot
sum up two legs...

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

I haven't found a precise definition either. Based on my
understanding, the measure is very subjective, and it is basically
what I described. Of course, it is not easy to visually identify the
largest diameter.

I hope I was able to clarify the problem for you a bit. If you find a
better definition, please post...

Thanks

Andriy Fedorov



> Thanks,
> -Steve
>
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