[Insight-users] How to calculate volume of an image

[Luis Ibanez]

Hi Mario,

You should simply get the Spacing value from the itkImage, as

     ImageType::SpacingType spacing =  myImage->GetSpacing();

  where

    spacing[0] is the spacing along X
    spacing[1] is the spacing along Y
    spacing[2] is the spacing along Z


The ITK DICOM reader will populate the spacing values
for you.


Please note also that is you already have a segmented
image, you could use several of the "Label" filters in ITK
in order to compute the volume of a labeled region.


     Regards,


           Luis


--------------------------
On Tue, Apr 20, 2010 at 12:24 PM, Mario Ceresa <mrceresa at gmail.com> wrote:

> Hello everybody!
>
> I'm completely lost on a seemingly stupid problem: how do I calculate
> the physical volume of an image (3D CT scan)?
>
> In the past I would have simply iterated over the interesting pixels
> in the image, accumulated them in a variable, say m_Vol, and then:
>
> std::cout << "Volume: " << m_VolLung*spacing[0]*spacing[1]*spacing[2]
>
> This believing that spacing 0 and 1 came from the "Pixel Spacing" tag
> of my DICOM header and spacing[2] from the "Slice Thickness" tag.
>
> But now I have some CT scan images for which the spacing along z is
> always 1 no matter what I try, while the Slice Thickness is different.
>
> I spent a while dwelling into the ImageHelper::GetSpacingValue of the
> gdcm factory but it is *really* complicated...
>
> Moreover a kind person from the GDCM mailing list pointed me that:
>
> "Pixel spacing is not guaranteed to be the same as slice thickness.
> You can have slices that overlapped also gaps and then with the case
> of helical CT the Slice Thickness does not make sense for the
> reconstruction."
>
> So know I'm not sure which is the best way to proceed, if any of you
> could give me an hint I would be more than grateful!
>
> Thanks and regards,
>
> Mario
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