[Insight-users] Physical Quantity of Dicom Image

[Mathieu Malaterre]

On Sun, May 17, 2009 at 10:59 AM, Madiha Shahab
<madiha.shahab at technologyorbit.com> wrote:
> HI All,
> I need to know what is physical quantity of the pixel i.e whether 1 pixel =
> 1mm or 1pixel = 1cm or 1pixel= 1km.

Your question is turned backward, you should first ask which DICOM
attribute should be used to compute the image spacing, then ask for
the unit :)
Anyway Pixel Spacing is expressed in mm (see DICOM PS 3.3 - 2008) this
will gives you the X/Y spacing for CT or MR image.

> which tag in header info of ITK tells this info.
> Secondly there are two tags:Sample Spacing and Spacing Between Slices.
> Which one of them should I use to calculate space between two pixels

You forgot to mention the IOD of your DICOM object (SOP Class). If
this is CT or MR Image Storage class then you most likely want: Image
Orientation (Patient) and Image Position (Patient). This is taken care
of internally by the itk::FileImageReader + ImageIO (GDCMImageIO in
your case).

BTW I've never heard of Sample Spacing before.

2cts
-- 
Mathieu