[vtkusers] voxel's volume

[Jean-Pierre Roux]

Mathieu Malaterre wrote:

> Laurent PAUL wrote:
>
>> Hi users,
>>
>> I'm wondering how voxels are mapped in my VolumeData.
>> I've got an ImageData coming from Dicom. Voxel size is 0.74*0.74*2.7, I
>> mean SizeX*SizeY*SizeZ(SizeZ=sliceThickness in dicom tag).
>> But acquisiton had been made with a spacing between slices=1.3
>>
>> So What is the voxel's volume?
>> Since I'm working in 3D, I'm wondering how voxels are mapped when
>> acquisition is overlapped.
>> I think I should consider the "spacing between slices" when it is 
>> smaller
>> than slice thickness. Am I right?
>
>
Laurent,
I do agree with Mathieu.
You cannot get the voxel Z Size reading just an image.
You need 2 images, get the Date Element 0x0020,0x0032 --> Image Position 
(Patient), and compute the Z spacing.
 Mathieu :
Don't you think we (I) should add GDCM a method to do that (you pass the 
2 "Image Position (Patient)", and it returns zspacing.
My question : I add it on *which* class (noy on File, not on FileHelper, 
not on Document ...?)

Jean-Pierre Roux

> Laurent,
>
>     This is definitely a question for DICOM people not viz people. 
> Please reread the PS3.3 of the DICOM spec, you'll see that Slice 
> Thickness is only the thickness of tissues where the signal is 
> acquired. What you are looking for, really is Spacing Between Slices.
>
>     As a side note using this tag is generally extremely dangerous, as 
> you generally don't know if slices are joints, overlapping or 
> disjoints. For a better implementation look at ITK-GDCM where we take 
> two slices, the 

--> Probabely a misstyping : Image Position (Patient) is the right one, 
isn't it?

> Image Orientation (Patient) 


> and compute the zspacing from those.
>
> HTH
> Mathieu
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