[Insight-users] Question about DICOM and CT scanner

[Remi Vieux]

Hi everyone,

My question is not about ITK but I thought somebody here could help me
with that: it's about CT scanner and DICOM image file format.

So, basically, what I learned during my lectures on medical imaging is
that a CT scan acquire its data, in Hounsfield Units, which may vary
depending on the actual scanner you are using. Then, depending on what
contrast you want to emphasize, you can choose a combination of window
width/window level, and save this view into a DICOM file, hence mapping
the H.U. into grey levels from 0 to 4095.

Now, I'm doing a project for my university dealing with CT images in
DICOM format. First thing I realised in the exams I have in my hand is
that the data I'm retrieving are not grey levels from 0 to 4095 but from
-1000 to 3095. Ok, not much harm done there, it is still 4096 grey
levels. But then, answering to a previous question of mine in this
mailing list, I've been told that I could not assume that it is always
the case (or so I understood).

So my question is: what exactly is saved in a DICOM file during a CT
scan exam? Is it the 4096 grey levels representing a "windowed" view of
the exam as I was teached? Is it the H.U. as I thought it could be for a
moment? Is it both? None? Whatever..?

That was quite a long speech for a short question, but, pardon me, I'm
kind of lost here... If anybody could help me out, answering it or
simply pointing me some reference in the litterature, I would deeply
appreciate it!

Best Regards,

Remi.
-- 
Remi Vieux <revieux at yahoo.fr>


PS: By the way, if somebody knows a good algorithm to perform a
segmentation of the teeth in a CT exam, it would also be appreciated,
but that's just because I'm stuck :-p


	

	
		
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