Posted by
Francesco Lassandro on
Jun 10, 2007; 3:01pm
URL: http://imagej.273.s1.nabble.com/Plugin-announcement-MosaicJ-tp3699175p3699178.html
----- Original Message -----
From: "M. Nur Heriawan" <
[hidden email]>
To: <
[hidden email]>
Sent: Friday, June 08, 2007 1:21 PM
Subject: CT value and cupping effect
> Dear ImageJ`ers,
>
> Firstly, I would like to make sure...is it correct
> that the CT values resulted from X-ray CT scanner is
> only ranging from -1000 to 2000?
Not exactly. the available range of CT numbers varies with scanners and bits
per pixel.
In this scale the unit is the Hounsfield unit (HU), -1000 represents the
attenuation of air, 0 is the attenuation of air. There is no upper limit to
the scale.
So, if we consider
> the relationship between CT value and bulk density of
> material (rho) is:
>
> CT value = 1000*rho - 1000
>
> then only material with bulk density from 0 to
> 3 g/cc can be detected by using X-ray CT scanning.
>
> In case our material contains a small material with
> bulk density more than 3 g/cc (for example: mineral
> pyrite has density around 5 g/cc), how we can detect
> it from the CT image?
I think you can't with conventional machines. furthermore, the relationship
between rho and CT value
holds true when atomic numbers of the substance is similar to that of water.
Anyway attenuation of substances with a high atomic number is strongly
influenced by the energy of the x-ray beam. With a 12-bit encoding of
CT-numbers are outside the range. Metals may cause almost complete
absorption with artifacts. 16-bit encoding scanners (maximum CT-number
>65,000 UH) may permit to evaluate also metallic structure.
ciao
Francesco