How to get HU values from CT image

[Manoj Nimbalkar]

Dear All,

Does someone knows how to get HU values from CT image?

Thank you,

-Manoj

[Matt J]

"Manoj Nimbalkar" wrote in message <jt6u2r$709$1...@newscl01ah.mathworks.com>...

> Dear All,
>
> Does someone knows how to get HU values from CT image?

=========

You need to know the attenuation of water. An attenuation value X is then converted by

HU = (X-attenWater)/attenWater*1000

[trison]

"Manoj Nimbalkar" wrote in message <jt6u2r$709$1...@newscl01ah.mathworks.com>...

The Hu values could be read according to DICOM information of its CT images. For different CT imaging equipments had different presentation means, you had better to read the DICOM part 3 -- information object definitions, firstly. You can find it at http://medical.nema.org/Dicom/2011/11_03pu.pdf.
Trison

[Jeff]

Manoj,

I believe what you need to do is to convert the displayed/generated pixel values, which are greyscale values, into the corresponding Hounsfield Unit (HU). To do this you use the following equation:

HU = pixel_value*slope - intercept

The intercept is found in the dicom header at 0028,1052 and the slope at 0028,1053. Plug these into the equation and you obtain the HU value which is simply a rescaling of the linear attenuation coefficient.

[Natalylun]

"Jeff" wrote in message <k38eak$7cd$1...@newscl01ah.mathworks.com>...

You need to do more than that. HU = Gray_Value * slope + intercept The stored value in DICOM file are basically the attenuation coefficients i.e CT numbers (DICOM tag (7FE0, 0010) - pixel data). These are converted to a linear scale (Hounsfield unit scale) by using HU = CTNumber (7FE0,0010) * rescale slope (0028, 1053) + y intercept (0028, 1052). These HU values have to be converted to pixel intensity f(x,y) using f(x,y) = ((HU-P1)*pow(2,i-1))/W, where P1 is the window left border, i is the radiometric resolution and W is the window width.