pixel intensity value definition.

Dear all,

Let say, i injected F-18 (5 mCi) into phantom, then i scan with PET_CT. I analyze the image using matlab, then i got the maximum pixel intensity is 32767. After that, i injected F-18 (1 mCi) into another phantom, i got the same maximum pixel intensity is 32767. That why i confused. Should be when we increased the activity of F-18, the maximum pixel intensity should be increased right? Do you understood what i mean?

Please help me

[Rik]

That value is the maximum value a DICOM file can store: 2^16-1. The interpretation of what that value means is stored in the DICOM header. It might even be the case that the scanner adjusts the slope and intercept to make use of the full possible data range.

None of this is actually a Matlab question, by the way.

Have a read here and here. It will greatly improve your chances of getting an answer.

[Walter Roberson]

It is not the general case that DICOM can store a maximum of 2^16-1 .

http://dicom.nema.org/medical/dicom/2015c/output/chtml/part05/chapter_8.html

"Pixel Data (7FE0,0010), Float Pixel Data (7FE0,0008), Double Float Pixel Data (7FE0,0009) and Overlay Data (60xx,3000) shall be used for the exchange of encoded graphical image data."

Most modalities are restricted to 8 or 16 bits for integer types, but http://dicom.nema.org/medical/dicom/2015c/output/chtml/part03/sect_C.8.8.3.4.html#sect_C.8.8.3.4.3 RT Dose is 16 or 32

I see that this particular question is about PET. PET is restricted to 16 bits, but it is valid for Pixel Representation to be set to either Unsigned or Two's Complement, in which case that maximum would be 2^15-1 .

We see more CT questions than PET questions; for CT it is common for signed to be used.