what does the minus value of pixel mean in MRI

I got one MRI image. when I read it into MATLAB with the function 'dicomread', I found that the pixel format was int16， some pixels got a minus value. how can I convert the pixel into 0-255?

[Walter Roberson]

What is the Photometric Interpretation set to?

Also is the negative after the rescale? CT images for example often want to use Hounsfield units, which can be negative; see https://www.medicalconnections.co.uk/kb/Hounsfield_Units

Answer 1

[Image Analyst]

Try using mat2gray():

image8bit = uint8(255*mat2gray(double(image16bit)));

This will scale it from min (the negative number) to max -> [0,255]. If you want to get rid of negative numbers in advance, do this:

image16bit(image16bit < 0) = 0;
image8bit = uint8(255*mat2gray(double(image16bit)));

[song]

thanks for your answer . but I get another questions why we get minus value in MRI data . what does that mean ? you know that the intensity of one pixel usually is a positive value.

[Image Analyst]

I have no idea why the data is signed instead of uint16, and why there are negative values. Perhaps ask the radiologist who created it.