Working with dicom images

I am working on a dataset of dicom images.

I tried reading the images using the code below:

img = dicomread(path) % path is the filename of the image

img is stored as type uint16.

Next, I need to calculate HU values[Hounsfield] for the image.

info = dicominfo(path);
b = info.RescaleIntercept;
m = info.RescaleScale;
HU = m .* img + b;

As per the HU values given in the link, range for lung is -700 to -600[Image contains lung, I am able to see the HU values in a dicom viewer]. But as HU is of type uint16, it doesn't contain negative values at all. How can I extract the HU values as such and plot a histogram?

Answer 1

[Rik]

You need to convert to either a double or a int16 (before applying the subtraction). The latter only has a maximum half as high as uint16, but since CT is almost always 12 bits, that should be fine. (16 bit CT dicom is sometimes referred to as extended CT scale)

[Sparkle89]

Thank you. It worked!