Consider the following image. The image content does not span the extent of the allowable range.
A = dicomread('CT-MONO2-16-ankle.dcm');
getrangefromclass(A) % standard data range for the class of A
[min(A(:)) max(A(:))] % show the actual range of the data
Normalize it and then scale/cast it to whatever the intended working image class is supposed to be. If you assume that it should remain int16:
B = im2int16(mat2gray(A)); % normalize, cast and scale
[min(B(:)) max(B(:))] % show the actual data range
Or if you want uint8:
C = im2uint8(mat2gray(A)); % normalize, cast and scale
[min(C(:)) max(C(:))] % show the actual data range
Or if you just want double:
D = mat2gray(A); % normalize
[min(D(:)) max(D(:))] % show the actual data range
