How do I encrypt a DICOM image?

I'm trying to encrypt a DICOM image that is 256*256*16 bits - using uint16 in MATLAB. I want to apply the AES algorithm to it, which only accepts 128-bit input; I don't want to undergo any compression that will result in a change in the decrypted image. I've split the image into rows; 1*256 and then further divided these into 16 pixels - representing my plaintext for AES input. However, because the data type is 'uint16', each pixel has 16 bits allocated to it, resulting in a 256-bit input for the plaintext; of which I do not know how to divide up any further. What is the best way to convert to a data type where I can regain the original data after the encryption process? Should I convert the whole image into a byte stream and then encrypt it?

Thanks in advanced!