A Study of DWT and SVD Based Watermarking Algorithms for Patient Privacy in Medical Images

Information and Communication Technologies (ICT) are being adopted widely to improve citizen´s health care. Health information systems (HIS) of different hospitals exchange electronic medical records including digital medical images of patients. Medical images and accompanying reports have special requirement of protecting the privacy of the patient by not revealing personal particulars especially when they are transmitted over networks. To increase the security of medical images and preserve patients´ privacy, digital watermarking has been proposed. In this paper, we study the performance of three different watermarking algorithms (DWT, SVD and DWT-SVD based watermarking algorithms). We have created two different watermarks with same watermark information but with different characteristics - one is QR Code as watermark image which is capable of carrying large information in small space, while the other one is a normal text image watermark and embedded inside medical images. We, then, have assessed the quality of watermarked images obtained after embedding the watermarks using both objective (PSNR) as well as subjective (opinions from physicians, a radiologist and a medical physicist) methods and found that watermarking has not resulted in loss of medical information. Further, we have conducted several experiments to evaluate the performance of these algorithms in terms of robustness, capacity, and embedding time. Experimental results show that DWT based method is suitable for medical applications where embedding time and imperceptibility are prime concerns while SVD based methods are suitable for medical applications where robustness and capacity are the main concerns.