Medical image data require strict security, confidentiality and integrity when transmitted between hospitals. The involvement of wireless transmission has made the medical data vulnerable to attacks like tampering, hacking etc. To dealing the challenges we have proposed a algorithm that introducing the digital watermarking technology to increase the security of medical images when they transmitted through a wireless network. The scheme uses a part of sign sequence of DWT-DCT coefficients as the feature vector of images for enhancing the robustness against common attacks and geometric attacks. The watermarking image is scrambled by Arnold transform to enhance its privacy. The experimental results show that the scheme has benefits at visual invisibility and robustness. Moreover, it can embed much more data, less complexity and more practicability than the existing watermarking techniques, because it avoids the sophisticated process of finding the Region of Interest (ROI) of medical images.