This paper proposes a novel pixel-based scrambling scheme to protect, in an efficient and secure way, the distribution of digital medical images. To provide an efficient encryption of a large volume of digital medical images, the proposed system uses simple pixel level XOR operation for image scrambling in an innovative way such that structural parameters of the encryption scheme have become a part of the cryptographic key. The cryptographic key of this operation is a true random number sequence generated from multi-scroll chaotic attractors. Cryptanalysis is provided. Simulation experiment has also validated the effectiveness of the proposed system.