Medical image encryption plays an important role in protecting sensitive health information from cyberattacks and unauthorized access. In this paper, we introduce a secure and robust encryption scheme that is multi-modality compatible and works with MRI, CT, X-Ray and Ultrasound images for different anatomical region of interest. The method utilizes hyperchaotic signals and multi-level diffusion methods. The encryption starts by taking DICOM image as input, then padding to increase the image area. Chaotic signals are produced by a logistic map and are used to carry out pixel random permutation. Then, multi-level diffusion is carried out by 4-bit, 8-bit, radial and adjacent diffusion to provide high randomness and immunity against statistical attacks. In addition, we propose a captcha-based authentication scheme to further improve security. An algorithm generates alphanumeric captcha-based image which is encrypted with the same chaotic and diffusion methods as the medical image. Both encrypted images(DICOM image and captcha image) are then superimposed to create a final encrypted output, essentially integrating dual-layer security. Upon decryption, the superimposed image is again decomposed back to original medical and captcha images, and inverse operations are performed to obtain the original unencrypted data. Experimental results show that the proposed method provides strong protection with no loss in image integrity, thereby reducing unauthorized data breaches to a significant level. The dual-encryption approach not only protects the confidentiality of the medical images but also enhances authentication by incorporating captcha.