Abstract
Reversible and imperceptible watermarking is recognized as a robust approach to confirm the integrity and authenticity of medical images and to verify that alterations can be detected and tracked back. In this paper, a novel blind reversible watermarking approach is presented to detect intentional and unintentional changes within brain Magnetic Resonance (MR) images. The scheme segments images into two parts; the Region of Interest (ROI) and the Region of Non Interest (RONI). Watermark data is encoded into the ROI using reversible watermarking based on the Difference Expansion (DE) technique. Experimental results show that the proposed method, whilst fully reversible, can also realize a watermarked image with low degradation for reasonable and controllable embedding capacity. This is fulfilled by concealing the data into ‘smooth’ regions inside the ROI and through the elimination of the large location map required for extracting the watermark and retrieving the original image. Our scheme delivers highly imperceptible watermarked images, at 92.18–99.94 dB Peak Signal to Noise Ratio (PSNR) evaluated through implementing a clinical trial based on relative Visual Grading Analysis (relative VGA). This trial defines the level of modification that can be applied to medical images without perceptual distortion. This compares favorably to outcomes reported under current state-of-art techniques. Integrity and authenticity of medical images are also ensured through detecting subsequent changes enacted on the watermarked images. This enhanced security measure, therefore, enables the detection of image manipulations, by an imperceptible approach, that may establish increased trust in the digital medical workflow.
Highlights
In most medical imaging domains traditional diagnosis has mostly migrated to e-diagnosis workflows
Nine images are selected from a publically available and standardized medical images dataset downloaded from The Cancer Imaging Archive (TCIA) (Fig. 6) [12]
The results demonstrated that the modification of the images to a level of Peak Signal to Noise Ratio (PSNR) = 82 dB or better is unnoticeable to all observers, and modification level to a PSNR = 80 dB should not be noticeable in the vast majority of cases
Summary
In most medical imaging domains traditional diagnosis has mostly migrated to e-diagnosis workflows. Difference Expansion presented a new approach for reversible watermarking [45] It encodes 1-bit into the LSB of the difference value of 2-pixels. To raise the embedding capacity, Alattar [2] developed previous DE techniques by encoding 2-bits into the difference values of a 3-pixels. The easiest way of determining the pixel quad is by selecting consecutive 2 × 2 pixel, and this approach can be further generalized [4] This generalized method encodes several bits in the difference values vectors of connected pixels instead of pairs, triplets and quads. The weakness of the DE watermarking technique is the reduction of the hiding capacity due to the need for a location map denoting the pixels where data is embedded. This significantly enhances hiding capacity whilst reducing potential image degradation
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