Steganography techniques for ECG signals : A survey

Optimizing Wavelet ECG Watermarking to Maintain Measurement Performance According to Industrial Standard

Abstract: Watermarking is currently investigated as an efficient and safe method of embedding additional patient or environment-related data into the electrocardiogram. This paper presents experimental work on the assessment of the loss of ECG (electrocardiogram signal) diagnostic quality from the industrial standard EN60601-2-25:2015 point of view. We implemented an original time-frequency watermarking technique with an adaptive beat-to-beat lead-independent data container design. We tested six wavelets, six coding bit depth values (including the automatic noise-dependent one) and two types of watermark content to find the conditions that are necessary for watermarked ECG to maintain the compliance with International Electrotechnical Commission (IEC) requirements for interpretation performance. Unlike other authors, we did not assess the differences of signal values, but errors in ECG wave delineation results. The results of a total of 7300 original and watermarked 10 s ECGs were statistically processed to reveal possible interpretation quality degradation due to watermarking. Finally we found (1) the Symlet of 11-th order as the best of the wavelets that were tested; (2) the important role of ECG wave delineation and noise tracking procedures; (3) the high influence of the watermark-to-noise similarity of amplitude and values distribution and (4) the stability of the watermarking capacity for different heart rates in atrial rhythms.

Integrating the Exercise and Environmental Data Into a Digital ECG Structure by Watermarking Technique

Abstract: Exercise test is worldwide recognized as a valuable tool for investigating ST segment-based ischemia markers. Due to load-related risk, the test is reserved for office use, what causes inconvenience, limits patients participation rate and precludes screening for early ischemia stages. Transferring the diagnosis to patients' premises and using everyday activities as a stimulus is an interesting alternative, but needs reliable recording of physical load data. This paper presents a method for integrating the exercise and environmental data into a digital ECG structure by watermarking technique. The method analyses the time-scale ECG representation, detects the bandgap, where the bandwidth of actual cardiac content is lower than the throughput of digital series, detects the noise and replaces it by exercise-related data. Unless in irregular signals, the capacity of data container can accommodate an accompanying accelerometer and environment-related signals without deteriorating the ECG content. This makes possible to perform ECG exercise test in home conditions without additional transmission channels or data structures. The method was tested with CSE database accordingly to EN60601-2-25:2015 and proved the watermarked ECG to maintain the wave borders accuracy within tolerance limits. Consequently, restoration of original ECG record is not necessary. The method was also tested with anonymized stress-test records, which were watermarked with accelerometer data and re-interpreted to yield results fairly comparable to original diagnoses.

Secure spread spectrum watermarking for multimedia

Abstract: This paper presents a secure (tamper-resistant) algorithm for watermarking images, and a methodology for digital watermarking that may be generalized to audio, video, and multimedia data. We advocate that a watermark should be constructed as an independent and identically distributed (i.i.d.) Gaussian random vector that is imperceptibly inserted in a spread-spectrum-like fashion into the perceptually most significant spectral components of the data. We argue that insertion of a watermark under this regime makes the watermark robust to signal processing operations (such as lossy compression, filtering, digital-analog and analog-digital conversion, requantization, etc.), and common geometric transformations (such as cropping, scaling, translation, and rotation) provided that the original image is available and that it can be successfully registered against the transformed watermarked image. In these cases, the watermark detector unambiguously identifies the owner. Further, the use of Gaussian noise, ensures strong resilience to multiple-document, or collusional, attacks. Experimental results are provided to support these claims, along with an exposition of pending open problems.

Expansion Embedding Techniques for Reversible Watermarking

Abstract: Reversible watermarking enables the embedding of useful information in a host signal without any loss of host information. Tian's difference-expansion technique is a high-capacity, reversible method for data embedding. However, the method suffers from undesirable distortion at low embedding capacities and lack of capacity control due to the need for embedding a location map. We propose a histogram shifting technique as an alternative to embedding the location map. The proposed technique improves the distortion performance at low embedding capacities and mitigates the capacity control problem. We also propose a reversible data-embedding technique called prediction-error expansion. This new technique better exploits the correlation inherent in the neighborhood of a pixel than the difference-expansion scheme. Prediction-error expansion and histogram shifting combine to form an effective method for data embedding. The experimental results for many standard test images show that prediction-error expansion doubles the maximum embedding capacity when compared to difference expansion. There is also a significant improvement in the quality of the watermarked image, especially at moderate embedding capacities

Reversible Watermarking by Difference Expansion

Abstract: Reversible watermark has drawn lots of interest recently. Different from other types of digital watermarks, a reversible watermark has a special feature that the original digital content can be completely restored. In this paper we describe a high capacity and high quality reversible watermarking method based on difference expansion. A noticeable difference between our method and others is that we do not need to compress original values of the embedding area. We explore the redundancy in the digital content to achieve reversibility.

Wavelet-Based ECG Steganography for Protecting Patient Confidential Information in Point-of-Care Systems

Abstract: With the growing number of aging population and a significant portion of that suffering from cardiac diseases, it is conceivable that remote ECG patient monitoring systems are expected to be widely used as point-of-care (PoC) applications in hospitals around the world. Therefore, huge amount of ECG signal collected by body sensor networks from remote patients at homes will be transmitted along with other physiological readings such as blood pressure, temperature, glucose level, etc., and diagnosed by those remote patient monitoring systems. It is utterly important that patient confidentiality is protected while data are being transmitted over the public network as well as when they are stored in hospital servers used by remote monitoring systems. In this paper, a wavelet-based steganography technique has been introduced which combines encryption and scrambling technique to protect patient confidential data. The proposed method allows ECG signal to hide its corresponding patient confidential data and other physiological information thus guaranteeing the integration between ECG and the rest. To evaluate the effectiveness of the proposed technique on the ECG signal, two distortion measurement metrics have been used: the percentage residual difference and the wavelet weighted PRD. It is found that the proposed technique provides high-security protection for patients data with low (less than 1%) distortion and ECG data remain diagnosable after watermarking (i.e., hiding patient confidential data) and as well as after watermarks (i.e., hidden data) are removed from the watermarked data.

A Cryptographic Key Management Solution for HIPAA Privacy/Security Regulations

Abstract: The Health Insurance Portability and Accountability Act (HIPAA) privacy and security regulations are two crucial provisions in the protection of healthcare privacy. Privacy regulations create a principle to assure that patients have more control over their health information and set limits on the use and disclosure of health information. The security regulations stipulate the provisions implemented to guard data integrity, confidentiality, and availability. Undoubtedly, the cryptographic mechanisms are well defined to provide suitable solutions. In this paper, to comply with the HIPAA regulations, a flexible cryptographic key management solution is proposed to facilitate interoperations among the applied cryptographic mechanisms. In addition, case of consent exceptions intended to facilitate emergency applications and other possible exceptions can also be handled easily.