# Blockchain-Based Distributed Patient-Centric Image Management System
## 2 Related Work  
The practice of medical health record registering and sharing has changed considerably in the past 20 years, largely because of strict practice standards, the use of complex technologies and accurate diagnosis and treatment. Medical images are typically shared on CDs or DVDs shipped between hospitals, physicians, and patients to conclude on diagnosis, however, applying this technology might lead to damage or interception of medical images resulting from patient or physician errors [13]. To overcome the shortcomings of physical media transfer, an internet-based standard communication technology called digital imaging and communications in medicine (DICOM) [14] was introduced to share, and store medical images across various healthcare enterprises. The two main components of DICOM standard are a DICOM file format and a network communication protocol which uses TCP/IP to communicate between systems. A DICOM file format consists of header tags and image data sets embedded into a single file which is unqualifiedly editable. Thus, the DICOM standard does not provide transmission security nor data protection [15]. The electronic transmission of DICOM medical images was developed by the Radiological Society of North America (RSNA) based on the image-sharing network (ISN) [16]. However, the ISN architecture employs picture archiving and communication systems (PACS) based centralized image storage, where images from multiple imaging modalities [17] are indexed by a cryptographic hash and managed by a third-party clearing house. In 2006, the publicly funded National Health Service (NHS) in England used a national broadband network service called N3 (the National network), which is a high-speed IP-based virtual private network (VPN) used to communicate between hospitals and general practitioners [18]. In April 2017, N3 was preceded by the Health and Social Care Network (HSCN) to provide a reliable, efficient, and flexible method for health care organizations to access and exchange electronic information. The researchers [19] found that default accounts, cross-site scripting, and vulnerabilities in the web server could lead to breaches in PACS access and permanent modifications of medical images. Furthermore, existing access sharing and storing models have shown multiple challenges such as privacy concerns caused by central repository storage of patient identifiers, image ownership controlled by authorities, and mismatching of patient information in the healthcare database registry [20]. Consequently, it is important to design a proper system that considers a decentralized architecture while providing privacy configurations, data provenance, security protocols, authenticity, and electronic consent for adopting a decentralized interoperability system. Recently, several researchers focused on developing a framework that combine a cloud service and a blockchain for the purpose of medical health record access sharing [21; 22; 23; 24; 25]. The authors in [21] presented a specialized blockchain-based system for dermatology. Patients can access encrypted images and selectively share medical records using a private digital key. The authors discussed the possibility of allowing machine learning algorithms to access various images stored on the blockchain network to drive the optimization of computer-assisted analysis, but the scalability and cost effectiveness issue must be considered before standardizing this technique. In [22], the authors designed a breadcrumb mechanism for a medical record search known as MedBlock. Breadcrumbs were aimed to record addresses of blocks containing the patient-related data. Unfortunately, these solutions are not applicable to the process of searching the data over the blockchain due to an increase in the fragmented data. The authors in [23] proposed MeDShare, a hybrid cloud-based sharing solution for EHRs that is based on a centralized cloud server provider. Then, this external server was replaced by two decentralized networks called MedChain [24].