## 5 A User-Centric Perspective for the Internet of Medical Things
The way they reached this goal was by registering each new device in the Blockchain by its owner, the one able to permit to access the Blockchain. Thus, the system is composed of the devices, the Blockchain, and the medical institutions (that maintains the Blockchain). The connection to the Blockchain is realized through a gateway (a smartphone) able to encrypt and route information to an off-chain IPFS database which can be accessed by authorized physicians and healthcare teams. The healthcare institutions are actually the full nodes of the network: they store pointers to data, validate transactions, and create new blocks as other similar centralized solutions, leading to a potential system-centric solution rather than user-centric. [PERSON] et al. [43] proposed a system for data sharing combined with a Blockchain network as a reliable data exchange among healthcare users. It is composed of a wearable sensor device, a mobile gateway, and a cloud server. They used the Ethereum Blockchain platform for the Blockchain network and design smart contracts to control user access on the cloud. Anyway, using the cloud as a storage is a risky solution and needs to be owned by someone, usually a central authority. Moreover, the system is more focused on secure sharing rather than preserving ownership. For this reason, in [PERSON] et al. [44], they substitute the cloud storage with the IPFS, going towards a user-centric system. [PERSON] et al. [47] used smart contracts to manage the ownership of IoMT devices with no trusted third-party. The proposed system consists of five key components: patient, manufacturer, and two smart contracts (one for the IoMT device and one owned by the manufacturer) and the healthcare provider. Basically the patient, which is the owner of the IoT Device, can set the rules and conditions on the IoMT device smart contract for device management. The healthcare provider includes professionals who are interested in knowing, owning, or transferring the ownership of the device. This kind of solution leverages totally on smart contracts, potentially even in a permissionless Blockchain, but anyway it is not thought to handle health data. At the same time, it is user-centric, since all the decisions made are handled by the user that could exit the system at any time. [PERSON] et al. [49] proposed a system for monitoring patients remotely and warning them about potentially dangerous situations. It uses smartphones to collect information and sends them to a remote cloud. In order to exchange data between healthcare parties, the system includes the deployment of a decentralized storage system that receives, processes, and stores the collected data and provides a cryptocurrency as an incentive for participation. The architecture consists in an interface for users that allows the access of the stored information: a decentralized storage system that replicates the collected information and distributes it automatically among multiple nodes; and a distributed ledger that uses smart contracts in order to reward participation. This kind of approach is interesting and goes towards data crowdsourcing with Blockchain that should be user-centric by design. [PERSON] et al. [50] proposes a conceptual Blockchain-based fall prediction model using smart contracts and the FHIR (Fast Healthcare Interoperability Resources) standard protocol. They identify four roles: person under care, primary care provider (or long-term provider), secondary care provider (or short term providers), and temporary caregiver. Each of these entities is maintaining their electronic health record management systems and can be considered as data sources for the final prediction model. The architecture is based on a Permissioned and private Blockchain that leverage smart contracts for accessibility, creating different access levels based on each user category, leading to a user-centric solution.