# Blockchain Technology in Healthcare: A Comprehensive Review and Directions for Future Research
## Internet of Medical Things
### Healthcare IoT Infrastructure and Data Security
The result means approximately three intrusion attacks could penetrate the system for every 200 user sessions. In an effort to reduce the security vulnerability of RFID in healthcare IoT infrastructure, [PERSON] et al. [154] proposed a smart hospital system that consist of hybrid-sensing network exploiting constrained application protocol, IoT smart gateway, and a user interface to provide third-parties the ability to empower patients with health monitoring system. However, the collected data from the IoT devices is stored in a central database which is prone to be forged. This could be addressed by using decentralized ledger such as blockchain since data blocks are replicated to distributed network nodes for enhanced transparency. Parallel to the above work, [PERSON] [155,156] proposed a novel approach for theinternet of entities which integrates Mobile and IoT networks into two main components: entities such as the user devices and a tracker that facilitates the transmission of information to the blockchain. The proposed architecture is a blend of Wireless and blockchain networks which can be used for healthcare services, but a proper implementation of such a large and complex network may unlock potential limitations; for example, computational overhead optimization of blockchain might be difficult [155; 156]. [PERSON] et al. [157] explored healthcare data security and privacy by introducing different forms of data structure in the blockchain. However, due to the overhead complexity of storing large volume of health data in the blockchain, the study uses only the hash of data as transaction. However, this alone cannot ensure data security. Reducing the overhead of Blockchain implementation in healthcare small area networks is a challenging prospect since adding blocks in the chain following mainstream cryptographic mining algorithms such as PoW requires enormous computational power. To address such challenge, [PERSON] et al. in [158; 159] proposed a novel lightweight architecture for networks comprising numerous IoT devices. A local computer is used as a Miner and a number of IoT devices are clustered together such that one is selected as a cluster head to reduce access verification using policy header. This scheme allows for the policy header to contain updated Access control list that is administered by network operator. In addition, this study used a shared overlay network where many data owners are permitted to insert data into the blocks which is controlled by single admin. However, this may lead to lack of trustworthiness among users. In the review paper of [PERSON] and [PERSON] [160], several security and privacy vulnerabilities in the current IoT ecosystem were identified for further research including protection during updating software of billions of IoT devices (healthcare, for instance) where blockchain could be used to enhance security. Protecting healthcare critical IoT infrastructure and sensitive data may eliminate potential security and privacy issues, for example, in mid-2016 3.62 million patients' data including personal information, social security number, and credit card numbers were compromised in Banner Health, Arizona [161]. According to the above discussion, we can infer that although conventional security systems is providing enhanced security, complete tamper proof systems cannot be ensured. Blockchain is considered by many as a potential solution among other state-of-the-art technologies to be implemented in a small and medium scale healthcare IoT systems.