Blockchain technology: principles and applications. browser download this paper.

Blockchain relies on encryption via public-key cryptography Fig. Each actor interacting with the blockchain has a separate public key and private key. As an example, Charlie can send Leah an encrypted message that is only readable by Leah. The data are unreadable without the private key and are thus encrypted.

Public key cryptography. Blockchain relies on public key cryptography which uses key pairs public keys are publicly available, and private keys are kept secret like passwords.

The data are encrypted as the message is unreadable without the private key. Hash functions H are an important component and map input data x to fixed size outputs h called hash values Fig. Hash functions H map input data x to fixed size outputs h called hash values. Cryptographic hash functions are non-invertible in that an input maps to a given hash value but not vice versa i. As with any blockchain implementation, there are many decisions that must be made about how it will operate.

One major decision is whether the blockchain should be permissionless or permissioned. Blockchains may be either public and accessible by everyone or private with only pre-approved participants having access.

Cryptocurrencies e. Most enterprise applications e. However, there exists a continuum between public and private blockchains, known as hybrid, partially decentralized, or consortium blockchains [ 11 ].

However, as blockchain technology matures and legislation catches up with the technology, storage of protected health information within permissionless blockchains may be a possibility in the future.

There have been several permissionless blockchain implementations of electronic medical records EMRs made possible by the usage of encryption, which is a necessary first step in any blockchain implementation which makes protected health information available to download by anyone on the Internet. Relational databases have been the mainstay of database implementations essentially since their inception in the s.

They are quite efficient and scalable. More recently, however, non-relational databases have become more and more popular. Blockchain vs. Traditional databases, in general, allow for modification of data and are therefore not immutable.

They have the advantage of having low latency allowing for many transactions to be performed concurrently as opposed to blockchain which has high latency and can only support a limited number of transactions at a time.

While traditional databases can have redundancy built in, they do not have the advantage of being replicated on every node like blockchain.

While immutable implementations of traditional databases are possible, it is not a key underlying principle of their technology as it is with blockchain. Traditional databases have the advantage of having low latency allowing for many transactions to be performed concurrently as opposed to blockchain which has high latency and can only support a limited number of transactions at a time. Blockchains, in general, are significantly more costly for data storage compared with traditional databases.

In fact, the Bitcoin protocol currently limits the size of each block to 1 megabyte [ 15 ], but there is a significant debate among the community if this should be increased [ 16 ]. As such, most public blockchain implementations are not a viable solution for the storage of large amounts of data such as medical images.

To counterbalance this, hashes of the data instead of the raw data can be stored within the blockchain. Large volume data, as would be expected from thousands of individual images in a multisequence cross-sectional examination, would thus pose a potential obstacle for blockchain storage.

While the feasibility of moving a PACS network onto the cloud has been demonstrated [ 18 — 21 ], this solution suffers from the pitfalls of centralization, and scalability to huge image-rich databases in the future may prove problematic. More research must be conducted as to whether image hashes could function as reference values to image data stored on cloud networks.

Completely decentralized storage networks have proven feasible for other applications. Filecoin, for example, is a proprietary decentralized storage network relying on blockchain principles. While blockchain has many potential use cases and benefits, it does have several key limitations. With an ever increasing number of blockchain implementations utilizing different underlying technologies, the ability of different systems to work together will suffer.

Additionally, there are bound to be unforeseen complications when smart contracts interact across different blockchain implementations without any human interaction. Much as the DICOM standard enabled interoperability between different vendors and systems, standardization will be necessary as healthcare blockchain implementations move forward.

Public blockchains are at risk of having the stored information exposed if vulnerabilities are 1 day discovered in their underlying encryption schemes. If the encryption is broken, all the data stored in the blockchain could be exposed. However, private or permissioned blockchain implementations can mitigate this risk. Blockchain is considerably slower than traditional databases, and adding new data is limited by the speed of the underlying consensus mechanisms.

Traditional database systems are able to scale by adding more servers and therefore more computational power to distribute the workload. With decentralized blockchains, however, every node must participate in consensus. Therefore, more computational power would have to be added to every single node to increase throughput. With the consensus algorithms most widely employed in the blockchains powering cryptocurrencies proof-of-work , the mathematical problems that must be solved to create new blocks are becoming increasingly more computationally demanding and thus require a significant amount of electricity [ 23 ].

Private blockchains can utilize a much less computationally demanding consensus algorithm but still require more energy than traditional databases. One method to reduce the transaction costs is to only allow certain nodes to participate in consensus [ 24 ]; however, some redundancy is lost by doing so. If a private key were lost, the data would be rendered permanently unreadable. For this reason, further research is warranted to develop novel ways to prevent keys from being lost or forgotten, such as biometric key generation.

Given these limitations, it is unlikely that blockchain will completely supplant the traditional database systems currently powering EMRs, picture archiving and communication systems PACS , and Vendor Neutral Archives VNAs but can instead supplement them to extend and enhance their capabilities.

As cryptocurrency was the original use case for blockchain technology, it is no surprise that it is the most widespread. As transactions stored within blockchains can utilize any kind of metadata and not just transfers of money, an increasing number of use cases utilize the technology for distributed databases or ledgers.

There have been few enterprise-level blockchain implementations in healthcare. However, there are many other use cases in healthcare in which the technology could be beneficial. Biomedical applications of blockchain technology include EMRs, wearables and embedded technology, mobile health, research and clinical trials, medical supply chains, biomedical databases [ 25 ], insurance claims [ 26 ], credentialing and licensure [ 27 , 28 ], and public health surveillance [ 29 ].

As of this writing, the main focus within the healthcare sector has been on EMRs [ 17 , 25 , 30 ]. Notable large-scale implementations of EMRs built on blockchain technology include MedRec [ 24 ], Gem Health Network [ 25 ], and Guardtime which has secured over 1 million medical records in Estonia [ 26 ]. Text-based healthcare notes and lab values are much more amenable to being distributed on a blockchain as the data size is much smaller than the large datasets common in medical imaging.

This is especially true because of the slow speed and high cost of storing large amounts of data in a public blockchain. Despite the unanimous adoption of the Internet by healthcare systems and initiatives such as RSNA Image Share [ 32 ], medical images are still largely transferred among institutions by compact disc CD or digital versatile disc DVD. Patients must frequently even pay out of pocket for the creation of the disc [ 33 ]. With medical images or their hashes stored across a blockchain, images could be easily be shared among healthcare systems and providers.

Image sharing via a blockchain could occur either through a public permissionless or private permissioned blockchain. With a private blockchain, individual users such as physicians or groups such as a hospital system , could be given permission to view images through transactions. Such an implementation could eliminate the need for medical imaging facilities to create and import discs and the need for patients to transport them, which may lead to repeat imaging and poor use of limited medical resources.

The blockchain carrying these transactions is used to verify that a requesting party—such as a physician or another hospital—is included on a list permitted to access a particular imaging study, and that the particular study corresponds to these permissions. Blockchain implementations for image sharing will not replace such standards but instead will supplement them. For instance, a commercially available medical image sharing platform, Nucleus. Medical images are not stored within the blockchain itself.

Implementations such as this could potentially allow for patient-centered ownership of their own medical records [ 19 ], which are increasingly dependent upon imaging. If patients are in control of their own imaging data within a blockchain, they can easily grant permission to healthcare providers to view those enabling physicians outside of their current healthcare system access to their data and enable them to easily seek a second opinion.

Since the data are stored in a blockchain, patients can be assured that the original data are immutable and unable to be altered. As such, DICOM is uniquely dynamic enough to be incorporated into many different blockchain platforms. A common non-healthcare implementation of blockchain technology is supply chain management [ 37 ].

Within healthcare, blockchain has been proposed for the management of pharmaceutical supply chains [ 38 , 39 ]. The principles of this utility can be applied to implanted medical devices and prostheses [ 31 , 32 ], especially with respect to the capacity of the device, its date of placement, its longevity, or its compatibility.

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