Networking

A data network is an essential component for the communication and transfer of data between devices. Most commonly data are transferred between computers, workstations and external hardware via an ethernet connection (a cable connected directly to a port on the hardware), which is favoured for its speed, reliability, availability and ease of use. As most hardware only has one physical ethernet port available, to send and receive data to and from multiple sources requires all PCs and hardware to be connected to a communal data network. In some cases, wireless networks can also be configured where a physical connection is not possible or suitable.

Without a data network, each workstation and computer operates as an isolated unit, with no simple capacity to transfer data or share attached peripheral equipment (e.g. printers, scanners). This may be a suitable scenario in smaller facilities, but as a facility’s size, complexity and level of integration with other modalities, work sites and hospitals increases, so does its reliance on a data network. Some worksites may already have an existing network infrastructure that can be utilized by the nuclear medicine facility. In some situations, however, it may be necessary to expand this network or create a new one in order to meet the requirements of the facility.

5.6.2. Local area networks

At its simplest level, data communication in nuclear medicine involves a single, direct connection between a gamma camera and a single workstation, with no other workstations or computers involved. However, if there is more than one workstation required, then a local area network (LAN) connecting the gamma camera and multiple workstations needs to be used. A LAN is a data network contained within a single geographical location, such as a nuclear medicine facility, a diagnostic imaging facility or a hospital. Each device, workstation or PC connects to an ethernet port and from each of these ports runs a cable connecting to a centralized location, such as a hub or switch. When data are sent from a PC or workstation through a network, it reaches this centralized location, where it is forwarded to another specific device or made available for access from all devices connected to the network.

5.6.3. Servers

If data need to be sent and stored for access from multiple PCs or workstations (i.e. for a RIS or PACS), then a server is also required. This is usually a dedicated computer or device that manages a network and stores data for access throughout that network. For example, a RIS server will store all patient and study information available, making the same data available for anyone using the RIS software. In addition to RIS and PACS servers, other types of server have a role in nuclear medicine facilities: file servers can be used to store software data (e.g. documents, spreadsheets); and print servers can manage multiple printers across a network.

Size requirements for a server are dependent on the data to be stored.

A RIS server storing only text based data has a relatively small size requirement compared to a PACS server which will be storing large amounts of diagnostic image data. The types of diagnostic data being stored can also affect server size requirements. Nuclear medicine data size is traditionally very small when

compared to high quality CT or MRI data and therefore can have smaller server size requirements.

The addition of a server to a network is burdened with increased costs, not just in the initial purchase price but for ongoing maintenance and, as more data are stored on the server, storage capacity must be continually increased to meet demands. This should be negotiated with the local supplier or maintainer of the server. If possible, the server space can be partitioned to provide storage and access for other departments, who can then share the costs for the server.

5.6.4. Data backup

The data stored on a server must be backed up daily, with disaster recovery plans in place, to prevent the chance of data loss in case of a server malfunction.

This is especially relevant to both RIS and PACS data where there are often legal requirements that govern the minimum time required for the long term storage of patient information.

Examples of disaster recovery plans include database mirroring and off-site backup. Data mirroring is where an up to date copy of the main server is created and maintained on a separate machine. In case of an error with the main server, the mirrored server can quickly take over. A mirrored server also ensures that data are continually accessible if maintenance is being performed on the main server. Off-site backup is where data are sent to a separate physical location for secured storage. Data can be transferred either electronically or via physical storage media. This will ensure that patient data are still recoverable even in the event of a significant disaster affecting the main server.

5.6.5. Network speed

A key goal of PACS is the efficient transfer of images for convenient viewing. The potentially large file size of images communicated across a PACS network requires a network infrastructure with the capacity to consistently transfer large amounts of data as quickly as possible. However, if a PACS network is not required, then the demands on the network are significantly reduced.

For the transfer of smaller data sizes, such as RIS data, document files or images from a gamma camera, a normal ethernet speed of 100 Mbps is suitable.

Higher transfer speeds, such as those delivered by a gigabit ethernet connection (1 Gbps) are also available but are only of added benefit if there is consistent viewing via PACS of high detailed diagnostic images such as MRI or CT. When implementing a network, any connection speed can be used, the only impact is the time it takes to transfer the data.

It is also important that a network is able to maintain its speed at all times.

The continual transfer of large amounts of data across a network can cause congestion which will slow network access for all users. By creating a virtual LAN for the PACS network, the transfer of image data will be isolated so that it does not negatively affect the rest of the hospital network’s speed.

5.6.6. Wide area network

For data transfer between individual physical locations i.e. between hospital campuses or diagnostic imaging worksites, a wide area network (WAN) can be used. A WAN is two or more LANs that can securely transfer information across separate geographical locations via telecommunications lines. It is also possible to use a virtual private network to create a secure network between locations across the Internet.