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Packet Data sent over a LAN is separated into blocks known as packets to create optimum transfer over a packet-switching network. One of the key features of a packet is that it contains the destination address in addition to the data. See Packet-switching.

Packet-switching Refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message. Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as e-mail messages and web pages. See Packet.

PACS See Picture Archiving and Communication System.

Picture Archiving and Communication System (PACS) The acquisition, archival and retrieval of digital images over a computer network, for diagnosis and review at dedicated workstations.

PACS broker A device that allows the PACS to interface with the Hospital Information System (HIS) and/or the Radiology Information System (RIS). This is not essential in all systems as the RIS and HIS may be able to interface directly with the PACS using the HL7 standard. See Hospital Information System (HIS), Radiology Information System (RIS) and Health Level 7 (HL7).

PACSnet The national evaluation centre funded by the MDA to evaluate PACS and its components (http://www.pacsnet.org.uk/). See Medical Devices Agency (MDA)and Picture Archiving and Communication System (PACS).

PaSA See Purchasing and Supply Agency.

Photo Multiplier Tube (PMT) A device that captures light and transforms it into a digital signal. Its use in the PACS context is in digitisers and CR readers. See Digitiser and Computed Radiography (CR).

Pixel This is a word defined from the term "picture element" and is the smallest viewable element, rectangular or square in an image or display. The function of a workstation will determine the number of pixels required in its display. See Workstation.

PMT See Photo Multiplier Tube.

POISE See Procurement of Image Systems Effectively.

Policy Directorate A division of the Department of Health which examines new methods in healthcare and develops policy for the NHS.

Preventative maintenance Maintenance performed on a regular basis which is intended to prevent failures or detect failures before they impact on the user. See Corrective maintenance.

Purchasing and Supply Agency (PaSA) A Department of Health funded agency involved in the purchasing and supply of all goods for the NHS (http:nww.pasa.nhs.uk/ , http://www.pasa.doh.gov.uk/).

PRINCE See Projects in Controlled Environments.

Procurement of Image Systems Effectively (POISE) This is a procurement model for the purchasing of information systems in the NHS.

Projects in Controlled Environments (PRINCE) This is a standard methodology used by the department of health which defines the responsibilities of a project and outlines the project control (http://www.ogc.gov.uk/prince/about_intro.htm).