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Hanging protocol See Default Display Protocol.

Header In DICOM an image, which is the standard medical image, has an associated DICOM header. This contains information pertaining to the image e.g. patient name or image information such as the size of the image. The header contains the information that allows the computer to exchange information related to the image with other devices and perform tasks on the data.

A header is also used in networking and is attached to each unit of data sent across the network, the size of header being dependant on the network protocol being used. The header holds information about the data which allows the computer to combine all the data units after transmission to form the file sent across the network.

Health Insurance Portability and Accountability Act (HIPAA) This is a USA law that comes into effect in 2002. Principally the goals are the standardisation of information management and exchange in medicine, to maintain security, improve accuracy and assure privacy (http://www.hipadvisory.com/ and http://www.scarnet,org/).

Health Level 7 (HL7) This is an ANSI accredited standard developed to allow transfer of data between different systems in healthcare. This operates at the top level of the open system integration model, the application layer (http://www.hl7.org/ and http://www.hl7.org.uk/). See Digital Imaging and Communications in Medicine (DICOM), Open System Interconnection (OSI) and Integrating the Healthcare Enterprise (IHE).

HealthCare Information and Management Systems Society (HIMSS) This is a society which provides a forum for multidisciplinary professionals in healthcare information services to discuss problems and provide educational facilities for its members. It also aids in the advancement of standards and initiative such as IHE (http:www.himss.org/) See Integrating the Healthcare Enterprise (IHE).

High tide The online storage in a PACS will have an upper limit to the number of images that can be stored. As this upper limit is approached, decisions have to be made about which exams are to remain online, and which can be deleted (note that copies of all exams will always be available from the archive). Deletion of exams from the online storage starts at a point when the number of stored images is a little below the maximum capacity, for example 90%. This point is known as the "high tide" point. See Low tide and Short Term Storage (STS).

HIMSS See HealthCare Information and Management Systems Society.

HIPAA See Health Insurance Portability and Accountability Act.

HIS See Hospital Information System.

HL7 See Health Level 7.

Hospital Information System (HIS) A computer system which stores demographic information on all patients It may also store appointment details, clerical data or pathology reports. See Radiology Information System (RIS).

Hub A device to link a number of peripherals to a network through a number of ports. All the packets on the network are sent to all ports and are then sent to all devices. See Bridge, Router and Switch.