Glossary

AE title (application entity title). The name of a DICOM system, up to 16 characters, such as CT01 or PACS. Every association names the system calling (calling AE title) and the one called (called AE title). Routes’ own is ROUTES by default.

Archive. A destination marked as one that can be queried and retrieved from: query/retrieve, prior studies and DICOMweb searches go to it. See Query/retrieve and archives.

Association. A DICOM connection between two systems. It opens with a negotiation of what will be exchanged (presentation contexts) and closes when they are done.

C-ECHO. The DICOM “ping” (Verification): checks that a system answers, and accepts the AE titles.

C-FIND, C-MOVE, C-GET. Query, and two ways to retrieve. C-MOVE asks the archive to send to a named AE title on a new association; C-GET returns the instances on the same association.

C-STORE. Sending one instance.

Central service. The service that keeps the configuration, serves the console, collects the history and raises alerts. Several can share one database. See How it works.

Dead letter. An instance a destination refused for good, kept on the node with the reason until it is sent again, purged, or deleted after Dead-letter retention.

De-identification. Removing or replacing what identifies a patient, by a profile, for research or AI services. See De-identification.

DICOMweb. DICOM over HTTPS: STOW-RS (store), QIDO-RS (search), WADO-RS (retrieve). See DICOMweb.

Destination. Where instances go: a DICOM system, a DICOMweb service, or a group of destinations.

Destination group. Destinations that fail over to each other or share the load. See Destination groups.

Drain. Stopping a node from accepting new associations while it finishes what it has, for maintenance. See Adding nodes.

Enrollment key. The shared key a new node presents once to join. The node then receives a key of its own.

Explicit / Implicit VR Little Endian. The two uncompressed transfer syntaxes. Implicit VR is the DICOM default that every system supports.

History. The record of every instance received and every delivery, kept by the central service for History retention. It holds patient names and IDs.

HL7 v2. The messaging standard of hospital systems: orders (ORM, OMI, OMG), patient updates and merges (ADT), results (ORU). Sent over MLLP, a simple framing over TCP.

Instance. One DICOM object: an image, a frame series, a report, a presentation state. Identified by its SOP Instance UID.

Lossless, lossy. A lossless compression gives back exactly the original pixels; a lossy one does not. Routes compresses with a lossy method only when a destination’s list allows it.

MPPS (Modality Performed Procedure Step). A modality’s report that an examination started, completed or was discontinued. See Modality worklist and MPPS.

MWL (Modality Worklist). The list of scheduled examinations a modality queries, so that patient and order details need not be typed.

Node. A server that receives, routes and sends. Nodes behind a load balancer share the work.

Patient ID map. A table that translates patient IDs between ID domains, such as two hospitals’ numbers for the same patient. See Patient ID maps.

PDU (protocol data unit). The packets of a DICOM association. The maximum PDU length is negotiated.

Presentation context. One kind of object (SOP class) proposed with the transfer syntaxes the sender can use. The receiver accepts it in one syntax, or refuses it.

Prior study. An earlier study of the same patient, fetched from an archive so that a radiologist can compare. See Prior studies.

Quarantine. Instances a node refused (no route, unreadable), kept for diagnosis when Quarantine (days) is set.

Reconciliation queue. Studies held because their patient does not match the order, waiting for someone to correct or release them. See Patient reconciliation.

Resend cache. Delivered instances a node keeps for Resend cache (hours), so they can be sent again from the history.

Route. Connects a source to destinations. Routes are checked top to bottom, and the first that matches wins.

SCP, SCU (service class provider, user). The two roles of a DICOM service: the SCU asks, the SCP answers. Routes is an SCP towards senders and an SCU towards destinations.

SOP class. A kind of DICOM object with a service, such as CT Image Storage or Study Root Query/Retrieve – FIND. Identified by a UID. See the conformance statement.

Source. Describes who sends: calling AE titles, called AE titles, addresses and ports, with optional header conditions, edits and transfer syntax rules.

Storage commitment. A sender’s request to be told when its instances are safely kept. See Storage commitment.

Study. One examination of one patient, made of series of instances. Identified by its Study Instance UID, and usually by an accession number.

Tag. One element of a DICOM header, written as (group,element), such as (0010,0020) for Patient ID. See Tag edits and scripts.

Transfer syntax. How an instance is encoded: byte order, VR, and compression such as JPEG 2000 or JPEG-LS. See Transfer syntaxes.

UID. A DICOM unique identifier: digits and dots, up to 64 characters. Studies, series, instances, SOP classes and transfer syntaxes each have one.

VR (value representation). The data type of a tag, such as PN for a person’s name or DA for a date.