Medical imaging glossary

A

Accession number

The identifier of the order an imaging study fulfills, assigned by the RIS. Stored in DICOM tag (0008,0050). The key that ties images to their order and report. More

ADT

Admit, Discharge, Transfer: the family of HL7 messages that carry patient registration, updates and merges between the EHR and other systems, including PACS.

AE Title

Application Entity Title: the name a DICOM application uses to identify itself on the network. Source and target AE Titles, hosts and ports must be configured on both sides before they can exchange data.

B

Breast Tomosynthesis Object (BTO)

The DICOM standard object for digital breast tomosynthesis (Breast Tomosynthesis Image Storage). The target format when converting proprietary Hologic SCO data. More

Burned-in annotation

Text that is part of the image pixels rather than the header, such as a patient name on an ultrasound screen or a slide label photo. Removing it requires image processing, not header editing. More

C

C-FIND

The DICOM query service. Used to search an archive by patient, study, series or instance attributes. The basis of most archive inventories.

C-MOVE and C-GET

DICOM retrieve services. C-MOVE asks an archive to send objects to a named destination; C-GET returns them on the same connection. Most migrations retrieve from the source with one of the two.

C-STORE

The DICOM service that sends an object to another system for storage. The receiver acknowledges each object with a status.

Conformance statement

A vendor document describing exactly which DICOM services, SOP classes and transfer syntaxes a product supports. The first thing to read when planning a migration between two systems.

D

De-identification

Removing or replacing information that identifies a patient, in headers, private tags, UIDs and pixel data, so images can be used for research or AI. DICOM PS3.15 Annex E defines standard profiles. More

DICOM

Digital Imaging and Communications in Medicine: the international standard for storing and exchanging medical images and related data, covering both file format and network services.

DICOMweb

The RESTful web services in DICOM: QIDO-RS to query, WADO-RS to retrieve and STOW-RS to store. Used by cloud imaging services and modern viewers.

Digital breast tomosynthesis (DBT)

A mammography technique that acquires a series of low-dose images to reconstruct the breast in slices. Produces large multi-frame objects.

E

EHR

Electronic Health Record: the hospital's primary clinical system, and usually the source of truth for patient identity.

Enterprise imaging

A strategy for managing all of a health system's clinical images (radiology, cardiology, pathology, dermatology, photos and video) in shared infrastructure, typically a VNA, linked to the EHR.

Expert Determination

One of the two HIPAA de-identification methods: a qualified expert determines that the risk of re-identification is very small, and documents the methods and results.

H

HL7

Health Level Seven: the standards family for exchanging clinical and administrative data. HL7 v2 messages (ADT, orders, results) connect the EHR, RIS and PACS. FHIR is the newer, web-based HL7 standard.

I

IHE

Integrating the Healthcare Enterprise: an initiative that defines integration profiles describing how standards like DICOM and HL7 are used together, such as Scheduled Workflow and Patient Information Reconciliation.

Instance

A single DICOM object: one image, one multi-frame object, one report or presentation state. Identified by a SOP Instance UID. More

K

Key Object Selection (KOS)

A DICOM object that flags specific images in a study as significant, for example key images for a report. It references other instances by UID, so references must survive a migration.

L

Lossless compression

Compression that reconstructs the original pixel values exactly. JPEG Lossless, JPEG-LS Lossless, JPEG 2000 Lossless, HTJ2K Lossless and RLE are common in DICOM. More

Lossy compression

Compression that discards some information to reach smaller sizes. Once an image is lossy, the original cannot be recovered. DICOM records it in Lossy Image Compression (0028,2110). More

M

Master patient index (MPI, EMPI)

The authoritative list of patient identities across systems and sites, mapping each person's local identifiers to one enterprise identity.

Modality worklist (MWL)

A DICOM service that sends scheduled exams, with patient and order details, from the RIS to the scanner, so technologists don't type them by hand. Exams done without it are a major source of unmatched studies.

P

PACS

Picture Archiving and Communication System: the system that stores, manages and displays medical images for reading and review.

Prefetch

Moving a patient's relevant prior studies to fast storage or a reading workstation ahead of a scheduled exam, so they are ready for comparison.

Presentation state (GSPS)

A DICOM object that stores how an image should be displayed (window level, zoom, annotations) without changing the image. Grayscale Softcopy Presentation State is the most common type.

Private tags

Vendor-defined DICOM attributes in odd-numbered groups. They can hold data viewers depend on, or PHI that standard de-identification would miss.

Pseudonymization

Replacing identifiers with consistent substitutes, so the same patient always gets the same pseudonym across studies and longitudinal research remains possible.

R

RIS

Radiology Information System: manages orders, scheduling and reporting for imaging, and issues accession numbers.

S

Safe Harbor

One of the two HIPAA de-identification methods: removing 18 specified types of identifiers, with no actual knowledge that the remaining information could identify the patient.

Secondary capture (SC)

A DICOM object holding an image that wasn't acquired directly by a modality: a screenshot, a scanned document, a converted image. Older Hologic tomosynthesis was stored as a proprietary secondary capture (SCO).

Series

A group of instances within a study, usually from one acquisition or reconstruction. Identified by a Series Instance UID. More

SOP class

The type of a DICOM object, for example CT Image Storage or VL Whole Slide Microscopy Image Storage, identified by a SOP Class UID. Targets accept only the SOP classes in their conformance statement. More

Storage commitment

A DICOM service in which the sender asks the receiver to confirm it has safely stored a set of objects and taken responsibility for them. Stronger than a C-STORE acknowledgment.

Structured report (SR)

A DICOM object that holds coded, structured content such as measurements, findings or dose reports, rather than pixel data.

Study

All the series from one imaging exam of one patient. Identified by a Study Instance UID. More

T

Tag

The (group,element) number that identifies a DICOM attribute, such as (0010,0020) for Patient ID. More

Tag morphing

Changing DICOM attribute values in flight, for example adding an issuer of patient ID, prefixing accession numbers or remapping MRNs during a migration.

Transfer syntax

How a DICOM object is encoded: byte order, explicit or implicit VR, and pixel compression. Identified by a UID that two systems negotiate before exchanging data. More

U

UID

Unique Identifier: a dotted numeric string, such as a Study Instance UID, that is meant to be globally unique. Studies, series, instances, SOP classes and transfer syntaxes all have one.

Unmatched study

A study whose patient or order information doesn't match a valid record in the RIS, EHR or MPI. Also called orphaned, unverified or broken studies. More

V

Value Representation (VR)

The data type of a DICOM attribute, such as PN (person name), DA (date), UI (UID) or SQ (sequence). More

VNA

Vendor Neutral Archive: an archive that stores images in standard formats, independent of any one PACS, often shared across departments and sites.

W

Whole-slide image (WSI)

A digital scan of an entire glass pathology slide, stored as a tiled multi-resolution pyramid. DICOM WSI is the standard format; many scanners also use proprietary formats such as SVS. More

X

XDS-I

An IHE profile for sharing imaging documents and studies across organizations through a registry and repositories.