Healthcare Standards

Health Level Seven Internationalis the global authority that publishes standards for the exchange, integration, sharing, and retrieval of electronic health information. "Level Seven" refers to the seventh (application) layer of the ISO OSI model.

Version History

MSH|^~\&|LAB|HOSP|HIS|HOSP|20240101120000||ORU^R01|MSG001|P|2.5
PID|||12345^^^HOSP^MR||Gupta^Sahil||19900115|M

<ClinicalDocument xmlns="urn:hl7-org:v3">
  <typeId root="2.16.840.1.113883.1.3" extension="POCD_HD000040"/>
  <title>Discharge Summary</title>
  ...
</ClinicalDocument>

GET /Patient/12345 HTTP/1.1
Host: fhir.hospital.org
Accept: application/fhir+json

→ { "resourceType": "Patient", "id": "12345", ... }

Key Message Types (v2)

FHIR(Fast Healthcare Interoperability Resources, pronounced "fire") is HL7's modern web standard, published in 2012 and now on Release 4 (R4). It models healthcare data as resources — JSON or XML documents accessible via a RESTful HTTP API, making it usable directly from web apps and mobile devices.

Core REST Operations

Key Resources (imaging-relevant)

SMART on FHIR

# SMART launch sequence (EHR-launch)
1. EHR opens app with ?iss=https://ehr.hospital.org/fhir&launch=abc123
2. App fetches /.well-known/smart-configuration  → auth/token endpoints
3. App redirects to authorization endpoint with scope="launch patient/*.read"
4. EHR returns authorization_code
5. App exchanges code for access_token + patient context (patient ID)
6. App calls GET /Patient/{id} with Bearer token

A PACS is the central nervous system of medical imaging in a hospital. It stores every scan taken on every modality, enables radiologists to read studies on high-resolution workstations, and distributes images to clinicians anywhere in the network. Modern PACS expose DICOMweb APIs and FHIR endpoints alongside the traditional binary DICOM services.

Architecture Components

Traditional DICOM Services (DIMSE)

Application Entity (AE) Titles

# Example DICOM association negotiation
SCU: VIEWER_WS  →  SCP: PACS_ARCHIVE  (host: 10.0.1.50, port: 104)

A-ASSOCIATE-RQ
  Calling AE Title: VIEWER_WS
  Called AE Title:  PACS_ARCHIVE
  Presentation Contexts:
    CT Image Storage  (1.2.840.10008.5.1.4.1.1.2)
    Explicit Little Endian Transfer Syntax

A-ASSOCIATE-AC  ← accepted

Search for studies, series, and instances without retrieving pixel data. Returns JSON metadata.

Endpoints

Example

GET /wado/rs/studies?PatientName=Gupta*&ModalitiesInStudy=CT
Accept: application/dicom+json

→ HTTP 200
[
  {
    "0020000D": { "vr": "UI", "Value": ["1.2.3.4.5.6"] },
    "00080020": { "vr": "DA", "Value": ["20240101"] },
    "00080060": { "vr": "CS", "Value": ["CT"] }
  }
]

Key Parameters / Headers

Retrieve studies, series, instances, frames, or metadata. Supports bulk data retrieval and thumbnail generation.

Endpoints

Example

GET /wado/rs/studies/1.2.3/series/1.2.3.4/instances/1.2.3.4.5
Accept: application/dicom

→ HTTP 200
Content-Type: multipart/related; type="application/dicom"
[Binary DICOM file bytes]

# Metadata only (JSON):
GET …/instances/1.2.3.4.5/metadata
Accept: application/dicom+json

Key Parameters / Headers

Store DICOM instances or bulk data to a server over HTTP. Equivalent to DICOM C-STORE but RESTful.

Endpoints

Example

POST /wado/rs/studies HTTP/1.1
Content-Type: multipart/related; type="application/dicom"
Accept: application/dicom+json

--boundary
Content-Type: application/dicom
[Binary DICOM instance bytes]
--boundary--

→ HTTP 200
{
  "00081190": { "vr": "UR", "Value": ["http://server/wado/rs/studies/1.2.3"] }
}

Key Parameters / Headers