DICOMweb Guide for IDC

DICOMweb Guide for IDC

IDC provides DICOMweb access through Google Cloud Healthcare API DICOM stores. This guide covers the implementation specifics and usage patterns.

When to Use DICOMweb

Use DICOMweb when you need:

• Integration with PACS systems or DICOMweb-compatible tools
• Streaming metadata without downloading full files
• Building custom viewers or web applications
• Using existing DICOMweb client libraries (OHIF, dicomweb-client, etc.)

For most use cases, idc-index is simpler and recommended. Use DICOMweb when you specifically need the DICOMweb protocol.

Endpoints

Public Proxy (No Authentication)

https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb

• Points to the latest IDC version automatically
• Daily quota applies (suitable for testing and moderate use)
• No authentication required
• Note: "viewer-only-no-downloads" in URL is legacy naming with no functional meaning

Google Healthcare API (Requires Authentication)

https://healthcare.googleapis.com/v1/projects/nci-idc-data/locations/us-central1/datasets/idc/dicomStores/idc-store-v{VERSION}/dicomWeb

Replace {VERSION} with the IDC release number. To find the current version:

from idc_index import IDCClient
client = IDCClient()
print(client.get_idc_version())  # e.g., "23" for v23

The Google Healthcare endpoint requires authentication and provides higher quotas. See Authentication section below.

Implementation Details

IDC DICOMweb is provided through Google Cloud Healthcare API DICOM stores. The implementation follows DICOM PS3.18 Web Services with specific characteristics documented in the Google Healthcare DICOM conformance statement.

Supported Operations

Not supported: URI Service, Worklist Service, Non-Patient Instance Service, Capabilities Transactions

Searchable DICOM Tags (QIDO-RS)

The implementation supports a limited set of searchable tags:

Important: Only exact matching is supported, except for:

• StudyDate: supports range queries
• PatientName: supports fuzzy matching

Query Limitations

• Maximum results: 5,000 for studies/series searches; 50,000 for instances
• Maximum offset: 1,000,000
• DICOM sequence tags larger than ~1 MB are not returned in metadata (BulkDataURI provided instead)

Code Examples

All examples use the public proxy endpoint. For authenticated access to Google Healthcare, see the authentication section.

Finding UIDs with idc-index

Use idc-index to discover data, then use DICOMweb for metadata access:

from idc_index import IDCClient

client = IDCClient()

# Find studies of interest
results = client.sql_query("""
    SELECT StudyInstanceUID, SeriesInstanceUID, PatientID, Modality
    FROM index
    WHERE collection_id = 'tcga_luad' AND Modality = 'CT'
    LIMIT 5
""")

# Use these UIDs with DICOMweb
study_uid = results.iloc[0]['StudyInstanceUID']
series_uid = results.iloc[0]['SeriesInstanceUID']
print(f"Study: {study_uid}")
print(f"Series: {series_uid}")

QIDO-RS: Search by UID

import requests

base_url = "https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb"

# Search for a specific study
study_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.307623500513044641407722230440"
response = requests.get(
    f"{base_url}/studies",
    params={"StudyInstanceUID": study_uid},
    headers={"Accept": "application/dicom+json"}
)

if response.status_code == 200:
    studies = response.json()
    print(f"Found {len(studies)} study")

QIDO-RS: List Series in a Study

import requests

base_url = "https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb"
study_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.307623500513044641407722230440"

response = requests.get(
    f"{base_url}/studies/{study_uid}/series",
    headers={"Accept": "application/dicom+json"}
)

if response.status_code == 200:
    series_list = response.json()
    for series in series_list:
        # DICOM tags are returned as hex codes
        series_uid = series.get("0020000E", {}).get("Value", [None])[0]
        modality = series.get("00080060", {}).get("Value", [None])[0]
        description = series.get("0008103E", {}).get("Value", [""])[0]
        print(f"{modality}: {description}")

QIDO-RS: List Instances in a Series

import requests

base_url = "https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb"
study_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.307623500513044641407722230440"
series_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.217441095430480124587725641302"

response = requests.get(
    f"{base_url}/studies/{study_uid}/series/{series_uid}/instances",
    params={"limit": 10},
    headers={"Accept": "application/dicom+json"}
)

if response.status_code == 200:
    instances = response.json()
    print(f"Found {len(instances)} instances")
    for inst in instances[:3]:
        sop_uid = inst.get("00080018", {}).get("Value", [None])[0]
        print(f"  SOPInstanceUID: {sop_uid}")

WADO-RS: Retrieve Series Metadata

import requests

base_url = "https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb"
study_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.307623500513044641407722230440"
series_uid = "1.3.6.1.4.1.14519.5.2.1.6450.9002.217441095430480124587725641302"

response = requests.get(
    f"{base_url}/studies/{study_uid}/series/{series_uid}/metadata",
    headers={"Accept": "application/dicom+json"}
)

if response.status_code == 200:
    instances = response.json()
    print(f"Retrieved metadata for {len(instances)} instances")

    # Extract image dimensions from first instance
    if instances:
        inst = instances[0]
        rows = inst.get("00280010", {}).get("Value", [None])[0]
        cols = inst.get("00280011", {}).get("Value", [None])[0]
        print(f"Image dimensions: {rows} x {cols}")

Combined Workflow: idc-index Discovery + DICOMweb Metadata

from idc_index import IDCClient
import requests

# Use idc-index for efficient discovery
idc = IDCClient()
results = idc.sql_query("""
    SELECT StudyInstanceUID, SeriesInstanceUID, Modality, SeriesDescription
    FROM index
    WHERE collection_id = 'nlst' AND Modality = 'CT'
    LIMIT 1
""")

study_uid = results.iloc[0]['StudyInstanceUID']
series_uid = results.iloc[0]['SeriesInstanceUID']
print(f"Found: {results.iloc[0]['SeriesDescription']}")

# Use DICOMweb to stream metadata without downloading files
base_url = "https://proxy.imaging.datacommons.cancer.gov/current/viewer-only-no-downloads-see-tinyurl-dot-com-slash-3j3d9jyp/dicomWeb"

response = requests.get(
    f"{base_url}/studies/{study_uid}/series/{series_uid}/metadata",
    headers={"Accept": "application/dicom+json"}
)

if response.status_code == 200:
    metadata = response.json()
    print(f"Retrieved metadata for {len(metadata)} instances without downloading files")

Common DICOM Tags Reference

DICOMweb returns tags as hexadecimal codes. Common tags:

Authentication for Google Healthcare API

To use the Google Healthcare endpoint with higher quotas:

from google.auth import default
from google.auth.transport.requests import Request
import requests

# Get credentials (requires gcloud auth)
credentials, project = default()
credentials.refresh(Request())

# Build authenticated request
base_url = "https://healthcare.googleapis.com/v1/projects/nci-idc-data/locations/us-central1/datasets/idc/dicomStores/idc-store-v23/dicomWeb"

response = requests.get(
    f"{base_url}/studies",
    params={"limit": 5},
    headers={
        "Authorization": f"Bearer {credentials.token}",
        "Accept": "application/dicom+json"
    }
)

Prerequisites:

1. Google Cloud SDK installed (gcloud)
2. Authenticated: gcloud auth application-default login
3. Account has access to public Google Cloud datasets

Troubleshooting

Issue: 400 Bad Request on search queries

• Cause: Using unsupported search parameters. The implementation only supports specific DICOM tags for filtering.
• Solution: Use UID-based queries (StudyInstanceUID, SeriesInstanceUID). For filtering by Modality or other attributes, use idc-index to discover UIDs first, then query DICOMweb with specific UIDs.

Issue: 403 Forbidden on Google Healthcare endpoint

• Cause: Missing authentication or insufficient permissions
• Solution: Run gcloud auth application-default login and ensure your account has access

Issue: 429 Too Many Requests

• Cause: Rate limit exceeded
• Solution: Add delays between requests, reduce limit values, or use authenticated endpoint for higher quotas

Issue: 204 No Content for valid UIDs

• Cause: UID may be from an older IDC version not in current data
• Solution: Verify UID exists using idc-index query first. The proxy points to the latest IDC version.

Issue: Large metadata responses slow to parse

• Cause: Series with many instances returns large JSON
• Solution: Use limit parameter on instance queries, or query specific instances by SOPInstanceUID

Issue: Response missing expected attributes

• Cause: DICOM sequences larger than ~1 MB are excluded from metadata responses
• Solution: Retrieve the full DICOM instance using WADO-RS instance retrieval if you need all attributes

Resources

• Google Healthcare DICOM Conformance Statement
• DICOMweb Standard
• dicomweb-client Python library
• IDC Documentation