Query and download public cancer imaging data from NCI Imaging Data Commons. Invoke for any question about IDC collections, cancer imaging datasets, DICOM data access, radiology (CT, MR, PET) or pathology AI training sets, metadata queries, visualization, or license checks — even when the user doesn't explicitly mention "IDC". No authentication required.
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Query and download public cancer imaging data from NCI Imaging Data Commons. Invoke for any question about IDC collections, cancer imaging datasets, DICOM data access, radiology (CT, MR, PET) or pathology AI training sets, metadata queries, visualization, or license checks — even when the user doesn't explicitly mention "IDC". No authentication required.
license
This skill is provided under the MIT License. IDC data itself has individual licensing (mostly CC-BY, some CC-NC) that must be respected when using the data.
Query and download public cancer imaging data from the National Cancer Institute Imaging Data Commons (IDC). No authentication required for data access.
Expected network access: IDC metadata is reachable three ways — a local DuckDB index shipped with the idc-index Python package (no network), or the hosted IDC service over MCP or REST (api.imaging.datacommons.cancer.gov, no authentication). File downloads use public GCS (storage.googleapis.com) and AWS S3 (s3.amazonaws.com) — no authentication required. DICOMweb access uses either the public IDC proxy (proxy.imaging.datacommons.cancer.gov, no auth) or the Google Cloud Healthcare API (, requires GCP authentication). Optional BigQuery queries () also require GCP authentication. No credentials or environment variables are accessed by this skill.
healthcare.googleapis.com
bigquery.googleapis.com
Current IDC Data Version: v24 (always verify — see Best Practices)
Choose the access path first. There is no single default: the cheapest correct path depends
on the session and the task.
Session already has the IDC MCP server? Route discovery and metadata there — see IDC
MCP Server.
Otherwise, is idc-index installed? Run python scripts/check_version.py. If it passes,
use idc-index for everything.
Not installed, and the task is read-only metadata — counts, attribute values, collection
lookups, SQL under 10 000 rows, licenses, citations, viewer URLs? Use the REST API over
curl; do not install anything. Installing costs ~77 MB of packaged index data plus
pandas, pyarrow, and duckdb, which a metadata question does not need. See Data Access
Options.
Not installed, and the task needs more than metadata — downloading files, pandas or
plotting, pydicom/SimpleITK, pathology tiling, results past 10 000 rows, or a version-pinned
script the user re-runs? Install idc-index: check_version.py exits non-zero and prints
the exact install command for the running interpreter. Prefer a virtual environment, then
restart Python.
idc-index (GitHub) is still the most
capable path and the only one that moves image bytes; the rule is just not to pay for it before
the task calls for it. check_version.py never installs anything itself — it also flags a newer
idc-index or skill release when one exists.
Setup for the idc-index path:
from idc_index import IDCClient
client = IDCClient()
# Verify IDC data version (should be "v24")print(f"IDC data version: {client.get_idc_version()}")
Core workflow: query metadata with client.sql_query() → download with
client.download_from_selection() → visualize with client.get_viewer_URL(). Python examples
below assume this client; Data Access Options has the REST equivalents. For current data
scale, run the summary query in references/sql_patterns.md or GET /v3/stats.
IDC MCP Server
IDC operates a hosted MCP server at https://api.imaging.datacommons.cancer.gov/mcp
(streamable HTTP, no authentication). Where it is available it complements — it does not
replace — the idc-index workflow below.
Identify it by the MCP resource idc://guide, or by three or more of the tool names
build_cohort, get_cohort_urls, list_analysis_results, and get_idc_version. Generic
names such as run_sql are not evidence on their own. If identification is ambiguous, use
idc-index.
If this session has the server, treat it as authoritative for discovery and metadata —
IDC version, counts, attribute values, cohort building, metadata SQL — and follow the
server's own instructions rather than re-deriving them from this file. Its data version is
whatever the server reports: call get_idc_version instead of relying on the version pinned
in this file.
Return here for what the server does not do: downloading files, local pandas/notebook
analysis, DICOMweb, BigQuery, digital pathology tiling, and reproducible scripts. Hand off by
passing SeriesInstanceUIDs from the server to client.download_from_selection(...), and run
scripts/check_version.py at that point.
If it is not available, the identical service is reachable with no configuration as a REST
API at https://api.imaging.datacommons.cancer.gov/v3 — use it for read-only metadata rather
than installing idc-index, per the routing gate in Overview. Suggest connecting the MCP
server at most once, only for repeated interactive discovery, and never change the user's
configuration yourself.
See references/mcp_guide.md for the tool inventory, handoff patterns, and per-host notes.
When to Use This Skill
Finding publicly available radiology (CT, MR, PET) or pathology (slide microscopy) images
Selecting image subsets by cancer type, modality, anatomical site, or other metadata
Downloading DICOM data from IDC
Checking data licenses before use in research or commercial applications
Visualizing medical images in a browser without local DICOM viewer software
Quick Navigation
Inline below: the MCP/REST routing rules, the IDC data model, the index tables and how they
join, the core API patterns (query, download, visualize, license, cite), best practices, and
troubleshooting.
Reference Guides (load on demand):
Guide
When to Load
index_tables_guide.md
Complex JOINs, schema discovery, DataFrame access
use_cases.md
End-to-end workflows: training datasets, batch downloads, DICOM reading with pydicom/SimpleITK, pipeline integration
sql_patterns.md
Quick SQL patterns for filter discovery, annotations, size estimation
clinical_data_guide.md
Clinical/tabular data, imaging+clinical joins, value mapping
IDC adds two grouping levels above the standard DICOM hierarchy (Patient → Study → Series → Instance):
collection_id: Groups patients by disease, modality, or research focus (e.g., tcga_luad, nlst). A patient belongs to exactly one collection.
analysis_result_id: Identifies derived objects (segmentations, annotations, radiomics features) across one or more original collections. Use it to find AI-generated or expert annotations, while collection_id finds original imaging data (which may itself include deposited annotations).
Key identifiers for queries:
Identifier
Scope
Use for
collection_id
Dataset grouping
Filtering by project/study
PatientID
Patient
Grouping images by patient
StudyInstanceUID
DICOM study
Grouping of related series, visualization
SeriesInstanceUID
DICOM series
Grouping of related series, visualization
Index Tables
The idc-index package provides multiple metadata index tables, accessible via SQL or as pandas DataFrames. The REST API exposes the same tables through GET /tables and POST /sql.
Important:client.indices_overview is the authoritative source for current table descriptions, available columns, and their types — query it when writing SQL or exploring data structure. It also answers "which table contains column X"; see references/index_tables_guide.md for that search pattern and full schema discovery.
Available Tables
Always call client.fetch_index("table_name") before querying any index table — it is safe and idempotent for all tables, including those loaded automatically at startup.
Family
Tables
Granularity
Core
index (primary metadata for all current data), collections_index, analysis_results_index
references/index_tables_guide.md has the full inventory with each table's columns and
contents — load it when you need to know what a specialized table actually holds.
prior_versions_index is for reproducibility only. It contains series permanently removed
from IDC, with zero overlap with index. Use it only to reproduce work against a prior IDC
version. Do NOT use it for version history or "what's new" questions — those use
series_init_idc_version / series_revised_idc_version in the main index table, which are
not equivalent to this table's min_idc_version / max_idc_version.
Joining Tables
SeriesInstanceUID is the universal join key for all series-level specialized tables: sm_index, sm_instance_index, seg_index, ann_index, ann_group_index, contrast_index, volume_geometry_index, rtstruct_index, ct_index, mr_index, pt_index. Always join these to index on SeriesInstanceUID. The exceptions below use different column names.
Link series to collection metadata or clinical data
analysis_result_id
index, analysis_results_index
Link series to analysis result metadata (annotations, segmentations)
source_DOI
index, analysis_results_index
Link by publication DOI
segmented_SeriesInstanceUID
seg_index → index
Link segmentation to its source image series (seg_index.segmented_SeriesInstanceUID = index.SeriesInstanceUID)
referenced_SeriesInstanceUID
ann_index → index, rtstruct_index → index
Link annotation or RTSTRUCT to its source image series
Note:subjects, updated, and description appear in multiple tables but have different meanings (counts vs identifiers, different update contexts). Joining prior_versions_index to index on SeriesInstanceUID always returns zero rows — see the warning above.
For detailed join examples, schema discovery patterns, key columns reference, and DataFrame access, see references/index_tables_guide.md.
Clinical Data Access
Clinical (non-imaging) attributes — staging, demographics, therapy — live in per-collection
tables. client.fetch_index("clinical_index") loads the dictionary mapping columns to
collections; client.get_clinical_table(name) returns one table as a DataFrame.
See references/clinical_data_guide.md for the discovery workflow, coded-value mapping, and
joining clinical data with imaging.
Data Access Options
Method
Auth
Best For
Reference
idc-index
No
Downloads, pandas analysis, unbounded queries — the most capable path
This document
IDC MCP server
No
Discovery, cohort building, metadata when the session already has it
mcp_guide.md
IDC REST API
No
Metadata with no install, from any language or shell — the default when idc-index is absent
rest_api_guide.md
Direct Parquet (GCS)
No
Version-pinned queries, or results past the REST row cap
parquet_access_guide.md
Cloud storage (S3/GCS)
No
Direct file access, bulk transfer, custom pipelines
cloud_storage_guide.md
DICOMweb via IDC proxy
No
Tool and PACS integration; daily quota, so testing and moderate use
dicomweb_guide.md
DICOMweb via Google Healthcare
Yes (GCP)
The same DICOMweb API at production volume, without the proxy quota
Full DICOM metadata, private elements, SR measurements — last resort
bigquery_guide.md
The IDC Portal (https://portal.imaging.datacommons.cancer.gov/) is interactive only —
browser-based exploration, manual cohort selection, and download. Unlike every option above it
has no programmatic interface, so point a user there to browse or click through data
themselves; never use it as a step in a script or workflow.
REST API — the no-install metadata path
https://api.imaging.datacommons.cancer.gov/v3, no authentication: discovery, cohort counts and
manifests, read-only SQL, clinical tables, viewer URLs, licenses, citations. It is the same
service as the MCP server over plain HTTP, so it needs no configuration. It never moves image
bytes — switch to idc-index to download, to get a DataFrame, or for results past 10 000 rows.
B=https://api.imaging.datacommons.cancer.gov/v3
curl -s $B/version # idc_version, idc_index_data_version, api_version
curl -s $B/stats # collections, patients, studies, series, instances, size_TB
curl -s "$B/attributes/Modality/values?limit=5"# real filter values, with counts
curl -s $B/sql -H 'content-type: application/json' \
-d '{"sql":"SELECT collection_id, COUNT(*) n FROM index GROUP BY 1 ORDER BY n DESC LIMIT 3"}'
curl -s $B/cohort/counts -H 'content-type: application/json' \
-d '{"filters":{"terms":{"collection_id":["rider_pilot"]}}}'
The filter object always goes under filters — on cohort/counts, cohort/manifest,
cohort/manifest.txt, licenses, and citations alike. A bare filter or an unrecognized key is
a 422 naming the fix; an unfiltered series-enumerating request is a 400, not the whole archive.
Every filtered response echoes filters_applied and warnings — read them, because they name
any predicate the server dropped. A zero count with empty warnings therefore means the filter
matched nothing, not that a value was miscased; miscasing produces a warning that says so.
POST /sql takes one read-only SELECT/WITH over the tables idc-index exposes plus
clinical.<table>; max_rows defaults to 5 000, caps at 10 000, and truncated flags clipping.
GET /attributes lists the 19 filterable attributes — clinical values, segmented anatomy, and
acquisition parameters are not among them and need SQL. There is no rate limit or quota. Use
v3 only: V1 and V2 are superseded and scheduled for shutdown, so port any /v1/- or
Modality_btw-style example a user brings rather than extending it.
Both sides build on idc-index-data, so compare the API's idc_index_data_version against local
idc_index_data.__version__ before mixing them: the major is the IDC data release (24.x.y
serves v24), so differing minor/patch means the series are identical. If the API is a whole
release ahead, idc-indexcannot download the extra series — it silently skips what its own
index does not list — so either upgrade it (run scripts/check_version.py for the right command)
or transfer directly from the bucket with s5cmd --no-sign-request.
See references/rest_api_guide.md for the endpoint reference, filter grounding, limits, and the
manifest-based download flow.
Cloud storage organization
All DICOM files live in public buckets mirrored between AWS S3 and GCS, organized by CRDC UUIDs
(not DICOM UIDs) to support versioning, as <crdc_series_uuid>/<crdc_instance_uuid>.dcm. Access
is free (no egress fees) via AWS CLI, gsutil, or s5cmd with anonymous access; use the
series_aws_url column for S3 URLs. Note that idc-open-data-cr / idc-open-cr (~4% of data)
is commercial-use restricted (CC BY-NC). See references/cloud_storage_guide.md for the full
bucket list and UUID mapping.
DICOMweb access
IDC data is available via DICOMweb (Google Cloud Healthcare API) for PACS integration and
DICOMweb-compatible tools: a public proxy (no auth, daily quota) for testing and moderate
queries, or Google Healthcare (GCP auth) for production volumes. See
references/dicomweb_guide.md.
Direct Parquet access
The idc-index metadata tables are also published as Parquet on a public GCS bucket
(idc-index-data-artifacts), queryable with DuckDB or pandas. This needs DuckDB installed
and cannot reach the per-collection clinical tables, so prefer REST /sql for ad-hoc metadata;
choose Parquet to pin a data version or for results past the REST row cap. See
references/parquet_access_guide.md.
Core Capabilities
The patterns below are the ones that go wrong when recalled from memory rather than checked.
Worked examples for each area live in the reference guides named inline.
1. Discovery — enumerate values before filtering on them
Filtering on a guessed Modality or BodyPartExamined string is the most common cause of an
empty result set. Enumerate first:
modalities = client.sql_query("""
SELECT DISTINCT Modality, COUNT(*) as series_count
FROM index
GROUP BY Modality
ORDER BY series_count DESC
""")
print(modalities)
The same pattern works for any filter column, optionally narrowed by another —
BodyPartExamined within a Modality, Manufacturer, collection_id. On the REST path this
grounding is a single call — GET /attributes/{attr}/values returns values with counts — and the
cohort endpoints report a miscased value in warnings rather than as an empty result.
Two indices carry curated collection-level metadata the primary index does not, both
requiring client.fetch_index(...) first: collections_index (cancer types, tumor locations,
species, subject counts) and analysis_results_index (derived datasets — AI segmentations,
expert annotations, radiomics — with their source collections and modalities).
Cancer type lives in collections_index.cancer_types, not in index — filtering by
cancer type requires a join:
client.fetch_index("collections_index")
results = client.sql_query("""
SELECT i.collection_id, i.PatientID, i.SeriesInstanceUID, i.Modality
FROM index i
JOIN collections_index c ON i.collection_id = c.collection_id
WHERE c.cancer_types LIKE '%Breast%'
AND i.Modality = 'MR'
LIMIT 20
""")
client.sql_query() returns a pandas DataFrame. Confirm column names with
client.get_index_schema('index') or client.indices_overview before writing a query rather
than assuming them.
See references/sql_patterns.md for filter-value discovery, annotation and segmentation
queries, size estimation, clinical linking, and version tracking ("what's new in vX" — use
series_init_idc_version / series_revised_idc_version in index, never
prior_versions_index).
2. Downloading DICOM files
The two download methods take their first two arguments in opposite order. This is the
most common source of broken IDC code — check it rather than recalling it:
Method
First arg
Second arg
Use when
download_from_selection
downloadDir (required)
filter kwargs (optional)
Filtering by collection, patient, study, or series
download_dicom_series
seriesInstanceUID (required)
downloadDir (required)
Downloading specific series by UID only
download_from_selection takes filter keyword arguments, NOT a DataFrame. The name
"from_selection" refers to filtering the IDC index by criteria — not to accepting a pandas
DataFrame. To download query results, extract the UIDs into a list first:
# Step 1: Query for series UIDs
series_df = client.sql_query("""
SELECT SeriesInstanceUID
FROM index
WHERE Modality = 'CT'
AND BodyPartExamined = 'CHEST'
AND collection_id = 'nlst'
LIMIT 5
""")
# Step 2: Extract UIDs as a list from the DataFrame
uids = list(series_df['SeriesInstanceUID'].values)
# Step 3: Pass the list to download_from_selection (NOT the DataFrame itself)
client.download_from_selection(
downloadDir="./data/lung_ct",
seriesInstanceUID=uids # list of strings, not a DataFrame
)
# Alternative: download_dicom_series has seriesInstanceUID as FIRST arg (different order!)
client.download_dicom_series(
seriesInstanceUID=uids, # FIRST arg here
downloadDir="./data/lung_ct"
)
# Whole collection: downloadDir is still the FIRST positional argument
client.download_from_selection(downloadDir="./data/rider", collection_id="rider_pilot")
Both methods default to AWS; pass source_bucket_location="gcs" to pull from Google Storage.
Downloaded files are named <crdc_instance_uuid>.dcm, not by SOPInstanceUID. The DICOM
UIDs are preserved inside the file metadata, not in the filename. Use the crdc_instance_uuid
column to map files back to the series they came from.
idc download <collection|series-uid|manifest> --download-dir ./data does the same from a
shell. See references/cli_guide.md for the dirTemplate hierarchy options (Python default:
%collection_id/%PatientID/%StudyInstanceUID/%Modality_%SeriesInstanceUID; dirTemplate=""
flattens), manifest downloads with resume, and dry-run size estimation.
3. Visualizing IDC images
viewer_url = client.get_viewer_URL(seriesInstanceUID=uid) # one series
viewer_url = client.get_viewer_URL(studyInstanceUID=study_uid) # all series in a study
Returns a browser URL — nothing is downloaded. The method selects OHIF v3 for radiology or
SLIM for slide microscopy automatically. Viewing by study is useful when a single DICOM Study
holds several Series (T1, T2, and DWI from one MRI session).
4. Licenses and citations — obligations, not optional steps
IDC data carries license terms and attribution requirements that follow it into any downstream
publication or product, and neither is inferable from the pixel data. Check the license
before use, and generate citations for whatever you download.
# License breakdown for a selection
licenses = client.sql_query("""
SELECT DISTINCT collection_id, license_short_name,
COUNT(DISTINCT SeriesInstanceUID) as series_count
FROM index GROUP BY collection_id, license_short_name
""")
# Citations for the same selection you downloaded (APA by default)for citation in client.citations_from_selection(collection_id="rider_pilot"):
print(citation)
About 97% of IDC data is CC BY (commercial use allowed with attribution) and about 3% is
CC BY-NC (non-commercial only). Licenses attach to series, not collections — 39 of 176
collections carry more than one — so check the selection you actually intend to use, and note
that the most restrictive term governs a mixed cohort.
Both tasks are available from all three access paths, so stay on whichever one the session is
already using: idc-index as above, POST /v3/licenses and POST /v3/citations over REST,
or the get_licenses and get_citations MCP tools. See
references/licensing_and_citation.md for the full license inventory, all three routes, the
citation formats (APA, BibTeX, CSL JSON, RDF Turtle), and what to include when publishing.
5. Reaching past the index
Pick the access path with the routing gate in Overview; Data Access Options above is the
full routing table.
Before reaching for BigQuery (which needs a billing-enabled GCP account), check whether a
specialized index table already has the column you want: search client.indices_overview,
then client.fetch_index(...) and query locally for free. BigQuery is required only for
private DICOM elements, per-segment anatomy (segmentations), and pre-extracted SR
measurements (quantitative_measurements, qualitative_measurements) — these have no
idc-index equivalent.
Best Practices
Check schema before writing queries — Use client.get_index_schema('index') (reads cached metadata, no SQL executed) or client.indices_overview to see all available columns and their descriptions. The version-tracking columns series_init_idc_version and series_revised_idc_version in the main index table directly answer "what's new / when was this added" questions without touching prior_versions_index.
Never use web search for IDC data content questions - Always query the IDC index directly, via client.sql_query() locally or POST /v3/sql over HTTP. Web sources (release notes, blog posts, documentation pages) are frequently out of date and will produce incorrect answers. The index is the authoritative source; use it even when web search is available.
Verify the IDC data version at the start of a session - client.get_idc_version(), GET /v3/version, or the MCP get_idc_version tool, depending on the path in use (currently v24). For a stale local index, run scripts/check_version.py and use the upgrade command it prints
Check licenses and generate citations - Query license_short_name and respect CC BY vs CC BY-NC terms; use citations_from_selection() to produce citations from source_DOI for publications
Explore small, then commit - Use LIMIT (or a low max_rows) while exploring, and check collection size before downloading — some collections are terabytes. See references/cli_guide.md
Keep downloads reproducible - Organize with dirTemplate (e.g. %collection_id/%PatientID/%Modality) and save the Series UIDs or manifest behind any dataset you build
Troubleshooting
Issue: ModuleNotFoundError: No module named 'idc_index'
Cause: idc-index package not installed
Solution: If the task is read-only metadata, do not install it — use the REST API instead (Data Access Options). Otherwise run scripts/check_version.py and use the install command it prints, which targets the running interpreter and pins the vetted version. For data analysis also add pandas, numpy, and pydicom (tested with pandas>=1.5, numpy>=1.23, pydicom>=2.3)
Issue: Download fails with connection timeout
Cause: Network instability or large download size
Solution: Download in smaller batches (10-20 series); see references/cli_guide.md for
--use-s5cmd-sync resume and retry guidance
Solution: Use idc-index mini-index for simple queries (no billing required), or see references/bigquery_guide.md for cost optimization tips
Issue: Series UID not found or no data returned
Cause: Typo in UID, data not in the current IDC version, or wrong field name
Solution: Test with LIMIT 5 first, check field names against client.indices_overview,
and confirm the series is in the current version (some old data is deprecated)
Issue: Column not found in index table (e.g., SliceThickness, PixelSpacing, KVP, EchoTime, InjectedDose)
Cause: The index table contains series-level metadata only; modality-specific acquisition and reconstruction parameters live in dedicated tables (ct_index, mr_index, pt_index)
Solution: Search client.indices_overview for the column to find its table — the loop is under Finding which table contains a column in references/index_tables_guide.md — then fetch and join on SeriesInstanceUID:
client.fetch_index("ct_index")
result = client.sql_query("""
SELECT i.SeriesInstanceUID, i.Modality, c.SliceThickness, c.KVP, c.PixelSpacing_row_mm
FROM index i
JOIN ct_index c USING (SeriesInstanceUID)
WHERE i.collection_id = 'your_collection'
""")
Issue: Downloaded DICOM files won't open
Cause: Corrupted download, or an object type the viewer does not handle — SEG, RTSTRUCT,
SR, and slide microscopy all need specialized tools
Solution: Check Modality and SOPClassUID first, validate with
pydicom.dcmread(file, force=True), try another viewer (3D Slicer, QuPath for pathology),
then re-download
Resources
Reference guides and their decision triggers are listed in Quick Navigation above.
indices_reference — external index-table docs (may be ahead of the installed version)
Citation: Fedorov, A., et al. "National Cancer Institute Imaging Data Commons: Toward Transparency, Reproducibility, and Scalability in Imaging Artificial Intelligence." RadioGraphics 43.12 (2023). https://doi.org/10.1148/rg.230180
