OpenDXA Schema

Vendor-agnostic, normalized schema for DXA bone density and body composition exams.

Overview

OpenDXA Schema provides a standardized JSON Schema for representing DXA (Dual-energy X-ray Absorptiometry) scan data across different vendors (Hologic, GE Lunar, Norland). It enables interoperability between systems that process bone density and body composition measurements.

Files

File	Description
opendxa-core-v0.1.schema.json	Core JSON Schema defining the structure for DXA exam data
opendxa-site-registry-v0.1.json	Registry of bone density measurement sites (ROIs)
opendxa-region-registry-v0.1.json	Registry of body composition regions
opendxa-site-registry.schema.json	Meta-schema for validating site registry files
opendxa-region-registry.schema.json	Meta-schema for validating region registry files

Schema Structure

The core schema defines:

• patient - Patient demographics (ID, sex, date of birth, age)
• exam - Exam metadata (ID, date, indication, facility, operator)
• device - Scanner information (manufacturer, model, software version)
• bone_density - BMD measurements including:
  • Sites (lumbar spine, hip, femoral neck, forearm, whole body)
  • T-scores and Z-scores
  • WHO classification (normal, osteopenia, osteoporosis)
  • FRAX fracture risk assessment
• body_composition - Body composition data including:
  • Total body metrics (fat mass, lean mass, BMC, percent body fat)
  • Regional measurements (appendicular, trunk, android, gynoid, visceral)
  • Derived metrics (android/gynoid ratio, appendicular lean mass index)
• quality_control - Scan quality indicators
• source - Data provenance (ingestion method, parser version)

Site Registry

The site registry defines canonical bone density measurement locations:

Lumbar Spine

• Individual vertebrae: L1, L2, L3, L4
• Composites: L1-L4 (primary diagnostic), L2-L4

Hip

• Femoral neck (left, right, worse)
• Total hip (left, right, worse)
• Trochanter (left, right)
• Ward's area (deprecated)

Forearm

• 1/3 radius (non-dominant preferred)
• Total forearm

Whole Body

• Whole body
• Total body less head (TBLH) - preferred for pediatric

Region Registry

The region registry defines body composition measurement areas:

Appendicular

• Arms (left, right, total)
• Legs (left, right, total)
• Appendicular total (for sarcopenia assessment)

Trunk

• Trunk, trunk less head
• Pelvis, ribs

Central Adiposity

• Android region
• Gynoid region
• Visceral fat

Total Body

• Total body
• Total body less head (TBLH)

Usage

Validate DXA data against the schema:

import json
import jsonschema

with open("opendxa-core-v0.1.schema.json") as f:
    schema = json.load(f)

with open("my-dxa-exam.json") as f:
    data = json.load(f)

jsonschema.validate(data, schema)

Validate registry files against their meta-schemas:

import json
import jsonschema

# Validate site registry
with open("opendxa-site-registry.schema.json") as f:
    site_schema = json.load(f)
with open("opendxa-site-registry-v0.1.json") as f:
    site_registry = json.load(f)
jsonschema.validate(site_registry, site_schema)

# Validate region registry
with open("opendxa-region-registry.schema.json") as f:
    region_schema = json.load(f)
with open("opendxa-region-registry-v0.1.json") as f:
    region_registry = json.load(f)
jsonschema.validate(region_registry, region_schema)

Versioning

Schema versions follow v{major}.{minor} format:

• Major: Breaking changes to required fields or structure
• Minor: Additions, deprecations, or non-breaking refinements

Current version: v0.1

References

• ISCD Official Positions - International Society for Clinical Densitometry guidelines
• WHO Fracture Risk Assessment Tool (FRAX) - 10-year fracture probability calculator
• JSON Schema 2020-12 - Schema specification

License

MIT License