Medical Image Quality Assurance with Automated Constraint Validation

1
Medical Image Quality Assurance with Automated
Constraint Validation

• Dongbai Guo
• Architect and Senior Development Manager
• Oracle Corporation
• db.guo_at_oracle.com, dbguo_at_ieee.org
• Nashua, NH 03062, USA

2
Market Trends

• Growth in medical imaging
• New applications and new branches of medicine
• Increased utilization
• Increased spatial and temporal resolution
• Exponential growth in data volume
• Computer aided detection (CAD) and diagnosis
  (CADx)
• Data integration and centralization
• Knowledge management, sharing and discovery

3
Impacts to DICOM

• Wider, but sometimes hasty, adoption
• Variant implementation quality
• Non-compliant images lead to integration
  nightmare for
• Clinical care
• Research
• Clinical trials
• We need ways to specify and validate constraints

4
Validation Applications

• Validate the conformance of a DICOM object with
  respect to
• The DICOM standard (www.dvtk.org)
• An institutional guideline
• A jurisdictional requirement
• A DICOM application

5
Formal Language Representation of Constraints

• Formal language representation
• Unambiguously specify constraints
• Unambiguously exchange constraints
• Object can be validated at the site of
  origination
• Stand-alone validation services
• Computer interpretable formal syntax

6
XML Encoding of Constraints

• Use an XML document to specify predicates to
  evaluate against a DICOM object
• Easy to exchange
• Constraint can be managed, enhanced,
  version-controlled
• Good readability
• Wide range of tools
• Using XML schema to validate syntax

7
Constraint Design
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Sample Constraint, 1

• (1) SOPCommonModule
• (1.0) / Based on P3.3 2007 table C.12-1
  /
• (1.1)           ( type1(00080016)
• (1.2)           AND
• (1.3)           type1(00080018) )
• (1.4)           when false log (SOP common
  module validation failed)
• (1.5)           when false error
  (Validation error missing mandatory attribute
  for SOP common module)

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XML Mapping, 1

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCONFORMANCE_CONSTRAINT_DEFINITION
  xmlns"http//xmlns.oracle.com/ord/dicom/constrain
  t" xmlnsdt"http//xmlns.oracle.com/ord/dicom/dat
  atype" xmlnsxsi"http//www.w3.org/2001/XMLSchema
  -instance" xsischemaLocation"http//xmlns.oracle
  .com/ord/dicom/constraint http//xmlns.oracle.com/
  ord/dicom/constraint"gt lt!-- line (0) --gt
• ltGLOBAL_RULE name"SOPCommonModule"gt lt!-- line
  (1) --gt
• ltDESCRIPTIONgtBased on P3.3 2007 table
  C.12-1lt/DESCRIPTIONgt lt!-- line (1.0) --gt
• lt!-- line (1.2) The child predicates of a rule
  and implicitly combined with logical AND --gt
• ltPREDICATEgt lt!-- line (1.1) --gt
• ltBOOLEAN_FUNC operator"notEmpty"gt
• ltATTRIBUTE_TAGgt00080016lt/ATTRIBUTE_TAGgt
• lt/BOOLEAN_FUNCgt
• lt/PREDICATEgt
• ltPREDICATEgt lt!-- line (1.3) --gt
• ltBOOLEAN_FUNC operator"notEmpty"gt
• ltATTRIBUTE_TAGgt00080018lt/ATTRIBUTE_TAGgt
• lt/BOOLEAN_FUNCgt
• lt/PREDICATEgt
• ltACTION action"log" when"false"gt SOP common
  module validation failed lt/ACTIONgt lt!-- line
  (1.4) --gt
• ltACTION action"error" when"false"gtmissing
  mandatory attribute for SOP common
  modulelt/ACTIONgt lt!-- line (1.5) --gt
• lt/GLOBAL_RULEgt

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Sample Constraint, 2

• (2) CTImage
• (2.1)
• (2.1.1) ( (000800161.2.840.10008.5.1.
  4.1.1.2)
• (2.1.2) implies
• (2.1.3) (( type1(00080008) AND
  (00080008 IN AXIAL, LOCALIZER ) )
• (2.2) AND
• (2.2.1) (000800161.2.840.10008.5.1.
  4.1.1.2)
• (2.2.2) implies
• (2.2.3) ( type1(00280002) AND
  (00280002 1 ))
• (2.3) AND SOPCommonModule)
• (2.4) when false warning(Validation
  warning not a valid CT image)

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XML Mapping, 2

• ltGLOBAL_RULE name"ctImage"gt lt!-- line (2) --gt
• ltPREDICATEgt lt!-- line (2.1.2) --gt
• ltLOGICAL operator"derive"gt
• ltPREDICATEgt lt!-- line (2.1.1) --gt
• ltRELATIONAL operator"eq"gt
• ltATTRIBUTE_TAGgt00080016lt/ATTRIBUTE_TAGgt
• ltSTRING_VALUEgt1.2.840.10008.5.1.4.1.1.2lt
  /STRING_VALUEgt
• lt/RELATIONALgt lt/PREDICATEgt
• ltPREDICATEgtlt!-- line (2.1.3) --gt
• ltLOGICAL operator"and"gt
• ltPREDICATEgt
• ltBOOLEAN_FUNC operator"notEmpty"gt
• ltATTRIBUTE_TAGgt00080008lt/ATTRIBUT
  E_TAGgt
• lt/BOOLEAN_FUNCgt lt/PREDICATEgt
• ltPREDICATEgt
• ltRELATIONAL operator"in"gt
• ltATTRIBUTE_TAGgt00080008lt/ATTRIBUTE_TA
  Ggt
• lt CODE_STRINGgtAXIALlt/ CODE_STRINGgt
• ltCODE_STRINGgtLOCALIZERlt/
  CODE_STRINGgt

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Sample Constraint, 3

• Context Sensitive Structure
• The value of an attribute determines the
  structure of a DICOM object
• Common in DICOM structured report
• Example Table C.17-4 SR document content module
  attributes, PS 3.3 2007,
• Can be broken down to attribute level predicates
• (value(0040A040)TEXT ? notNULL(0040A160))

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Validation Flow
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Implementation

• System implemented with PL/SQL, Java and C
• Part of Oracle database 11gR1
• Data model manages user-defined constraints
• Changes to constraints does not interrupt
  database services
• Can batch-validate DICOM content stored in or
  managed by a database

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Quality Assurance (QA)

• Validation of DICOM content
• By the capturing device
• At the PACS protocol layer
• Within an image archive
• At enterprise data exchange gateway
• As a quality assurance service component of any
  service oriented architecture
• Prevent application errors
• Avoid costly rescan of patients
• Eliminate waste in computation and network
  bandwidth

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Using the QA Components

• Distributed QA agent
• Enable nation-wide radiation safety monitoring

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Experiment Setup

• A clinical trial requires images contain all
  DICOM image related tags for an image processing
  application
• Verify part-10 file header exist
• Verify all general image module tags exist
• Image size (row/column) fell within the required
  range
• Pixel data exist and is either not compressed or
  compressed with a compatible codec

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Experiment Result

• 15413 sample images collected from clinical trial
  sites
• 121 of them failed validation.
• All images passed validation can be analyzed by
  the image processing software

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Conformance-aware Data Set

• The same DICOM object can be verified by
  different QA requirements
• Passed CT content validation
• Failed CT CAD application validation
• DICOM object and data flow can be associated with
  conformance results

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Conformance-aware Dataflow
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Summary

• Formal language representation of DICOM
  constraint
• XML encoding of constraint document
• User-defined constraints
• Conformance-aware data flow