DICOM INTERNATIONAL DICOM INTERNATIONAL CONFERENCE & SEMINAR April 8-10, 2008 Chengdu, China Medical Image Quality Assurance with Automated Constraint Validation Dongbai Guo Architect and Senior Development Manager Oracle Corporation Nashua, NH 03062, USA

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

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

Validation Applications Validate the conformance of a DICOM object with respect to –The DICOM standard ( –An institutional guideline –A jurisdictional requirement –A DICOM application

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

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

Constraint Design

Sample Constraint, 1 (1) SOPCommonModule::= (1.0) /* Based on P table C.12-1 */ (1.1) ( type1( ) (1.2) AND (1.3) type1( ) ) (1.4) when false log (“SOP common module validation failed”); (1.5) when false error (“Validation error: missing mandatory attribute for SOP common module”);

XML Mapping, 1 Based on P table C SOP common module validation failed missing mandatory attribute for SOP common module

Sample Constraint, 2 (2) CTImage ::= (2.1) (2.1.1) ( ( ==” ”) (2.1.2) implies (2.1.3) (( type1( ) AND ( IN {“AXIAL”, “LOCALIZER”} ) ) (2.2) AND (2.2.1) ( ==” ”) (2.2.2) implies (2.2.3) ( type1( ) AND ( ==’1’ )) (2.3) AND SOPCommonModule) (2.4) when false warning(“Validation warning: not a valid CT image”);

XML Mapping, AXIAL LOCALIZER

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))

Validation Flow

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

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

Using the QA Components Distributed QA agent –Enable nation-wide radiation safety monitoring

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

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

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

Conformance-aware Dataflow

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