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Towards Clinically-relevant Standardization of Image Quality

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Presentation on theme: "Towards Clinically-relevant Standardization of Image Quality"— Presentation transcript:

1 Towards Clinically-relevant Standardization of Image Quality
Ehsan Samei, Duke University Alan Rowberg, University of Washington Ellie Avraham, Eastman Kodak Company Craig Cornelius, Eastman Kodak Company 22-Sept-2003

2 Objectives Describe current medical image quality and consistency performance efforts Identify limitations in existing standards Outline 3 specific proposals: Add new image quality factors to standards Update DICOM IQ performance services Research technical-clinical connection 22-Sept-2003

3 DICOM Image Consistency Efforts
Three DICOM initiatives ( ): Grayscale Standard Display Function (GSDF) Presentation LUT (P-LUT) Grayscale Softcopy Presentation State (GSPS) And in actual practice… Are widely & effectively implemented Via IHE Consistent Presentation of Images solution: Promoted conformance testing Demonstrated inter-vendor consistency 22-Sept-2003

4 DICOM GSDF: Barten Curve
L2 ~150 cd/m2 J2 Absolute luminance increment L1 << L2 L1 ~3 cd/m2 J1 Number of perceptual levels J1 = J2 22-Sept-2003

5 AAPM Task Group 18 Efforts
Team of academic, clinical, and industry contributors “Assessment of Display Performance for Medical Imaging Systems” (2002): Practical guidelines for qualitative & quantitative display assessment Includes all key aspects of display performance Defines IQ test patterns and procedures Recommends specific IQ acceptance criteria 22-Sept-2003

6 Standardization gaps DICOM GSDF: AAPM TG18 report: Pros: Pros:
Mathematical definition based on Human Visual System model Limitations: Tonescale consistency only: no other IQ factors No acceptance criteria / conformance procedures Only for grayscale images No Display Device Services (Capabilities) AAPM TG18 report: Pros: Provides Professional recommendations Covers all key display performance aspects Acceptance Criteria Quantitative measures Limitations: Only guidelines Not a “standard” 22-Sept-2003

7 The technical-clinical gap:
The connection between quantifiable IQ metrics & clinical performance is unknown: Luminance: deviations from GSDF, number of gray levels displayed Spatial: resolution, noise, geometric distortion Chromaticity variations Environmental: ambient light, glare, reflection, Amount of acceptable variation is unknown 22-Sept-2003

8 3 proposals to bridge the gaps:
Extend DICOM standard beyond luminance response Add and update DICOM Service Classes for image quality / performance Promote research on clinical - technical image quality relationship 22-Sept-2003

9 1. Display Image Quality (DIQ) Initiative
Add measurable and quantifiable elements of AAPM display performance procedures Include testing methodologies & defined limits for clinical / diagnostic performance Quantify visual performance using Simple test images Specific observer protocols Relative acceptance indicators For both softcopy and hardcopy presentation 22-Sept-2003

10 DIQ Softcopy Examples Quantify % deviation from GSDF curve
Define criteria for min & max luminance Define visual luminance evaluation Evaluate specific image quality factors: Ambient light limits: specular and diffuse Spatial resolution with TG18-QC/CX Check geometric distortion with TG18-QC 22-Sept-2003

11 Contrast response comparison
GSDF contrast +/- 10% Non-standardized display contrast 22-Sept-2003

12 AAPM TG18 Patterns TG18-MP: bit-depth / continuous grayscale
TG18-CT:contrast / luminance response 22-Sept-2003

13 Comprehensive TG18-QC The comprehensive TG18-QC test pattern for evaluation of key display characteristics: Resolution Luminance Geometric distortion 22-Sept-2003

14 Other DIQ Extensions Hardcopy quality metrics: Color extensions:
Media & printer quality (e.g., visible coating variations, distortions, artifacts) GSDF compliance, # of JNDs theory vs. actual Printable matrix size Spatial frequency response fidelity Color extensions: Standardize for grayscale areas of color images Add descriptions for color image characterization Color display and print device calibration 22-Sept-2003

15 2. DICOM Service Extensions
Add Display Performance Service Class Query image quality / performance information Control / configure manageable settings Include new IQ factors, e.g., MTF, ambient, … Extend Printer Configuration Retrieval Service Class Include access to additional IQ factors Note: Measurables include both human-evaluated and automatically-measured values 22-Sept-2003

16 Use cases: Standardizing Output
Printing application Retrieves matrix size and MTF of film printer Determines type of magnification, if any, to be applied to the image for smallest artifact Display Performance Service Class User Requests the luminance characteristic curve from its workstation’s display system Determines if the display is standardized If needed, computes an internal image tonescale correction, producing GSDF standardized result 22-Sept-2003

17 Real device  standardized performance
300.00 250.00 Target GSDF 200.00 Actual device 150.00 Luminance Desired output 100.00 Modified Input 345 50.00 Original Input 443 0.00 100 200 300 400 500 600 700 Digital Value 22-Sept-2003

18 Use Case: Quality Control Management
Centralized management application: Queries devices for calibration date, luminance characteristics, ambient light settings, etc. Records the results in a central database Creates maintenance lists for displays and printers Reporting application uses database for: Regulatory and management reports Stability and lifetime statistics on displays to support replacement schedules and budgets 22-Sept-2003

19 Network-wide Quality Control
Diagnostic display S ummary data Administrator’s Summary data Film Printer Characteristic curve, MTF, other performance measures Request Response Characteristic curve, MTF, other performance measures Web - based displays Modality Capture console Clinical display Reflective Hardcopy C linical display Regulatory Reports Performance & Lifetime Statistics 22-Sept-2003

20 More use cases… Consultation: Capture Consoles:
Maximize perceptual similarity to ensure “What I see is what you will get!” Display performance information gives confidence Capture Consoles: “The technologist sees what the doctor will get.” Reduce errors, retakes, miscommunication Extend quality control program to consoles 22-Sept-2003

21 What the Radiologist Displays: What the Reviewing Physician Sees:
Consistent Presentation of Images On a Calibrated Display Area Of Interest Annotate Zoom Area Of Interest With Presentation State Flip The Radiologist’s Transformations Are Saved Original Image Inconsistent Presentation On an Uncalibrated Display Window Level Original Image Original Image Original Image The Radiologist’s Transformations Are Lost 22-Sept-2003

22 3. Clinical Significant of IQ Measures
Hmm… We assume there is a connection… What deviations matter, and how much? Physical metrics Clinical performance 22-Sept-2003

23 Clinical impact: unknown
Rendered with DICOM GSDF Not rendered with DICOM GSDF 22-Sept-2003

24 Goals of proposed research:
Determine the clinical consequence of variations in image quality metrics (e.g., GSDF conformance, MTF, noise, …) Define what constitutes image quality from a diagnostic perspective Incorporate results into new joint standards that will utilize standardized test patterns, procedures, and clinical use cases 22-Sept-2003

25 Suggested research approach
Form inter-society committee to: Design specific research projects Obtains & review data sets Solicit & encourage active participation by researchers: radiologists, scientists, … Arrange reporting of results Define recommendations to standards and professional groups Sample research: Obtain images from 3 radiographic modalities Present images, simulating nonstandard display behavior Run observer performance experiments at major professional meetings and events Analyze by ROC methods 22-Sept-2003

26 Conclusions Existing standards are insufficient to assure consistent, high quality medical image output. Steps are proposed to further the reach and impact of DICOM toward quality medicine. New directions will provide benefits for PACS users, administrators, vendors, and patients. 22-Sept-2003

27 Contact Information Ehsan Samei, Duke University Alan Rowberg, M.D., University of Washington, Ellie Avraham, Eastman Kodak Company, Craig Cornelius, Eastman Kodak Company, AAPM Task Group 18 web site: 22-Sept-2003

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