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22-Sept-20031 Towards Clinically-relevant Standardization of Image Quality Ehsan Samei, Duke University Alan Rowberg, University of Washington Ellie Avraham,

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Presentation on theme: "22-Sept-20031 Towards Clinically-relevant Standardization of Image Quality Ehsan Samei, Duke University Alan Rowberg, University of Washington Ellie Avraham,"— Presentation transcript:

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2 22-Sept 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

3 22-Sept 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

4 22-Sept 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

5 22-Sept DICOM GSDF: Barten Curve J1 J2 L1 ~3 cd / m 2 L2 ~ 150 cd/ m 2 Number of perceptual levels J1 = J2 Absolute luminance increment L1 << L2

6 22-Sept 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

7 22-Sept Standardization gaps DICOM GSDF: –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”

8 22-Sept 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

9 22-Sept proposals to bridge the gaps: 1.Extend DICOM standard beyond luminance response 2.Add and update DICOM Service Classes for image quality / performance 3.Promote research on clinical - technical image quality relationship

10 22-Sept 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

11 22-Sept 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

12 22-Sept Contrast response comparison Non-standardized display contrast GSDF contrast +/- 10%

13 22-Sept TG18-MP: bit-depth / continuous grayscale TG18-CT:contrast / luminance response AAPM TG18 Patterns

14 22-Sept The comprehensive TG18-QC test pattern for evaluation of key display characteristics: Resolution Luminance Geometric distortion Comprehensive TG18-QC

15 22-Sept Other DIQ Extensions Hardcopy quality metrics: –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

16 22-Sept 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

17 22-Sept 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

18 22-Sept Digital Value Luminance Target GSDF Actual device Desired output Original Input 443 Modified Input 345 Real device  standardized performance

19 22-Sept 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

20 22-Sept Request Film Printer Film Printer Diagnostic display Response Characteristic curve, MTF, other performance measures Summary data Administrator’s Characteristic curve, MTF, other performance measures Summary data Network-wide Quality Control Regulatory Reports Performance & Lifetime Statistics

21 22-Sept More use cases… Consultation: –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 22-Sept What the Radiologist Displays: What the Reviewing Physician Sees: The Radiologist’s Transformations Are Saved With Presentation State Original ImageWindow LevelFlip Zoom Area Of Interest Annotate Area Of Interest The Radiologist’s Transformations Are Lost Original Image Image Original Image Original Image Consistent Presentation of Images On a Calibrated Display Inconsistent Presentation On an Uncalibrated Display

23 22-Sept Clinical Significant of IQ Measures Hmm… Physical metrics We assume there is a connection… What deviations matter, and how much? Clinical performance

24 22-Sept Rendered with DICOM GSDFNot rendered with DICOM GSDF Clinical impact: unknown

25 22-Sept 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

26 22-Sept Suggested research approach Sample research: 1.Obtain images from 3 radiographic modalities 2.Present images, simulating nonstandard display behavior 3.Run observer performance experiments at major professional meetings and events 4.Analyze by ROC methods Form inter-society committee to: 1.Design specific research projects 2.Obtains & review data sets 3.Solicit & encourage active participation by researchers: radiologists, scientists, … 4.Arrange reporting of results 5.Define recommendations to standards and professional groups

27 22-Sept 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.

28 22-Sept 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:


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