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Spie Press Book

High-Fidelity Medical Imaging Displays
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Book Description

This tutorial, based on a short course presented at the SPIE Medical Imaging Symposium, explains performance and quality considerations in medical imaging displays. After defining performance requirements for high-fidelity displays, the book introduces the display technologies (CRT, AMLCD) that are or likely will be used in medical imaging workstations, including an emerging technology (OLED) that may enable the design of portable display devices. The book concludes with methods to assess image quality. Although not a collection of step-by-step procedures, this book can be used in a clinical environment by those with access to the appropriate instrumentation.

Book Details

Date Published: 2 September 2004
Pages: 174
ISBN: 9780819451910
Volume: TT63

Table of Contents
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List of Figures
List of Tables
Preface
Chapter 1 Introduction
1.1 Medical Imaging Display Markets
1.2 Units of Measure
Chapter 2 High-Fidelity Display Performance
2.1 Contrast Sensitivity
2.2 Luminance Response
2.3 Luminance Range
2.4 Adaptation
2.5 Retinal Anatomy and Visual Acuity
2.6 Veiling Glare
2.6.1 Glare in the human eye
2.6.2 Veiling glare in displays
2.6.2.1 Sources of glare
2.6.2.2 Effect of veiling glare
2.7 Ambient Light Reflections
2.7.1 Specular reflection
2.7.2 Diffuse reflection
2.8 High-Fidelity Display Requirements
Chapter 3 Cathode-Ray Tubes
3.1 Cathodes
3.2 Electron Optics
3.3 Emissive Structure
3.4 Signal Electronics
3.5 Color CRTs
3.6 Spot Size
3.7 Monochrome Phosphors
3.8 Antireflection Surface Treatments
3.9 Face-plate Absorption
3.10 Gray-scale Controllers
Chapter 4 Active-Matrix Liquid Crystal Displays
4.1 The Liquid Crystal Cell
4.2 Efficiency of Light Transmission
4.3 Addressing Methods
4.4 Elements of an AMLCD
4.5 Crosstalk in AMLCDs
4.6 Luminance Variations with Viewing Angle
4.7 Solutions to Viewing Angle Problem
4.7.1 Compensation foils
4.7.2 Multiple domain cells
4.7.3 Symmetry micro-cells
4.7.4 In-plane switching
4.7.5 Vertical alignment
Chapter 5 Active-Matrix Organic Light-Emitting Displays
5.1 Introduction to OLEDs
5.1.1 History of OLEDs
5.1.2 OLEDs for displays
5.1.3 OLED structures
5.1.4 EL organic materials
5.2 Evaluation of Device Opto-Electronic Performance
5.3 Device Configuration and Display Fabrication
5.3.1 Conventional OLED
5.3.2 Side-by-side subpixels
5.3.3 White OLED filtering
5.3.4 Blue OLED down-conversion
5.3.5 Microcavity OLEDs
5.3.6 Color-tunable OLEDs
5.3.7 Pyramid-shaped pixel OLEDs
5.3.8 Stacked OLEDs
5.4 OLED Stability and Encapsulation for Displays
5.4.1 Impact of moisture and oxygen
5.4.2 Influence of dark spots
5.4.3 Encapsulation methods
5.5 Display Addressing and Driving Circuit
5.5.1 PM-addressing method
5.5.2 AM-addressing method
5.6 TFT Technology for AM Displays
5.6.1 a-Si:H TFT technology
5.6.2 Poly-Si TFT Technology
5.6.3 Pixel electrode circuits
5.7 Methods to Improve AMOLED Contrast Ratio
5.8 Current Market and Future Trends
5.8.1 Comparison between OLED and non-LED displays
5.8.2 Comparison between OLEDs and inorganic LEDs
5.8.3 Current and future challenges
Chapter 6 Display Image Quality Metrics
6.1 Luminance Response
6.1.1 Luminance calibration
6.1.2 Angular emission
6.2 Contrast Ratio
6.2.1 Veiling glare
6.2.2 Electronic crosstalk
6.3 Spatial Frequency
6.4 Noise
6.5 Reflectance
6.5.1 Reflectance models
6.5.2 Measuring display reflections
6.5.3 Bidirectional reflection distribution function
6.6 Evaluation Software and Standards
References
Index

Preface

This book is based on a short course given by the authors at SPIE's Medical Imaging International Symposium from 1999 to 2002. During those years, the number of commercially available medical display systems increased considerably. For instance, during the 84th annual meeting of the Radiological Society of North America (RSNA) held in Chicago in 1998, three different liquid crystal prototypes were showcased on the commercial exhibit floor by just a few vendors. In the 88th RSNA meeting held in the same city in 2002, more than 20 different liquid crystal technologies in more than 100 models were present on the exhibit floor.

At the same time, we have witnessed a significant increase in the interest level of the community about display system performance and application requirements. We have also experienced an exciting feeling that this is just the beginning of a rapidly evolving story that will be nurtured by new technologies and new applications. The number of modalities that rely on the electronic presentation of image data is growing rapidly, including computed tomography, mammography, chest and bone radiography, ultrasound, and image-guided interventional procedures. Moreover, this growth has been emphasized by the availability of powerful computer networks that allow remote users to receive large image datasets and display them in their portable computers or personal digital appliances. This changing scenario also brings challenges regarding how these devices and systems are used, and about how physical measurements can be used to assess image quality. It is in this spirit that we present in this book the expanded content of the short course.

This book is organized into six chapters. Chapters 1 and 2 introduce medical imaging displays by defining the requirements for a high-fidelity display performance, and by summarizing human visual system characteristics with respect to luminance, contrast, resolution, glare, and reflection. Chapters 3 and 4 introduce the different display technologies that have, or are likely to have, an impact on medical imaging workstations today or in the future. Chapter 3 presents a review of the ubiquitous cathode-ray tube (CRT), and Chapter 4 describes the active-matrix liquid crystal display (AMLCD). Chapter 5 presents the current challenges in the development of an emerging display technology based on light-emitting organic molecules and polymer devices that will likely be present in many portable display solutions in the coming few years. Having described the requirements for a high-fidelity display and its intrinsic device properties, we develop, in Chapter 6, methods for the assessment of display image quality. In this chapter, we focus on methods that are useful to characterize display performance while allowing the measurement of image quality up to, and even beyond, the limits of the human visual system.

Most of the methods presented in this book are described in a way that clinical engineers and medical physicists can utilize them in a clinical environment as long as they have access to the appropriate instrumentation. This tutorial is not, however, a collection of ready-to-use procedures or techniques. Readers interested in more practical aspects of display quality assessment should consider the recommendations of the American Association of Physicists in Medicine (AAPM), or the collection of measurement methods assembled in the Flat Panel Display Measurement Standard. Our perspective in this book is to offer a more general tutorial on display image quality, its relationship to device technology, and the methodologies for its assessment. At the same time, the methods and techniques described will allow other readers who are involved in the design, manufacture, marketing, purchase, and management of displays for digital radiology systems to make informed judgments about display devices and display image quality by better understanding the device requirements and specifications.

Much of the effort in this book was supported by the Center for Devices and Radiological Health (CDRH) from the Food and Drug Administration (FDA), the National Institutes of Health (NIH), and the Defense Advanced Research Projects Agency (DARPA). I would like to express our thanks to the many reviewers of the manuscript in its various forms including Rachel Leimbach, Susan Hipper, Ben Imhoff, and Sarah Drilling - all student interns from the Department of Biomedical Engineering at Marquette University. We are also thankful for the useful discussions with Ehsan Samei (Duke University), Sandrine Martin (University of Michigan), Ken Compton (National Display Systems), Robert J. Jennings (CDRH, FDA), Robert M. Gagne (CDRH, FDA), Kyle J. Myers (CDRH, FDA), and Robert F. Wagner (CDRH, FDA) that have made this book better.

Aldo Badano July 2004


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