Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006
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Ultrasonography of the Eye and Orbit
Authors
Front Matter
Preface
Dedication
Acknowledgments
1 - Physics of Ultrasound
2 - Ultrasonic Systems
3 - Ocular Diagnosis
4 - Very High Frequency Digital Ultrasound Scanning in LASIK and Phakic Intraocular Lenses 5 - Orbital Diagnosis
Appendices
Color Plates
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Front of Book > Authors
Authors
D. Jackson Coleman MD, FACS
The John Milton McLean Professor of Ophthalmology
Director, Margaret M. Dyson Vision
Research Institute
Chairman, Department of Ophthalmology
Weill Medical College of Cornell University
New York Presbyterian Hospital
Senior Research Physician
Riverside Research Institute
New York, New York
Ronald H. Silverman PhD
Professor of Computer Science in Ophthalmology
Research Director, Bioacoustic Research Facility
Margaret M. Dyson Vision Research Institute
Department of Ophthalmology
Weill Medical College of Cornell University
Member of Research Staff
Biomedical Engineering Directorate
Riverside Research Institute
New York, New York
Frederic L. Lizzi EngScD*
Research Director
Biomedical Engineering Directorate
Riverside Research Institute
Adjunct Professor of Ophthalmic Physics in
Ophthalmology
Weill Medical College of Cornell University
New York, New York
*Deceased
Harriet Lloyd MS
Research Associate in Ophthalmology
Department of Ophthalmology
Weill Medical College of Cornell University
New York, New York
Mark J. Rondeau
Research Associate in Ophthalmology
Associate Director, Bioacoustic Research Facility
Margaret M. Dyson Vision Research Institute
Department of Ophthalmology
Weill Medical College of Cornell University
New York, New York
Dan Z. Reinstein MD, FRCSC, DABO
Clinical Assistant Professor of Ophthalmology
Department of Ophthalmology
Weill Medical College of Cornell University
New York, New York
Medical Director
London Vision Clinic
London, UK
Suzanne W. Daly BSN, RDMS, CRNO
Senior Lecturer in Ophthalmology
Department of Ophthalmology
Weill Medical College of Cornell University
New York, New York
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CONTRIBUTORS FOR DVD
Walter Cronkite
Introduction
C. P. Wilkinson MD
Professor and Chairman
Department of Ophthalmology Greater Baltimore Medical Center
Vitreous Hemorrhage
Mario Stirpe MD
GB Bietti Eye Foundation
Subhyaloid Hemorrhage
Mark Blumenkranz MD
Professor and Chairman
Department of Ophthalmology Stanford University
Vitreous Membrane
George Blankenship MD
Vitreo-retinal Surgeon Hershey, PA
Retinal Detachment
Charles Pavlin MD
Professor
University of Toronto
Endophthalmitis
Donald J. D'Amico MD
Professor of Ophthalmology
Director of Diabetic Retinopathy Unit Harvard Medical School
Retinal Detachment
Stanley Chang MD
Edward S. Harkness Professor of Ophthalmology Chairman of the Department of Ophthalmology Columbia Presbyterian Medical Center
Residual Perfluorocarbon Bubbles
Evangelos Gragoudas MD
Director of Retina Service Massachusetts Eye and Ear Infirmary
Choroidal Melanoma
H. Culver Boldt MD
Department of Ophthalmology and Visual Sciences University of Iowa
Ocular Melanoma
Thomas C. Lee MD
Associate Professor of Ophthalmology Weill Medical College of Cornell University
Subretinal Hemorrhage
Yale Fisher MD
Director of the Surgical Retinal Service Manhattan Eye, Ear & Throat Hospital
Orbital Cyst
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Front of Book > Front Matter
Front Matter
Four things come not back: the spoken word, the spent arrow, time past, the neglected opportunity.
Omar Ibn Al-Halif
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Front of Book > Preface
Preface
It has been nearly a score and 10 years since we prepared the first edition of this book. These past 30 years have seen the development of power spectrum analysis, 3-D scans, very high frequency or UBM, arc scans, wavelets, Doppler and digital processing, and swept scans. On the horizon are contrast agents, and linear and phased transducer arrays as well as computational power that will further facilitate ultrasonic diagnosis of the eye. The past is merely an adumbration of future developments.
We are saddened that our long-time friend and colleague, Fred Lizzi, is no longer with us and will not join us in the next edition. It is possible, however, that the physics will not change and that Chapter 1 might remain the same. In any event, treasure this chapter. He was a genius, with humor and insight.
Our ultrasound group here at Weill Cornell has worked together for a generation—researching, collecting data, and trying to improve the diagnostic millieux. In this second edition, we have retained the introduction of basic physical principles, which remains unchanged, but have attempted to illuminate the technological advances that provide improved definition, resolution, and diagnostic capability to ultrasound imaging. We have not attempted, as we did in the first edition, to provide complete references of all ophthalmic ultrasound publications. Instead, we acknowledge the work of many other investigators. Ultrasound is clearly an established and vital part of the ophthalmic diagnostic armamentarium. In the ocular diagnosis section, we have stressed the advantages of multi-frequency and digital processing techniques. In the orbital section, we have stressed the complementary nature of ultrasound and other imaging modalities, such as computed tomography and magnetic resonance, as these imaging techniques have also improved.
We have added a DVD to this edition to stress the real-time nature of ultrasound diagnosis, and have asked outstanding surgeon colleagues to describe some of the features best seen in real time.
We thank the National Institutes of Health for supporting our research, The Dyson Foundation, the St. Giles Foundation, the Whitaker Foundation, and Research to Prevent Blindness for their trust and support.
And above all—we thank our families for letting us work for love….
D. Jackson Coleman
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Front of Book > Dedication
Dedication
This book is dedicated to
Frederic L. Lizzi, EngScD 1942-2005
Our treasured colleague for 38 years. A brilliant biophysicist, innovator, and researcher. He played a major role in our ultrasound research and will be sorely missed.
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Front of Book > Acknowledgments
Acknowledgments
We are grateful to numerous colleagues for their referral of patients and for allowing us to reprint some of their images, such as the foreign bodies of unusual character.
Harriet Lloyd deserves very special thanks for her research skills and particularly for her help in writing, as well as editing and preparing the entire manuscript. We thank Sue Daly for her hours of scan time and recovery of patient data.
We thank George Simoni, BSEE, who has provided innumerable hours of engineering expertise and many innovative and critical ideas for our research. We thank our colleagues at Riverside Research Institute for their help with our research and the inestimable resource their Biomedical Staff provide. We would like to thank the many medical students, residents, and fellows who have provided enthusiasm that keeps our work exciting.
We would like to thank Lisa Kairis and Jonathan Pine of Lippincott Williams & Wilkins, and Rebecca Dodson and Bridget Nelson of Schawk Publishing Solutions, whose skill, assistance, and encouragement have brought this book to publication.
Authors: Coleman, D. Jackson; Silverman, Ronald H.; Lizzi, Frederic L.; Lloyd, Harriet; Rondeau, Mark J.; Reinstein, Dan Z.; Daly, Suzanne W. Title: Ultrasonography of the Eye and Orbit, 2nd Edition
Copyright ©2006 Lippincott Williams & Wilkins
> Table of Contents > 1 - Physics of Ultrasound
1
Physics of Ultrasound
Since its first ocular application (1) in 1956, ultrasound has had a broad impact on the practice of ophthalmology. It is now a standard clinical modality for measuring ocular dimensions, diagnosing and monitoring ocular diseases, and providing information regarding orbital diseases. Modern ultrasound systems provide real-time, highly detailed images of ocular structures in a rapid, noninvasive manner, posing no significant threat of tissue damage. Ultrasonic biometry quantifies ocular dimensions needed to plan and evaluate sight restoration and improvement by intraocular lens implants and corneal surgery. Real-time ultrasound images, unaffected by optical opacities, have significantly advanced the diagnosis and management of virtually all ocular diseases and abnormalities. Ultrasonic imaging of orbital disease and blood-flow patterns complements data obtained by other imaging modalities, such as magnetic resonance imaging (MRI).
The effective use of ophthalmic ultrasound requires a basic knowledge of its physical nature and the phenomena associated with its propagation and scattering. This understanding is important for proper interpretation of clinical results and avoidance of misleading artifacts that can arise in ocular examinations. It is also important for evaluating emerging techniques that promise to extend the scope of ultrasonic examinations in the future as well as to best use other techniques for complementary diagnostic value.
Ultrasound is an acoustic wave comprising compressions and rarefactions that propagate within fluid and solid substances (2, 3, 4). By definition, ultrasonic waves exhibit frequencies above 20 kHz,1 and they differ from sound waves because these high frequencies render them inaudible. Because it is a wave, ultrasound can be directed, focused, and reflected according to the same general principles that govern these phenomena with other waves, such as light. The high frequencies (typically 10 MHz) and small wavelengths (e.g., 150 µm) available with ultrasound can provide the detailed resolution required for ocular examinations. Newer techniques use even higher frequencies (e.g., 50 MHz) to obtain wavelengths near 30 µm for very fine resolution within the anterior chamber (5,6).
Ultrasonic examinations of soft tissues use reflective (“pulse-echo”) systems analogous to those used in radar and sonar. This approach allows examination within a thin “slice” through tissue structures. A piezoelectric transducer serves as the ultrasonic transmitter and receiver. It generates a short burst of ultrasonic energy that propagates through the eye and undergoes partial reflection at tissue boundaries that exhibit abrupt changes in mechanical properties, including density and rigidity. These reflections, or echoes, return to the transducer where they are electronically detected. A-mode, or A-scan, systems graphically display these echoes as a function of time on a video monitor. B-mode systems generate cross-sectional gray-scale images (the gray scale corresponds to the A-scan amplitude) by scanning the transducer to address a series of lines through the eye; the amplitudes of received echoes control the brightness (or gray scale) along corresponding lines of a video image (B-scan). The terms A-scan and B-scan as well as C-scan and M-scan derive from early radar terms, using pulse position indicator (PPI) display.
Subsequent chapters describe how these A- and B-mode results are interpreted for diagnostic purposes. Proper interpretation requires an understanding of how A- and B-mode signals are related to underlying tissue properties and how they are affected by the characteristics of the ultrasonic system and transducer. The principles involved with ultrasonic imaging differ from those encountered with other imaging modalities. Computed
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tomography (CT) measures the partial absorption of xradiation transmitted through the body, and MRI senses molecular phenomena elicited within tissue. Optical coherence tomography (OCT) senses light that is backscattered by local changes in optical refractive indices rather than mechanical properties (7). OCT can produce high-resolution cross-sectional images of ocular tissues, such as the retina, but, as with other optical techniques, its depth of penetration is limited by optically opaque media, such as the sclera and intravitreal substances.
The physical principles of ultrasonic imaging are reviewed in this chapter, which describes how ultrasound is generated and detected, how it is reflected and absorbed in tissue, and how various factors influence the resolution that can be achieved in examining the eye and orbit. (References 2, 3, 4 are comprehensive texts treating the physics of ultrasound.)
GENERATION AND DETECTION OF ULTRASOUND
The key element in any ultrasonic system is a piezoelectric transducer, which is used to generate an ultrasonic wave from an applied voltage signal and to detect ultrasonic echoes returning from within the eye. A typical transducer unit (Figure 1.1) consists of a thin disk of piezoelectric material, such as lead zirconate titanate (PZT), a backing section, and an acoustic lens, which focuses the generated ultrasonic beam. The entire unit is commonly referred to as the transducer, although this term applies most correctly to only the piezoelectric element; common usage is adopted in this text. In most clinical systems, the transducer is coated with a thin layer of coupling gel and held in contact with the globe or lid. The gel affords a transmission path for ultrasound, which is rapidly absorbed in air. Coupling can also be provided by fluid solutions confined in small chambers or surgical drape.
Generation and detection of ultrasound take place in the piezoelectric material. The molecular configuration of a simple piezoelectric crystal is shown schematically in Figure 1.2. The molecules exhibit net charge polarizations that are forced into alignment by the crystalline structure so that effective positive charge centers are oriented along the same direction. In the transmission mode, an ultrasonic pulse is generated by applying a voltage pulse across external electrodes plated on the crystal surfaces. The molecules tend to stretch or contract, depending on whether the voltage polarity causes attraction or repulsion of the charge centers. These molecular effects alter the overall crystal thickness in proportion to the amplitude of the applied voltage. When the polarity of the applied voltage is rapidly varied, the crystal executes corresponding rapid expansions and contractions, which constitute ultrasonic vibrations.
Figure 1.1. Cutaway view of transducer.
In the receive mode, the crystal is compressed and expanded by an impinging ultrasonic echo pulse; the concomitant changes in molecular charge separation induce an output voltage whose amplitude and waveform depend upon the echo pulse. The voltage is readily measured as a function of time, enabling ultrasonic echoes to be detected as they return from the eye.
In the past, piezoelectric transducers were often fabricated from precisely oriented cuts of quartz crystals, which require large excitation voltages. Now, most transducers are fabricated from more sensitive materials, including lithium sulfate, ceramics (such as PZT), composite materials, and, for high frequencies, polyvinylidene fluoride (PVDF) membranes (8). Modern transducer materials can detect small ultrasonic signals, containing only microwatts of power. Some of these materials must be “poled” before they can be used in transducers. In this process, piezoelectric domains are brought into alignment by applying large, constant voltages at elevated temperatures. Once this alignment is achieved, these materials can generate and detect ultrasound in the manner described previously.
A piezoelectric transducer responds most actively to voltage signals and ultrasonic pulses that have frequencies near its resonant frequency. This frequency is determined by the material's thickness, increasing as it is made thinner. Resonance effects can lead to prolonged series of ultrasonic vibrations, which are suppressed by using backing sections to achieve high resolution, as discussed in a subsequent section.
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Figure 1.2. Schematic representations of molecular configuration in a piezoelectric material illustrating
contraction induced by an applied voltage.
PROPAGATION OF ULTRASOUND
When a piezoelectric transducer is immersed in a fluid and electrically excited, its thickness vibrations generate an ultrasonic wave of compression and rarefaction that propagates through the fluid. These waves, termed longitudinal or compressional ultrasonic waves, are the type used for tissue visualization. They propagate through soft tissues in the same manner as they propagate through fluids.