Ebook Point of care - Ultrasound: Part 1

(BQ) Part 1 book Pocket protocols for ultrasound presents the following contents: Evolution of point-of-care ultrasound, ultrasound physics, transducers, orientation, basic operation of an ultrasound machine, imaging artifacts, overview, lung and pleural ultrasound technique, lung ultrasound interpretation,...

Trang 2

Point-of-Care Ultrasound

NILAM J SONI, MD

Associate Professor of Medicine

Division of Hospital Medicine

University of Texas Health Science Center

London Health Sciences Centre

London, Ontario, Canada

PIERRE KORY, MPA, MD

Fellowship Program Director

Division of Pulmonary, Critical Care, and Sleep Medicine

Mount Sinai Beth Israel Medical Center

Icahn School of Medicine at Mount Sinai

New York, New York

Trang 3

1600 John F Kennedy Blvd.

Ste 1800

Philadelphia, PA 19103-2899

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without per-mission in writing from the publisher Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein)

Notices

Knowledge and best practice in this field are constantly changing As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein In using such infor-mation or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility

With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications It is the responsibility of practitioners, relying on their own experience and knowl-edge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, neg-ligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas con-tained in the material herein

ISBN: 978-1-4557-7569-9

Senior Content Strategist: Maureen Iannuzzi

Content Development Specialist: Maria Holman

Publishing Services Manager: Patricia Tannian

Senior Project Manager: John Casey

Designer: Steven Stave

Printed in China

Last digit is the print number: 9 8 7 6 5 4 3 2 1

Trang 4

C O N T R I B U T O R S

Samuel Acquah, MD, FCCP

Assistant Professor

Director, Medical Intensive Care Unit

Division of Pulmonary, Critical Care, and

Sleep Medicine

New York, New York

San Antonio, Texas

Phillip Andrus, MD, FACEP, RDMS

Assistant Professor of Emergency Medicine

Division of Emergency Ultrasound

New York, New York

Robert Arntfield, MD, FRCPC, FCCP, RDMS

Assistant Professor

Division of Emergency Medicine and

Division of Critical Care Medicine

Western University

Michel Boivin, MD

Associate Professor

Sleep Medicine

University of New Mexico

Albuquerque, New Mexico

Pedro Campos, MD

Director, Emergency Ultrasound

Sutter Medical Center of Santa Rosa

Clinical Instructor

University of California, San Francisco

San Francisco, California

Carolina Candotti, MD

Assistant Professor

Penn State Hershey Medical Center

Hershey, Pennsylvania

Anita Cave, MD, FRCPC

Assistant ProfessorDepartment of Anesthesia and Perioperative Medicine

London Health Sciences CentreLondon, Ontario, Canada

Gregg L Chesney, MD

Fellow, Critical Care MedicineDivision of Pulmonary and Critical Care Medicine

Stanford University School of MedicineStanford Hospital and Clinics

Stanford, California

Alan T Chiem, MD, MPH

Assistant Clinical ProfessorDirector, Emergency UltrasoundDepartment of Emergency MedicineUniversity of California, Los AngelesOlive View–UCLA Medical CenterLos Angeles, California

Christopher Dayton, MD

Fellow, Critical Care MedicineDivision of Critical Care MedicineAlbert Einstein College of MedicineMontefiore Medical CenterNew York, New York

Orlando Debesa, DO

Assistant Clinical Professor of MedicineDivision of Pulmonary and Critical Care Medicine

Virginia Commonwealth UniversityRichmond, Virginia

Eitan Dickman, MD, FACEP

Vice-Chair of AcademicsDirector, Division of Emergency Ultrasound

Department of Emergency MedicineMaimonides Medical CenterNew York, New York

Peter Doelken, MD

Associate Professor of MedicineAlbany Medical CollegeAlbany, New York

Trang 5

vi

Lewis A Eisen, MD

Associate Professor of Clinical Medicine

Assistant Professor of Clinical Neurology

Albert Einstein College of Medicine

Montefiore Medical Center

New York, New York

Daniel Fein, MD

Sleep Medicine

New York, New York

Stephanie Fish, MD

Associate Professor

Department of Medicine, Endocrine

Division

Memorial Sloan Kettering Cancer Center

New York, New York

Ricardo Franco, MD

Rush University Medical College

John H Stroger, Jr Hospital of Cook County

Emergency Medicine Consultant

Rotorua Hospital, Lakes District

Rotorua, New Zealand

Behzad Hassani, MD, CCFP (EM)

Assistant Professor

Division of Emergency Medicine

Ahmed F Hegazy, MD, FRCPC

Assistant Professor

Department of Anesthesia and Perioperative

Medicine

Western University

Patrick T Hook, MD, MS

Fellow, RheumatologyDepartment of RheumatologyBoston University School of MedicineBoston, Massachusetts

J Terrill Huggins, MD

Associate Professor of MedicineDivision of Pulmonary, Critical Care, Allergy, and Sleep Medicine

Medical University of South CarolinaCharleston, South Carolina

Adolfo Kaplan, MD, FCCP

PulmonologistMcAllen Health Sciences CenterMcAllen, Texas

Chan Kim, MD

Clinical InstructorDepartment of RheumatologyBoston University School of MedicineBoston, Massachusetts

Eugene Kissin, MD

Associate Professor of MedicineDepartment of RheumatologyBoston University School of MedicineBoston, Massachusetts

Pierre Kory, MPA, MD, MHS

Associate Professor of MedicineFellowship Program DirectorDivision of Pulmonary, Critical Care, and Sleep Medicine

Mount Sinai Beth Israel Medical CenterIcahn School of Medicine at Mount SinaiNew York, New York

Daniel Lakoff, MD

Associate Director, Emergency UltrasoundDepartment of Emergency MedicineIcahn School of Medicine at Mount SinaiNew York, New York

Trang 6

CONTRIBUTORS vii

Viera Lakticova, MD

Assistant Professor of Medicine

Director, Interventional Pulmonology

North Shore–Long Island Jewish Medical

Center

New Hyde Park, New York

Catherine Y Lau, MD

Assistant Clinical Professor of Medicine

Director, Neurological Surgery Patient

Safety and Quality

Department of Medicine

Alycia Lee, BS, RDCS, RVT

School of Medicine and Health Sciences

The George Washington University

Washington, DC

Peter M.J Lee, MD, MHS

Division of Pulmonary, Critical Care,

and Sleep Medicine

New York, New York

W Robert Leeper, MD, FRCSC

Trauma and Acute Care Surgery Fellow

Department of Surgery, Division of Acute

Care Surgery

Johns Hopkins University School of Medicine

Baltimore, Maryland

Shankar LeVine, MD

Alameda Health System

Highland General Hospital

Oakland, California

Ken Lyn-Kew, MD

Assistant Professor of Medicine

Division of Pulmonary Science and Critical

Department of Emergency Medicine

Alameda Health System

Highland General Hospital

Ottawa, Ontario, Canada

Paul K Mohabir, MD

Clinical Associate ProfessorDirector, Adult Cystic Fibrosis ProgramDivision of Pulmonary and Critical Care Medicine

Stanford University School of MedicineStanford, California

Arun Nagdev, MD

Director, Emergency UltrasoundAlameda Health SystemHighland General HospitalOakland, California

Mangala Narasimhan, DO, FCCP

Section Head, Critical Care MedicineAssociate Professor of MedicineNorth Shore–Long Island Jewish Medical Center

Paru Patrawalla, MD

Assistant Professor of MedicineDivision of Pulmonary, Critical Care, and Sleep Medicine

New York University School of MedicineNew York, New York

Daniel R Peterson, MD, PhD, FRCPC, RDMS

Clinical Assistant ProfessorAcademic Department of Emergency Medicine

University of CalgaryFoothills Medical CentreCalgary, Alberta, Canada

Nitin Puri, MD, FCCP

Assistant Professor of MedicineMedical Director, Cardiac Surgery Intensive Care Unit

Virginia Commonwealth UniversityInova Fairfax Hospital

Falls Church, Virginia

Shideh Shafie, MD

Department of Emergency MedicineMaimonides Medical CenterBrooklyn, New York

Trang 7

viii

Ariel L Shiloh, MD

Director, Critical Care Consult Service

Assistant Professor of Clinical Medicine and

Neurology

Division of Critical Care Medicine,

Albert Einstein College of Medicine

Jay B Langner Critical Care Service

Montefiore Medical Center

Bronx, New York

Michael Silverberg, MD

Sleep Medicine

New York, New York

Craig Sisson, MD, RDMS

Clinical Associate Professor

San Antonio

San Antonio, Texas

Diane Sliwka, MD

Associate Clinical Professor of Medicine

Director, Mt Zion Medical Service

Nilam J Soni, MD, FHM, FACP

San Antonio

San Antonio, Texas

Kirk T Spencer, MD, FASE

Christopher R Tainter, MD, RDMS

Fellow, Critical Care MedicineMassachusetts General HospitalHarvard Medical SchoolBoston, Massachusetts

Stefan Tchernodrinski, MD, MS

Division of Hospital MedicineJohn H Stroger, Jr Hospital of Cook CountyAssistant Professor of Medicine

Rush University Medical CollegeChicago, Illinois

Christopher Walker, MD

Fellow, Critical Care MedicineDivision of Pulmonary and Critical Care Medicine

Stanford University School of MedicineStanford, California

Ralph C Wang, MD

Associate Professor of Emergency MedicineDepartment of Emergency MedicineUniversity of California, San FranciscoSan Francisco, California

Michael Y Woo, MD, CCFP(EM), RDMS

Associate ProfessorDirector, Emergency Medicine UltrasoundProgram Director, Emergency Medicine Ultrasound Fellowship

Department of Emergency MedicineUniversity of Ottawa and The Ottawa Hospital

Ottawa, Ontario, Canada

Trang 8

This book is dedicated to all the compassionate and dedicated clinicians who strive to provide the best bedside care to their patients.

To those who inspire me — my parents, Jay and Niru, and

my children, Riya and Devak — and to the one whose sacrificial support makes it all possible, Perla

NS

To my parents, Peg and David, for their lifelong support,

my children, Amelia and John, for reminding me what is most important, and my wife, Shannon, for her boundless love and encouragement

RA

To my angels, Amy, Ella, Eve, and Violet, along with

my dear parents, Leslie and Odile, for their unwavering patience, support, and love

PK

Trang 9

Point-of-care ultrasound has been rapidly integrated into clinical practice in recent years, and its role in medicine will continue to expand in coming decades Point-of-care ultrasound has been shown to make procedures safer, expedite diagnoses, and raise confidence in clinical decision making In addition to these clinical benefits, point-of-care ultrasound is one of few technologies that brings providers closer to patients, putting them right at the bedside, raising the satisfaction

of providers and patients alike

This book is intended for providers of any healthcare discipline interested in learning about the principles and diverse applications of point-of-care ultrasound Covered in detail are specific point-of-care ultrasound applications that are most generalizable to healthcare providers from a broad spectrum of specialties and practice settings All chapters are based on the best available evidence supplemented by expert opinion

Nilam J Soni Robert Arntfield Pierre Kory

P R E F A C E

Trang 10

For contributing ultrasound images:

Danny Duque, MD, RDMS, FACEP

Assistant Professor

Elmhurst Hospital Center

New York, New York

Laleh Gharahbaghian, MD

Clinical Assistant Professor

Stanford University Medical Center

Alycia Paige Lee, BS, RDCS, RVT

School of Medicine and Health Sciences

The George Washington University

New York, New York

Bret P Nelson, MD, RDMS, FACEP

Associate Professor

Mt Sinai Hospital

New York, New York

Roya Etemad Rezai, MD, FRCPC

Associate Professor

Department of Diagnostic Radiology and

Nuclear Medicine

Western University

London Health Science Centre

Assistant Clinical Professor

University of California San Francisco

Drew Thompson, MD, FRCPC

Associate Professor

Western University

Brita E Zaia, MD, FACEP

Director, Emergency Department UltrasoundDepartment of Emergency MedicineKaiser Permanente San Francisco Medical Center

For developing original illustrations and photography:

Victoria Heim, CMI

Medical IllustratorLoganville, Georgia

Jade Myers

Graphic DesignerMatrix Art ServicesYork, Pennsylvania

Lester Rosebrock

PhotographerUniversity of Health Science Center San Antonio

San Antonio, Texas

Sam Newman

Medical AnimatorUniversity of Texas Health Science Center San Antonio

San Antonio, Texas

Gary White, PhD

Editor, The Physics Teacher

American Association of Physics TeachersAdjunct Professor of Physics

George Washington UniversityWashington, DC

A C K N O W L E D G M E N T S

Trang 11

Point-of-care ultrasound has revolutionized

the practice of medicine, influencing how care

is provided in nearly every medical and

surgi-cal specialty For more than a century, clinicians

had been limited to primitive bedside tools,

such as the reflex hammer (c 1888) and

stetho-scope (c 1816), but with bedside ultrasound,

providers are equipped with a tool that allows

them to actually see what they can only infer

through palpation or auscultation The

tech-nologic miniaturization of ultrasound devices

has outpaced integration of these devices into

clinical practice Many professional societies

and national organizations have recognized

the potent impact of point-of-care ultrasound

and have endorsed its routine use in clinical

practice In 2001 the American Medical

Asso-ciation stated, “Ultrasound has diverse

applica-tions and is used by a wide range of physicians

and disciplines Ultrasound imaging is within

the scope of practice of appropriately trained

physicians.”1 Thus, it has been well

recog-nized for over a decade that providers from

diverse specialties can and should be trained to

use ultrasound within their scope of practice This chapter reviews the major milestones in the history of medical ultrasound with a focus

on important considerations of point-of-care ultrasound

History

Acoustic properties of sound were well described

by ancient Greek and Roman civilizations In the twentieth century, the sinking of the Titanic followed by the start of World War I served as catalysts for the development of sonar, or sound navigation and ranging, which was the first real-world application of the principles of sound.2,3Although several physicians were simulta-neously competing for recognition as the first

to use ultrasound in medicine, Karl Theodore Dussik, an Austrian psychiatrist and neurolo-gist, is credited as being the first physician to use ultrasound in medical diagnostics when

he attempted to visualize cerebral ventricles and brain tumors using a primitive ultrasound device in 1942 (Figure 1.1)

During the 1940s and 1950s, many neers advanced the field of medical ultrasound

pio-K E Y P O I N T S

• Point-of-care ultrasound is defined as a goal-directed, bedside ultrasound examination performed by a healthcare provider to answer a specific diagnostic question or to guide performance of an invasive procedure

• Diagnostic ultrasound was first developed and used in medicine during the 1940s, but point-of-care ultrasound has been integrated into diverse areas of clinical practice since the early 1990s

• Important considerations when using point-of-care ultrasound include provider training and skill level, patient characteristics, and ultrasound equipment features

Trang 12

1—FUNDAMENTAL PRINCIPLES OF ULTRASOUND

4

John Julian Wild described various clinical

applications of ultrasound, including the

dif-ference in appearance of normal and cancerous

tissues Douglass Howry and Joseph Holmes

focused on ultrasound equipment

technol-ogy They built immersion-tank ultrasound

systems, including the “somascope” in 1954

(Figure 1.2), and they published the first

two-dimensional ultrasound images Ian Donald

contributed significant amounts of research

in obstetric and gynecologic ultrasound

Inge Edler and Carl Hellmuth Hertz gated cardiac ultrasound and established the field of echocardiography in the early 1950s Shigeo Satomura, a Japanese physician isolated from the pioneers in the United States and Europe, is credited as being the first physician

investi-to use Doppler ultrasound in his studies of diac valve motion.3

car-Advancements in ultrasound technology accelerated the field in the 1960s and 1970s Early ultrasound machines used open-shutter photography to capture screen images Multiple still images of moving structures were captured, sequentially displayed, and interpreted by try-ing to imagine the structures in motion In

1965, Siemens released the Vidoson, the first real-time ultrasound scanner, which was able to display 15 images per second The Vidoson was quickly incorporated into obstetric care over the next decade and became a standard component

of assessing pregnant women Sector scanning became possible with development of phased-array transducers in the early 1970s, giving rise

to echocardiography as an independent field.3Ultrasound technology continued to advance during the 1970s and 1980s with the development of more sophisticated transduc-ers along with refinements in image quality Following the “early adopters” of ultrasound, namely, radiology, cardiology, and obstetrics/gynecology, ultrasound began to be used in emergency care, a role that marked the begin-ning of the era of point-of-care ultrasound use

by healthcare providers from diverse medical specialties.3 Life-threatening conditions could

be assessed rapidly at the bedside with table ultrasound Frontline physicians, mostly surgeons and emergency medicine physicians, started assessing trauma patients with ultra-sound in the 1970s, and the term FAST exam,

por-or Focused Assessment with Sonography in Trauma, was coined in the early 1990s.4–6 The FAST exam was incorporated into Advanced Trauma Life Support (ATLS) guidelines in the late 1990s.7,8 From its early description in the 1970s in Europe to its incorporation into ATLS guidelines in the 1990s in the United States, the FAST exam established a precedent for development of point-of-care ultrasound applications and incorporation of these appli-cations into routine clinical practice

Since the 1990s, point-of-care ultrasound has become a part of nearly every specialty’s practice In addition to development of specific point-of-care ultrasound applications in the

Figure 1.1 Karl Theodore Dussik and the first

medical ultrasound device in 1946 (From

Frentzel-Beyme B Vom Echolot zur

Farbdopplersonogra-phie Der Radiologe April 2005;45(4):363–370.)

Figure 1.2 Immersion-tank ultrasound machine

from the 1950s (From Hagen-Ansert SL

Text-book of Diagnostic Sonography 7th ed., St Louis,

Mosby, 2011.)

Trang 13

1—EVOLUTION OF POINT-OF-CARE ULTRASOUND 5

1990s, such as the FAST exam, general

medi-cal ultrasound applications, broadly applicable

to many specialties, started to emerge In the

mid-1980s, ultrasound artifacts of the lung

and pleura—an organ long felt to have little

utility in ultrasound diagnostics—began to be

described The identification and codification

of these artifacts with discrete forms of lung

pathology was developed by Daniel

Lichten-stein, a French critical care physician, which

gave rise to the field of lung ultrasonography.9

Even though lung ultrasound was first used by

intensivists to evaluate critically ill patients,

lung ultrasound is broadly applicable to

eval-uate any patient with pulmonary symptoms,

is more accurate than chest x-ray, and can be

used by any healthcare provider, regardless of

specialty.10 Another broadly applicable use of

ultrasound that evolved was in the guidance of

invasive bedside procedures Multiple studies

since the 1990s have demonstrated reduced

mechanical complications when ultrasound is

used to guide common procedures, in

particu-lar central venous catheterization.11,12

Cur-rent guidelines recommend that all providers,

regardless of specialty, use ultrasound

guid-ance when placing internal jugular central

venous catheters

Ultrasound technology was well advanced

by the 2000s, which saw the development of

three-dimensional ultrasound for select

diag-nostic applications; however, two-dimensional

ultrasound has remained the standard for the

majority of indications The more

impor-tant change during the 2000s was continued

reduction in the size and price of ultrasound

machines The increased portability and

affordability of ultrasound devices led to an

exponential increase in use of ultrasound by

all providers Subsequently, many professional

societies published guidelines on use of

point-of-care ultrasound, including the American

Institute of Ultrasound in Medicine (AIUM),

American College of Emergency Physicians

(ACEP), American College of Chest

Physi-cians (ACCP), and American Society of

Echo-cardiography (ASE) Furthermore, consensus

guidelines between imaging and specialty

soci-eties have been established, such as the

guide-lines on obstetrical ultrasound collaboratively

developed by the American College of

Radi-ology (ACR), American College of

Obstetri-cians and Gynecologists (ACOG), American

Institute of Ultrasound in Medicine (AIUM),

and Society of Radiologists in Ultrasound

(SRU) and the ACEP–ASE statement on focused cardiac ultrasound in the emergent setting.13,14 Specialty-specific guidelines also emerged, such as the American Association

of Clinical Endocrinologists guidelines on thyroid ultrasound that defined a pathway for endocrinologists to earn a certificate of compe-tency in thyroid and neck ultrasound.15Medical educators recognized the impor-tance of a basic understanding of ultrasound in the early 2000s and started to explore how to incorporate ultrasound training into curricula for medical students, residents, and fellows The Accreditation Council for Graduate Med-ical Education (ACGME) has started to man-date certain residency and fellowship programs

in the United States include basic ultrasound education; for example, critical care ultrasound and ultrasound-guided thoracentesis and cen-tral venous catheterization are now required components of pulmonary/critical care fellow-ship training Several medical schools world-wide have started to expose their students

to the principles and practice of ultrasound, most often in conjunction with anatomy and physical examination courses.16–19 The com-ing generation of physicians will thus be more adept at point-of-care ultrasound applications and will consider use of bedside ultrasound to

be routine in most clinical encounters While past generations’ contributions established the utility of ultrasound as a valuable bedside tool in diagnostics and procedural guidance, the next generation will advance the field by studying how point-of-care ultrasound can be best incorporated into patient care algorithms and its impact on healthcare outcomes, cost- effectiveness, and patient satisfaction

Key Considerations

Point-of-care ultrasound exams differ from prehensive ultrasound exams in several aspects Point-of-care exams are generally employed to detect acute, potentially life-threatening condi-tions where detection at the bedside expedites patient care An evaluation with point-of-care ultrasound requires less time due to its focus on

com-a single or limited set of findings for com-a specific clinical complaint or syndrome In contrast, comprehensive diagnostic exams thoroughly evaluate all anatomic structures related to an organ or organ system The process of ordering, performing, interpreting, and reporting such comprehensive ultrasound exams usually takes

Trang 14

6

hours, whereas acquisition and interpretation of

point-of-care ultrasound exams takes minutes,

providing more immediate information for

decision making.20 Although information can

be obtained rapidly, an important challenge

is overcoming the multiple time constraints

put on providers who are regularly performing

point-of-care ultrasound exams

Key considerations to improve the

effi-ciency and quality of point-of-care

ultra-sound exams for different clinical applications

include optimization of provider training,

patient factors, and ultrasound equipment

features

CLINICAL APPLICATIONS

A point-of-care ultrasound exam is aimed

at answering a specific question through a

focused, goal-directed exam and can be used

to assess most body systems (Figure 1.3)

Generally, the goal is to “rule in” or “rule out”

a specific condition or answer a “yes/no”

ques-tion Clinical applications can be categorized

as follows:

□ Procedural guidance: Ultrasound guidance

has been shown to reduce complications

and improve success rates of invasive

bed-side procedures Procedures commonly

performed with ultrasound assistance

include vascular access, thoracentesis, paracentesis, lumbar puncture, arthrocen-tesis, and pericardiocentesis

□ Diagnostics: Based on the patient’s

pre-senting signs and symptoms, a focused bedside ultrasound exam can narrow the differential diagnosis and guide addition-

al investigations, especially in urgent or emergent situations Focused ultrasound exams are commonly performed to evalu-ate the lungs, heart, gallbladder, aorta, kidneys, bladder, gravid uterus, joints, and lower-extremity veins

□ Monitoring: Serial ultrasound exams can

be performed to monitor a patient’s dition or to monitor the effects of an in-tervention without exposing patients to ionizing radiation or intravenous contrast Common applications include moni-toring inferior vena cava distention and collapsibility as a surrogate for central ve-nous pressure during fluid resuscitation, monitoring left ventricular contraction

con-in response to con-inotrope con-initiation, and monitoring for resolution or worsening

of a pneumothorax or pneumonia on lung ultrasound

□ Resuscitation: Use of ultrasound during

resuscitation for cardiac arrest is a unique but underutilized application Bedside

Trang 15

1—EVOLUTION OF POINT-OF-CARE ULTRASOUND 7

ultrasound can direct emergent

inter-ventions by rapidly detecting tension

pneumothorax, cardiac tamponade, and

massive pulmonary embolism with acute

right ventricular failure Additionally,

ultrasound can be used to assess cardiac

contractions to help determine when to

cease resuscitative efforts Visualization

of cardiac standstill or clotting within the

heart chambers allows providers to stop

futile interventions, whereas visualization

of subtle or weak cardiac contractions

typically justifies continuation of

resusci-tative efforts

□ Screening: Screening with ultrasound is

potentially advantageous because it is

noninvasive and avoids ionizing

radia-tion Although screening for abdominal

aortic aneurysm or asymptomatic left

ventricular function using point-of-care

ultrasound has been described, more

widespread screening applications have

been slow to develop due to the challenge

of weighing benefits of early detection

against the harms of false-positive

find-ings that lead to unnecessary testing and/

or procedures.21–23

PROVIDER TRAINING

The amount of training required to achieve

competency in point-of-care ultrasound

applications varies by provider skill and exam

type Prior experience with ultrasound greatly

facilitates learning new applications The skills

required relate to the provider’s scope of

practice; for example, a rheumatologist may

be proficient with musculoskeletal

ultra-sound but less proficient with cardiac or

abdominal ultrasound, while the opposite

may be true for a critical care physician

Pro-tocols from published studies on ultrasound

education have differed, but it is generally

accepted that training must include

hands-on image acquisitihands-on and interpretatihands-on

practice supplemented by focused didactics

Current studies have provided general

guid-ance on the average number of exams needed

to acquire skills depending on the exam type;

for example, novice users have been able to

achieve an “acceptable” skill level in focused

cardiac ultrasound after performing 20–30

limited exams.24 Although a minimum

number of exams will likely continue to be

required to earn certain certificates, future

generations will focus on competency-based education, with competency determined by achievement of certain milestones rather than completion of a predetermined number

of exams

PATIENT FACTORS

Body habitus, positioning, and acute illness are important considerations when imaging patients Similar to plain film radiography, ultrasound waves are attenuated by adipose tissue, and ultrasound has limited penetration

in morbidly obese patients Lower frequencies must be used for deeper penetration, result-ing in lower-resolution images Positioning can limit ultrasound examination; for exam-ple, acquisition of apical cardiac ultrasound images is often limited in patients who cannot

be placed in a left lateral decubitus position Similarly, providers often have to adjust their own position to evaluate pleural effusions and perform thoracentesis when patients are unable to sit upright On the contrary, ascites and pleural effusions improve visualization

of deep organs due to deeper penetration of sound waves

ULTRASOUND EQUIPMENT

With the development of newer, more pact ultrasound devices, lack of familiarity with the varying features and controls can present

com-a bcom-arrier to use Fortuncom-ately, mcom-any mcom-achines are designed specifically for point-of-care ultrasound applications with “ease of use” as

a primary feature, an important consideration when purchasing a machine Providers must

be familiar with basic operations of available ultrasound equipment, including entering patient information, selecting the appropriate imaging mode, and adjusting the image depth and gain The diminution in size of portable ultrasound machines comes with certain limi-tations: smaller screen size, limited transducer selection, fewer imaging modes, and fewer adjustable parameters to optimize the image Transducer availability is an important consid-eration because certain exams can be performed with multiple transducer types, whereas others can be performed only with a single transducer type; for example, a curvilinear or phased-array transducer can be used to evaluate the abdo-men but only a phased-array transducer can be used to evaluate the heart

Trang 16

8

Vision

Point-of-care ultrasound use has increased

and spread rapidly over the past 20 years,

and we anticipate that all healthcare

provid-ers, including students, nurses, advanced care

providers, and physicians, will have integrated

point-of-care ultrasound into clinical practice

in the next 20 years (Figure 1.4) Healthcare

systems throughout the world are striving to provide high-quality, cost-effective healthcare, and point-of-care ultrasound can contribute to achieving these goals by reducing procedural complications, expediting care, decreasing costly ancillary testing, and reducing imaging that uti-lizes ionizing radiation Realizing such objec-tives can further the ultimate goal of improving patient satisfaction and healthcare outcomes

1960 1970 1980 1990 2000 2010 2020 2030 2040 Cardiology

Obstetrics

Emergency Med & Surgery

Med StudentsMidlevel Providers

Critical CareAnesthesiaInternal Medicine + SubspecialtiesPediatrics

NursesAll Providers

Figure 1.4 Integration of point-of-care ultrasound in medicine specialties.

Trang 17

References

1 Cardenas E Emergency medicine ultrasound policies and reimbursement guidelines Emerg Med Clin

North Am August 2004;22(3):829–838, x–xi

2 Woo J A Short History of the Development of Ultrasound in Obstetrics and Gynecology ultrasound.net/history1.html

3 Newman PG, Rozycki GS The history of ultrasound Surg Clin North Am April 1998;78(2):179–195

4 Eckel H Sonography in emergency diagnosis of the abdomen, [author’s trans.] Rontgenblatter May

1980;33(5):244–248

5 Plummer D Principles of emergency ultrasound and echocardiography Ann Emerg Med December

1989;18(12):1291–1297

6 Jehle D, Guarino J, Karamanoukian H Emergency department ultrasound in the evaluation of blunt

abdominal trauma Am J Emerg Med July 1993;11(4):342–346

7 Han DC, Rozycki GS, Schmidt JA, Feliciano DV Ultrasound training during ATLS: an early start for

surgical interns J Trauma August 1996;41(2):208–213

8 Rozycki GS Surgeon-performed ultrasound: its use in clinical practice Ann Surg July 1998;228(1):16–28

9 Lichtenstein D L’échographie générale en reanimation Germany: Springer-Verlag; 1992

10 Xirouchaki N, et al Lung ultrasound in critically ill patients: comparison with bedside chest

radiogra-phy Intensive Care Med 2011;37(9):1488–1493

11 Weiner MM, Geldard P, Mittnacht AJ Ultrasound-guided vascular access: a comprehensive review

J Cardiothorac Vasc Anesth April 2013;27(2):345–360

12 Wu SY, Ling Q, Cao LH, Wang J, Xu MX, Zeng WA Real-time two-dimensional ultrasound

guid-ance for central venous cannulation: a meta-analysis Anesthesiology February 2013;118(2):361–375

13 ACR-ACOG-AIUM-SRU practice guideline for the performance of obstetrical ultrasound http://www.acr.org/∼/media/ACR/Documents/PGTS/guidelines/US_Obstetrical.pdf; (revised 2013)

14 Labovitz AJ, Noble VE, Bierig M, et al Focused cardiac ultrasound in the emergent setting: a consensus statement of the American Society of Echocardiography and American College

of Emergency Physicians J Am Soc Echocardiogr December 2010;23(12):1225–1230

15 Endocrine Certification in Neck Ultrasound Candidate Handbook and Application American Association of

Clinical Endocrinologists; 2014 https://www.aace.com/files/ecnu-candidatehandbook.pdf

16 Rao S, van Holsbeeck L, Musial JL, et al A pilot study of comprehensive ultrasound education

at the Wayne State University School of Medicine: a pioneer year review J Ultrasound Med May

2008;27(5):745–749

17 Hoppmann RA, Rao VV, Poston MB, et al An integrated ultrasound curriculum (iUSC) for medical

students: 4-year experience Crit Ultrasound J April 2011;3(1):1–12

18 Bahner DP, Royall NA Advanced ultrasound training for fourth-year medical students: a novel

training program at The Ohio State University College of Medicine Acad Med February

2013;88(2):206–213

19 Bahner DP, Adkins EJ, Hughes D, Barrie M, Boulger CT, Royall NA Integrated medical school

ultrasound: development of an ultrasound vertical curriculum Crit Ultrasound J July 2, 2013;5(1):6

20 Kory PD, Pellecchia CM, Shiloh AL, et al Accuracy of ultrasonography performed by critical care

physicians for the diagnosis of DVT Chest 2011;139:538–554

21 Frederiksen CA, Juhl-Olsen P, Andersen NH, Sloth E Assessment of cardiac pathology by

point-of-care ultrasonography performed by a novice examiner is comparable to the gold standard Scand J

Trauma Resusc Emerg Med December 13, 2013;21:87

22 Martin LD, Mathews S, Ziegelstein RC, et al Prevalence of asymptomatic left ventricular systolic

dysfunction in at-risk medical inpatients Am J Med January 2013;126(1):68–73

23 Nguyen AT, Hill GB, Versteeg MP, Thomson IA, van Rij AM Novices may be trained to screen for

abdominal aortic aneurysms using ultrasound Cardiovasc Ultrasound November 22, 2013;11(1):42

24 Spencer KT, Kimura BJ, Korcarz CE, Pellikka PA, Rahko PS, Siegel RJ Focused cardiac ultrasound:

recommendations from the American Society of Echocardiography J Am Soc Echocardiogr June

2013;26(6):567–581

Trang 18

Ultrasound has been used for diagnostic

pur-poses in medicine since the late 1940s, but

the history of ultrasound physics dates back

to ancient Greece In the sixth century BC,

Pythagoras described harmonics of stringed

instruments, which established the unique

characteristics of sound waves By the late

eighteenth century, Lazzaro Spallanzani had

developed a deeper understanding of sound

wave physics based on his studies of

echoloca-tion in bats The field of ultrasonography would

not have evolved without an understanding

of piezoelectric properties of certain

materi-als, as described by Pierre and Jacques Curie

in 1880.1 Multiple other milestones, such

as the invention of sonar by Fessenden and

Langevin following the sinking of the Titanic

and the development of radar by Watson-Watt,

improved our understanding of ultrasound

physics Ultrasound use in medicine started in

the late 1940s with the works of Dr George

Ludwig and Dr John Wild2,3 in the United

States and Karl Theodore Dussik4 in Europe

Modern ultrasound machines still rely on

the same original physical principles from

centuries ago, even though advances in

tech-nology have refined devices and improved

image quality A thorough understanding of

ultrasound physics is essential to capture quality images and interpret them correctly This chapter broadly reviews the physics of ultrasound

high-Principles

Sound waves are emitted by piezoelectric material, most often synthetic ceramic mate-rial (lead zirconate titanate [PZT]), that is contained in ultrasound transducers When a rapidly alternating electrical voltage is applied

to piezoelectric material, the material ences corresponding oscillations in mechanical strain As this material expands and contracts rapidly, vibrations in the adjacent material are produced and sound waves are gener-ated Mechanical properties of piezoelectric material determine the range of sound wave frequencies that are produced Sound waves propagate through media by creating com-pressions and rarefactions of spacing between molecules (Figure 2.1) This process of gener-ating mechanical strain from the application

experi-of an electrical signal to piezoelectric material

is known as the reverse piezoelectric effect The

opposite process, or generation of an electrical signal from mechanical strain of piezoelectric

material, is known as the direct piezoelectric

effect Transducers produce ultrasound waves

K E Y P O I N T S

• Understanding ultrasound physics is essential to acquire and interpret images accurately

• Higher-frequency transducers produce higher-resolution images but penetrate shallower Lower-frequency transducers produce lower-resolution images but penetrate deeper

• Basic modes of ultrasound include two-dimensional, M-mode, and Doppler

Trang 19

10

by the reverse piezoelectric effect, and reflected

ultrasound waves, or echoes, are received by the

same transducer and converted to an

electri-cal signal by the direct piezoelectric effect The

electrical signal is analyzed by a processor and,

based on the amplitude of the signal received,

a gray-scale image is displayed on the screen

Key parameters of ultrasound waves include

frequency, wavelength, velocity, power, and

intensity.5

FREQUENCY AND WAVELENGTH

By definition, “ultrasound” refers to sound waves

at a frequency above the normal human audible

range (>20 kHz) Frequencies used in

ultraso-nography range from 2 to 18 MHz Frequency

(f ) is inversely proportional to wavelength ( λ)

and varies according to the specific velocity of

sound in a given tissue (c) according to the

for-mula: λ = c/f Two important considerations in

ultrasonography are the penetration depth and resolution, or sharpness, of the image; the latter

is generally measured by the wavelength used For example, when wavelengths of 1 mm are used, the image appears blurry when examined

at scales smaller than 1 mm Ultrasound waves with shorter wavelengths have higher fre-quency and produce higher-resolution images, but penetrate to shallower depths Conversely, ultrasound waves with longer wavelengths have lower frequency and produce lower-resolution images, but penetrate deeper The relationship between frequency, resolution, and penetration for a typical biologic material is demonstrated

in Figure 2.2 Maximizing axial resolution while maintaining adequate penetration is a key consideration when choosing an appropriate

Figure 2.1 Sound waves propagate through media by creating compressions and rarefactions,

correspond-ing with high- and low-density regions of molecules.

Figure 2.2 Relationship of

ultra-sound wave frequency, penetration,

and wavelength (image resolution)

High-frequency transducers

pro-duce higher-resolution images but

penetrate shallower Low-frequency

transducers produce lower-resolution

images but penetrate deeper.

Wavelength (resolution) Penetration

20

Trang 20

2—ULTRASOUND PHYSICS 11

transducer frequency Higher frequencies are

used in linear-array transducers to visualize

superficial structures, such as vasculature and

peripheral nerves Lower frequencies are used

in curvilinear and phased-array transducers to

visualize deeper structures in the thorax,

abdo-men, and pelvis

POWER AND INTENSITY

Average power is the total energy incident on a

tissue in a specified time (W) Intensity is the

concentration of power per unit area (W/cm2),

and intensity represents the “strength” of the

sound wave The intensity of ultrasound waves

determines how much heat is generated in

tis-sues Heat generation is usually insignificant

in diagnostic ultrasound imaging but becomes

important in therapeutic ultrasound

applica-tions, such as lithotripsy (see “Safety”)

Resolution

Image resolution is divided into axial, lateral,

ele-vational, and temporal components (Figure 2.3)

Axial resolution is the ability to differentiate two

objects along the axis of the ultrasound beam

and is the vertical resolution on the screen Axial resolution depends on transducer frequency Higher frequencies generate images with bet-ter axial resolution, but higher frequencies have shallower penetration Lateral resolution, or horizontal resolution, is the ability to differenti-ate two objects perpendicular to the ultrasound beam and is dependent on the width of the beam

at a given depth Lateral resolution can be mized by placing the target structure in the focal zone of the ultrasound beam The focal zone is the narrowest portion of the ultrasound beam The ultrasound beam has a curved shape, and the focal zone is the region of highest intensity

opti-of the emitted beam Lateral resolution decreases

as deeper structures are imaged due to gence and increased scattering of the ultrasound beam Elevational resolution is a fixed property

diver-of the transducer that refers to the ability to resolve objects within the height, or thickness, of the ultrasound beam The number of individual PZT crystals emitting and receiving ultrasound waves, as well as their sensitivity, affects image resolution, precision, and clarity Temporal reso-lution refers to the clarity, or resolution, of mov-ing structures (See Chapter 3, Transducers, for additional details about image resolution.)

Figure 2.3 Axial, lateral, and elevational

image resolution in relation to the sound beam and display.

Trang 21

12

Generation of Ultrasound

Images

Sound waves are reflected, refracted,

scat-tered, transmitted, and absorbed by tissues

due to differences in physical properties of

tis-sues (Figure 2.4) Ultrasound images are

gen-erated by sound waves reflected and scattered

back to the transducer Transducers receive

and record the intensity of returning sound

waves Specifically, mechanical deformation

of the transducer’s piezoelectric material

gen-erates an electrical impulse proportional to

the amplitude of these returning sound waves Electrical impulses cumulatively generate a map of gray-scale points seen as an ultrasound image Depth of structures along the axis of the ultrasound beam is determined by the time delay for echoes to return to the trans-ducer The process of emitting and receiving sound waves is repeated sequentially by the transducer, resulting in a dynamic picture (Figure 2.5) Reflection and propagation of sound waves through tissues depend on two important parameters: acoustic impedance and attenuation

Figure 2.5 Generation of ultrasound images (1) Oscillating voltage is applied to piezoelectric crystals

(2) Piezoelectric crystals vibrate rapidly, producing sound waves (3) Ultrasound beam penetrates tissues (4) Echoes (reflected sound waves) return to transducer (5) Echoes are converted to electrical signals that

are processed into gray-scale images.

Trang 22

ACOUSTIC IMPEDANCE

Propagation speed is the velocity of sound in

tissues and varies depending on physical

prop-erties of tissues Acoustic impedance is the

resis-tance to propagation of sound waves through

tissues and is a fixed property of tissues

deter-mined by mass density and propagation speed

of sound in a specific tissue (Table 2.1)

Dif-ferences in acoustic impedance determine

reflectivity of sound waves at tissue interfaces

Greater differences in acoustic impedance

lead to greater reflection of sound waves For

example, sound waves reflect in all directions,

or scatter, at air-tissue interfaces due to a large

difference in acoustic impedance between air

and bodily tissues Scattering of sound waves at

air-tissue interfaces explains why sufficient gel

is needed between the transducer and skin to

facilitate propagation of ultrasound waves into

the body Ultrasound machines are calibrated

to rely on small differences in impedance

because only 1% of sounds waves are reflected

back to the transducer The majority of sound

waves (99%) do not return to the transducer

ATTENUATION

As sound waves travel through tissues, energy

is lost, and this loss of energy is called

attenu-ation Attenuation is due to absorption,

deflec-tion, and divergence of sound waves and is

dependent on the attenuation coefficient of

tissues, frequency of sound waves, and distance

traveled by sound waves.9 Absorption, the most

important cause of attenuation, refers to energy

transferred from the ultrasound beam to tissues

as heat Heat production is an important safety

limitation of ultrasonography,10 and each type

of tissue has an intrinsic attenuation coefficient

(Table 2.2) Absorption is the most important

determinant of depth of ultrasound wave etration High-frequency sound waves are more readily absorbed and therefore penetrate shallower compared to low-frequency sound waves Deflection, a second cause of attenua-tion, refers collectively to reflection, refraction, and scattering of energy within tissues Deflec-tion results in a reduction in echo amplitude, especially when the observed interfaces between tissues is not perpendicular to the beam Diver-gence refers to loss of ultrasound beam inten-sity as the beam widens, and a fixed amount

pen-of acoustic energy is spread over a wider beam Attempts at overcoming attenuation can be made by increasing the gain, or amplifying the signal in postprocessing However, increasing gain affects both signal and noise Adjusting gain only manipulates the computer-generated image and does not improve signal quality

Modes

Multiple modes of ultrasound imaging have been developed to enhance image acquisi-tion Here we discuss two-dimensional (2-D), M-mode, color flow Doppler, and spectral Doppler

TABLE 2.1 n Acoustic Impedance of Different Tissues 6–8

Tissue or Material Density (g/cm 3 ) Speed of Sound (m/s)

Acoustic Impedance (kg/(s m 2 )) × 10 6

Metal (e.g., titanium) 4.5 5090 22.9

TABLE 2.2 n Attenuation Coefficients

of Different Materials Tissue or Material Attenuation (dB/cm/MHz)

Trang 23

14

TWO-DIMENSIONAL MODE

Two-dimensional (2-D) mode is the default

mode of most ultrasound machines, and the

majority of bedside diagnostic ultrasound

imag-ing is performed in 2-D mode This mode is

also called B-mode, for “brightness,” because

echogenicity, or brightness, of observed

struc-tures depends on the intensity of reflected

sig-nals Structures that transmit all sound waves

without reflection are called anechoic and appear

black on ultrasound Most fluid-filled

struc-tures appear anechoic Strucstruc-tures that reflect

some sound but less than surrounding

struc-tures appear hypoechoic, whereas strucstruc-tures

that reflect sound waves similar to surrounding

structures appear isoechoic Both hypoechoic

and isoechoic structures appear as shades of gray

and are generally soft tissue structures

Hyper-echoic structures reflect most sound waves and

appear bright white on ultrasound Calcified

and dense structures, such as the diaphragm

or pericardium, are hyperechoic Some

hyper-echoic structures, such as bones, create shadows

due to near-total reflection of sound waves and

often preclude visualization of distal structures

Figure 2.6 illustrates different tissue

echogenici-ties in the right upper quadrant of the abdomen

M-MODE

M-mode, or “motion” mode, is an older mode

of imaging but is still frequently used today to

analyze movement of structures over time.11

After a 2-D image is acquired, M-mode

imag-ing is applied along a simag-ingle line within the 2-D

image A single-axis beam is emitted along a

select line and gathers data on movement of all tissues along that line All points on the line are plotted over time to evaluate the dimen-sions of cavities or movement of structures For example, M-mode is used to measure the size of cardiac chambers or movement of car-diac valves throughout the cardiac cycle Other frequent point-of-care applications include measurement of change in inferior vena cava diameter with respiration, and evaluation of the lung-pleura interface to rule out pneumo-thorax Figure 2.7 is an example of M-mode imaging

DOPPLER IMAGING

The Doppler effect is a shift in frequency of sound waves due to relative motion between the source and observer.12 The primary source

of sound waves is the transducer, and the same transducer is the observer for returning echoes Movement of tissues, such as blood flow, pro-duces a shift in frequency of returning sound waves Blood flow moving toward the trans-ducer shifts the echoes to a higher frequency while blood flow moving away from the trans-ducer shifts the echoes to a lower frequency (Figure 2.8) The change in frequency between the emitted and received sound waves is called

Doppler shift.13 Variables that determine the amount of Doppler shift are:

1 Frequency of ultrasound beam

2 Velocity of blood flow

3 Angle of insonationThe angle of insonation, or angle between the ultrasound beam and direction of the mea-sured flow, is critical (Figure 2.9) No Doppler shift can be measured when the ultrasound beam is perpendicular to the direction of blood

Isoechoic

Hyperechoic

Anechoic

Figure 2.6 Two-dimensional (B-mode) ultrasound

image with isoechoic, hypoechoic, and hyperechoic

tissues. Figure 2.7 M-mode imaging of the left ventricular chamber.

Trang 24

flow Ideally, the ultrasound beam should be

placed parallel to the direction of blood flow,

but a near-parallel intercept angle is more often

achievable Angling the ultrasound beam toward

the direction of blood flow causes a positive

Doppler shift, whereas angling the ultrasound

beam away from the direction of blood flow

causes a negative Doppler shift (Figure 2.10) A

correctional factor for the angle of insonation is

used in the Doppler equation to better estimate

velocities

Spectral Doppler

Doppler effect may be represented

graphi-cally using velocity (y-axis) plotted over time

(x-axis) in a display method called spectral

Doppler (Figure 2.11) By convention, the frequency shifts displayed above the baseline represent velocities toward the transducer, and shifts below baseline represent velocities mov-ing away from the transducer Spectral Doppler permits quantitative assessment of velocities and is divided into two types: pulsed wave and continuous wave

Pulsed-wave Doppler refers to the sion of sound waves in pulses that allows measurement of Doppler shift at certain depths After a pulsed signal is sent into tis-sues, the transducer must await the returning echo before emitting another pulse This cycle

emis-Figure 2.8 Doppler shift in frequency of

sound waves Movement of the source

or reflector of sound waves toward

or away from transducer causes an increase or decrease in sound wave frequency, respectively.

Reflector movingaway from transducer

Figure 2.9 Doppler interrogation and

Trang 25

16

of emitting a wave into tissues and

captur-ing the returncaptur-ing echo is repeated rapidly at

a rate called pulse repetition frequency (PRF)

Ideally, the maximum possible PRF is used;

however, the maximum PRF is determined by

wave travel time, and wave travel time is

lim-ited by tissue depth Deeper depths require

longer wait times for returning echoes,

reduc-ing the maximum PRF before ambiguous

signaling, or aliasing, occurs When aliasing

occurs, the true velocity and vector

direc-tion cannot be determined The maximum

Doppler frequency or velocity that can be

measured before aliasing occurs is called the

Nyquist limit The Nyquist limit is one half

of the PRF because ultrasound waveforms

must be sampled at least twice per

wave-length to reliably assess velocity and direction

(Figure 2.12).14 Significance of the Nyquist limit is exemplified by severe aortic stenosis The aortic valve is a relatively deep structure, which limits the the PRF and makes accurate measurement of the high velocities of severe aortic stenosis difficult Techniques to avoid aliasing include maximizing the PRF to raise the Nyquist limit, reducing imaging depth, selecting a lower-frequency transducer, or switching to continuous-wave Doppler imag-ing The advantage of pulsed-wave Doppler is reduced interference from surrounding struc-tures, but its main disadvantage is susceptibil-ity to aliasing because of the Nyquist limit

In contrast, continuous-wave Doppler

allows measurement of blood velocities along the entire ultrasound beam These transduc-ers have two different sets of piezoelectric crystals to continuously emit and receive signals, and therefore PRF has no limit and aliasing does not occur Continuous-wave Doppler is mostly used to measure high velocities, such as in patients with aortic stenosis, that pulsed-wave Doppler cannot accurately measure The main limitation of continuous-wave Doppler is the inability to measure velocities at specific depths because Doppler signals are received from all tissues

in the path of the ultrasound beam In both pulsed- and continuous-wave Doppler imag-ing, the accuracy of measurements depends

on signal quality, which is determined by the sharpness of peaks of the curves used to determine velocities

Figure 2.10 Relationship of angle of

in-sonation and Doppler effect Aligning the

ultrasound beam parallel with the

direc-tion of flow increases Doppler frequency.

SkinBeam

direction

VesselFlow

Doppler

Figure 2.11 Spectral Doppler imaging of femoral

artery velocities (using pulsed Doppler).

Trang 26

Color Flow Doppler

Color flow Doppler images display

color-coded maps representing Doppler shifts

that are superimposed on 2-D ultrasound

images (Figure 2.13 and Video 2.1) Color

flow Doppler relies on the same principles as

pulsed-wave Doppler, but shorter pulses are

obtained from multiple small areas to build a

color-coded map When velocities exceed the

Nyquist limit, pixels appear as a mosaic color

pattern (blue, red, and white) as the tion of flow cannot be reliably ascertained In general, color flow Doppler image brightness corresponds to velocity, and color corresponds

direc-to direction of flow Conventionally, blue resents blood flow away from the transducer (longer wavelength) and red represents blood flow toward the transducer (shorter wave-lengths); however, red or blue is not specific for arteries or veins because the color depends on the direction of flow relative to the transducer

rep-Power Doppler

A newer Doppler technique, called power

Doppler, has unique characteristics.15 Power Doppler assesses echo signals similar to color flow Doppler, but power Doppler analyzes only the amplitude of returning echoes ( Figure 2.14 and Video 2.2) Thus, power Doppler is superimposed on a 2-D image, and the lev-els of brightness correlate with magnitudes of flow Sensitivity for detecting flow is three to five times higher than conventional color flow Doppler Two important limitations of power Doppler are: (1) no information regarding direction of flow is given, limiting its use in cardiac imaging; and (2) images are more

Panel A: wavelength = 4, sampling (PRF) = 1 Panel B: wavelength = 2, sampling (PRF) = 1

Panel C: wavelength = 1, sampling (PRF) = 1

Panel D: wavelength = 1, sampling (PRF) = 1.2

Figure 2.12 Illustration of the Nyquist limit In panels A and B, when the sampling (red circles) is at least

twice as fast as the full wavelength (blue line), the signal can be recreated and analyzed reliably (the lines superimpose) In panels C and D, when the sampling is less than twice a wavelength (below the Nyquist limit), a reliable signal cannot be obtained, leading to aliasing PRF, pulse repetition frequency.

Figure 2.13 Color flow Doppler of internal jugular

vein and common carotid artery.

Trang 27

18

susceptible to artifacts, called flash artifacts,

caused by surrounding soft tissue motion

Practical uses of power Doppler include

low-flow states, such as venous thrombosis and

testicular or ovarian torsion, or when direction

of flow is not critical, such as in parenchymal

or tumor flow studies.16

Safety

Ultrasound imaging is considered to be a

very safe imaging modality, but limitations

must be considered When applied to

tis-sues, intense ultrasound beams can

poten-tially cause two types of injuries: thermal (heat

generation) and nonthermal (cavitation) from

contrast-enhanced ultrasound The intensities generated by current ultrasound systems range from 10 to 430 mW/cm2, with the highest intensity occurring with pulsed-wave Doppler imaging due to its focused target area Current recommendations from the American Institute

of Ultrasound in Medicine include exposure to intensities <1 W/cm2, which corresponds to a calculated possible elevation of tissue tempera-ture <1° C above baseline.17 The exact elevation

of temperature in the human body is difficult to measure Temperatures rapidly dissipate, espe-cially with high-perfusion organs and blood vessels, but could theoretically be as high as 4° C with prolonged exposure at the focal point.18Because of this theoretical risk, societies advo-cate the As Low As Reasonably Achievable (ALARA) principle, with minimization of duration of exposure at a single point being the most important modifiable risk factor.19 These principles are especially important when imag-ing sensitive tissues, such as fetuses and eyes.Modern ultrasound machines provide oper-ators with an easy way to estimate potential risk from ultrasound by displaying two measures: mechanical index (MI) and thermal index (TI) TI is subdivided into TIs (soft tissues), TIb (bone), and TIc (cranium) Both MI and

TI are calculated ratios TI is a ratio of total emitted acoustic power to theoretical power required to raise tissue temperature by 1° C Mechanical and thermal indices less than one are considered safe

Figure 2.14 Power Doppler of internal jugular vein

and common carotid artery.

Trang 28

References

1 Curie J, Curie P Développement par compression de l'électricité polaire dans les cristaux hémièdres à

faces inclinées Bull Soc Mineral Fr 1880;3:90–93

2 Ludwig GD The velocity of sound through tissues and the acoustic impedance of tissues J Acoust Soc

Am 1950;22(6):862–866

3 Wild JJ The use of ultrasonic pulses for the measurement of biologic tissues and the detection of tissue

density changes Surgery 1950;27(2):183–188

4 Dussik KT, Fritch DJ, Kyriazidou M, Sear RS Measurements of articular tissues with ultrasound

Am J Phys Med Rehab 1958;37(3):160–165

5 Angelsen BA Waves, Signals and Signal Processing Ultrasound Imaging Trondheim, Norway: Emantec;

2000

6 Azhari H Appendix A: Typical Acoustic Properties of Tissues Basics of Biomedical Ultrasound for Engineers

John Wiley & Sons, Inc.; 2010: 313–314

7 Duck FA Propagation of sound through tissue In: ter Haar G, Duck FA, eds The Safe Use of

Ultrasound in Medical Diagnosis London: British Institute of Radiology; 2000:4–15

8 Kaye GWC, Laby TH Tables of Physical & Chemical Constants; 1995 http://www.kayelaby.npl.co.uk Accessed 30.12.12

9 Ziskin MC Fundamental physics of ultrasound and its propagation in tissue Radiographics May 1,

1993;13(3):705–709

10 Barnett SB, Ter Haar GR, Ziskin MC, Rott H-D, Duck FA, Maeda K International

recommen-dations and guidelines for the safe use of diagnostic ultrasound in medicine Ultrasound Med Biol

2000;26(3):355–366

11 Edler I, Hertz CH The use of ultrasonic reflectoscope for the continuous recording of the movements

of heart walls K Fysiogr Saellsks I Lund Förhand 1954;24(5):40–58

12 Doppler CA Über das farbige licht der Doppelsterne und einiger anderer Gestirne des Himmels

Abhandlungen der königl böhm Gesellschaft der Wissenschaften 1843;2:465–482

13 Evans DH, McDicken WN Doppler Ultrasound 2nd ed New York: John Wiley and Sons; 2000

14 Powis R, Schwartz R Practical Doppler Ultrasound for the Clinician Baltimore: Williams & Wilkins;

1991

15 Rubin JM, Bude RO, Carson PL, Bree RL, Adler RS Power Doppler US: a potentially useful

alterna-tive to mean frequency-based color Doppler US Radiology March 1994;190(3):853–856

16 Hamper UM, DeJong MR, Caskey CI, Sheth S Power Doppler imaging: clinical experience and

correlation with color Doppler US and other imaging modalities Radiographics March 1, 1997;17(2):

499–513

17 Fowlkes JB American Institute of Ultrasound in Medicine consensus report on potential bioeffects of

diagnostic ultrasound: executive summary J Ultrasound Med April 2008;27(4):503–515

18 O’Brien Jr WD Ultrasound-biophysics mechanisms Prog Biophys Mol Biol January–April 2007;

93(1–3):212–255

19 National Council on Radiation Protection Measurements (NCoRPM), Scientific Committee 46-3 on ALARA for Occupationally-Exposed Individuals in Clinical Radiology Implementation of the prin-ciple of as low as reasonably achievable (ALARA) for medical and dental personnel: recommendations

of the National Council on Radiation Protection and Measurements: The Council; 1990

Trang 29

Ultrasonography utilizes the piezoelectric effect, or

ability of certain crystals to generate vibrations

with the application of electricity The vibrating

crystals, also known as piezoelectric elements,

generate ultrasonic waves that are transmitted to

an apposed object Reflected waves return to the

transducer and generate mechanical distortion

of the crystals, which is converted to an electric

current via the same piezoelectric effect The

electric current is interpreted by the ultrasound

machine’s computer processor and rendered

into an image Transducers are a fundamental

component of ultrasound imaging

Point-of-care ultrasound users should have a basic

under-standing of transducer characteristics, including

types and construction, and an understanding of

determinants of image resolution

Transducer Construction

Ultrasound transducers are designed for

opti-mal transmission and reception of sound

waves (Figure 3.1) An electrical shield lines

the transducer case to prevent external

electri-cal interference from distorting sound wave

transmission A thin acoustic insulator

damp-ens vibrations from the case to piezoelectric

elements and prevents transmission of

spuri-ous electric current to the machine’s computer

processor At the tip of the transducer, a thin

matching layer improves efficiency of sound

wave transmission from piezoelectric elements

to skin and deeper structures Backing

mate-rial is an essential component of transducers

Backing material is fixed behind the layer of piezoelectric elements to dampen ongo-ing vibrations of elements Sound energy is absorbed by backing material when elements are generating and receiving sound waves.1Transducers are sensitive instruments, and the internal components of the transducer head, including the piezoelectric elements, can break easily with minor impact Providers must be trained to safeguard transducers at all times

Resolution

Resolution of ultrasound images depends on three complementary properties of the trans-ducer: axial, lateral, and elevational resolution (Figure 3.2) Axial resolution is the ability to differentiate distinct objects on the same path

as the ultrasound beam Lateral resolution is the ability to differentiate objects that are per-pendicular to the ultrasound beam Axial reso-lution is determined by sound wave frequency, with higher frequencies giving better axial resolution (Figure 3.3A) Lateral resolution is determined by width of the ultrasound beam, which is influenced by diameter and frequency

K E Y P O I N T S

• The four main types of ultrasound transducers—linear, curvilinear, phased-array, and intracavitary—differ by crystal arrangement, size, and footprints, which

determine their suitability in different imaging applications

• Higher-frequency transducers produce high-resolution images of superficial structures, whereas low-frequency transducers produce low-resolution images of deep structures

• Resolution of ultrasound images is divided into four different types: axial, lateral, tional, and temporal

Trang 30

eleva-1—FUNDAMENTAL PRINCIPLES OF ULTRASOUND

20

of piezoelectric crystals Small-diameter

crys-tals that produce high-frequency pulses

gen-erate narrow ultrasound beams, and thereby

increase lateral resolution.2 More important,

the narrowest portion of the ultrasound beam,

or focal zone, has the greatest lateral resolution

Depth of the focal zone can be adjusted to the

level of the target structure to maximize lateral

resolution (Figure 3.3B) Ultrasound computer

processors adjust sound wave frequency to

max-imize axial and lateral resolution when depth

settings are changed

Elevational resolution, referred to as slice

thickness resolution, is least influenced by

piezo-electric crystal diameter or frequency of sound

waves (Figure 3.4) In point-of-care ultrasound systems, elevational resolution is determined

by actual transducer thickness Sound waves return to the transducer from the various planes that constitute the ultrasound beam, and sig-nals from these various planes are averaged to produce a single two-dimensional image Ele-vational resolution is analogous to looking into

a swimming pool from above where shallow and deep objects are blended into one plane Thus, an important principle in ultrasonogra-phy is to visualize structures in two planes to account for limited elevational resolution.Temporal resolution refers to the ability to image moving structures, similar to frame rate

or shutter speed of a camera High temporal resolution indicates a high frame rate and bet-ter capture of movement Temporal resolution

is affected by both transducer pulse frequency and imaging depth Pulse frequency is the rate

at which transducers emit sound waves and is distinct from frequency range of transducers

A higher pulse frequency and shallower depth increase temporal resolution because reflected sound waves can be received by the transducer

in more rapid succession.3 The limiting factor

of temporal resolution with most point-of-care ultrasound machines is computer processing speed Temporal resolution may be increased, but at the expense of axial and lateral resolution being decreased

Transducer Types

Transducers typically contain 60 to 600 electric elements and are described by the arrangement of their elements, as well as by

piezo-Matchinglayer

Backing

PiezoelectricelementsProtective

case

Acousticinsulator

Powersupply

Transducer construction

Figure 3.1 Transducer construction Electrical current excites the piezoelectric elements that generate

sound waves The matching layer minimizes reverberations as sound waves travel to the skin Backing terial dampens crystal vibrations to prevent unintended, continued sound wave transmission An acoustic insulator, electric shield, and case serve to protect the piezoelectric elements from external electrical and acoustic interference.

ma-Lateral (y)

Elevational (z)

(slice thickness)

Axial (x)

Figure 3.2 Three dimensions of an ultrasound beam

are the length (x), width (y), and slice thickness (z)

Axial, lateral, and elevational resolution describe

spatial resolution in these three planes, respectively.

Trang 31

3—TRANSDUCERS 21

their function and beam shape There are four

basic types of transducers: linear, curvilinear,

phased-array, and intracavitary (Figure 3.5)

Beam steering differs with linear- and

phased-array transducers and determines image

for-mat Linear-array transducer elements fire

in sequence, producing a series of parallel

beams that generate a rectangular image

for-mat Phased-array transducer elements fire

sequentially in different directions, producing

a diverging beam that generates a pie-shaped

image format (Figure 3.6)

Linear transducers have elements that

are arranged in a flat matrix producing

par-allel, linear ultrasound beams Generally,

linear transducers generate high-frequency (5–10 MHz), shorter-wavelength sound waves with excellent axial and lateral resolution Lin-ear transducers also have excellent elevational,

or slice thickness, resolution because sound beam shape is relatively flat.4 However, linear transducers are limited to visualization

ultra-of superficial structures in a relatively narrow field of view because attenuation decreases resolution and penetration at depths >5 cm Although not well suited for imaging deep structures, linear-array transducers are ideal for evaluating superficial structures, including eyes, blood vessels, muscles, nerves, and joints, and for performing ultrasound-guided procedures

Axial resolution Lateral resolution

Focal zone

Figure 3.3 Axial (A) and lateral (B) resolution depend on ultrasound wave frequency and beam width

Higher-frequency transmissions have shorter wavelengths, allowing for improved axial resolution Lateral resolution depends on beam width and is highest in the narrowest portion of the ultrasound beam, the focal zone.

FocalzoneSlice

Figure 3.4 Elevational resolution, or slice thickness resolution, is determined by actual transducer thickness

Elevational resolution is greatest in the focal zone and least in the far field as the ultrasound beam diverges.

Trang 32

22

Curvilinear transducers are named for a curvilinear or convex arrangement of crystals The ultrasound beam is broad and trapezoi-dal with a wide field of view, but resolution

is not as good as linear transducers Overlap

of transmitted ultrasound waves in deep sues provides consistent lateral resolution Curvilinear transducers utilize lower frequen-cies (2–5 MHz) with longer wavelengths that penetrate deep structures with relatively less attenuation, particularly for structures 5–25 cm deep.5 Curvilinear transducer beams have a greater slice thickness than linear transducers, and a larger volume of structures is rendered

tis-in a two-dimensional ultrasound image Thus elevational resolution is reduced because each imaging plane includes thicker “cuts” of struc-tures that are averaged on the display into a sin-gle image Curvilinear transducers are ideal for imaging intraabdominal organs, including liver,

Heart Inferior vena cava Lungs

Pleura Abdomen

Uterus/ovaries Pharynx

Figure 3.5 Basic types of transducers and characteristics.

Linear

Array

Phased

Focal zone Scanned region

Figure 3.6 Ultrasound beam contour of linear and

phased-array transducers.

Trang 33

3—TRANSDUCERS 23

spleen, kidneys, and bladder, and for imaging

larger musculoskeletal structures, such

shoul-ders and hips Because of poor near-field

reso-lution, curvilinear transducers are not optimal

for lung or cardiac imaging or for certain biliary

ultrasound techniques

Phased-array transducers combine a

low-frequency ultrasound beam (1–5 MHz) with a

small, triangular-shaped footprint with

adjust-able focusing and steering Differential

excita-tion of elements creates rapid electronic beam

sweeping by sequentially pulsing multiple

small crystals within the transducer

Steer-ing and focusSteer-ing the ultrasound beam allows

for a wider field of view than linear

transduc-ers.6 Phased-array technology allows for more

efficient two-dimensional imaging and is ideal

for moving structures, such as the heart The

ability to steer ultrasound beams with phasing

permits accurate velocity measurements when

the vector of movement is not completely

par-allel with the beam (Figure 3.7) These unique

characteristics make phased-array transducers

ideal for cardiac and thoracic imaging

Intracavitary transducers combine a small,

micro-convex footprint with a high frequency

range (5–8 MHz) The field of view is wider than a linear transducer but with similar high image resolution Intracavitary transducers are ideal for transvaginal and transrectal ultra-sound and also for intraoral evaluation of peri-tonsillar abscess.7 Similar to linear transducers, they are not ideal for deeper structures, such as intraabdominal organs

Areaimaged

Delay profile

PulsePulse

Linear array of elements

Figure 3.7 Phased-array transducers electronically steer sound waves to image a wider field of view, as well

as improve image resolution over a wide range of depths.

• Transducers are sensitive instruments and are expensive to replace The internal components of the transducer head, including the piezoelectric elements, can break easily with minor impact Safe-guard the transducer by keeping it in your hand or hung on the ultrasound rack at all times

• Linear transducers are ideal for imaging superficial structures <5 cm, such as blood vessels, muscles, joints, nerves, and eyes Ultrasound-guided procedures using real-time needle tracking is most often performed with a linear transducer

PEARLS AND PITFALLS

Trang 34

24

• Low-frequency transducers are optimal

for visualizing structures deeper than

5 cm In general, curvilinear transducers

are used for abdominal and pelvic

scan-ning A phased-array transducer can

also be used to image the abdomen and

pelvis but is the only transducer that can

be used to image the heart

• Axial resolution is determined primarily

by sound wave frequency, and lateral resolution is determined primarily by beam width To improve lateral resolu-tion when imaging deep structures, increase the depth of the focal zone to the level of the target structure

Trang 35

References

1 Lawrence JP Physics and instrumentation of ultrasound Crit Care Med 2007;35(8):S314–S322

2 Jensen JA Medical ultrasound imaging Prog Biophys Mol Biol 2007;93:153–165

3 Williams D The physics of ultrasound Anaesth Intensive Care 2012;13(6):264–268

4 Fischetti AJ, Scott RC Basic ultrasound beam formation and instrumentation Clin Tech Small Anim

Pract 2007;22:90–92

5 Abu-Zidan FM, Hefny AF, Corr P Clinical ultrasound physics J Emerg Trauma Shock 2011;4(4):

501–503

6 Smith RS, Fry WR Ultrasound instrumentation Surg Clin N Am 2004;84:953–971

7 Coltrera MD Ultrasound physics in a nutshell Otolaryngol Clin N Am 2010;43:1149–1159

Trang 36

Point-of-care ultrasound allows providers to

perform focused exams at the bedside to answer

specific clinical questions, guide management,

and ultimately improve care of patients.1 This

chapter focuses on orientation of providers to

the ultrasound screen, transducer, and patient,

as well as standard imaging planes An

impor-tant principle in bedside ultrasound imaging is

understanding orientation of three-dimensional

structures that are being displayed in two

dimen-sions A major advantage of real-time ultrasound

scanning is the capability to visualize an object

in multiple planes to better understand its

three-dimensional structure

Operator Orientation

Performing point-of-care ultrasound begins

with operator orientation Providers must use

a systematic approach to consistently acquire

images of high quality Traditionally, providers

have performed bedside scans standing on the

left side of the bed, similar to the physical exam,

with the ultrasound machine directly in front

of them One hand holds the transducer on the

patient and the other hand operates the sound machine Providers might stand on the right side of the bed when scanning the heart due to the heart’s position in the left chest.2The height of the patient’s bed and position

ultra-of the ultrasound machine should be adjusted

to optimize patient and operator comfort The machine should be close to the bedside so that controls can be reached The transducer should

be held with the same hand, whether left or right, to help develop consistent habits and muscle memory

Screen Orientation

During the early evolution of diagnostic sound from the 1940s until the 1970s, general medical and cardiac ultrasound imaging devel-oped two independent conventions for display-ing images on the screen In both conventions, the top of the screen corresponds with the probe face Superficial structures are viewed

ultra-at the top of the image and deeper structures are viewed at the bottom The structure of interest should be maintained in the center of the screen for best image resolution with most portable ultrasound machines

K E Y P O I N T S

• Providers must understand the orientation between patient, transducer, and ultrasound screen because ultrasound imaging generates two-dimensional images of three-dimensional structures

• Sagittal and coronal planes are along the long axis of the body, and these planes are

often referred to as the longitudinal plane The transverse plane is along the short axis of

the body

• Providers can use real-time ultrasound to guide invasive procedures by tracking the needle tip using either a longitudinal (in-plane) or a transverse (out-of-plane) approach

Trang 37

26

General medical ultrasound utilizes a

con-vention with the transducer marker

corres-ponding to the left side of the screen, usually

depicted by a small colored circle or square on

the screen (Figure 4.1) The majority of

special-ties performing diagnostic ultrasound imaging

follow this convention, including radiology and

emergency medicine Thus, imaging in a

trans-verse plane generates cross-sectional images as

if the patient were viewed from the foot of the

bed; i.e., the liver is on the left, the spleen on

the right Some providers may choose to invert

images generated by transvaginal ultrasound

so that structures nearest the transducer are

viewed at the bottom of the ultrasound screen

Cardiac ultrasound, on the other hand,

uti-lizes a convention with the transducer marker

corresponding to the right side of the screen

(Figure 4.2) This orientation is maintained

throughout cardiac ultrasound imaging

regard-less of transducer position.2

Transducer Orientation

The transducer should be held loosely in the

scanning hand, like a pen, with the thumb

and index finger The remaining fingers can

be held against the transducer or spread out

on the patient’s body to anchor the transducer

and maintain location and stability This grip

improves patient comfort by minimizing

pres-sure applied with the transducer and allows

better operator control to make fine

adjust-ments All transducers have a notch or marker

on one side that corresponds with the screen

marker for orientation (Figure 4.3)

There are four principal transducer

move-ments described in ultrasound imaging Using

standard definitions is important for

pro-vider training and communication Standard

nomenclature was defined by the American Institute of Ultrasound in Medicine (AIUM)

in 1999 Although other conventions exist, the AIUM nomenclature is the most cited across specialties The following definitions are used throughout this textbook (Figure 4.4):

□ Sliding: The transducer is held at a fixed angle, and the entire transducer is moved

on the body This maneuver helps tify the optimal location to obtain desired views, particularly when imaging in be-tween ribs

iden-□ Tilting: Tilting is also called fanning or

sweeping The transducer is held in place on

the skin, and the transducer is angled on the long axis of the transducer face to aim the ultrasound beam at structures in different planes Tilting is often used to obtain serial cross-sectional images of solid organs, such

as short-axis views of the heart, or to preciate the extent of a fluid collection

ap-Figure 4.1 Ultrasound image using conventional

orientation with marker at left side of screen (arrow).

Figure 4.2 Ultrasound image using cardiac screen

orientation with marker at right side of screen (arrow).

TransducerorientationmarkerAttachmentpoint for

a needle guide

Figure 4.3 An ultrasound transducer is held gently

like a pencil with the first three fingers and can be bilized by the fourth and fifth fingers on patient’s body.

Trang 38

sta-4—ORIENTATION 27

□ Rocking: The transducer is held in place

and angled side to side on the transducer

face’s short axis either toward or away

from the transducer orientation marker

This “in-plane” movement pushes one of

the transducer corners into the skin

sur-face Rocking is often used to center the

image on the screen

□ Rotating: The transducer position is held

constant while the transducer is turned

along its central axis like a corkscrew

Rotation is often used to align the

ultra-sound beam with the long or short axis of

a structure.3,4

Patient Orientation

Maintaining consistent transducer

orienta-tion relative to the patient is vital to interpret

images accurately Optimal patient

position-ing varies based on the exam of interest, but

orientation of the transducer marker remains

constant, in keeping with the convention

being used Using the standard convention, the operator faces the patient from the foot

of the bed, and the transducer marker points either toward the operator’s left (patient’s right side) or toward the patient’s head An important distinction is that when imaging from the head of the bed, such as in internal jugular central line placement, orientation with the screen is maintained by keeping the transducer marker pointing toward the opera-tor’s left, which is the patient’s left side in this situation

Imaging Planes

The body is divided into three primary planes

in ultrasound imaging: sagittal, transverse, and coronal Oblique images may also be obtained

in planes not parallel to the three standard

planes Additional terms often used are long

axis, or longitudinal plane, referring to sagittal

and coronal planes, and short axis, referring to

the transverse plane (Figure 4.5)

Trang 39

28

SAGITTAL PLANE

The sagittal plane is a vertical plane that divides the body into left and right halves The midsagittal plane refers to the plane run-ning through the midline of the body, passing through midline structures, such as the spine and umbilicus Parasagittal planes are verti-cal planes parallel to the midline By standard convention, the transducer marker is directed superiorly toward the patient’s head so that superior structures are seen on the left side of

the ultrasound screen The term sagittal view

refers to an image acquired in either the sagittal plane or one of the parallel parasagittal planes (Figure 4.6)

mid-CORONAL PLANE

The coronal plane, also known as the frontal

plane, is the plane that divides the body into

ventral and dorsal, or anterior and posterior, halves By standard convention, the transducer marker is kept pointed toward the patient’s head, creating a long axis or longitudinal image with the patient’s head toward the left side of the screen (Figure 4.7)

TRANSVERSE PLANE

The transverse plane, also known as the

short-axis plane, is the plane that divides the body

into superior and inferior parts and is pendicular to the sagittal and coronal planes

per-

Short-axis

Sagittalplane

Transverseplane

Long-axis

(longitudinal plane)

Coronalplane

Figure 4.5 Planes of the body: sagittal, coronal,

and transverse The sagittal and coronal planes are

often referred to as longitudinal or long-axis planes,

and the transverse plane is often referred to as the

short-axis plane.

AnteriorSagittal plane

Posterior

Figure 4.6 Sagittal plane.

Trang 40

4—ORIENTATION 29

These are the same planes seen in computed

tomography scans By standard convention,

the transducer marker points to the

opera-tor’s left side so that the patient’s right-sided

structures appear on the left side of the screen5

(Figure 4.8)

Needle Orientation

Many invasive procedures, such as central venous catheter insertion, are performed with real-time ultrasound guidance to decrease complications Maintaining appropriate needle orientation with

Superior

LateralCoronal plane

Right lateral

AnteriorPosterior

Figure 4.8 Transverse plane.

Định dạng
Số trang	188
Dung lượng	17,23 MB