Ultrasound Teaching Manual E-Book

Matthias Hofer

• Herausgeber: Thieme
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 322

Veröffentlichungsjahr: 2020

Beschreibung

Step by Step to Proficiency in Diagnostic Ultrasound

This workbook is divided into lessons that guide you—like an instructor in an ultrasound course—systematically through the individual organ systems and body regions.

Key features of the fourth edition:

• Special multiple-exposure photos demonstrate the dynamics of handling the transducer
• Triplet-image units vividly illustrate transducer positioning, the ultrasound image, and relevant anatomy
• Reference numbers on the accompanying diagrams help you to both actively develop your knowledge and to test it at any time. The legend located on the back cover flap is the key to the reference numbers that are used consistently in each diagram.
• Quiz images at the end of each chapter are the perfect tool for rigorous self-evaluation
• Physical fundamentals are presented in vibrant, illustrative diagrams
• Numerous practical tips and tricks make it easy to familiarize yourself with ultrasound
• A primer on ultrasound interpretation explains specialized terminology concisely and clearly
• Precise descriptions of algorithms for transducer positioning facilitate real-time examinations

Videos (online access) showing relevant ultrasound anatomy, optimal transducer positioning, and the images you will see on the monitor during examination let you experience the content live—a perfect complement to the book that will greatly improve your retention of the material.

This book includes complimentary access to a digital copy on https://medone.thieme.com.

Leseprobe

The Most Important Planes in Abdominal Ultrasound

In this book, the point at the end of the position mark on the transducer corresponds to the right edge of the respective image. Think about which organs will be visualized in which respective imaging plane. To find the solutions, fold this page out and look on the back.

Standard Planes with Appropriate Transducer Position and Drawing Templates

Ultrasound Teaching Manual

The Basics of Performing and Interpreting Ultrasound Scans

Fourth expanded and revised edition

Matthias Hofer, MD, Associate Professor, MPH, MME (Univ. Bern)Director of Education at the University Institute of Diagnostic, Interventional and Pediatric Radiology (DIPR)Dept. Head: Univ.-Prof. Johannes Heverhagen, MD, Inselspital Bern, Bern University, Switzerland

With Ultrasound Images from:

Alexis Müller-Marbach, MDHead of Dept. of Gastroenterology, Hepatology and Palliative CareHelios Hospital Niederberg, Germany

Jasmin D. Busch, MD, Associate ProfessorSection Head of Pediatric Radiology, Inselspital Bern, Bern University, Switzerland

930 Images

Library of Congress Cataloging-in-Publication Datais available from the publisher.

This book is an authorized translation of the 10th German edition published and copyrighted 2020 by Georg Thieme Verlag, Stuttgart.Title of the German edition: Sono-Grundkurs

Translator: John GrossmanIllustrators: Dr. Willi Kuhn, Ramona Sprenger

© 2021 Georg Thieme Verlag KG

Georg Thieme Verlag KGRüdigerstrasse 14, 70469 Stuttgart, Germany+49 [0]711 8931 421, [email protected]

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Cover design: Thieme Publishing GroupTypesetting by Ramona Sprenger, Colognewww.einraumapartment.dePrinted in Germany byDruckerei Steinmeier, Deiningen

DOI 10.1055/b000000431

ISBN 978-3-13-243760-9     5 4 3 2 1

Also available as an ebook:eISBN (PDF): 978-3-13-243761-6eISBN (ePub): 978-3-13-243762-3

Important note:

Medicine is an ever-changing science undergoing continual development. Research and clinical experience are continually expanding our knowledge, in particular our knowledge of proper treatment and drug therapy. Insofar as this book mentions any dosage or application, readers may rest assured that the authors, editors, and publishers have made every effort to ensure that such references are in accordance with the state of knowledge at the time of production of the book.

Nevertheless, this does not involve, imply, or express any guarantee or responsibility on the part of the publishers in respect to any dosage instructions and forms of applications stated in the book. Every user is requested to examine carefully the manufacturers’ leaflets accompanying each drug and to check, if necessary in consultation with a physician or specialist, whether the dosage schedules mentioned therein or the contraindications stated by the manufacturers differ from the statements made in the present book. Such examination is particularly important with drugs that are either rarely used or have been newly released on the market. Every dosage schedule or every form of application used is entirely at the user’s own risk and responsibility. The authors and publishers request every user to report to the publishers any discrepancies or inaccuracies noticed. If errors in this work are found after publication, errata will be posted at www.thieme.com on the product description page.

Some of the product names, patents, and registered designs referred to in this book are in fact registered trademarks or proprietary names even though specific reference to this fact is not always made in the text. Therefore, the appearance of a name without designation as proprietary is not to be construed as a representation by the publisher that it is in the public domain.

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Contents

Standard planes (front cover flap)

Physical principles

Image generation, sound transmission, reflection

Echogenicity, frequency ranges

Operation and features of ultrasound units

Selection of ultrasound units, types of transducers

New techniques

Panoramic imaging, 3D, Clarify Vascular Enhancement

Harmonic imaging, phase inversion,

Contrast agents

Ultrasound CT

Pulse compression, precision upsampling

Diagnostic ultrasound catheter

Artifacts

Reverberation, section thickness, acoustic enhancement

Acoustic shadowing, mirror-image artifacts

Side-lobe artifact, quiz for assessing progress

Practical tips and tricks for the beginner

Lesson 1

Retroperitoneum, Sagittal plane

Anatomy

Upper retroperitoneum, normal findings

Lower retroperitoneum, normal findings

Aortic aneurysm

Right heart failure

Quiz

Lesson 2

Retroperitoneum, Transverse Plane

Anatomy

Normal findings

Age-related echogenicity

Acute pancreatitis, chronic pancreatitis

Pancreatic tumors

Retroperitoneal lymph nodes

Quiz

Lesson 3

Porta Hepatis, Gallbladder, Biliary Tract

Anatomy

Porta hepatis

Normal findings

Portal hypertension

Portal vein thrombosis, lymph nodes

Gallbladder

Cholecystitis

Differential diagnosis of cholecystitis

Gallstones

Gallbladder polyps, cholestasis

Biliary tract

Lesson 4

Liver

Anatomy of the segments of the liver

Sagittal plane, organ size, lateral angle

Transverse plane, hepatic veins

Right heart failure

Normal variants, fatty liver

Focal fatty infiltration, focal sparing in fatty infiltration

Cysts, echinococcosis (CE)

Echinococcosis (CE), hepatic hemangiomas

Focal nodular hyperplasia (FNH)

Cirrhosis of the liver

Hepatocellular carcinomas, liver abscesses

Liver metastases, hypervascular metastases

Hypovascularized liver metastases

Quiz

Lesson 5

Kidneys, Adrenal Glands, Renal Transplants, Spleen

Anatomy of the kidneys and adrenal glands

Normal findings

Normal variants, renal cysts

Kidney degeneration, nephritis

Urinary obstruction

Differential Diagnosis of Urinary Obstruction

Renal calculi, renal infarction

Benign renal tumors, malignant renal tumors, adrenal tumors

Normal findings

Determining the size of a renal transplant, lymphoceles

Spleen

Anatomy, examination technique

Spleen size, splenomegaly

Splenomegaly, splenic infarcts, practical suggestion

Lymphomatous infiltration, splenic hematomas, hyperechoic lesions, splenic cysts

Quiz

Lesson 6

Thyroid Gland, Lymph Nodes, Gastrointestinal Tract

Anatomy, volumetric measurements, normal values

Normal findings

Goiter

Focal solid nodules, thyroiditis

Lymph nodes

Neck: lymph nodes

Differential diagnostic criteria, perfusion parameters

Differential diagnostic criteria, reactive inflammatory

Retroperitoneal lymph nodes

Gastrointestinal tract

Anatomy, wall layers

Gastric tumors

Crohn’s disease

Intestinal intussusception, hernias, contrast enema

Wall thickening, diarrhea, appendicitis

Fecal impaction, colitis, colon carcinoma

Diverticulitis

Quiz

Lesson 7

Bladder and Reproductive Organs

Anatomy

Bladder

Examination technique, determining postvoiding residual bladder volume

Indwelling catheter and differential diagnosis of cystitis, wall thickening, internal echoes and sedimentation, ureteral peristalsis

Reproductive organs

Prostate and testis

Undescended testis, orchitis, hydrocele

Endovaginal ultrasound, image orientation

Uterus: normal findings

Uterine tumors

Ovaries: volume, menstrual cycle phases

Ovarian cysts and tumors

Pregnancy testing

Placenta position and gender determination

Quiz

Lesson 8

FAST, eFAST, Lung, FAST algorithm eFAST algorithm

Seashore sign, barcode sign

Lung mobility, pulmonary pulse

Lung point in pneumothorax

Pleura

Quantifying pleural effusions

Pleuritis, empyema, mesothelioma

Ribs

Costal fractures, costal metastases

Lung

Pneumonia, pulmonary infarct, bronchial carcinoma

Quiz

Lesson 9

Pediatrics

Skull and central nervous system

Anatomy of the CSF spaces

Normal findings in the sagittal plane

Normal variants

Normal findings in the coronal plane

Cerebral hemorrhage

Hydrocephalus

Spinal canal

Hip

Preparation and positioning

Normal findings

Setup and measurement errors

Graf’s classification of Infant Hips

Kidneys, Bladder, Spleen

Kidneys in newborns

Diffusely increased echogenicity, nephrocalcinosis

Urinary obstruction and reflux

Urinary obstruction, voiding cystourethrogram

Renal and adrenal tumors

Urachus, ureterocele, spleen size

Gastrointestinal tract

Pyloric hypertrophy, reflux, Hirschsprung’s disease

Appendices

Primer of Ultrasound Findings

Index

Template for Report of Normal Findings

Template for Report of Normal Findings

Answers to Quizzes

Thanks to Contributors, Hands-on Ultrasound Courses

List of Abbreviations

Examination Algorithms

References

Space for Your Notes and Drawing Exercises

Where Do I Find Which Chapter?

Physical Principles

Lesson 1

Retroperitoneum, Sagittal Plane

Lesson 2

Retroperitoneum, Transverse Plane

Lesson 3

Porta hepatis, Gallbladder, Biliary Tract

Lesson 4

Liver

Lesson 5

Kidneys, Adrenal Glands, Renal Transplants, Spleen

Lesson 6

Thyroid Gland, Lymph Nodes, Gastrointestinal Tract

Lesson 7

Bladder and Reproductive Organs

Lesson 8

FAST, eFAST, Lung

Lesson 9

Pediatrics

Appendices

Tips for the Reader

How can you best profit from this book?

How can you use this manual optimally?

As you work through the individual chapters, you can benefit from several methodical and didactic features.

Find it quickly …

• Find a chapter: You will find the respective tab for each chapter on page 5.

• Find tough quiz questions for in-depth study.

• Find cross-referenced figures: The figures are numbered according to the page on which they appear. For example, Fig. 115.2 is on page 115.

• Find an explanatory figure or diagram supplementing the text. They are highlighted in the accompanying text in color and are almost always on the same page, eliminating the need to page through the book looking for them.

• Find numbered structures. Their reference numbers appear in bold in the accompanying text or on the back cover flap (the same number for each structure is used throughout the entire book).

• Find keywords on page 148 (or on pages 4-6).

• Find for each structure normal values and checklists. These are also provided on laminated, water-resistant, pocket-sized cards.

Why we call this book a “workbook”?

A unique feature of this book is that you can use each page as a quiz to test your knowledge. The diagrams contain reference numbers instead of labels. This means you can go through the material a second time and use any figure to test which structures you know and which you still have to learn. The quiz questions and drawing exercises have a similar purpose. In this way, you can become familiar with several efficient study methods that allow you to integrate new material into your long-term memory faster – even though this requires you to take a more active approach to learning. Not only do I wish you good luck with this course, I also hope you have fun doing it!

Matthias Hofer, MD, Associate Professor, MPH, MME, Summer 2020Director of Education at the University Institute of Diagnostic, Interventional and Pediatric Radiology (DIPR) Inselspital Bern, Bern University, Switzerland

What does the respective color coding mean in the diagrams?

Introduction

Physical Principles and Technical Fundamentals

New Techniques

Artifacts

Quiz

Practical Tips and Tricks for the Beginner

Physical Principles and Technical Fundamentals

Image Generation

Ultrasound images are generated not by X-rays but by sound waves that are sent by a transducer into the human body and reflected there. In abdominal ultrasound, the frequencies used generally are between 2.5 and 5.0 megahertz (MHz; see p. 11). The primary condition required for sound wave reflections is the presence of so-called “impedance mismatches.” These occur at the interface between two tissue layers with different sound transmission properties (interfaces in Fig. 8.1). It is interesting to note that different soft tissues show only minor differences in the transmission speed of sound (Table 8.1).

Only air and bone are marked by massively different sound transmission in comparison with other human tissue. For this reason ultrasound units can be operated at a preselected medium frequency of approximately 1540 m/s without producing any major inaccuracies in the calculated origin (”depth”) of the echo.

The processor computes the depth of origin of the echo from the time difference detected between emission of the sound impulse and return of the echo.

Echoes from tissue close to the transducer (A) arrive earlier (tA) than echoes from deeper tissues (tB, tC in Fig. 8.1a). The mean frequency is strictly theoretical since the processor cannot know which type of tissue the sound waves traversed.

Table 8.1

Fig. 8.1ab

Which Component of the Sound Wave is Reflected?

Fig. 8.1a shows on the left three tissue blocks traversed by sound waves that differ only minimally in their transmission velocity (indicated by similar gray values). Each interface only reflects a small portion of the original sound waves () as echo (). The right–hand diagram shows a larger impedance mismatch at the interface A between the different tissues (Fig. 8.1b). This increases the proportion of reflected sound waves () in comparison to the tissues shown on the left. However, what happens if the sound waves hit air in the stomach or a rib? This causes a so-called “total reflection,” as illustrated at interface B in Fig. 8.2b: The transducer does not detect any residual sound waves deep to this structure from which it can generate an image. Instead, the total reflection creates an acoustic shadow (45).

Conclusion:

Intestinal or pulmonary air and bone are impenetrable by sound waves, precluding any imaging deep to these structures. The goal will later be to work around intestinal air or ribs by maneuvering the transducer. The pressure applied to the transducer against the abdominal wall (see p. 21) and the acoustic gel that displaces air between the surface of the transducer and the patient’s skin (see p. 22) play a significant role.

From a “Snowstorm” to an Image …

Do not get discouraged if at first you can only make out a blinding “snowstorm” on ultrasound images. You will be surprised how soon you will learn to recognize the ultrasound morphology of individual organs and vessels. Fig. 8.2 visualizes the gallbladder (14) as a black structure and shows two round polyps (65) within it. The surrounding gray “snowstorm” corresponds to the hepatic parenchyma (9) which is traversed by hepatic vessels (10, 11). How can you quickly work out which structures in the image appear bright and which are dark? The key lies in the concept of echogenicity (see p. 9).

Fig. 8.2a Gallbladder with polyps b

What Does the Term “Echogenicity” Mean?

Please use the following terms:

These fluids are anechoic (= black):

Hyperechoic (= bright)

pericardial or pleural effusion,

Hypoechoic (= dark)

ascites, cysts, blood, urine, bile,

Anechoic (= black)

cerebrospinal fluid

This is due to the lesser density of fat in comparison with normal liver tissue. On ultrasound the fatty deposits produce more impedance mismatches (Fig. 9.1c) than in normal liver tissue (Fig. 9.1d). Consequently, a fatty liver appears more echogenic (brighter) on ultrasound despite its significantly lower physical density.

A common misunderstanding:

What do ultrasound examiners mean when they refer to a “dense liver”? Either they are not expressing themselves clearly or they have failed to grasp the fundamental principle of ultrasound imaging and how it differs from radiography. Ultrasound does not visualize physical tissue densities but differences in sound transmission (impedance mismatches) which are unrelated to density.

Fig. 9.1a CT: Fatty liver b CT: Normal liver c Ultrasound: Fatty liver d Ultrasound: Normal liver

Generation and Frequency Ranges of Sound Waves

Sound waves are generated by the reverse “piezoelectric effect.” The pressure waves of an echo distort crystals, causing them to emit an electrical impulse. The reverse takes place during transmission. A transducer includes many such crystals. Depending on the impulse applied, they can produce sound waves of various frequencies specified in megahertz (MHz). A “3.75–MHz” transducer does not exclusively emit pressure waves (sound waves) at a frequency of 3.75 MHz. That is merely the specified median frequency (= “center frequency”). In fact, such a transducer may emit sound wave frequencies between, for example, 2 and 6 MHz. So-called “multi frequency transducers” have the additional capability to increase or decrease this center frequency and the surrounding bandwidth of transmitted sound frequencies. In thin patients or children, for instance, the bandwidth can be shifted (say 4–8 MHz with a center frequency of 6 MHz) to achieve better spatial resolution. However, this decreases the depth penetration of the sound waves.

In very obese patients, the use of lower frequencies (1–5 MHz with a center frequency of 2.5 MHz) can be appropriate to achieve the necessary penetration, but at the cost of lower resolution (see p. 11). Newer methods base their image generation on frequency shifts or harmonic frequencies of the echo in relation to the original ultrasound impulse (see p. 13).

Operating an Ultrasound Unit

Many controls on different ultrasound units are quite similar in function and arrangement regardless of the manufacturer. Therefore this section will look at the console of one unit supplied by Samsung (Fig. 10.1), which will then be used to introduce common technical terms.

Selection of Transducer and Preset

After you have switched on the unit (A) and it has booted, select the appropriate preset (PS) and the appropriate transducer for the respective examination and enter the current patient data (PD). You will usually select a linear array transducer (L) for evaluating the thyroid gland and the extremities but a convex array transducer (C) for abdominal examinations. The sector transducer (E) is used primarily in echocardiography, and the endovaginal transducer (G) is used for gynecologic examinations.

Selecting the Image Mode, Gain, and Focus

Usually you will begin with “normal” black and white or B-mode ultrasound (B), before later possibly switching to color-coded imaging (C). If you also wanted to obtain a flow profile from a blood vessel, you would then activate the Doppler mode (D) as well. This unit is equipped with control knobs that increase the respective signal (gain) of the active imaging mode when turned clockwise and reduce it when turned counterclockwise. The amplification (gain) can also be adjusted using the depth gain compensation feature (G). The transducer angle (A) must also be entered to determine flow velocities in Doppler mode. If you wish to display the change in a line of the image over time, switch to M-mode (MM). You can also set the specific depth range that is to have the best spatial resolution; here you use a toggle switch to set one or more focal zones (FZ) in your penetration depth. A few units also have a CW Doppler (CW) that measures frequency shifts (= flow speeds) not by means of depth gain compensation but as the summation of all speeds over an entire line of the image.

Magnification and Zoom Function

Especially with smaller target structures, you can significantly increase your detection of pathologic changes by magnifying the target organ (Mag) organ or zooming (Z) certain parts of the image. One common feature on almost all units is the position of the freeze or stop button (St) in the lower right corner of the console. This freezes the moving image. It is recommended to rest one finger of your left hand lightly on this button during the examination to minimize delay in capturing a desired image.

Size and Distance Measurements

After freezing (St) you can retrieve individual images from digital storage with the cine loop function: To do so, turn the trackball (T) to the left to 9:00 o’clock and go back image by image until you reach the desired one. Depending on the manufacturer and preset, up to eight simple measurements (M) can be performed one after the other on the frozen image. Use the trackball (T) and the set button(S) to define the beginning and end positions of your measured distances. It may be helpful to switch to double image mode (2x) for comparative measurements in different planes. Right next to this on most units is another button for switching back to single image mode (1x). More complex measurements such as volume measurements or flow indexes can be accessed with the measurement program (MP).

Helpful Extras

When you want to explain the imaging findings to the patient or a colleague, it is helpful to activate a pointer (P) which you can move across the frozen image with the trackball (T) to point out the findings you are explaining. If you really want to score points with your patients, install an additional monitor below the ceiling in their field of view. Well equipped units also offer automatic image optimization (QS), several hot keys for frequently used settings (P1-P3), and also several transducer sockets (SP) spare you the time and hassle of plugging and unplugging probes.

Fig. 10.1 Console and keypad

Selection of Ultrasound Units

In addition to large color Doppler units, ultrasound units with connections for several multi frequency transducers have proven especially useful in a hospital setting. Such mobile units are easily moved from the ultrasound suite to the ward or intensive care unit (Fig. 11.1).

The most important precaution when transporting the unit is to make sure that transducers are safely stowed so that dangling cables cannot become caught on doorknobs, gurneys, etc. A transducer that falls on the floor can easily represent a loss of €3000–7000 ($3300–7700) depending on the model. For the same reason, the transducer should never be left unattended on the patient’s abdomen when the examination is interrupted, for instance by a telephone call. Stowing the transducer in the frame with the cable hanging avoids unnecessary kinking that can lead to broken conductors in the cable.

Types of Transducers

Of the many types of transducers, only the three most important ones will be discussed here (endovaginal transducers, see p. 103).

A linear array transducer or “parallel scanner” emits parallel sound waves into the tissue and produces a rectangular image (Fig. 11.2a). The width of the image and the number of scan lines remain constant at all tissue levels. Linear array transducers have the advantage of good near-field resolution and are primarily used with high frequencies (5.0–10.0 MHz or higher) for evaluating soft tissue and the thyroid gland. Their disadvantage is the large contact surface. This can lead to air gaps between skin and transducer when it is applied to a curved body contour (loss of acoustic coupling). Further-more, acoustic shadowing (45) caused by ribs, lungs, or intestinal gas can greatly degrade image quality. Consequently, linear array transducers are rarely used for visualizing abdominal organs.

A sector transducer produces a fanlike image that is narrow near the transducer and increases in width with deeper penetration (Fig. 11.2b). This type of transducer has become established primarily in cardiology with lower frequencies (2.0–3.0 MHz) allowing deeper penetration. Due to the fanlike propagation of the sound waves, the heart can be well visualized through a small intercostal window without acoustic shadows from the ribs. The disadvantages of this type of transducer are their poor near-field resolution and decreasing line density in the far field with correspondingly decreasing resolution. Moreover, finding the desired imaging plane is difficult and takes some practice.

A curved or convex array transducer is a combination of the two types described above (Fig. 11.2c). The shape of the monitor image resembles a coffee filter and combines good near-field resolution with relatively good far-field resolution. The major advantage of the slightly curved contact surface is its ability to displace interfering intestinal air outside the imaging plane by applying increasing pressure (see p. 21). With this type of transducer, however, one has to accept decreasing resolution with increasing depth and, in certain locations, acoustic shadowing behind the ribs. This type is usually used in abdominal ultrasound with center frequencies from 2.5 MHz (in very obese patients) to 5.0 MHz (in slender patients).

The average frequency (center frequency) is usually 3.5–3.75 MHz. Memory aid: The higher the frequency, the better the resolution and the worse the penetration. The best way to remember this is to compare it to that loud music from your neighbor’s apartment. Which tones best penetrate even thick walls? The basses. These lower frequencies travel farther (i.e., penetrate deeper), see page 9.

Fig. 11.1

Fig. 11.2abc

New Techniques

Panoramic Imaging (SieScape®)

New high-performance image processors generate extensive ultrasound images from data acquired as the examiner moves the transducer slowly and continuously over the region of interest. With some practice, the examiner can produce impressive and undistorted images that allow distance measurements accurate to within 1–3% even on a curved body surface. Fig. 12.1 shows a sagittal scan with massive pleural effusion (69), compressive atelectasis of the lung (47), and, inferior to the liver (9), anechoic ascites (68) that appears to inundate the small bowel (46).

Fig. 12.2 impressively illustrates the position of the placenta (94) relative to the fetus. The high contrast resolution even allows evaluation of the interface between the fetal liver (9) and heart (114).

Fig. 12.1

Fig. 12.2

(With kind permission of Drs. C.F. Dietrich and D. Becker, from Farbduplexsonographie des Abdomens, Schnetztor-Verlag, Konstanz, Germany)

3-D Visualization

Especially in obstetrics, the three-dimensional visualization of fetal facial features improves the diagnosis of malformations such as cleft lip and palate. This technique can now visualize the physiognomy of the fetal skull with amazing accuracy (Fig. 12.3).

Of course, conventional cross-sectional imaging techniques can also detect skeletal and other malformations, albeit less impressively and clearly than three-dimensional ultrasound.

Fig. 12.3

Clarify Vascular Enhancement Technology

This technique is based on an algorithm that is able to significantly reduce the blurring on B-mode scans resulting from partial volume or section thickness artifacts. Flow information from the power Doppler mode is used, which helps to improve the spatial resolution of vascular contours on the B-mode image.

The result is significantly improved visualization of findings such as the contours of hard and soft plaque in the carotid arteries (Fig. 12.4b) compared with the visualization achieved by the conventional technique shown in Fig. 12.4a. It also facilitates evaluation of peripheral vascular rarefaction in the liver as the lumens of the hepatic veins and portal venous branches are more clearly visualized in the hepatic parenchyma (Fig. 12.5).

Fig. 12.4a “Normal” image of the carotid artery … b … with Clarify

Fig. 12.5 Hepatic vessels

The material on the following five pages is not an absolute prerequisite for the first practice sessions and can be skipped. Beginners may prefer to move from here directly to the preparations for Lesson 1 (see p. 21). After some initial practice they should return to these pages to reinforce their fundamental understanding of ultrasound imaging.

Tissue Harmonic Imaging (THI): This technique does not use the fundamental frequency of the original ultrasound impulse but their harmonics, integer multiples of the fundamental frequency (for example 7.0 MHz for a fundamental frequency of 3.5 MHz). These harmonics increase with increasing penetration, but their amplitude (intensity) remains far less than that of the base signal. The advantage of these harmonics is that they hardly arise at all near the transducer, but only develop with increasing penetration depth (Fig. 13.1). Consequently, they are less affected by the major sources of scattered image noise, which occurs especially in the anterior abdominal wall. Why do harmonics develop only with increasing penetration depth? Ultrasound waves are distorted as they traverse tissues with varying acoustic properties. Their pressure waves compress and relax the tissue as they penetrate it. Compressed tissue increases the speed of sound. However, as the tissue relaxes, the speed decreases, causing the trough of the pressure wave to propagate more slowly. The resulting distortion of the wave form (Fig. 13.2) induces harmonics. This is a cumulative effect that increases with the depth of penetration. Consequently, the amplitudes of the harmonic frequencies initially increase with penetration depth until this increase is offset by general absorption (Fig. 13.1).

Fig. 13.1

Fig. 13.2

Second Harmonic Imaging: This technique uses only the doubled frequency of the base signal for imaging. To avoid any overlapping of the range of the fundamental frequency (Fig. 13.3a) a narrowband signal must be used to distinguish the stronger components of the fundamental frequency from the weaker components of the harmonic (Fig. 13.3b). However, the narrower bandwidth of the signal leads to a slight reduction in contrast and spatial resolution. In spite of these short-comings, this technique has markedly improved the detection of details (Fig. 13.4b) compared with conventional ultrasound imaging (Fig. 13.4a), especially in obese patients (whose abdominal wall produces excessive scattering).

Fig. 13.3

Fig. 13.4ab

Fig. 13.5a Linear b Nonlinear

If the echoes of both signals are added, the sum equals zero as long as the signal has not undergone any changes in the body. As a result, both fundamental frequency echoes are suppressed (Fig. 13.5a) whereas the second harmonic signal components are enhanced (Fig. 13.5b).

Fig. 14.2 depicts a case showing acoustic shadowing () deep to intrarenal calcifications (b) that are undetectable by conventional imaging (a). In addition, the renal cyst () appears better demarcated and can be classified as benign with greater confidence.

Fig. 14.1abc

Fig. 14.2ab

Fig. 14.3

Fig. 14.4

Contrast Enhancement

The echogenicity of blood and tissue can be enhanced with microbubbles with a diameter of 3–5 μm that pass through the capillaries and create more impedance mismatches within the blood stream (Fig. 14.3). So far, several contrast enhancement agents have been introduced and about 50 additional agents are under development. The contrast agent Levovist® consists of tiny air bubbles () about 3 μm in diameter (95% < 10 μm), which are stabilized with a thin envelope of palmitic acid (Fig. 14.4). They are initially bound to galactose microparticles that dissolve in the blood and release the microbubbles. The dry powder can be mixed by the examiner in different concentrations. The suspension passes through the pulmonary circulation, but is only injectable for about 8 minutes after preparation. Hypergalactosemia is a contraindication. Measuring just a few millimeters, the microbubbles are comparable in size to erythrocytes (Fig. 14.5), which explains how they are able to pass through the capillaries.

Ultrasound impulses with low sound pressure make these microbubbles vibrate at what is known as a low “mechanical index” of 0.05–0.2. Contrast images are created using the nonlinear resonance frequency exclusively. Alternatively, one can use a higher mechanical index around 1.0–1.5 to cause the microbubbles to burst and emit a significantly stronger signal (although only during a single passage). This is known as the burst method.

The contrast agent Sonovue® consists of an aqueous solution of sulfur hexafluoride (SF6) stabilized by a phospholipid layer (Fig. 14.6). The median size of the bubbles is about 2.5 μm (90% < 8 μm) with an osmolality of 290 mOsmol/kg. One possible advantage of this contrast agent is that the suspension remains stable for over 6 hours, allowing it to be used for several applications. The best results are achieved in conjunction with the tissue harmonic imaging (THI) technique, referred to as ”contrast harmonic ima-ging (CHI).” Frequently, the term contrast-enhanced ultrasound (CEUS) is also used.

A specific sound pressure causes the bubbles to vibrate and emit harmonic echoes. As a result, contrast harmonic imaging (Fig. 14.7b) can detect multiple liver metastases significantly better than noncontrasted imaging (Fig. 14.7a).

Fig. 14.5 Microbubbles

Fig. 14.6 Sonovue®

Fig. 14.7a Noncontrasted b CEUS

Spatial Compounding (SonoCT®T)

There is another technique for suppressing artifacts. “Real-time compound imaging” does not scan an image line by line (Fig. 15.1a), instead it scans from different angles and merges this data into an image in real time (Fig. 15.1b). Up to nine different slices can be scanned, allowing more precise visualization of tissue information. This is illustrated here by the morphology of arteriosclerotic plaque in the carotid artery ( in Fig. 15.2a) compared with conventional imaging (Fig. 15.2b).

Fig. 15.1ab

This technique has exhibited obvious advantages in ultrasound imaging of the breast and musculoskeletal system. Fig. 15.3b shows improved visualization of an entire biopsy needle () in the breast parenchyma in comparison with conventional imaging (Fig. 15.3a), making it possible to advance the needle to the suspicious lesion with greater precision.

Fig. 15.2ab

Fig. 15.3ab

Fig. 15.4

The combination of SonoCT® scanning with tissue harmonic imaging (see p. 13) has shown promising results. It allows detailed visualization of hepatic lesions (Fig. 15.5) or fetal morphology in prenatal ultrasound screening (Fig. 15.6). The high performance computer systems now available can easily combine SieClear® or SonoCT®