Ebook Pediatric ultrasound: Part 1

(BQ) Part 1 book Pediatric ultrasound presents the following contents: Theory and basics, ultrasound guided interventions, neurosonography in neonates, infants and children, ultrasound of the neck, basics of paediatric echocardiography.

Pediatric

Ultrasound

With contributions by

Brian Coley Andreas Gamillscheg Bernd Heinzl

Gerolf Schweintzger

Requisites and Applications Michael Riccabona

123

Division of Pediatric Radiology

Department of Radiology

University Hospital Graz

Graz

Austria

First edition originally published by © Georg Thieme Verlag, 2000

ISBN 978-3-642-39155-2 ISBN 978-3-642-39156-9 (eBook)

DOI 10.1007/978-3-642-39156-9

Springer Heidelberg New York Dordrecht London

Library of Congress Control Number: 2014931858

© Springer Berlin Heidelberg 2014

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Ultrasound (US) has become the mainstay of paediatric radiology, particularly as neonates, infants and children offer ideal scanning conditions Furthermore, with growing concern about radiation risks imposed to children for medical imaging, it has become even more important to exploit all options US may offer Numerous papers have been written on this topic focusing on the child’s increased radiation sensitivity Many campaigns have been initiated to promote radiation protection awareness throughout the world, such as the Image Gently campaign in the United States However, children will continue to need medical imaging, and when trying

to avoid irradiating methods such as CT and fl uoroscopy, alternative non-invasive imaging must be available Ultrasound is a relatively inexpensive, non-invasive and non-radiating imaging modality that promises to comply with all this requirements and must be promoted as the major initial modality As a consequence of this para-digm, high standard paediatric US must become available to all children in need throughout the world, 24 h a day, 7 days a week, throughout the year

When trying to support and educate people to properly perform high level atric US I was often asked by participants of various courses and lectures, if I know

paedi-a repaedi-asonpaedi-ably priced comprehensive booklet thpaedi-at covers paedi-all mpaedi-ain paedi-aspects of ppaedi-aedipaedi-at-ric US It shouldn’t be too big, and should address not only all relevant aspects and diseases but also modern methods and must offer image examples This request came particularly from colleagues from less wealthy countries such as the Third World and Asia, but also from sonographers and technicians, students, young col-leagues and residents in training, as well as paediatricians, paediatric surgeons, and radiologists who are not full time paediatric radiologists

So I set out to try and create such booklet In order to achieve these goals the text had to be short - thus this book is written in a checklist like style The text is less extensive, and the legends are compact Some less important conditions and aspects are only briefl y mentioned or omitted, and image examples are focused on either very common important entities or on rare but still essential conditions that should not be overlooked or mistaken (i.e., relevant for differential diagnosis) Particular emphasis has been given to new approaches that widen US potential such as peri-neal US, contrast-enhanced US or fi lling techniques, using modern equipment and routinely encompassing Doppler sonography However, basic features and rules also remain valid and important, particularly as they need to be respected and be addressed with any standard equipment; the description of those should enable the

reader to make an US diagnosis provided careful and proper selection of adequate transducers and correct device settings is available Further and more detailed infor-mation must, however, be retrieved from respective established textbooks

This project could only be realized by the help and support of Springer company,

my colleagues at work, the input (and images) from my co-authors, and the patience

of my partner Barbara And the enterprise was further spurred by the motivation and inspiration I got from all the children and parents I encountered during daily work, their needs and suffering, but also their gratitude or their rewarding smile I can only hope that you will fi nd this booklet helpful for your daily needs and that it will achieve its goal, to contribute and improve access to dedicated paediatric US for all children in need, inspiring sonographers and physicians to outmost exploit US potential, to use creative approaches and apply US whenever there is an option that this might offer a diagnostic or therapeutic solution to the child’s condition Even if

US is fi nancially not as rewarding as other imaging methods, it will hopefully be rewarding in terms of diagnostic success at reduced invasiveness and without radia-tion burden - an aspect I particularly learned to pursue and value from my four children to whom I want to dedicate this work

January 2013

I thank my co-authors for also providing many images for the various chapters of the book, and I am furthermore particular thankful to Prof Coley for all the hard work he must have had with English editing, as well as Mrs Einspieler for typing the scripts

1 Theory and Basics 1

1.1 Ultrasound (US) Physics 2

1.1.1 US Waves 2

1.1.2 Propagation and Modulation of US 2

1.2 Practical Application in US Device 4

1.2.1 Emission, Transmission, Reception and Amplifi cation 4

1.2.2 Signal Processing 5

1.2.3 Components of US Device 6

1.3 US Methods 9

1.3.1 A (Amplitude)-Mode 9

1.3.2 (T)M-Mode (Time-Motion-Mode) 9

1.3.3 B (Brightness)-Mode 10

1.3.4 Doppler Sonography 11

1.4 Artefacts 11

1.4.1 General Remarks 11

1.4.2 Common Artefacts 12

1.5 Biologic Effects 15

1.5.1 General Remarks 15

1.5.2 Thermal Effects 16

1.5.3 Mechanical Effects and Resonance 16

1.5.4 Potential Risks of Diagnostic US 17

1.5.5 Various Methods and Indices That Allow Estimation of Biological Risks 18

1.6 How to Perform Paediatric US 19

1.6.1 Requisites 19

1.6.2 Positioning 20

1.6.3 Device Handling 21

1.6.4 Transducer Selection 22

1.6.5 Course of Investigation and Measurements 23

1.7 Documentation and Interpretation 25

1.7.1 Image Documentation 25

1.7.2 Report 26

1.8 Doppler Sonography 27

1.8.1 The Doppler Phenomenon 27

1.8.2 Different Techniques and Applications of Doppler Sonography 28

1.8.3 Artefacts in (Colour) Doppler Sonography 34

1.8.4 How to Perform (Colour) Doppler Investigations 37

1.8.5 Limitations 37

1.8.6 Interpretation 37

1.9 Modern and Future US Methods and Techniques 39

1.9.1 High-Resolution US (HR-US) 39

1.9.2 Image Compounding 39

1.9.3 Harmonic Imaging (HI) 39

1.9.4 Extended Field of View US 39

1.9.5 US Texture Analysis 41

1.9.6 Sonoelastography 41

1.9.7 US with Contrast Enhancement (Echo-Enhanced US – ee-US, Contrast-Enhanced US – ce-US/CEUS) by Ultrasound Contrast Media (US-CM) 42

1.9.8 Three- and Four-Dimensional US (3D-/4DUS) 50

1.9.9 Potential Future for Other Modern Paediatric US Applications 57

2 Ultrasound-Guided Interventions 59

2.1 General Aspects 60

2.1.1 Requisites 60

2.1.2 Precautions and Preparations 60

2.2 US-Guided Filling of Structures for Diagnostic or Therapeutic Purpose 61

2.2.1 General Remarks for Assessing Physiologic Cavities (e.g Bladder, Vagina, Intestines and Stomach) 61

2.2.2 Diagnostic Sonographic Enema 61

2.2.3 Therapeutic Sonographic Enema 62

2.2.4 US Genitography 64

2.2.5 Contrast-Enhanced Voiding Urosonography (ce-VUS) 64

2.2.6 Other Intracavitary Contrast Applications 67

2.2.7 Intravenous ce-US 68

2.3 Biopsies and Punctures 69

2.4 Drainage 71

2.5 Vascular Access 73

2.6 Lumbar Puncture 74

2.7 Foreign Body Removal 75

3 Neurosonography in Neonates,

Infants and Children 77

3.1 Requisites 78

3.1.1 Equipment and Transducer Needs 78

3.1.2 Indications for Brain US 79

3.1.3 How to Investigate 79

3.2 Normal Findings 81

3.2.1 Transfontanellar Access 81

3.2.2 Alternate Access Findings 83

3.2.3 Colour Doppler Sonography (CDS) 84

3.2.4 Normal Variances in Preterm Babies 87

3.3 Pathologic Findings 92

3.3.1 Neural Tube Defects 92

3.3.2 Migration and Gyration Alterations and Disturbances 94

3.3.3 Phakomatoses 98

3.3.4 Cerebral Cysts 98

3.3.5 Ischemic Encephalopathy 100

3.3.6 Infl ammation 105

3.3.7 Dilatation of CSF Spaces: Hydrocephalus 107

3.3.8 Cerebral Haemorrhage 114

3.3.9 Tumours and Space-Occupying Lesions 119

3.3.10 Cerebral Calcifi cations 122

3.4 Ultrasound of the Skull 122

3.4.1 Introduction 122

3.4.2 Haematoma 122

3.4.3 Space-Occupying Lesions and Tumours 123

3.4.4 Skull Fracture 123

3.5 Additional Imaging 123

3.5.1 Plain Film 123

3.5.2 CT 123

3.5.3 MRI 124

3.5.4 Catheter Angiography 124

3.5.5 Additional Supporting Procedures 124

3.6 Ultrasound of the Eye and the Orbit 124

3.6.1 Introduction 124

3.6.2 Normal Findings 124

3.6.3 Sonographically Depictable Pathology 125

3.7 Ultrasound of the Spinal Canal 127

3.7.1 Requisites 127

3.7.2 Transducers and Technique 127

3.7.3 Indications 127

3.7.4 Normal Findings 128

3.7.5 Pathologic Findings of the Spinal Cord 130

3.7.6 Trauma 134

3.7.7 Tumours 134

3.7.8 Other Spinal and Vertebral Pathology 135

3.7.9 Additional Imaging 135

3.7.10 Value of US 136

4 Ultrasound of the Neck 137

4.1 Indications, Requisites and Techniques 138

4.1.1 Transducers 138

4.1.2 Positioning and Handling 138

4.1.3 Typical Examinations 138

4.2 Normal Findings 140

4.2.1 Lymph Nodes 140

4.2.2 Cervical Glands 140

4.2.3 Other Cervical Soft Tissues 143

4.2.4 Cervical Vessels 144

4.3 Pathologic Findings 146

4.3.1 Lymph Nodes 146

4.3.2 Pathology of Cervical Soft Tissue 146

4.3.3 Thyroid Gland 152

4.3.4 Salivary Glands (Parotid, Sublingual, Submandibular Gland) 155

4.3.5 Cervical Vessels 157

5 Basics of Paediatric Echocardiography 163

5.1 Introduction 164

5.2 Equipment Needs and Specifi c Considerations 165

5.2.1 Transducers 165

5.2.2 Standard US Techniques 165

5.2.3 Patient Position 165

5.2.4 Sedation 165

5.3 Standard Planes and Standardised Course of Examination 165

5.4 Normal 2D Echocardiogram Findings 166

5.4.1 Parasternal Views 166

5.4.2 Apical Views 167

5.4.3 Subcostal Views 169

5.4.4 Suprasternal View 169

5.5 Other Techniques 170

5.5.1 M (Motion)-Mode Echocardiography 170

5.5.2 Doppler Sonography 171

5.5.3 Other Calculations and Functional Parameters 171

5.6 Special Echocardiographic Techniques 172

5.6.1 Transoesophageal Echocardiography (TEE) 172

5.6.2 Three-Dimensional (3D) Echocardiography 172

5.6.3 Tissue Doppler Imaging (TDI) 172

5.6.4 Contrast-Enhanced US 172

5.7 Normal Values 172

5.8 Pathologic Findings 173

5.8.1 Congenital Heart Defects with Left-to-Right Shunt 173

5.8.2 Obstructions of Left Ventricular Outfl ow 177

5.8.3 Obstructions of the Right Ventricular Outfl ow 179

5.8.4 Miscellaneous Congenital Heart Defects 181

5.9 Acquired Paediatric Heart Diseases 184

5.9.1 Cardiomyopathies (CMP) 184

5.9.2 Acute Myocarditis 184

5.9.3 Acute (Infective) Endocarditis 184

5.9.4 Pericarditis/Pericardial Effusion 185

5.9.5 Kawasaki Disease 185

5.9.6 Intracardiac Thrombi 186

5.9.7 Cardiac Tumours 186

5.10 Complementing Investigations 186

5.10.1 Cardiac Catherisation and Angiography 186

5.10.2 Cardiac MRI and CT 187

5.11 When to Do What 187

5.11.1 Imaging in Typical Clinical Scenarios 187

5.11.2 Trauma and Emergency 188

6 Ultrasound of the Chest 189

6.1 Requisites 190

6.1.1 Transducers 190

6.1.2 Positioning 190

6.1.3 Indications 190

6.1.4 How to Perform Chest US 191

6.2 Normal Findings 191

6.2.1 Chest Wall 191

6.2.2 Breast 191

6.2.3 Pleural Space 192

6.2.4 Diaphragm 192

6.2.5 Lung 192

6.2.6 Mediastinum 193

6.2.7 CDS 195

6.3 Pathology of Chest Wall 195

6.3.1 Aplasia, Variations of Ribs 195

6.3.2 Congenital Malformations 195

6.3.3 Traumatic Changes 195

6.3.4 Chest Wall Tumours 196

6.3.5 Breast 196

6.3.6 Role of US and Additional Imaging 198

6.4 Pathology of Pleural Space 198

6.4.1 Pleural Effusion 198

6.4.2 Empyema 198

6.4.3 Other Pleural Pathology 200

6.4.4 Role of Imaging 200

6.5 Pathology of Diaphragm 201

6.5.1 Diaphragmatic Hernia 201

6.5.2 Diaphragmatic Motion Disturbance 202

6.5.3 Role and Potential of Imaging 202

6.6 Lung Pathology 203

6.6.1 Pneumonia 203

6.6.2 Lung Abscess 203

6.6.3 Atelectasis 204

6.6.4 Respiratory Distress Syndrome (RDS)/Hyaline Membrane Syndrome 205

6.6.5 Sequestration 206

6.6.6 Congenital Cystic Adenomatoid Malformation (CCAM) 207

6.6.7 Cysts 208

6.6.8 Infarction 208

6.6.9 Tumours and Space-Occupying Lesions 210

6.7 Other Miscellaneous and Rare Applications 210

6.7.1 US for Interstitial Lung Disease 210

6.7.2 US for Pneumothorax 211

6.8 Additional Imaging 211

7 Liver and Bile System 213

7.1 Requisites and Investigation 214

7.1.1 Preparation 214

7.1.2 Positioning 214

7.1.3 Transducers 214

7.1.4 Course of Investigation 215

7.1.5 Standard Planes 215

7.2 Normal Findings 216

7.2.1 Structure 216

7.2.2 Ligaments 217

7.2.3 Hepatic Veins (HV) 217

7.2.4 Portal Vein (PV) 217

7.2.5 Hepatic Artery (HA) 218

7.2.6 Gall Bladder 218

7.2.7 Common Bile Duct (Commonly Addressed as Hepato- Choledochal Duct) 218

7.2.8 Intrahepatic Bile Ducts 219

7.2.9 Doppler Findings 219

7.2.10 Special Aspects of Newborns and Infants 220

7.3 Pathology of the Liver 222

7.3.1 Congenital Changes and Normal Variance 222

7.3.2 Infl ammatory Conditions 223

7.3.3 Other Parenchymal Liver Disease 225

7.3.4 Portal Hypertension and Vascular Problems 230

7.3.5 Liver Trauma 234

7.3.6 Space-Occupying Liver Lesions 237

7.4 Biliary Tract and Gall Bladder 245

7.4.1 General Findings 245

7.4.2 Congenital Conditions and Normal Variants of Biliary Tract 245

7.4.3 Biliary Tract Diseases 248

7.4.4 Tumour-Like Conditions 251

7.4.5 Role of US 252

7.4.6 US-Guided Biopsy (See also Entry Interventional US, Chap 2) 253

7.4.7 Additional Imaging 253

7.5 US in Liver Transplantation 254

7.5.1 Pretransplant US 254

7.5.2 Intraoperative US 254

7.5.3 Postoperative Assessment 254

7.5.4 Typical Complications 255

8 Spleen and Pancreas 257

8.1 Spleen 258

8.1.1 Requisites 258

8.1.2 Positioning 258

8.1.3 Indications 258

8.1.4 Course of Investigation 258

8.1.5 Normal Anatomy 259

8.1.6 Normal Variants 260

8.1.7 Malformations 260

8.1.8 Splenomegaly 261

8.1.9 Trauma 261

8.1.10 Splenic Infarction 264

8.1.11 Space-Occupying Lesions of the Spleen 265

8.2 Pancreas 268

8.2.1 Requisites 268

8.2.2 Indication 268

8.2.3 Course of Investigation 268

8.2.4 Normal Findings 269

8.2.5 Variations and Malformations 270

8.2.6 Infl ammation: Pancreatitis 270

8.2.7 Trauma 272

8.2.8 Space-Occupying Lesions 274

8.2.9 Role of US 275

8.2.10 Additional Imaging 275

8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures, Abdominal Vessels and Abdominal Wall 276

8.3.1 Abdominal Vessels 276

8.3.2 Vascular Pathology 278

8.3.3 Mesentery 281

8.3.4 Mesenteric Lymph Nodes 283

8.3.5 Free Intraperitoneal Air 283

8.3.6 Free Intraperitoneal Fluid: Ascites 285

8.3.7 Retroperitoneal Soft Tissues 287

8.3.8 Abdominal Wall 288

9 US of the Gastrointestinal (GI) Tract 289

9.1 Stomach 289

9.1.1 Requisites 289

9.1.2 How to Investigate 290

9.1.3 Normal Findings 291

9.1.4 Normal Variants 291

9.1.5 Malformations 292

9.1.6 Pathologic Findings 292

9.1.7 Role of US 298

9.2 Bowel 298

9.2.1 Preparation and Requisites 298

9.2.2 Course of Investigation 299

9.2.3 Normal US Findings 300

9.2.4 Pathology 300

9.2.5 Acquired Obstructive Pathology 306

9.2.6 Infl ammatory Conditions 310

10 Ultrasound of the Urogenital Tract 321

10.1 Requisites 322

10.1.1 Indications 322

10.1.2 Preparation 322

10.1.3 Transducers 322

10.1.4 Positioning 323

10.1.5 How to Investigate 323

10.2 Normal Findings 324

10.2.1 Bladder 324

10.2.2 Kidney 325

10.3 Pathology of the Kidney 330

10.3.1 Congenital Conditions 330

10.3.2 Infl ammatory Renal Parenchymal Conditions 344

10.3.3 Vascular Conditions 348

10.3.4 Nephrocalcinosis 352

10.3.5 Urolithiasis 353

10.3.6 Other Important Renal Parenchymal Disease 354

10.3.7 Renal Failure (RF) 355

10.3.8 Renal/Urinary Tract Trauma 355

10.3.9 Renal Tumours 357

10.4 Renal Biopsy and Interventions 359

10.4.1 Renal Biopsy 359

10.4.2 Drainage/Nephrostomy 360

10.4.3 Postoperative Imaging 361

10.5 Renal Transplant 363

10.5.1 Normal US Findings in Renal Transplant 363

10.5.2 Pathologic US Findings 364

10.6 Adrenal Glands and Pararenal Space 365

10.6.1 General Remarks 365

10.6.2 Typical Normal US Finding 365

10.6.3 Pathologic Findings 366

10.7 US of Urinary Bladder 370

10.7.1 Requisites 370

10.7.2 Pathologic Findings 371

10.7.3 Paravesical Changes 376

10.7.4 Role of US 377

10.8 US of Male Genitals 377

10.8.1 US Technique 377

10.8.2 Normal Findings 378

10.8.3 Common Pathologic Findings 378

10.8.4 Infl ammation – Orchitis, Ependymitis 381

10.8.5 Scrotal Trauma 383

10.8.6 Torsion 383

10.8.7 Testicular Tumours 384

10.8.8 Role of US and Additional Imaging 385

10.9 Female Genitals 385

10.9.1 Indications 385

10.9.2 Requisites 386

10.9.3 Transducers 386

10.9.4 How to Perform Investigation 386

10.9.5 Normal Findings 386

10.9.6 Pathologic Findings 388

11 Small Part and Hip Ultrasound 397

11.1 Hip US 398

11.1.1 General Remarks 398

11.1.2 Examination Technique 399

11.1.3 Normal Anatomy 402

11.1.4 Pathologic Findings 404

11.2 Other Conditions of Hip Joint 407

11.2.1 Arthritis and Infl ammation of Hip Joint 407

11.2.2 (Femoral Head) Epiphysiolysis/Slipped (Capital Femoral) Epiphysis 408

11.2.3 Perthes Disease 409

11.3 Investigation of Bones, Joints, Tendons 410

11.3.1 Requisites and Technique 410

11.3.2 Typical Normal Findings 411

11.3.3 Pathologic Findings 412

11.4 US for Peripheral Vessels 424

11.5 US-Guided Interventions 424

Index 427

M Riccabona, Pediatric Ultrasound,

DOI 10.1007/978-3-642-39156-9_1, © Springer Berlin Heidelberg 2014

1

Michael Riccabona

M Riccabona

Division of Pediatric Radiology, Department of Radiology,

University Hospital Graz, Auenbruggerplatz 36,

Graz 8036, Austria

e-mail: michael.riccabona@klinikum-graz.at

Contents

1.1 Ultrasound (US) Physics 2

1.1.1 US Waves 2

1.1.2 Propagation and Modulation of US 2

1.2 Practical Application in US Device 4

1.2.1 Emission, Transmission, Reception and Amplification 4

1.2.2 Signal Processing 5

1.2.3 Components of US Device 6

1.3 US Methods 9

1.3.1 A (Amplitude)-Mode 9

1.3.2 (T)M-Mode (Time-Motion-Mode) 9

1.3.3 B (Brightness)-Mode 10

1.3.4 Doppler Sonography 11

1.4 Artefacts 11

1.4.1 General Remarks 11

1.4.2 Common Artefacts 12

1.5 Biologic Effects 15

1.5.1 General Remarks 15

1.5.2 Thermal Effects 16

1.5.3 Mechanical Effects and Resonance 16

1.5.4 Potential Risks of Diagnostic US 17

1.5.5 Various Methods and Indices That Allow Estimation of Biological Risks 18

1.6 How to Perform Paediatric US 19

1.6.1 Requisites 19

1.6.2 Positioning 20

1.6.3 Device Handling 21

1.6.4 Transducer Selection 22

1.6.5 Course of Investigation and Measurements 23

1.1 Ultrasound (US) Physics

1.1.1 US Waves

Definition

• Mechanical waves, usually created by electric current applied to piezoelectric crystal in transducer; used to emit sound waves and receive reflected echoes

• Frequencies used in diagnostic medicine range from 1 to 20 MHz

Sound Velocity

• Depends on material; the higher the density the higher the sound velocity

• In air, sound velocity is approximately 330 m/s; average sound velocity of human (soft) tissue = 1,540 m/s

1.1.2 Propagation and Modulation of US

US energy emitted into tissue is handled differently between different tissue layers: modu-lated, partially absorbed, partially transmitted and reflected on border of different tissue The most important principles for propagation phenomena:

1.1.2.1 Acoustic Impedance

Relation of sound pressure to resulting molecular motion

Tissues with high density need less energy to start undulating than tissues with little density

1.7 Documentation and Interpretation 25

1.7.1 Image Documentation 25

1.7.2 Report 26

1.8 Doppler Sonography 27

1.8.1 The Doppler Phenomenon 27

1.8.2 Different Techniques and Applications of Doppler Sonography 28

1.8.3 Artefacts in (Colour) Doppler Sonography 34

1.8.4 How to Perform (Colour) Doppler Investigations 37

1.8.5 Limitations 37

1.8.6 Interpretation 37

1.9 Modern and Future US Methods and Techniques 39

1.9.1 High-Resolution US (HR-US) 39

1.9.2 Image Compounding 39

1.9.3 Harmonic Imaging (HI) 39

1.9.4 Extended Field of View US 39

1.9.5 US Texture Analysis 41

1.9.6 Sonoelastography 41

1.9.7 US with Contrast Enhancement (Echo-Enhanced US – ee-US, Contrast-Enhanced US – ce-US/CEUS) by Ultrasound Contrast Media (US-CM) 42

1.9.8 Three- and Four-Dimensional US (3D-/4DUS) 50

1.9.9 Potential Future for Other Modern Paediatric US Applications 57

imped-Degree of reflection depends on surface structure (e.g smooth or rough and straight

or bent), angle between tissue surface and US beam

1.1.2.4 Absorption

US waves gradually weakened when crossing different media Loss depends on sue density and content, also proportional to US frequency (greater loss = less penetration):

tis-• Low frequency: good penetration but restricted resolution

• High frequency: decreased penetration but increased resolution

1.1.2.5 Deflection

When US wave passes small opening, US beam scattered depending on dimension

of this “lens”; scattered sound waves may cause artefacts

1.1.2.6 Focus

In modern diagnostic US, multiple crystals create multiple individual US waves These need to be focused at specific areas in order to create detailed images of defined area

Focusing achieved by:

• Hollow mirror effect: US field gets smaller and smaller by concave shape of emitting crystals

• Additional lenses

• Electronic focusing by dedicated steering of single elements with proper timing

Optimising focal zone:

Single and multiple focus techniques available – need to be constantly optimised/updated during investigation for optimal results

1.1.2.7 Resolution

Definition: minimal distance between two neighbouring structures that can still be discriminated

Two different phenomena:

• Lateral resolution: discrimination of objects side by side at same depth:

– Mostly dependent upon beam width

• Longitudinal and axial resolution: discrimination of objects in direction of US beam

– Mostly dependent upon frequency: the lower the frequency the worse the resolution (see Table 1.1)

1.2 Practical Application in US Device

1.2.1 Emission, Transmission, Reception and Amplification

• More reflected sound – more electric impulse – brighter, more echogenic signal

• Moderate reflection – poor echo

• No reflection – echo free or anechoic

Spatial location of reflecting structure defined by time interval between emitting and receiving:

• The deeper a structure the longer the sound beam needs to travel to it and back

• Measured time between sound emission and reception of certain reflected energy defines position/depth of certain structure within US field/image (in B-Mode US) The longer sound takes to travel, the deeper position of respective structure

Frequency (MHz)

Resolution (mm)

Depth (mm) Axial Lateral

1.2.1.4 Amplification

Electric signals created by incoming reflected US waves in crystals amplified within

US system for further processing

1.2.2.2 Post-processing

Performed once data collected, i.e on frozen image Many different electronic ulation tools can be applied to improve image quality, modulate contrast, weight certain gray levels, etc

mod-1.2.2.3 Time Gain Compensation (TGC)

Reflected echoes from deeper areas have to pass through much more tissue, fore suffer from more absorption: these signals are proportionally amplified to com-pensate for signal loss

there-NOTE: TGC should be constantly optimised during investigation, varies with

echodensity/absorption of more superficial transmitted structures (Fig 1.1)

1.2.2.4 Sound Energy = Output

Maximum output intensity defined by equipment depending on manufacturer

To avoid unnecessary overexposure of tissue/deterioration of image: decrease

US intensity as much as possible Definable partially by presets (e.g fetal exams,

Fig 1.1 TGC – image example (a) incorrect (b) correct TCG adaptation (a) Incorrect image of

the magnified retrovesical cross-section view without proper TGC adaptation – causes echogenic retrovesical structures reducing differentiation of anatomy; particularly the dilated left ureter can- not be clearly depicted (TCG settings recognisable by the dotted line on the right side of the

image) (b) Same section as in (a) – TGC adapted: better image quality – the slightly prominent

left ureter clearly visible distal as circular hypoechic structure

transcranial/transfontanellar brain US, US of eye/testis) or individually at beginning

of examination Can (must) be seen on display – usually as percentage of maximum output gain

NOTE: Every investigation should be performed at lowest possible sound output.

Impact of sound energy on tissue important to maintain safe sound pressure levels:

• Parameters depend on many factors such as focal zone, frequency and output gain setting

• New indices established: reflect impact of US energy on tissue (mechanical index = MI, thermal index = TI); should (must) be displayed during every investi-gation – monitor/observe closely

• In general, MI/TI should be kept below 1 to maintain safe sound exposure levels:

– For further details, see biological effects

1.2.2.5 Gain

Defines overall amplification of incoming signals:

• Optimise receive gain individually depending on output gain, patient, anatomy and area of investigation

1.2.2.6 Frame Rate/Persistence

Persistence: defines speed of image update:

• High frame rate – fast series of individual images, reduced susceptibility to motion artefacts – but usually at cost of slightly reduced resolution

• High persistence (information from series of individual images used to create final displayed image) – increased tissue density information and resolution – at cost of slower update of individual displayed image

Frame rate (Hertz, Hz): usually US investigations operate at 4–60 Hz; faster frame

rates are possible, e.g for cardiac studies

adapt-Sector Transducers

Small active surface (footprint) where sound beams emitted in sector format (Fig 1.2):

• Causes poor image quality in near field, improved visualisation of deeper fields

• Particularly useful for structures with only small access area (e.g raphy – access between ribs or brain US – transfontanellar access)

echocardiog-Different techniques used to create sector-like field:

• Mechanical devices that make crystal (or series of crystals) rotate or wobble:– Sector angle usually between 60 and 120° used for imaging

NOTE: Mechanical transducers may deteriorate over time by physical use – not

only proper handling but also exact production and alignment important (Fig 1.2a) Important to freeze image (i.e transducer) whenever one does not actually investigate to prevent early transducer deterioration/aging

• Electronic-phased array transducers – consist of series of crystals:

– By individual steering of consecutive crystals with varying time intervals (presently most common technique), effective US beam can be directed in many directions creating sector-like imaging field (Fig 1.2b)

• Annular array transducers – combination of mechanical and electronic technology:– Various concentric rings of crystals selectively activated during scanning pro-cess create sector-like field with homogeneous focus zone throughout entire imaging field

Fig 1.2 Sector transducers – all creating a sector-like triangular image; good for small footprint

access with wide view in far field (a) Conventional sector: sector-like images created by dedicated

array design or wobbling of a normal plane array The wobbler technique hardly used anymore Image is in a sector format; the shaded area represents the part of the structure that will be dis-

played on the monitor (b) Phased/electronic (vector/sector) transducer: most commonly used

for-mat (alternatively mostly micro-curved arrays used) Image created by electronic steering of

parallel-placed single elements (c) Annular array: annular concentric US array which is shaped by

specific lenses creating a very homogenous focal zone throughout the image field

Linear Array Transducers

• Parallel linear US beams created by multiple crystals – create rectangular image frame (Fig 1.3a):

– Homogeneous resolution throughout entire imaging field, particularly valuable for near-field assessment

– Generally used for superficial structures (e.g small-part applications, cervical vessels, infant hips, lymph nodes, soft tissue processes and bowel/ appendiceal US)

• New techniques allow for “phasing” of electronic linear transducer – creates

“virtual sector” image (“trapezoid”) – larger field of view in far field, at cost of frame rate and penetration

Curved Linear Array

• Crystals aligned on curved surface – diverging US waves create sector-like ing field (angle depends on radius of curvature); the larger surface (than sector transducer) offers good near-field information:

imag-– Combines abilities and benefits from sector and linear transducers

– Offer reasonable near-field resolution at large field of view at depth (Fig 1.3b).– Typical application: abdominal US

Other Transducers

• Matrix – 1.5-/2-dimensional arrays: enable sound emission in two perpendicular planes by assembling elements in parallel rows:

– Allow volume scanning (see 3DUS)

– Improve lateral (out of plane/elevational plane) resolution by bidirectional focussing of US beam

– Parallel columns of elements allow for simultaneous handling of different tasks (improving frame rate, e.g for image compounding or colour/duplex/triplex Doppler) by splitting individual operation modes to different parallel rows or cristals.

• Intracavitary probes: mainly intravascular or endoscopic probes, transrectal/intravaginal probes:

– Usually very small design, thus less elements

– Often higher frequencies – better resolution than with racic access but at restricted penetration

transabdominal/tho-– Enable visualisation of areas impossible to properly depict by standard access.– Attached to endoscopic devices/intravascular catheters

– Often limited use for paediatric applications, as other access often works sufficiently and size relatively large for paediatric cavities

– Dedicated small paediatric devices rarely available (e.g for transoesophageal echocardiography, transrectal pelvic floor US)

– Some applications uncommon, non-existent or not accepted in paediatrics (e.g transvaginal US)

1.2.3.2 Other Parts of US Device

• Keypad (may be mobile and flexible)

• Monitor (may be mobile and flexible, can and must be adjustable)

• Printer/CD recorder

• In-/output options

• Cooling device with filters (need to be cleaned regularly)

• Potentially gel bottle warming device and transducer stands

dur-1.3.2 (T)M-Mode (Time-Motion-Mode)

Used to show positional changes of reflecting interfaces over time

Principle: on x-axis of monitor graph, changes in position of individual image

pixels displayed; change in intensity of reflected echo is encoded by variation in

brightness, whereas time is encoded on y-axis.

Method frequently used in echocardiography and in some dedicated tions, e.g for assessment of peristalsis or motion (e.g ureteral peristalsis, diaphrag-matic motion) (Fig 1.4c).

applica-1.3.3 B (Brightness)-Mode

The commonly used real-time US imaging technique (Fig 1.4b)

Technique: transmitted US waves reflected when encountering various interfaces:

• Brightness of individual image pixels defined by intensity of reflected echoes (the stronger the echo the brighter the corresponding pixel)

• Position of pixels defined by direction of transmitted beam inducing individual

echo (encoded on x-axis) and time between sending and receiving (depth, encoded on y-axis).

• All reflected echoes displayed on monitor correspond to travel time within predefined beam direction – calculated sectional image

• Repetitive frequent updates of such sectional images create movie-like impression enabling what is called “real-time US”

a

b

c

Fig 1.4 US modes (a) A (amplitude)-Mode – oldest US technique: US signals emitted along

single line, amplitude of reflected echo encodes spike height on y-axis, whereas depth of origin

of reflection from individual structures encoded on x-axis (time between emission and receive)

(b) B (brightness)-Mode: transducer emits sound waves; the reflected echoes are received

Energy of echo encodes brightness of respective pixel on monitor; position of respective pixel calculated from individual travel time (i.e time between sound emission and receiving, with

known sound speed in tissue) (c) M (motion)-Mode : US image (of a prominent ureter, cross

section through bladder) shows a dotted line defining the section where changes (i.e motion, in this case ureteral peristalsis) over time are displayed as graph in lower part of image (blue)

Originally this was applied in echocardiography without orienting B-Mode image, just ing the lower graph to analyse heart wall or valve movements

• Frequency shift of received echoes can be measured; thus flow direction and flow velocity can be calculated and displayed in various ways (Fig 1.5b – also see below in Chap 1.8).

1.4 Artefacts

1.4.1 General Remarks

Artefacts caused by phenomena that interfere with image formation and cannot be sufficiently corrected:

• Impair image (e.g bowing artefacts, reflection artefacts)

• Can also be diagnostically valuable (e.g posterior enhancement/through mission for identification of liquids, posterior shadowing for identification of calcifications)

trans-• Knowledge of artefacts essential for proper image interpretation

Fig 1.5 Doppler US (a) Doppler scheme: US signal emitted; frequency shift of received echo

measured, thus flow velocity and flow direction can be calculated using Doppler equation; for correct velocity estimation, angle between incoming US signal and movement direction of

reflecting particle (i.e mostly erythrocytes) must be measured (b) Doppler display: besides

audio signal typically Doppler information displayed as flow graph after spectral analysis using Fourier transformation All velocities throughout spectrum are displayed at any time (of cardiac

circle), with intensity encoding number of reflectors at the individual velocity Y-axis encodes flow velocity; x-axis encodes time

1.4.2 Common Artefacts

1.4.2.1 Side Loop Artefact

Transducer does not only emit central beam but also side loops – can produce nificant echoes when reflected by strong interfaces Some of these echoes reflected into direction of central beam and received by transducer – these echoes appear projected into main beam, get used for image calculation, although deriving from structures out of main beam direction

sig-Only cause image impairment when encountering highly reflective surface; respective echoes are displayed as if arisen from central beam (wrong position), usu-ally only recognisable when occurring in fluid-filled or low-echogenicity structure

• Typical example: adjacent bowel gas surface alters image of gall bladder icking sludge

mim-• Can be identified by change of transducer position (e.g tilt transducer)

• Can usually be eliminated by repositioning transducer and reducing gain, ing angulation, etc

alter-1.4.2.2 Bowing Artefact

Arise by wrong projection of reflected echoes into anatomic incorrect position.Caused by oblique reflections of beam – reflected echo received by “wrong” crystal, position wrongly assigned for further processing

• Can usually be eliminated and identified by tilting of transducer

1.4.2.3 Noise

Definition: Signal-like monitor appearance throughout image is created by electronic processing and amplification Background noise is increasingly ampli-fied with reduced signal strength (e.g TGC adaptation or high-receive gain) Near limits of penetration: differentiation between noise and real signals may become impossible

Depending on gain settings, noise can also create artificial echoes within anechoic lesions such as fluid or cysts, making differentiation difficult or impossible – particularly when small

• For differentiation/identification: change focus position, output gain and ducer frequency

trans-1.4.2.4 Marginal Shadowing

Created by spherical structures with clear limit that exhibit significant acoustic impedance interval at its lateral borders – appears as line-like sound mitigation at lateral borders behind object

Physical cause – tangential impact of sound beam, additional scattering and reflection at lateral wall – then transmitted into deeper image sections

• Helpful for identification of cysts and tubular structures but may be mistaken for acoustic shadowing from small concretions, e.g in gall bladder or kidneys (Fig 1.6)

1.4.2.5 Posterior Enhancement – Increased Through Transmission

When sound passes through completely fluid-filled anechoic structure, intensity of

US beam is not altered by absorption and reflection: causes different echo intensity

of area deep to such fluid-filled structures compared to adjacent area of same depth where US beam has been more attenuated by intervening tissue

TGC correction artificially adapts for intensity drop by depth – areas behind fluid displayed more echoic than surrounding structures

• Helpful to identify fluid/fluid-filled structures

NOTE: In order to properly assess tissue behind large fluid-full structures,

adapta-tion of TGC correcadapta-tion to account for this phenomenon is essential (Fig 1.7)

Fig 1.6 Artefact – marginal shadowing, reverberations Artificial anechoic lines originating from margins of venous sinus in this axial liver view not corresponding to any specific anatomic or patho- logic findings Note echoic spots with reverberations within liver indicating intrahepatic air/gas

Fig 1.7 Artefact – through transmission Artificially increased echogenicity behind fluid-filled bowel structure due to increased through transmission but deteriorating differentiation of respec- tive structures (i.e gastric dublication cyst)

1.4.2.6 Reverberation Artefact

Definition: Multiple reflections of sound travelling between two parallel layers with strong acoustic interfaces – create repeated parallel echogenic lines that usually get weaker with depth:

• Typically observed parallel to transducer at superficial layers (e.g skin)

• Can be reduced by altering focus and decreasing (output) gain

“Ring-down artefact” caused by resonance from gas; short ring-down artefacts called comet tail artefact – special form of reverberation phenomenon, usually

appears behind gas/air-filled structures

• Created by scattering and reflection of incoming sound beam with irregular reflections and noise behind sonographically non-penetrable surface (Fig 1.8)

1.4.2.7 Increment or Slice Thickness/Beam Width Artefact

Sound beam dimensions vary depending on kind of transducer, frequency and focus settings Depending on relation of beam width with distance between solid and liquid structures, particularly at curved interfaces, small layer of low-degree echoes may appear May mimic second/hazy wall structure, can be mistaken for sludge within fluid A sort of partial volume phenomenon

• Can usually be eliminated by optimising focus setting and changing transducer

or frequency

1.4.2.8 Mirror Image Artefact

Strong reflecting interface (mostly gas – i.e air at lung base) met by sound beam in

an angle around 45°– acts as acoustic mirror – artificial mirror images observed behind reflecting border due to prolonged travel duration of incoming signal (Fig 1.9a)

• Also encountered on colour Doppler sonography (CDS), may be quite confusing

• Can be identified by changing transducer position/tilting transducer

Fig 1.8 Artefact – reverberation/comet tail artefact and dorsal shadowing Chest wall US: genic reverberations caused by aerated lung surface (↔) and dorsal shadowing (→) caused by

echo-ossified rib

sig-or bsig-order between low- and high-echogenicity tissues).

• Can cause duplication artefacts (duplicating structures) – also affects length measurements (e.g kidney)

• Refractive shadowing (see above – marginal shadowing artefact) caused by cusing and variations in beam energy or intensity at edge of fluid-filled structures

defo-• Can usually be eliminated by changing transducer position

1.4.2.11 Anisotropy

Occurs in tissues composed of very structured strong reflectors (e.g fibrillar pattern) – echoes vary with insonation angle (typically with muscles and tendons)

• Can usually be eliminated by changing transducer position/angulation

• Of utmost importance in muscular US – if unrecognised may lead to incorrect interpretation (i.e tear, etc.)

1.5 Biologic Effects

1.5.1 General Remarks

Biologic effects of diagnostic US based on physical phenomena caused by interaction

of emitted US with tissue depending on frequency, wave length and output energy

Fig 1.9 Artefact – mirror image artefact The echogenic border of skull bone causes mirroring of subcutaneous extracranial collection into subcalvarian intracranial compartment, mimicking a non-existing intracranial collection NOTE: artifacts from malattachment of tranducer to bowed skin surface in upper right corner of image

Different devices may cause variable tissue impact with same application – because of different output gain settings/other device-specific presets.

1.5.2 Thermal Effects

1.5.2.1 Tissue Heating

Caused by energy absorption – amount of temperature rise depends on output energy and intensity of sound field Increases with higher frequency by deposition

of higher amounts of energy in smaller volume (less penetration)

Additionally, temperature-handling ability of tissue is important, e.g ised and well-perfused tissue can better tolerate temperature changes than little or non-perfused tissue

vascular-Human tissue with highest thermal absorption is bone; therefore experiences highest temperature rise with secondary biologic effects particularly on neighbour-ing tissue

NOTE: some heat generated by transducer itself is also transmitted to skin/tissue 1.5.2.2 Biological Effects, Tissue Heating

Even on routine diagnostic scans using modern diagnostic US devices, measurable increase in temperature may occur; particularly important for fetal examinations and (trans)cranial US However, temperature that causes degeneration of proteins (i.e >45 °C) or potentially cell death (>41.5 °C) does usually not occur in diag-nostic applications

This effect must be considered when examining patients with high fever to avoid potential dangerous heat production; e.g relatively short insonation of individual areas advisable Commonly used parameter = thermal index (TI) Three different types of TI defined depending on tissue examined: TIS – small part, TIB – bone, TIC – cranial (see below):

• General rule of thumb: TI never >3, TIC <1.7, in neonatal brain TIC <1 (or better

<0.7) advisable

1.5.3 Mechanical Effects and Resonance

Resonance of molecules proportional to applied frequency depends on output energy, separate from mechanical impact on tissue by sound pressure

In order to maintain safety, diagnostic US devices initially did not allow energies

>100 mW/cm2 According to newer experimental observations, intensity measure changed – at present sound pressure levels considered more important:

• Relative upper limit of negative peak pressure is defined by 1 mPa; no relevant mechanical and resonance-induced tissue damage should occur below this level

• (Sound)Pressure waves have positive and negative partition; the latter is called suction force This negative pressure causes a sort of vacuum – has highest potential for tissue damage by implosion or cavitation

Danger/risk of mechanic effects estimated by mechanical index (MI): in general

MI should be kept below 1.7; in more risky areas <1; in very sensitive areas

<0.7: (e.g neonatal brain) and for low-MI contrast-enhanced US (ce-US) MI around 0.1–0.3 (see below)

1.5.3.1 Cavitation

Acoustic Cavitation

Sound-induced occurrence of hollow areas as well as gas bubbles in insonated material – may undulate and change size These small cavities and their activity cause wide spectrum of physical, chemical and biological effects

Negative Peak Pressure

Crucial parameter for estimation of cavitation effect: negative peak pressure within insonation field Additionally need cavitation seed – usually microscopic gas bub-bles that explosively increase in size during negative sound pressure

NOTE: Cavitation effects are independent from thermal effects; e.g US impulse

with high pressure and low frame rate can cause cavitation without any significant thermal changes

In human tissue, inert cavitation is no major problem – practically no cavitation seeds, except for tissue containing air or gas such as lung or intestines However, if

US contrast media (based on stabilised microbubbles) used, cavitation effects may become relevant, as for US of target adjacent to aerated structures:

• When respecting given limits/application guidelines, no clinical relevant damage

by diagnostic US (even using US contrast media) is currently reported

1.5.4 Potential Risks of Diagnostic US

Significant effects can be produced by US on all kinds of tissues This potential is used therapeutically (e.g lithotripsy, sonophoresis and treatment of tendinous calcifications)

Diagnostic US uses much lower energy levels than therapeutic US, though – using maximum output gain and long sound exposure on single site – biological effects can be demonstrated in animal experiments (cavitation, mechanic and ther-mal effects added, duration of exposure essential)

With prudent use, no significant impact in human medical diagnostic use in terms of carcinogenesis, teratogenesis or higher mutation rates found

1.5.4.1 Specific Risks

Long duration of pulsed duplex-Doppler and amplitude-coded CDS (aCDS) tigations with stationary US beam, particularly in vicinity to bone (for these appli-cations higher sound energy with focused focal pulse is usually used); i.e transcranial US, echocardiography – particularly in border areas with vicinity to aerated lung:

inves-• M-Mode: slightly higher-output energies used for depicting clear M-Mode signal

NOTE: Try to avoid focused pulsed duplex Doppler and M-Mode for fetal

echocar-diography (risk-benefit ratio to be considered)

1.5.4.2 Guidelines and Recommendations

In order to maintain biologic sound-induced risks as low as possible, some aspects need to be considered:

1 Diagnostic US – medical imaging; there should be clear indications on firm ical grounds for every investigation (with some exceptions for scientific and edu-cational needs)

2 Always try to minimise output gain by using maximum receive gain

3 Keep exposure times of specific area as short as possible; make use of frozen images for analysis instead of looking at same structure for long times under real-time US conditions (unless you need dynamic-functional observation)

4 Always first optimise image, particularly for Doppler investigations: only activate your colour box or PW-duplex gate after area of interest has been defined, measurement point/gate has been adjusted, angle correction has been defined, etc

5 Try to avoid cavitation seeds or bones in vicinity of duplex-Doppler beam

6 Further recommendations can be found in literature and with various US societies (e.g EFSUMB; AIUM; OEGUM/DEGUM)

1.5.5 Various Methods and Indices That Allow Estimation

of Biological Risks

1.5.5.1 Mechanical Index (MI)

Introduced to describe peak pressure in tissue (in mPa); depends on output gain The used frequency and focus pre-describe potential risk of sound pressure-induced tis-sue damage as well as cavitation risk

Mostly used in B-Mode sonography and should be kept below 1; short increases (if diagnostically necessary) up to 1.5 mPa acceptable in individual situations

NOTE: MI should be lower for fetal exams, for examination of the neonatal brain

(transfontanellar), for eye US and for ce-US to avoid damage of specifically tive structures or to minimise danger in t presence of cavitation seeds (see also above)

sensi-1.5.5.2 Thermal Index (TI)

Describes risk of tissue heating with consecutive tissue damage:

1 TIS (soft tissue thermal index) – used for soft tissue

2 TIB (bone thermal index) – used for bone

3 TIC (cranial thermal index) – used for transcranial applications

Mainly depends on tissue, output gain, focal zone and frequency used

TI – most important in Doppler sonography as well as for fetal US TI should be kept below 1 – brief increase accepted if diagnostically necessary in individual examinations (e.g Doppler sonography usually works with higher TI values)

1.5.5.3 Display of Actual Indices

Indices must be displayed by equipment throughout investigation and constantly

updated depending on individually altered settings (gain, focus zone, frequency, etc.); should also be documented on saved images

1.6 How to Perform Paediatric US

1.6.1 Requisites

1.6.1.1 Indications

Every investigation must rely on thorough indication Referring physician has to provide detailed question; US investigation must potentially offer diagnostically relevant result with therapeutic or prognostic consequence

Only exceptions:

• Screening investigations (e.g urinary tract and hip) – should have significant preventive effects:

– Increasingly under discussion, with widespread fetal US and new knowledge

on impact of screening approaches in last decade

• For scientific or educational purpose

1.6.1.2 Environmental Requisites

• Proper and comfortable positioning facilities

• Quiet room with sufficient light dimming

• Proper and ergonomic positioning of investigator

• Ergonomic styling of surrounding working area – includes separate reading facility with monitors and separate sitting area for consultation with patients and parents

NOTE: Sufficient chairs must be available, as there are usually more people than

just the patient

• Proper room temperature with additional heating available for neonates and infants

• Even with children, privacy must be respected; therefore proper changing rooms and towels mandatory, furthermore cleaning facilities, and adjacent restroom desirable

1.6.1.3 Specific Needs in Children

• Usually accompanying persons are present during investigation and for tion afterwards – rooms must be adequately sized and equipped

consulta-• Accompanying parents and brothers or sisters can help pacify infant during investigation, additionally monitors for displaying either US image or movies and toys are helpful Other pacifying measures: books, music

• Warm US gel, but prevent bacterial and fungal growth in gel bottle

• Initial introductory comment understandable to child and accompanying persons

is helpful – enables them to understand investigation, what is going to happen and to reduce fears Explain equipment as well as procedure

• Effort of establishing good relation prior to starting investigation – often tial to enable peaceful and diagnostically valuable investigation.

essen-NOTE: Empathetic action is important! Try to avoid strong and abrupt transducer

pressure as well as fast movements Sometimes also helpful to keep skin contact with hand/finger that holds transducer

1.6.1.4 Specific Needs in Infants and Newborns

• Higher room temperature, additional heating and swaddling facilities are mandatory

• Helpful to have some warm tea/formula and pacifiers ready at hand:

– Pacifiers can furthermore be enhanced by specific tastes such as glucose and fruit extracts

1.6.2 Positioning

• Abdominal US: usually lying supine, sometimes prone or lateral decubitus tion is helpful Some abdominal areas can also be investigated with baby lying in arms of mother – e.g urinary tract screening in anxious and excited infants, provided acceptable position for the investigator is granted, too

posi-• Urinary tract US: same as abdominal US standard; additional prone positioning for examining kidneys from dorsal approach is advisable Additional approach: perineal US

• US of neonatal brain/transtemporal US: any position where head can be kept still and stable with sufficient acoustic access for US probe; for posterior fossa inves-tigation, transoccipital or transnuchal access in lateral decubitus position with flexed cervical spine is helpful

• US of neonatal spine and spinal canal: prone or lateral decubitus – try to avoid hyperextended back to assure sufficient access to spinal canal

• Echocardiography: usually supine position with slight lateral rotation; additional pillows underneath back may be helpful For suprasternal access, neck extension with some support of shoulder and side turning of head is helpful – provided the baby can tolerate positioning

• Hip US: standardised procedure with standardised positioning partially using dedicated positioning devices; depends on technique applied (see Chap 11)

• Small-part and neck US: sometimes helpful to comfortably position targeted area by help of supporting pillows and towels (see Chap 4)

NOTE: In adults and bigger children, positioning manoeuvres or breath holding

and flexion or rotation is routinely used to optimise US window for proper access to diagnostically relevant deeper regions In children, particularly infants and neonates, this is practically impossible, therefore “golden rule for US in infants”: do not move child towards transducer trying to depict pathology, but try to move transducer to sonographic window that allows optimal access to targeted areas

If in older children positioning manoeuvres are attempted, try to use age- adequate commands such as “show me your big belly” or “take a deep breath and hold it as if you were diving”.

• Remember also to have a comfortable examinier position for health reasons- avoid degenerative disease

1.6.3 Device Handling

General Remarks

Particularly in paediatric US, investigator must be accustomed with device and its handling, as child motion and agitation as well as need for communication and devoted emphasis would impair capabilities to struggle with equipment Additionally, experi-enced handling speeds up investigations allowing for better results and focused concen-tration on child and image – without withdrawing attention towards handling of device.Therefore it is practical to import all data (such as patient name/numbers) and set

up machine (selecting transducers/presets) prior to positioning of child

Choice of Device and Transducer

• Handling of different US equipments varies – large variability in requirements

• A particularly helpful feature is cine loop – store video clips for retrospective review:– Depending on device, varying number of images is constantly stored to hard disc at any time during investigation Allow for review of preceding parts of investigation; video clip is constantly updated

– Review of cine loop: single frames can be captured and stored; some machines and picture archiving and communication systems (PACS) also allow storage

of clips

– As children are often less cooperative, this feature is particularly helpful for selecting optimal frames for measurements and documentation as well as image analysis

How to Start Investigation

Once machine is set up, select transducer and the respective preset, and position patient:

• After positioning of transducer, adapt receive gain and TGC as well as focus, frame, size and penetration All these parameters need to be constantly updated during inves-tigation – as different body areas and positions request different equipment settings.Modern devices offer automated adaptation and optimisation algorithms – so they can speed up investigations, helpful for general overview Additional adapta-tion and variation of settings will still be necessary for certain queries, for detailed investigations or in certain body areas (such as behind urinary bladder) Particularly post-processing, sufficiently fast frame rate and proper placement of focal zone are essential – need to be changed and adapted constantly; this task cannot reliably be performed by automated image optimising programmes

Once you have chosen an adequate preset, changes of preprocessing factors, etc become only necessary in rare cases:

• Presets usually selected by deciding on certain investigation category – optimised towards dedicated queries