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E-kniha: Ultrasound examination of the lower limbs -- 2nd edition, revised and updated - Dalibor Musil; al. et

Ultrasound examination of the lower limbs -- 2nd edition, revised and updated

Elektronická kniha: Ultrasound examination of the lower limbs
Autor: Dalibor Musil; al. et
Podnázev: 2nd edition, revised and updated

?This monograph focuses on the clinical use of ultrasound in phlebology. The core of the book is a description of the principal nosological units in phlebology and methods for their sonographic ... (celý popis)
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ISBN: 978-80-271-0657-8
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?This monograph focuses on the clinical use of ultrasound in phlebology. The core of the book is a description of the principal nosological units in phlebology and methods for their sonographic diagnosis. The second edition is available in English language and you can buy it in digital version (epub or pdf) only.

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2

nd

edition, revised and updated

Dalibor Musil, et al.

Ultrasound examination

of the lower limbs


Dedicated to my teacher and outstanding physician

Professor MUDr. Ivo Krč, DrSc.


2

nd

edition, revised and updated

Dalibor Musil, et al.

Ultrasound examination

of the lower limbs


Notice to readers

All rights reserved. No part of this electronic publication may be reproduced, stored and soled

in any form without the prior written permission of the publisher: unauthorized use of this

book will be prosecuted. Doc. MUDr. Dalibor Musil, Ph.D., and his colleagues ULTRASOUND EXAMINATION OF THE LOWER LIMBS 2

nd

edition, revised and updated

Main author: Doc. MUDr. Dalibor Musil, Ph.D. (1

st

Internal Clinic – Cardiology, Faculty of Medicine

and Teaching Hospital, Palacký University, Olomouc) Co-authors: Doc. MUDr. Jiří Herman, Ph.D. (2

nd

Surgical Clinic – vascular transplantation,

Faculty of Medicine and Teaching Hospital, Palacký University, Olomouc) MUDr. Ivo Hofírek, CSc. (1

st

Department of Cardioangiology, Masaryk University,

Faculty of Medicine and St. Anne’s Hospital, Brno) Doc. MUDr. David Kachlík, Ph.D. (Institute of Anatomy of the 3

rd

Medical Faculty

of Charles University, Prague) Translator: Dr. Alexander Oulton, Ph.D. Reviewers: MUDr. Karel Roztočil, CSc. Doc. MUDr. Debora Karetová, CSc. The publication of this monograph has been approved by the Scientific Editor of Grada Publishing, a.s. © Grada Publishing, a.s., 2019 Cover Design © Grada Publishing, a.s., 2019 Published by Grada Publishing, a.s., U Průhonu 22, Prague 7 As its 7186. publication Responsible Editor Mgr. Marek Chvátal Typsetting and breaks Helena Mešková Diagrams and drawings Dalibor Musil Cover photographs and archived ultrasound images Dalibor Musil 2

nd

edition in Czech, Prague 2016

1

st

English edition, Prague 2019

The authors express their gratitude to the translator and editor Dr. Alexander Oulton, Ph.D. Publishing of this book was supported by Servier. The product names, business logos, etc. used in this book may be trademarks or registered trademarks of the companies designated unless otherwise specified. The procedures and examples used as well as information on medication, (forms, dosages and applications), have been compiled to the best of the knowledge of the authors. No practical use of the information has any legal consequences for either the authors or the publishers. ISBN 978-80-271-2699-6 (ePub) ISBN 978-80-271-2698-9 (pdf)

Contents

List of abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

1 Ultrasound in phlebology (Dalibor Musil, Ivo Hofírek). . . . . . . . . . . . . . . . . . .11

1.1 Technical Principles of Examination . . . . . . . . . . . . . . . . . . . . . . . .11

1.1.1 What is ultrasound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.1.2 Creation of an ultrasound image . . . . . . . . . . . . . . . . . . . . . 13 1.1.3 Processing ultrasound signals. . . . . . . . . . . . . . . . . . . . . . .14 1.1.4 Doppler effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.1.4.1 Rheology – patterns of blood f low through blood vessels . . . . . 15

1.1.4.2 Continuous Doppler . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.1.4.3 Pulsed Doppler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.1.4.4 Color Flow Mapping (CFM, color Doppler) . . . . . . . . . . . . . 17

1.1.4.5 Duplex and triplex ultrasound examination. . . . . . . . . . . . .18

1.1.4.6 Power Doppler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.2 Clinical use of ultrasound in phlebology. . . . . . . . . . . . . . . . . . . . . .20

1.2.1 Setting the ultrasound machine. . . . . . . . . . . . . . . . . . . . . .21 1.2.2 Examination of the deep vein system. . . . . . . . . . . . . . . . . . .22

1.2.2.1 Inferior vena cava and iliac veins . . . . . . . . . . . . . . . . . . .22

1.2.2.2 Common femoral vein and popliteal vein . . . . . . . . . . . . . . 23

1.2.2.3 Distal thigh (Hunter’s canal) . . . . . . . . . . . . . . . . . . . . . 23 1.2.3 Examination of the superficial veins . . . . . . . . . . . . . . . . . . . 23

1.3 Ultrasound modes in phlebology . . . . . . . . . . . . . . . . . . . . . . . . . .24

1.3.1 B-mode (2D imaging) . . . . . . . . . . . . . . . . . . . . . . . . . . .24 1.3.2 Colour Flow Mapping (CFM) . . . . . . . . . . . . . . . . . . . . . . .24 1.3.3 Acoustic signal and graphic spectral record of blood f low

(Pulse Wave Doppler, PW Doppler) . . . . . . . . . . . . . . . . . . .26

Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

2 Anatomical notes on the venous system of the lower limbs (Dalibor Musil,

David Kachlík) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.1 Ontogenesis of the vein system of the lower limbs . . . . . . . . . . . . . . . . 31

2.2 Division of the lower limb system. . . . . . . . . . . . . . . . . . . . . . . . . .33

2.2.1 Deep (muscular) compartment . . . . . . . . . . . . . . . . . . . . . . 33 2.2.2 Superficial (subcutaneous) compartment . . . . . . . . . . . . . . . . 35

2.3 Superficial veins (venae superficiales) . . . . . . . . . . . . . . . . . . . . . . . 35

2.3.1 Saphenous veins (venae saphenae) . . . . . . . . . . . . . . . . . . . . 35

2.3.1.1 The great saphenous vein (GSV) . . . . . . . . . . . . . . . . . . . 37

2.3.1.2 The small saphenous vein (SSV) . . . . . . . . . . . . . . . . . . . 41 2.3.2 Accessory saphenous veins (venae saphenae accessoriae) . . . . . . .42

2.3.2.1 Accessory great saphenous veins in the region of the groin

and, anterior and lateral thigh. . . . . . . . . . . . . . . . . . . . .42

2.3.2.2 Accessory saphenous veins in the popliteal fossa

and dorsal side of the thigh . . . . . . . . . . . . . . . . . . . . . .44

2.3.3 Other superficial veins . . . . . . . . . . . . . . . . . . . . . . . . . . .44

2.4 Deep veins (venae profundae) . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

2.4.1 Thigh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 2.4.2 Lower Leg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.4.3 Foot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

2.5 Perforators (venae perforantes) . . . . . . . . . . . . . . . . . . . . . . . . . . .49

2.5.1 Division of the perforators. . . . . . . . . . . . . . . . . . . . . . . . .50

2.5.1.1 Ankle perforators (venae perforantes tarsales). . . . . . . . . . . .52

2.5.1.2 Lower leg perforators (venae perforantes cruris). . . . . . . . . . .52

2.5.1.3 Knee perforators (venae perforantes genus) . . . . . . . . . . . . . 52

2.5.1.4 Thigh perforators (venae perforantes femoris). . . . . . . . . . . .53

2.6 Venous valves (valvulae venosae) . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.7 Venous malformations and variations . . . . . . . . . . . . . . . . . . . . . . . 55

2.7.1 Agenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2 . 7. 2 A p l a s i a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2 . 7. 3 Hy p o p l a s i a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2 . 7. 4 D y s p l a s i a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2.7.5 Atrophy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2.7.6 Venous aneurysm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56 2.7.7 Venomegaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 2.7.8 Venous duplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

3 Chronic venous disease (Dalibor Musil) . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3.1 Brief pathogenesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

3.1.1 Vein muscle pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.1.2 Changes in the macrocirculation . . . . . . . . . . . . . . . . . . . . . 62 3.1.3 Changes in the microcirculation . . . . . . . . . . . . . . . . . . . . . 62

3.2 Diagnosis of chronic venous disease . . . . . . . . . . . . . . . . . . . . . . . . 62

3.3 Ultrasound in the diagnosis of chronic venous disease . . . . . . . . . . . . .64

3.3.1 The contribution of ultrasound to clinical practice. . . . . . . . . . .65 3.3.2 Why perform ultrasound before varicose vein surgery? . . . . . . . . 67

3.3.2.1 Is surgical treatment appropriate? . . . . . . . . . . . . . . . . . . 67

3.3.2.2 Will surgical treatment be successful? . . . . . . . . . . . . . . . . 67

3.4 Continuous Wave Doppler (CW Doppler, Pocket/Pen,

Hand -Held Doppler) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.4.1 The saphenofemoral junction (SFJ). . . . . . . . . . . . . . . . . . . .68 3.4.2 The saphenopopliteal junction (SPJ) . . . . . . . . . . . . . . . . . . .68

3.5 Duplex and triplex ultrasound imaging . . . . . . . . . . . . . . . . . . . . . . 69

3.5.1 B-mode and CFM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

3.5.1.1 Groin and thigh. . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

3.5.1.2 Popliteal fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

3.5.1.3 Determination of proximal and distal insufficient points . . . . .75 3.5.2 Pulse Wave Doppler (PW Doppler). . . . . . . . . . . . . . . . . . . .78

3.5.2.1 Presence, velocity and phasicity of venous f low. . . . . . . . . . .78

3.5.2.2 Ref lux duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

3.5.2.3 Ref lux severity (quantification). . . . . . . . . . . . . . . . . . . .82 3.6 Perforators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 3.7 Practical instructions on investigating chronic venous disease

of the lower limbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

3.7.1 Groin and thigh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

3.7.2 Popliteal fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

3.7.3 Perforators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

4 Superficial venous thrombosis (SVT) (Dalibor Musil) . . . . . . . . . . . . . . . . . . . . 93

4.1 Types of SVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4.1.1 Thrombophlebitis vulgaris superficialis

(primary thrombophlebitis/phlebitis, SVT of non varicose veins) . . 93

4.1.2 Varicophlebitis (SVT of varicose veins) . . . . . . . . . . . . . . . . .94

4.1.3 Thrombophlebitis saltans (migrans) . . . . . . . . . . . . . . . . . . . 95 4.2 Complications of SVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

4.2.1 Deep vein thrombosis . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

4.2.2 Pulmonary embolism(PE) . . . . . . . . . . . . . . . . . . . . . . . . .96

4.2.3 Other complications . . . . . . . . . . . . . . . . . . . . . . . . . . . .97 4.3 Diagnosis of SVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97 4.4 Ultrasound diagnosis of SVT . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

4.4.1 Setting the ultrasound machine. . . . . . . . . . . . . . . . . . . . . .99

4.4.2 Chief contribution of ultrasound to investigation of SVT . . . . . . 100 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

5 Deep vein thrombosis (DVT) (Dalibor Musil). . . . . . . . . . . . . . . . . . . . . . . . 102

5.1 Clinical diagnosis of DVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.2 Ultrasound in the diagnosis of DVT . . . . . . . . . . . . . . . . . . . . . . . 104 5.3 Ultrasound image of DVT over time . . . . . . . . . . . . . . . . . . . . . . . 105

5.3.1 New venous thrombus . . . . . . . . . . . . . . . . . . . . . . . . . . 105

5.3.2 Organization of a vein thrombus. . . . . . . . . . . . . . . . . . . . 107

5.3.3 Recanalisation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.4 Ultrasound diagnostic criteria for DVT . . . . . . . . . . . . . . . . . . . . . 110

5.4.1 B -mode, compression ultrasound – direct evidence of venous

thrombosis and post -thrombotic changes . . . . . . . . . . . . . . . 110

5.4.2 Color f low mapping (CFM, color Doppler) – evidence

of f luttering thrombus, residual blood f low, collaterals,

post -thrombotic residual obstruction . . . . . . . . . . . . . . . . . 111

5.4.3 Pulse Wave Doppler (PW Doppler) – evidence of residual

blood f low, indirect evidence of venous thrombosis,

evidence of valvular insufficiency . . . . . . . . . . . . . . . . . . . 112

5.4.4 Summary of Ultrasound Signs of DVT. . . . . . . . . . . . . . . . . 113 5.5 Differential diagnostics of DVT. . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.6 DVT at various sites on the lower limb. . . . . . . . . . . . . . . . . . . . . . 114

5.6.1 Proximal DVT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

5.6.2 Distal DVT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

5.6.3 DVT of the plantar veins. . . . . . . . . . . . . . . . . . . . . . . . . 115

5.6.4 Thrombosis in unusual vein sites of the lower limb . . . . . . . . . 116 5.7 Post -thrombotic syndrome (PTS). . . . . . . . . . . . . . . . . . . . . . . . . 116

5.7.1 Diagnosis of post -thrombotic syndrome (PTS) . . . . . . . . . . . . 117

5.7.2 Gradual recanalisation of thrombosis . . . . . . . . . . . . . . . . . 118

5.7.3 Damage to the vein wall (pachysclerosis -thickening, hardening). . 119

5.7.4 Damage to vein valves (post -thrombotic ref lux) . . . . . . . . . . . 119

5.7.5 Venous atrophy (permanent obstruction syndrome). . . . . . . . . 119

5.7.6 Total thrombolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 5.8 Practical instructions for investigation of DVT in lower limbs . . . . . . . . 120

5.8.1 Groin and thigh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120

5.8.2 Popliteal fossa and calf . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

6 Congenital vein malformations (Dalibor Musil). . . . . . . . . . . . . . . . . . . . . . 125

6.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 6.2 Clinical picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 6.3 Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 6.4 Complex congenital venous malformations . . . . . . . . . . . . . . . . . . . 130 6.5 Persisting embryonic veins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.6 Valveless syndrome (avalvulia) . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.7 Clinical syndromes associated with congenital vein malformations

of the lower limbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

6.7.1 Klippel -Trénaunay syndrome (haemangiectasia hypertrophica) . . 131

6.7.2 Klippel -Trénaunay -Weber syndrome. . . . . . . . . . . . . . . . . . 132

6.7.3 Sturge -Weber syndrome (neuroangiomatosis encephalofacialis) . . 132

6.7.4 Maffucci’s syndrome (chondrodystrophia cum angiomatosi). . . . 132

6.7.5 Bean syndrome (Blue rubber bleb nevus syndrome) . . . . . . . . . 132 6.8 Venous aneurysms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

6.8.1 Definitions of venous aneurysm . . . . . . . . . . . . . . . . . . . . 134

6.8.2 Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

6.8.3 Aneurysms of deep veins. . . . . . . . . . . . . . . . . . . . . . . . . 135

6.8.4 Aneurysmatic superficial veins . . . . . . . . . . . . . . . . . . . . . 136

6.8.5 Ultrasound in the diagnosis of venous aneurysms . . . . . . . . . . 136 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

7 Case reports (Dalibor Musil) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

7.1 Acute DVT of the muscle veins on left calf . . . . . . . . . . . . . . . . . . . 139 7.2 Recurrent varicose veins in the right lower limb . . . . . . . . . . . . . . . . 139 7.3 Baker’s cyst in the right popliteal fossa. . . . . . . . . . . . . . . . . . . . . . 141 7.4 Insufficiency of the SSV in the right lower limb . . . . . . . . . . . . . . . . 145

8 Duplex sonography in local thrombolysis under ultrasound control

(Ivo Hofírek) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

9 The importance of duplex ultrasound examination for surgery

of the superficial veins (Jiří Herman) . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152


9

Seznam zkratek

List of abbreviations

2D, 3D two -Dimensional, three -Dimensional

a., aa. artery, arteries

CAI Color Amplitude Imaging

CD Continuous Doppler

CEAP Clinical, Etiological, Anatomical, Pathophysiological Classification

CFM Color Flow Mapping

CPA Color Power Angio

CW Continuous Wave

DIP Distal Insufficient Point

DVT Deep Vein Thrombosis

GSV Great Saphenous Vein

IUA International Union of Angiology

IUP International Union of Phlebology

LLL Left Lower Limb

LL Lower Limb

m., mm. musculus, musculi

n., nn. nervus, nervi

PD Pulsed Doppler

PDGF Platelet Derived Growth Factor

PE Pulmonary Embolism

PIP Proximal Insufficient Point

PRF Pulse Repetition Frequency

PW Pulsed Wave

RR Relative Risk

RVI Ref lux Volume Index

SFJ Saphenofemoral Junction

SPJ Saphenopopliteal Junction

SSV Small Saphenous Vein

st. p. status post

TG Total Gain

TGC Time Gain Compensation

UGS Ultrasound -Guided Sclerotherapy

US UltraSound

v., vv. vena, venae

VEGF Vascular Endothelial Growth Factor

V

max.

Maximum rate of return vein f low

VSP vena saphena parva

VSM vena saphena magna


10

ULTRASOUND EXAMINATION OF THE LOWER LIMBS

Preface Seven years have elapsed since the first edition of this monograph which at the time, was given a very positive reception by the professional public. One of the chief reasons for this was that the book filled a large gap in the Czech market on the theory and practice of ultrasound diagnosis in venous disorders of the lower limbs. Appreciation of the first edition prompted us to write a second, revised and updated version.. Guiding our efforts in this were the discussions with doctors at congresses and the many fruitful suggestions gained from sonography workshops.

Routine use of ultrasound is revolutionising medicine in the diagnosis and treatment of a large number of diseases and conditions. In phlebology, it has become crucial. When carried out properly, ultrasound simplifies and makes everything easier for both doctors and patients. It enables fast and reliable diagnosis of superficial and deep vein thrombosis, identifies primary ref lux sites in chronic venous disease and allows long -term follow -up of patients with vein disorders. For vascular surgeons, ultrasound mapping of the superficial veins should be indispensable before each varicose vein surgery.

Confronted with everyday practice, with the specific requirements and questions which doctors have when they refer their patients for ultrasound examination of the lower limbs, we have made efforts to develop the techniques that suit our particular clinical conditions and systematically expand our knowledge from the medical literature and lectures.

Following the first edition, this book updates the view of vein disease and the current position of ultrasonography in phlebology. It aims to be a useful text on ultrasound, a hands -on guide for new doctors and those in routine practice who are looking for answers to professional questions arising from their work. The publication is thus dedicated not only to doctors in the diagnosis of vein diseases, i.e. angiologists and radiologists, but also to the specialists who most often send their patients for scanning-s urgeons, dermatologists, internists, cardiologists and general practitioners.

Each chapter is written as an independent unit and for this reason a certain amount of redundancy is unavoidable. Parts may be overly simple to readers familiar with ultra s ound principles. It would be untrue however, to assume that all those who come in contact professionally with ultrasound, understand the technology.

As an imaging mode, an integral part of the book is drawings and images taken during an ultrasound examination and presented to the reader as they are seen in common practice. We hope you find this monograph useful.

doc. MUDr. Dalibor Musil, Ph.D.

Olomouc, 15

th

September 2015


1

11

Ultrasound in phlebology

1 Ultrasound in phlebology

Dalibor Musil, Ivo Hofírek

1.1 T echnical Principles of Examination 1.1.1 W hat is ultrasound Ultrasound (US) refers to high frequency mechanical oscillations transmitted to particles in a medium. If we imagine the waves as the concentric circles that expand on the surface of water following the impact of a stone, the circles are the regions of pressure change as from gas to liquid to solid. Ultrasound waves have a frequency greater than 20 k Hz (20,000 Hz). This creates vibrations inaccessible to the human ear. Production of these higher frequencies is due to piezoelectric crystals in the ultrasound probe which have the ability to convert electrical impulses into mechanical vibrations, transmitted in pulses to the body in relation to their frequency. For ultrasound diagnosis in medicine, the frequency band 2 MHz to 50 MHz is used, in common practice 3 MHz to 10 MHz.

The sound is always propagated as longitudinal waves – the waves are parallel to the direction of propagation. In solids, the sound spreads not only as longitudinal but also transverse waves when the beam is perpendicular to the direction of the propagation. Ultrasound vibrations in media such as the soft tissues and f luids of the human body, spread along the longitudinal wave. Transverse waves only spread in bones. With increasing frequency, at high and very high frequencies (in the order of MHz), ultrasound waves behave like electromagnetic waves. The average rate of ultrasound propagation in the human body is 1540 m/s. The velocity is independent of the frequency used but depends on acoustic impedance, that is, the resistance that a US beam encounters in the tissue receiving it. Acoustic impedance is the characteristic that determines the relationship of US waves to the surroundings in which the ultrasound spreads. It is defined as the density of a substance multiplied by the sound velocity in the material (kg m

–2

s

–1

). An analogy is the optical refractive index. The acoustic impedance is pro

portional to the elasticity and density of the tissue and increases in the order of: lung – blood – soft tissues (internal organs) – muscle, bone (Table 1.1).

An acoustic interface (e.g. fat/muscle, bone/muscle, muscle/blood, etc.) is created at the point of contact of two media with different sound propagation properties. At this interface, the ultrasound waves partly ref lect and partly transmit, provided the beam is perpendicular to the medium. If it is oblique, the waves are partly ref lected and partly dispersed (Figure 1.1). Ultrasound waves are also absorbed by the tissues and acoustic energy is transformed into thermal energy (heating the tissues). Higher frequency US waves are absorbed the most. The US signal at an acoustic interface changes its energy (amplitude). The ratio of the amplitude of the transmitted and ref lected ultrasound signal is called the ref lection coefficient and is dependent on the acoustic impedance of the media (Table 1.1). Dispersion is the propagation of US waves into space in all directions. It occurs when the acoustic interface is less than the wavelength of the incident wave (e.g. erythrocyte dispersion). Ref lected back to the probe,

1

12

ULTRASOUND EXAMINATION OF THE LOWER LIMBS

US probe

US probe

reflected waves (echo)

reflected US wave

incident US wave

αβ

γ

interface of two tissues

interface between two media

(tissues)

A.

B.

incident US wave

transmitted US waves

US wave transmitted

Fig. 1.1 US wave propagation – At the tissue interface, a percentage of US waves reflect

at the same angle but in the opposite direction to the incident wave, non ‑reflected waves

pass through the second medium in the direction of impact (α = β = γ) – A. acoustic

waves perpendicular to the interface of two media, B. acoustic waves incident obliquely

at the interface of two media at an angle α

1

13

Ultrasound in phlebology

is a US signal (echo) with a certain frequency, intensity and time delay. The crystals

in the probe, convert the US waves into electrical impulses.

The ratio of the intensity of the ref lected wave to the incident wave:

The greater R is, the greater the degree of ref lection, i.e. R for a soft tissue interface

such as liver and kidney is 0.01, i.e. only 1 % of the sound is ref lected. For muscle/bone

interface, 40 % is ref lected and for a soft tissue/air interface 99 % is ref lected.

Tab. 1.1 Acoustic impedance for different tissues

Medium Impedance (kg m

–2

s

–1

)

air 0,000 4 × 10

6

lung 0,46 × 10

6

blood 1,61 × 10

6

soft tissues 1,63 × 10

6

muscle 1,70 × 10

6

bone 7,80 × 10

6

1.1.2 Creation of an ultrasound image

The basic and simplest type of ultrasound image is a one -dimensional recording of

time sequence and magnitude (intensity) of the acoustic energy of ref lections (echo)

of the US signals transmitted to a tissue. This view is called the A mode (Eng. ampli

tude). Moving structures can be displayed in a continuous A view, which is called M

(Eng. motion). In angiology and phlebology, the M image is not used being mainly

the domain of cardiology.

A  more advanced display type uses the brightness changes of individual screen

dots emitted by incoming echoes in a range of up to 256-degrees -gray scale. This is

referred to as the B -mode, brightness modulation and it produces a 2D image. The

dynamic B -mode enables rapid simultaneous emission of signal and echo processing.

Ultrasound machines used in phlebology usually work in pulse mode (pulse

Doppler, PW Doppler, see further). The probe sends a short pulse, an ultrasound signal

of a certain frequency and the ref lected echo is converted into electrical impulses that

are processed as a 2D image. Each point on the monitor corresponds to the intensity

of the received US signal – a specific brightness intensity in the gray scale from white

to black. If pulses are transmitted parallel to received echoes, we refer to a linear view.

The US image is rectangular. If the transmitted pulses and echoes are divergent, this

is a sector view and the US image is diverging from the probe.

R =

(Z

2

– Z

1

)

2

(Z

2

+ Z

1

)

2 14

ULTRASOUND EXAMINATION OF THE LOWER LIMBS

1.1.3 Processing ultrasound signals We can simplify the capture and processing of US images if we imagine processing the images from a digital camera. The quality of the image depends on the conditions of taking the first shot (“photo”), adjusting the camera settings to obtain the type of picture desired (for example, sports, landscape, night scenery, etc.), the subject, lighting and a number of other parameters (preprocessing), chip resolution and chip size, data processing and noise reduction programs. In this way, the data is edited with specialised computer software (postprocessing – editing of the image).

Today, digital technologies allow for a number of adjustments to the final US image.

These conform to the programs and technologies used in various types of US machines which of course make comparison difficult and create variation in the appearance of the same tissue.

Other settings that can edit and optimise the image, are gain (signal gain) and

compression (signal condensation). These work differently in 2D display and color f low mapping (CFM) (see further). Gain and compression may also be default settings

US signals on absorption (change in acoustic energy through heat) are weakened,

especially if they come from a greater depth. For this reason, the ref lected echo from the human body must be sufficiently amplified called gain. Gain in US signal is achieved in three ways: 1. Total gain (all incoming US signals are amplified) – using the total gain function

(TG – Total Gain), which is referred to in US machines as gain or 2D gain, and will

amplify the image. 2. Selective gain (gain is greater for US signals coming from greater body depth,

i.e. later) – using the compensation time gain (TGC – Time Gain Compensation)

which is regulated in some US devices by slider keys, each key regulating gain from

a certain tissue depth. 3. Active amplification (amplifies the US signal coming from the pulse Doppler record). The dynamic range expresses the ratio between the strongest and weakest measurable echo in decibels (dB). This is important for image quality. Another image improvement is harmonic imaging which was originally used in cases of technically difficult US exams but it has found application in all other areas of US investigation. Instead of increasing the US power and extending the investigation time, a strong signal of a given frequency is transmitted to the area displayed to obtain a satisfactory image. The probe recursively retrieves the natural harmonic waves with the 2

nd

harmonic.

Harmonics occur spontaneously in tissues due to the non -linear propagation of US waves. However, they are weak and need a powerful scanner to capture and appro priate software. The natural harmonic display shortens the scanning time, increases the contrast during routine screening and allows for better imaging in technically difficult to investigate patients. One caveat however, is that a better 2D image with harmonic display can compromise color mapping and Doppler measurements. 1.1.4 Doppler effect For quantitative and qualitative blood f low investigation, the Doppler effect is indispensable. This phenomenon, first described by Austrian physicist, Christian Doppler

15

Ultrasound in phlebology

in 1842 while he was in Prague, was used in medicine for measuring the velocity of blood for the first time in 1960 by the Japanese, Satomura.

The Doppler effect is a physical phenomenon whereby the wavelength, electromagnetic or mechanical (sound, ultrasound) transmitted by a source is perceived by an observer as increased or decreased, if the source (transmitter) and the observer (recei ver) change distance. Between the moving transmitter and the stationary or moving receiver, the acoustic signal is subject to a frequency shift, to a lower or higher frequency depending on whether the transmitter is away from (lower frequency) or towards the observer (higher frequency).

The probe transmits US waves to the body in constant frequency pulses. For immobile objects, US ref lects without changing frequency.

The US waves picked up by the probe, are processed as the image (B -mode). from moving structures (e.g. erythrocytes), US waves are ref lected as frequency. The difference between the frequency of transmitted and received waves, is called the frequency shift. The amount of frequency shift is proportional to the velocity of erythrocytes (blood f low rates). This relationship is expressed by the Doppler equation:

F

d

· c

v =

2F

v

· cos θ

v – blood f low velocity F

v

, F

d

– frequency of emitted (v) and incident (d) US waves

c – a constant indicating the rate of US propagation in the blood (1540 m/s) θ (theta) – the angle between the direction of impact of the US wave and the direction of the erythrocyte movement v – velocity of erythrocytes If the angle of incidence is 90°, the Doppler equation is 0 (cos 90° = 0) and blood velocity measurement is impossible. To measure absolute speeds, it is advisable to select the smallest incidence angle. At an angle of up to 10°, the difference between the measured and actual speed is only about 1.5 %.

The absolute value of the frequency shift is dependent on the frequency used. For this reason, it is preferable to use higher operating frequencies for recording low speeds and lower operating frequencies when measuring high blood velocities. In practice, frequencies from 1 MHz to 10 MHz are used. At blood f low rates from 1 cm/s  to 500 cm/s, there is a frequency shift in the range of audible sound which allows sound in addition to the video recording. 1.1.4.1 Rheology – patterns of blood flow through blood vessels Blood, a non -Newtonian f luid, has a laminar f low under physiological conditions. We can imagine the f low in a single direction as sliding concentric cylinders parallel to the vascular endothelium where the velocity of blood components in each cylinder is the same. The slowest moving is the layer of blood adjacent to the vascular endothelium. The closer to the center of the cylinder, the faster the layers move. The velocity of the other layers of blood gradually increases to a maximum in the blood vessel axis. The 16

ULTRASOUND EXAMINATION OF THE LOWER LIMBS

laminar f low results in a cylindrical or parabolic profile where the rates of individual blood cells differ only slightly.

The frequency shifts according the the basic Doppler effect (see above). The smallest frequency shift is created by the slow moving cells at the edge of the vascular lumen. In contrast, the largest frequency shift is ref lected by the US waves from fast moving blood cells in the center of the blood vessel. Graphic recording of laminar blood flow is then a narrow frequency spectral curve with a small spectrum of fast moving blood flowing through the blood vessel. A narrow frequency line spectral curve with a characteristic shape appears on the monitor.

In the case of turbulent f low, the erythrocyte velocity spectrum is considerably broader and the linear narrow frequency spectral curve expands on the monitor until it completely disappears. The area under the curve is filled with a number of spectral velocities. 1.1.4.2 Continuous Doppler In vascular diagnostics, the first clinically used Doppler method was continuous Doppler (Continuous Wave Doppler – CWD). Continuous Doppler uses an unmodulated wave of 4 MHz or 8 MHz US signal that is continuously transmitted and received.

The probe for continuous Doppler scanning contains two crystals (piezoelectric transducers). One is a permanent transmitter and the other continuously receives ref lected signals. The crystals are positioned in the probe so that the transmitted and received beams overlap in a  sensitive area a  few centimeters long. The US signal is transmitted and scanned continuously. It is more powerful than the pulse Doppler (see below), but as the sum of all the tissues through which the signal passes, it lacks precise spatial focusing of target structures. The US waves are converted into electric current by the piezoelectric transducer and an audible sound is heard as a stereoacoustic signal from a speaker or headphones. Computerised processing of the electrical signal leads to a graphic record of blood velocity simultaneously appearing on the monitor. This is a Doppler record of the velocity of blood through the vessel.

Inexpensive CD systems, without 2D image, are equipped with small pencil probes (4 MHz and 8 MHz). Pocket Dopplers serve as an orientative functional examina ti on of the veins in the standing or lying patient. Pencil transducers, also called CW Doppler probes, are utilised to measure blood f low and speed of sound in blood. This probe has a small footprint and uses low frequency (typically 2–8 MHz).

Their great disadvantage however, is lack of spatial resolution. This prevents blood velocity measurement at a specific 2D image location. All the vessels located in the longitudinal axis of the US beam at different depths and sites are scanned at the same time and the resulting acoustic signal is mixed.

Since continuous Doppler has no limit for frequency shift, its main function is accurate measurement of high blood velocities in cardiology and detection of f low in superficial blood vessels. 1.1.4.3 Pulsed Doppler Current US devices for vascular investigation use Pulsed Doppler (P u ls e d Wave Doppler, PWD), where one piezoelectric element in the probe alternately transmits

17

Ultrasound in phlebology

and receives the US waves to and from the tissue. These are ref lected from the interface of different densities (blood/tissue, tissue/tissue) and received by the same transducer after a short delay. At a constant rate of US propagation in soft tissues, the time between transmission and pulse reception is directly proportional to the vessel’s distance from the probe. The Pulsed Doppler system, therefore, allows precise determination of the depth the ref lected signals are coming from. For this reason, Pulsed Doppler can be used to select a site in a particular vessel and place there a sampling volume (measurement volume, sampling volume) from which the Doppler signal is recorded. This is the main difference to continuous Doppler.

The low signal -to -noise ratio of Pulsed Doppler however, precludes its use for very slow f low rates. Another ultrasound mode should be used here – Power Doppler (see Chapter 1.1.4.6). 1.1.4.4 Color Flow Mapping (CFM, color Doppler) In color f low mapping, the blood f low record of pulse Doppler is superimposed on a 2D image (B -mode) in real time. As a result, CFM has the limitations of both modes B -mode and PW Doppler (see above). The CFM allows a color display of the hemodynamics, i.e., different velocities and direction of blood f low in real time.

Pulse Doppler detects the velocity and direction of blood f low in several sample volumes simultaneously. The number of sample volumes is determined by the size of the CFM display box which constitutes a part of the 2D image in gray scale (B -mode). The size of the display box is determined by the machine settings. Selecting a too large box for CFM, especially in terms of width, is associated with reduced spatial resolution.

To identify vessels through CFM and PW Doppler, it is important to set the correct pulse repetition frequency (PRF) emitted by the probe. This must match the velocity of blood f low in the vein examined. For a slow velocity, set a lower PRF and a higher PRF for a fast f low rate. If the PRF is set too low, a frequency error (ambiguity) is generated. Frequencies (blood f low rates) that exceed the set frequency and thus speed range of the machine cause the computer to automatically re -set to the zero line, i.e. to negative values. These frequencies (speeds) are then relabelled (aliasing) as the opposite (negative or positive) frequency, indicating the opposite direction of f low. If the PRF is set too high, there is a spatial error. At the location of a slow -f lowing vessel (the f low is slower than the PRF setting), no blood f low appears. There is an error in the identification of the vessel, i.e. the vessel can be overlooked as another anechoic structure (Figure 1.2).

The resulting CFM is a color flow map. This, as mentioned, is superimposed on a 2D image (B -mode), which forms the image background at the site of the blood f low investigation, and is defined by the CFM box boundaries (Figure 1.3). Blood f low is represented by points (voxels, pixels) in blue and red with intensity of color showing blood velocity – red showing blood f low back to the probe and blue f lowing away from the probe. The quality of the 2D image covered by a color map is however somewhat poorer in places than without a map.



       
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