Diagnostic Imaging of the Chest E-Book
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- Sprache: Englisch
Your one-stop source of complete imaging information for the evaluation of thoracic conditions and diseases in all modalities
Due to the remarkable concentration of various vital organs that can be visualized in thoracic imaging, the region occupies a firm central place in the spectrum of diagnostic imaging.
The book is based on the contents of the curriculum for thoracic imaging of the European Society of Radiology and covers the gamut of issues in thoracic imaging that radiologists are faced with in their daily clinical practice.
Contents are divided into four main sections: fundamentals of diagnostic thoracic imaging, diseases of the chest and special findings, differential diagnostic considerations and incidental findings, and glossary.
Key Features:
- Full coverage of all disease entities as they affect the lungs, airways, pleura, mediastinum, thorax wall and diaphragm, thoracic arteries and veins, and the heart
- All imaging modalities are covered in detail: projection radiography, fluoroscopy, ultrasound, CT, and MRI, as well as digital image postprocessing
- Subsections concentrate on the more critical findings, such as pulmonary nodules and cavitary lesions
- Special section on occupational pulmonary diseases
- Congenital malformations of the thorax, and much more
Diagnostic Imaging of the Chest is an essential reference guide for radiologists, both in training and in practice.
This book includes complimentary access to a digital copy on https://medone.thieme.com.
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Veröffentlichungsjahr: 2020
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Diagnostic Imaging of the Chest
Dag Wormanns, MDMedical DirectorHead of Department of RadiologyELK Berlin Chest HospitalBerlin, Germany;Medical FacultyInstitute for Clinical RadiologyUniversity of MünsterMünster, Germany
644 illustrations
ThiemeStuttgart • New York • Delhi • Rio de Janeiro
Library of Congress Cataloging-in-Publication Data is available from the publisher
Translator: Sarah Venkata, London, UK
© 2020. Thieme. All rights reserved.
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ISBN 978-3-13-241565-2
Also available as an e-book:eISBN 978-3-13-241566-9
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Contents
Preface
Contributors
Abbreviations
Part I Fundamentals of Diagnostic Thoracic Imaging
1 Examination Technique
1.1 Projection Radiography
1.1.1 Standing Position
1.1.2 Supine Radiographs
1.2 Fluoroscopy
1.3 Computed Tomography
1.3.1 High-Resolution Computed Tomography
1.3.2 Low-Dose Computed Tomography
1.3.3 Special CT Examination Techniques
1.3.4 Dual-Energy Computed Tomography
1.4 Magnetic Resonance Imaging
Jürgen Biederer
1.4.1 Introduction
1.4.2 Equipment Technology
1.4.3 Pulse Sequences for Diagnostic Imaging
1.4.4 Recommendations for Examination Protocols
1.5 Ultrasonography
1.6 Positron Emission Tomography–Computed Tomography
1.7 Image Reformatting
1.8 Computer-Assisted Diagnosis
1.8.1 Computer-Assisted Detection
1.8.2 Volumetry
2 Basic Anatomy
2.1 The Mediastinum
2.1.1 The Vascular System
2.1.2 The Lymphatic System
2.1.3 The Trachea and Bronchi
2.1.4 The Thymus
2.2 The Heart and Pericardium
2.3 The Lung
2.3.1 Hilar Structures
2.3.2 The Lobes and Segments of the Lung
2.3.3 Connective Tissue Compartments
2.3.4 The Lobule
2.4 The Pleura
2.5 The Diaphragm
3 General Symptomatology
3.1 Projection Radiography
3.1.1 Generic Signs
3.1.2 Unilateral Changes in Radiolucency
3.1.3 Atelectasis
3.2 Computed Tomography
3.2.1 Linear and Reticular Opacities
3.2.2 Nodular Opacities
3.2.3 Increased Lung Opacity
3.2.4 Decreased Lung Opacity
3.2.5 Cysts
3.2.6 Radiologic Signs of Fibrosis
4 Indications
Part II Diseases of the Chest and Special Findings
5 Pneumonia
5.1 Community-Acquired Pneumonia
5.2 Hospital-Acquired/Nosocomial Pneumonia
5.3 Opportunistic Pneumonia
5.3.1 Fungal Pneumonia
5.3.2 Viral Pneumonia
5.4 Mycobacteriosis
5.4.1 Tuberculosis
5.4.2 Atypical Mycobacteriosis
5.5 Summary
6 Diffuse Parenchymal Lung Diseases
6.1 Idiopathic Interstitial Pneumonias
6.1.1 The Role of Radiology
6.1.2 Idiopathic Pulmonary Fibrosis
6.1.3 Idiopathic Nonspecific Interstitial Pneumonia
6.1.4 Cryptogenic Organizing Pneumonia
6.1.5 Acute Interstitial Pneumonia
6.1.6 Respiratory Bronchiolitis-Interstitial Lung Disease
6.1.7 Desquamative Interstitial Pneumonia
6.1.8 Rare Idiopathic Interstitial Pneumonias
6.1.9 Familial Idiopathic Interstitial Pneumonia
6.1.10 Unclassifiable Idiopathic Interstitial Pneumonias
6.2 Diffuse Parenchymal Lung Diseases of Known Origin
6.2.1 Lung involvement in Systemic Autoimmune Diseases
6.2.2 Drug-Induced Lung Disease
6.2.3 Parenchymal Lung Diseases Due to Extrinsic Noxae
6.3 Granulomatous Parenchymal Lung Diseases
6.3.1 Sarcoidosis
6.3.2 Other Granulomatous Parenchymal Lung Diseases
6.4 Other Types of Diffuse Parenchymal Lung Diseases
6.4.1 Pulmonary Langerhans Cell Histiocytosis
6.4.2 Lymphangioleiomyomatosis
6.4.3 Pulmonary Alveolar Proteinosis
6.4.4 Vasculitis and Other Autoimmune Diseases of the Lung
6.5 Summary
6.5.1 Idiopathic Interstitial Pneumonia
6.5.2 Diffuse Parenchymal Lung Diseases of Known Origin
6.5.3 Granulomatous Parenchymal Lung Diseases
6.5.4 Other Diffuse Parenchymal Lung Diseases
7 Immunologic Diseases of the Lung
7.1 Allergic Pulmonary Diseases
7.1.1 Asthma
7.1.2 Allergic Bronchopulmonary Aspergillosis
7.1.3 Hypersensitivity Pneumonitis
7.2 Eosinophilic Lung Diseases
7.2.1 Simple Pulmonary Eosinophilia (Loeffler Syndrome)
7.2.2 Acute Eosinophilic Pneumonia
7.2.3 Chronic Eosinophilic Pneumonia
7.2.4 Bronchocentric Granulomatosis
7.2.5 Idiopathic Hypereosinophilic Syndrome
7.3 Summary
8 Chronic Obstructive Pulmonary Disease
8.1 Pulmonary Emphysema
8.1.1 Emphysema on Computed Tomography
8.1.2 Emphysema on Chest Radiography
8.2 Chronic Bronchitis
8.3 Bronchiectasis
8.4 Summary
9 Tumors of the Lung
9.1 Hamartoma
9.2 Atypical Adenomatous Hyperplasia
9.3 Lung Cancer
9.3.1 Classification
9.3.2 Imaging Findings
9.3.3 Staging
9.3.4 Treatment Concepts
9.3.5 Early Detection and Lung Cancer Screening
9.4 Carcinoid
9.5 Rare Malignant Tumors of the Lung
9.6 Pulmonary Lymphoma
9.7 Lung Metastases
9.7.1 Nodular Metastasis
9.7.2 Lymphangitic Carcinomatosis
9.8 Inflammatory Pseudotumor
9.9 Summary
10 Airway Diseases
10.1 Diseases of the Trachea and Mainstem Bronchi
10.1.1 Tracheal Stenosis and Stenosis of the Mainstem Bronchi
10.1.2 Tracheal Diverticula
10.1.3 Tracheal Rupture
10.1.4 Foreign Body Aspiration
10.1.5 Benign Tumors
10.1.6 Malignant Tumors
10.1.7 Inflammatory and Other Systemic Diseases
10.1.8 Saber Sheath Trachea
10.1.9 Tracheomalacia and Bronchomalacia
10.2 Small Airway Diseases
10.2.1 Infectious Bronchiolitis
10.2.2 Bronchiolitis Obliterans and Constrictive Bronchiolitis
10.2.3 Other Forms of Bronchiolitis
10.3 Summary
11 Pleural Diseases
11.1 Pneumothorax
11.1.1 Imaging Findings
11.1.2 Differential Diagnosis
11.2 Pleural Effusion
11.3 Pleural Empyema
11.4 Pleural Fibrosis
11.4.1 Pleural Plaques
11.4.2 Pleural Thickening
11.5 Pleural Tumors
11.5.1 Lipoma
11.5.2 Pleural Mesothelioma
11.5.3 Solitary Fibrous Pleural Tumor
11.5.4 Pleural Carcinosis
11.6 Summary
12 Mediastinal Diseases
12.1 Mediastinal Lymphadenopathy
12.2 Mediastinitis
12.3 Pneumomediastinum
12.4 Esophageal Tumors
12.5 Mediastinal Tumors and Tumor-Like Masses
12.5.1 Mediastinal Masses of Low Density
12.5.2 Solid Mediastinal Tumors of the Anterior Mediastinum
12.6 Summary
13 Diseases of the Chest Wall and Diaphragm
13.1 Infection
13.2 SAPHO Syndrome
13.3 Tumors of the Chest Wall
13.3.1 Benign Tumors
13.3.2 Malignant Tumors
13.4 Diaphragmatic Paresis
13.5 Diaphragmatic Hernia
13.6 Deformities of the Chest Wall
13.7 Summary
14 Vascular Diseases
14.1 Diseases of the Pulmonary Arteries
14.1.1 Acute Pulmonary Embolism
14.1.2 Chronic Thromboembolic Disease and Chronic Thromboembolic Pulmonary Hypertension
14.1.3 Pulmonary Hypertension
14.1.4 Swyer–James Syndrome
14.2 Diseases of the Pulmonary Veins
14.3 Diseases of the Aorta and Major Arteries
14.3.1 Acute Aortic Syndrome
14.3.2 Vasculitis of the Great Vessels
14.4 Summary
15 Chest Trauma
15.1 Blunt Chest Trauma
15.1.1 Lung Parenchyma
15.1.2 Mediastinum
15.1.3 Pleural Space
15.1.4 Trunk Wall
15.1.5 Diaphragm
15.2 Penetrating Chest Trauma
15.3 Summary
16 Diagnostic Imaging of the Chest in Intensive Care Medicine
16.1 Indications for Chest Radiography in Intensive Care Medicine
16.2 Detection and Malposition of Implanted Devices
16.2.1 Tracheal Tubes
16.2.2 Central Venous Catheters
16.2.3 Pulmonary Artery Catheters (Swan-Ganz Catheter)
16.2.4 Nasogastric Tubes
16.2.5 Chest Tubes
16.2.6 Intra-Aortic Balloon Pump
16.2.7 Other Implanted Devices
16.3 Typical Findings in Intensive Care Unit Patients
16.4 Congestive Heart Failure
16.4.1 Left-sided Congestive Heart Failure
16.4.2 Right-sided Congestive Heart Failure
16.5 Pulmonary Edema
16.5.1 Hydrostatic Edema
16.5.2 Permeability Edema
16.6 Adult Respiratory Distress Syndrome
16.7 Summary
17 Treatment-Related Changes
17.1 The Postoperative Thorax
17.1.1 Partial Lung Resection
17.1.2 Pneumonectomy
17.1.3 Surgery for Pleural Diseases
17.1.4 Surgery for Pneumothorax
17.1.5 Lung Transplantation
17.1.6 Heart Surgery
17.1.7 Esophageal Surgery
17.1.8 General Complications of Thoracic Surgery
17.2 Bronchoscopic and Surgical Procedures for Treatment of Pulmonary Emphysema
17.2.1 Bronchoscopic Procedures
17.2.2 Lung Volume Reduction Surgery
17.3 Radiotherapy
17.4 Chemotherapy
17.5 Stem Cell Transplantation
17.5.1 Complications of Stem Cell Transplantation
17.5.2 Graft-versus-Host Disease
17.6 Summary
18 Occupational Lung Diseases
Beate Rehbock
18.1 Introduction
18.2 Imaging Modalities
18.2.1 Chest Radiography
18.2.2 Computed Tomography
18.2.3 Other Imaging Modalities
18.3 Disease Entities
18.3.1 Inorganic Dust-Induced Lung Diseases (Pneumoconiosis)
18.3.2 Organic Dust-Induced Lung Diseases
18.3.3 Acute Inhalation Toxicity
18.3.4 Chronic Bronchitis and Asthma
18.3.5 Malignant Occupational Diseases of the Lung and Pleura
18.4 Diagnostic Imaging of Special Disease Entities
18.4.1 Asbestosis and Asbestos Dust–Related Pleural Disease
18.4.2 Silicosis
18.4.3 Hypersensitivity Pneumonitis
18.4.4 Occupational Malignant Thoracic Tumors
18.5 Summary
19 Congenital Thoracic Diseases and Malformations
19.1 Congenital Lobar Emphysema
19.2 Bronchial Atresia
19.3 Congenital Pulmonary Airway Malformation
19.4 Bronchogenic Cysts
19.5 Vascular Anomalies
19.5.1 Anomalies of the Pulmonary Arteries
19.5.2 Anomalous Pulmonary Venous Drainage
19.6 Pulmonary Arteriovenous Malformation
19.7 Underdevelopment of the Lung
19.8 Bronchopulmonary Sequestration
19.9 Scimitar Syndrome
19.10 Summary
20 Nonvascular Interventions
20.1 Biopsy
20.1.1 Indications
20.1.2 Preprocedure Assessment
20.1.3 Technique
20.1.4 Complications
20.2 Drainage Therapy
20.2.1 Indications
20.2.2 Preprocedure Assessment
20.2.3 Technique
20.2.4 Complications
20.3 Thermal Ablation of Lung Tumor
20.3.1 Indications
20.3.2 Technique
20.3.3 Complications
Part III Differential Diagnostic Considerations and Incidental Findings
21 Pulmonary Nodules
21.1 Solitary Nodule
21.1.1 Differential Diagnosis
21.1.2 Management
21.2 Multiple Nodules
21.2.1 Differential Diagnosis
21.2.2 Management
22 Cavities
23 Persistent or Migratory Pulmonary Infiltrates
23.1 Raised Inflammatory Markers
23.1.1 Infection
23.1.2 Cryptogenic Organizing Pneumonia
23.1.3 Eosinophilic Pneumonia
23.1.4 Vasculitis
23.1.5 Radiation Pneumonitis
23.2 Normal Inflammatory Markers
23.2.1 Lung Cancer
23.2.2 Diffuse Alveolar Hemorrhage
23.2.3 Allergic Bronchopulmonary Aspergillosis
23.2.4 Pulmonary Alveolar Proteinosis
24 Diagnostic Schema for Typical Computed Tomography Findings of Diffuse Pulmonary Diseases
24.1 Main Finding: Interlobular Septal Thickening
24.2 Main Finding: Intralobular Lines
24.3 Main Finding: Nodules
24.4 Main Finding: Ground-Glass Opacities
24.5 Main Finding: Consolidations
24.6 Main Finding: Cysts
Part IV Glossary
25 Fleischner Society Glossary of Terms for Thoracic Imaging
25.1 Preliminary Remarks
25.2 Glossary
25.3 Additional Definitions
Index
Preface
No radiologist can get away from diagnostic imaging of the thorax. After all, chest radiography is the most common imaging examination. As such, all radiologists do in fact have practical experience in this area. Nonetheless, lectures on topics such as HRCT or parenchymal lung diseases regularly attract record audiences. Presumably, while radiologists do time and again come across these issues, they are too rare to become established routine practice.
This book provides information on virtually all the key questions related to diagnostic imaging of the thorax arising in the everyday clinical setting. The systematic organization of the sections of the book contains descriptions of all common diseases affecting the chest organs. It is based on the European Society of Radiology Training Curriculum for Subspecialisation in Radiology. The summary at the end of chapters comprises the subject matter featured in the curriculum, thus assuring efficient preparation of examination for trainee radiologists.
Furthermore, this book is intended as a useful reference for radiologists, with its synoptic section serving as a rapid guide through the diagnostic maze. Differential diagnoses and clinical management of frequently encountered findings are presented. For diffuse parenchymal lung diseases, there is a diagnostic guide structured like an identification book. The main findings quickly signpost the most probable differential diagnosis, which are shown in tables and figures.
The Fleischner Society’s Glossary of Terms for Thoracic Imaging is featured at the end of the book.
In general, diagnostic imaging plays a pivotal role in diagnosis of thoracic diseases. Diagnosis of several diseases is exclusively confirmed on the basis of the imaging findings. This includes well-known diseases such as community-acquired pneumonia or usual interstitial pneumonia as well as rare disorders like lymphangioleiomyomatosis. Hence, the corresponding diagnostic criteria are an important component of this book. Thanks to our imaging data, we as radiologists are able to make the diagnosis, and it is up to us not to leave that task to the clinicians.
Encouraged by the success of the first German edition of this book which was published in late 2016, the idea of an English translation was born. It soon became obvious that this project comprises more than a simple translation. References to German guidelines had to be replaced by their international (and at times inconsistent) counterparts, and some classifications had to be updated. Hence, the translation turned into an updated second edition to the first German edition.
I would like to thank Thieme Publishers, especially Ms. Angelika Find-gott and Mr. Marcus Laithangbam, for their kind and competent assistance in making this book happen. Ms. Sarah Venkata deserves my special thanks for translating the book, very rapidly and successfully acquainting herself with the specific vocabulary of chest radiology and shaping a straightforward English from the more complicated German language.
Finally, I thank my wife Ms. Anita Wormanns for her continued support and patience while this book was being written.
Dag Wormanns, MD, PD
Contributors
Jürgen Biederer, MDProfessorDepartment of Diagnostic and Interventional RadiologyUniversity Hospital HeidelbergHeidelberg, Germany
Beate Rehbock, MDConsultantDiagnostic Radiology with Specialty Thoracic RadiologyBerlin, Germany
Dag Wormanns, MDMedical DirectorHead of Department of RadiologyELK Berlin Chest HospitalBerlin, Germany;Medical FacultyInstitute for Clinical RadiologyUniversity of MünsterMünster, Germany
Abbreviations
AAH
atypical adenomatous hyperplasia
AEP
acute eosinophilic pneumonia
AIDS
acquired immunodeficiency syndrome
AIP
acute interstitial pneumonia
AIS
adenocarcinoma in situ
ANA
antinuclear antibody
ANCA
antineutrophil cytoplasmic antibodies
c-ANCA
cytoplasmic antineutrophil cytoplasmic antibodies
p-ANCA
perinuclear antineutrophil cytoplasmic antibodies
AP
anteroposterior
ARDS
adult respiratory distress syndrome
BALT
bronchus-associated lymphatic tissue
BG
bronchocentric granulomatosis
BiVAD
biventricular assist devices
BOOP
bronchiolitis obliterans with organizing pneumonia
CAD
computer-assisted diagnostic
CEP
chronic eosinophilic pneumonia
COP
cryptogenic organizing pneumonia
CPAM
congenital pulmonary airway malformation
CT
computed tomography
CTA
computed tomography angiography
CTED
chronic thromboembolic disease
CTEPH
chronic thromboembolic pulmonary hypertension
CTPA
computed tomography pulmonary angiography
CUP
cancer of unknown primary
CWP
coal workers’ pneumoconiosis
DAD
diffuse alveolar damage
DECT
dual-energy computed tomography
DIP
desquamative interstitial pneumonia
DVT
deep vein thrombosis
DWI
diffusion-weighted imaging
ECMO
extracorporeal lung assist device
FDG
18F-fludeoxyglucose/fluorodeoxyglucose
FEV1
forced expiratory volume in 1 second
FSE
fast spin-echo
FVC
forced vital capacity
GE
gradient echo
GGO
ground-glass opacities
GvHD
graft-versus-host disease
HIV
human immunodeficiency virus
HRCT
high-resolution computed tomography
HU
Hounsfield units
IABP
intra-aortic balloon pump
IASLC
International Association for the Study of Lung Cancer
ICD
implantable cardioverter defibrillator
ICOERD
International Classification of HRCT for Occupational and Environmental Respiratory Diseases
ICU
intensive care unit
IGRA
interferon-γ release assay
IHS
idiopathic hypereosinophilic syndrome
IIPs
idiopathic interstitial pneumonias
ILO
International Labour Organization
IPAF
interstitial pneumonia with autoimmune features
IPF
idiopathic pulmonary fibrosis
IPS
idiopathic pneumonia syndrome
IV
intravenous
LAM
lymphangioleiomyomatosis/lymphangiomyomatosis
LDH
lactate dehydrogenase level
LIP
lymphoid interstitial pneumonia
LPAs
lepidic predominant adenocarcinomas
LV
left ventricle
LVAD
left ventricular assist devices
MAC
Mycobacterium avium complex
MCTD
mixed connective tissue disease
MDR-TB
multidrug-resistant tuberculosis
MIA
minimally invasive adenocarcinoma
MinIP
minimum intensity projection
MIP
maximum intensity projection
MOTT
mycobacteria other than tuberculosis
MPO
myeloperoxidase
MPR
multiplanar reformation
MRA
magnetic imaging angiography
MRI
magnetic resonance imaging
NK
natural killer
NLST
National Lung Screening Trial
NSIP
nonspecific interstitial pneumonia
OP
organizing pneumonia
PA
posteroanterior
PAP
pulmonary alveolar proteinosis
PAVM
pulmonary arteriovenous malformation
PCH
pulmonary capillary hemangiomatosis
PCT
pulmonary cytolytic thrombi
PEEP
positive end-expiratory pressure
PET-CT
positron emission tomography–computed tomography
PFT
pulmonary function testing
PLCH
pulmonary Langerhans cell histiocytosis
PMF
progressive massive fibrosis
PPFE
pleuroparenchymal fibroelastosis
PVOD
pulmonary veno-occlusive disease
RA
rheumatoid arthritis
RB
respiratory bronchiolitis
RB-ILD
respiratory bronchiolitis-interstitial lung disease
RECIST
Response Evaluation Criteria in Solid Tumors
RV
right ventricle
RVAD
right ventricular assist devices
SAPHO
synovitis, acne, palmoplantar pustolosis, hyperostosis, and osteitis
SARS
severe acute respiratory syndrome
SFT
solitary fibrous tumor
SSc
systemic sclerosis
SLE
systemic lupus erythematosus
SPE
simple pulmonary eosinophilia
STIR
short-tau inversion recovery
SUV
standard uptake value
T1w
T1-weighted
T2w
T2-weighted
UIP
usual interstitial pneumonia
VQ
ventilation/perfusion
VRT
volume rendering technique
XDR-TB
extensively drug-resistant tuberculosis
Part I
Fundamentals of Diagnostic Thoracic Imaging
1 Examination Technique
2 Basic Anatomy
3 General Symptomatology
4 Indications
Chapter 1
Examination Technique
1.1 Projection Radiography
1.2 Fluoroscopy
1.3 Computed Tomography
1.4 Magnetic Resonance Imaging
1.5 Ultrasonography
1.6 Positron Emission Tomography–Computed Tomography
1.7 Image Reformatting
1.8 Computer-Assisted Diagnosis
1 Examination Technique
This chapter describes specific aspects of examining the chest organs with the different imaging modalities. It is outside the scope of this textbook to give a comprehensive overview of the technical aspects of the equipment or the positioning techniques. These details can be consulted in the pertinent literature.1,2
1.1 Projection Radiography
The following descriptions relate to digital radiography (flat panel detector or image plate). By now this is available in most radiology institutions. This chapter does not take account of older, conventional screen-film radiography systems but many aspects are very similar to that of digital radiography.
For almost all chest diseases, chest radiography constitutes the first step in diagnostic imaging. The few exceptions to that rule (e.g., suspected pulmonary embolism) will be pointed out in the relevant sections.
1.1.1 Standing Position
Patients are X-rayed in a standing position, whenever their condition permits. The standing patient is X-rayed in the PA (posteroanterior) beam path with the chest placed against the detector (PA image), while the focus detector distance is 1.4 to 2 m. ▶Table 1.1 summarizes the technical radiographic parameters. To avoid overlapping of the pulmonary fields, the scapulae must be rotated laterally. To that effect, the patient places his/her hands on the hips while rotating the elbows anteriorly as far as possible. Alternatively, the patient clasps the detector with their arms; this, too, assures anterior rotation of the scapulae.
If because of the patient’s general condition an X-ray cannot be taken in a standing position, this can be done with the patient sitting down. The patient leans his/her back against the detector; the beam path is therefore oriented in an AP direction (anteroposterior; AP image). As a result, the diaphragm will be positioned at a higher level than seen in a standing radiograph, the inspiration depth is reduced, and, accordingly, the basal lung segments are less well ventilated.
Likewise, a lateral radiograph is obtained with the patient standing and the arms raised. Normally, the patient’s left side rests against the detector. In general, a clearer image will be obtained of the lung closer to the detector compared with that farther away from the detector. If the clinical diagnostic indication calls for maximum image quality and the critical details are difficult to identify, in certain cases to visualize a right-sided pathology it may be advisable to take an image with the right side placed against the detector.
All radiographs of the chest organs should be obtained in deep inspiration. The expiratory image usually used in the past to exclude pneumothorax is now obsolete for several reasons3,4:
• The expiratory radiograph does not permit assessment of the cardiopulmonary status since the lung is inadequately ventilated and the pulmonary vessels appear dilated. This can obscure other relevant findings, e.g., small pulmonary infiltrates or incipient congestive heart failure.
• Comparability with previous or subsequent radiographs is not possible.
• With modern digital equipment technology, a pneumothorax of clinically relevant size can also be recognized on an inspiratory radiograph.
The European Guidelines on Quality Criteria for Diagnostic Radiographic Images issued by the European Commission define criteria to be met by radiographs.5▶Table 1.2 lists the criteria specified for the image quality of overview chest radiographs.
Note
For radiographic diagnosis of chest organs, a high-energy X-ray taken with a high tube voltage is used. Calcified structures will appear radiolucent on such radiographs. This reduces the otherwise disruptive overlying of the pulmonary fields by the ribs (▶Fig. 1.1). Besides, osseous structures allow only limited assessment. Therefore, for diagnostic issues related to the thoracic skeleton, e.g., exclusion of rib fractures, a low-energy X-ray is needed with 60 to 75 kV tube voltage.
1.1.2 Supine Radiographs
For diagnostic imaging of bedridden patients, in particular in intensive care settings, supine radiographs are normally obtained. The mobile detector is positioned beneath the thorax of the supine patient and the tube of the mobile radiography unit is placed above the patient. The focus detector distance should be 90 to 120 cm. For several reasons, supine radiographs have poorer image quality than standing or sitting radiographs:
Table 1.1 Radiographic parameters for PA and lateral radiographs5
Table 1.2 Quality requirements for chest radiographs5
Requirements
PA/AP thorax
Lateral thorax
Image criteria
• Performed at full inspiration (as assessed by the position of the ribs above the diaphragm—either 6 anteriorly or 10 posteriorly) and with suspended respiration
• Symmetrical reproduction of the thorax as shown by central position of the spinous process between the medial ends of the clavicles
• Medial border of the scapulae should be projected outside the lung fields
• Reproduction of the whole rib cage above the diaphragm
• Visually sharp reproduction of the vascular pattern in the whole lung, particularly the peripheral vessels
• Visually sharp reproduction of:
– The trachea and proximal bronchi
– The borders of the heart and aorta
– The diaphragm and lateral costophrenic angles
• Visualization of the retrocardiac lung and the mediastinum
• Performed at full inspiration and with suspended respiration
• Arms should be raised clear of the thorax
• Superimposition of the posterior lung borders
• Reproduction of the trachea
• Reproduction of the costophrenic angles
• Visually sharp reproduction of the posterior border of the heart, the aorta, mediastinum, diaphragm, sternum, and thoracic spine
Important image details
• Small round details in the whole lung, including the retrocardiac areas:
– High contrast: 0.7 mm diameter
– Low contrast: 2 mm diameter
• Linear and reticular details out to the lung periphery:
– High contrast: 0.3 mm in width
– Low contrast: 2 mm in width
• Small round details in the whole lung:
– High contrast: 0.7 mm diameter
– Low contrast: 2 mm diameter
• Linear and reticular details out to the lung periphery:
– High contrast: 0.3 mm in width
– Low contrast: 2 mm in width
Fig. 1.1 High-energy and low-energy chest radiographs. Different detectability of bone structures. Bronchopneumonia in the left upper lobe is much easier to detect on the high-energy radiograph (a,arrow). (a) High-energy radiograph with 125 kV tube voltage. (b) Low-energy radiograph with 70 kV tube voltage.
Fig. 1.2 Geometric distortion in standing and supine radiographs. Schematic diagram. (a) Standing PA radiograph with large focus detector distance: low magnification of cardiac opacity. (b) Supine AP radiograph with small focus detector distance: high magnification of cardiac opacity.
Fig. 1.3 Grid artifact because of decentered X-ray tube. Schematic diagram. (a) Normal image: symmetric radiolucency of both hemithoraces. (b) Grid artifact: the decentered tube causes right hemithorax opacity.
Fig. 1.4 Grid artifact. Radiograph (supine radiograph). Different radiolucency of both axillae (arrows) as distinguishing feature of that artifact.
• The reduced focus detector distance results in greater geometric distortion; the mediastinal width and heart size appear enlarged on the supine radiograph (▶Fig. 1.2); the heart is farther away from the detector, showing greater geometric enlargement.
• The diaphragm is higher, resulting in reduced inspiration depth.
• Lung perfusion has no gravity-mediated caudocranial gradient; it is not possible to diagnose pulmonary blood flow redistribution.
• Since the tube voltage used is lower, bone superimposition is more pronounced.
• The lower generator power of mobile radiography units results in a longer exposure time and is likely to cause motion blur due to breathing or heart pulsations.
Note
The imaging position (standing, sitting, supine) should be noted on the radiograph. Besides, for mechanically ventilated patients, information on the ventilation parameters is helpful for image interpretation, in particular on the positive end expiratory pressure (PEEP).
The use of an antiscatter grid can enhance the image quality for obese patients, albeit at the expense of higher radiation exposure. A characteristic artifact is observed if the X-ray tube is not positioned above the middle of the detector fitted with an antiscatter grid (▶Fig. 1.3). To distinguish this artifact from pathologic hemithorax opacity, it may be useful to compare radiolucency of both axillae (▶Fig. 1.4). Unequal radiolucency is suggestive of a grid artifact.
Skin folds on the patient’s back result from placement of the X-ray detector between the bed and patient and can mimic pneumothorax (pseudo-pneumothorax).
1.2 Fluoroscopy
Chest fluoroscopy is mainly used for functional assessment of diaphragmatic movement. A standardized fluoroscopy examination procedure is described.6
Before commencing fluoroscopy examination, the patient practices deep breathing with the mouth open. In addition, the patient should repeat the sniff test around twice: the patient breathes deeply in and out with the mouth open, closes the mouth, and, again, with the mouth closed, breathes in deeply and strongly as fast as possible. The patient repeats this procedure once.
During examination, the patient stands against the vertically tilted fluoroscope. If the patient cannot be examined in a standing position because of their general condition, the patient sits on the footplate of the fluoroscope. The image section is centered vertically on the diaphragm and the image is collimated laterally as far as necessary. Next the patient breathes normally two to three times under fluoroscopic guidance, and then takes two to three forced breaths in and out. This is followed by conduct of the sniff test, also two to three times. The patient is then rotated by 90° and the examination sequence described is repeated in the lateral beam path.
The image documentation comprises the fluoroscopy video sequences of the PA and lateral fluoroscopy images which are digitally archived.
1.3 Computed Tomography
The enormous innovative boost experienced over the past two decades in computed tomography (CT) technology has greatly enhanced scanner performance. This, too, has led to increasing diversification of the technical features of CT equipment. Currently, scanners with a row count of between 1 and 640 are used for routine imaging. As such, standardization of examination protocols is virtually impossible. Various valuable internet sources of information provide vendor-specific CT examination protocols (e.g., www.ctisus.com). Below are listed some basic aspects to be considered in CT examination protocols:
•Radiation exposure: Tube voltage, tube current, and pitch should be adjusted such that the radiation exposure complies with the reference values specified for diagnostic imaging of patients of normal weight. Relevant reference values vary greatly among different countries.7
•Tube voltage: For most applications, a tube voltage of 110 to 120 kVp is suitable. For computed tomography angiography (CTA), the tube voltage may be reduced in certain circumstances to 80 to 100 kVp, in particular for pediatric or slim patients.8,9
•Automatic tube current modulation: Due to the major differences in the absorption profiles of the thorax in the craniocaudal and axial directions, the use of automatic tube current modulation has greatly contributed to dose reduction.8 However, there is a risk of this automated facility preselecting a very high tube current for obese patients. It is therefore recommended to limit the maximum tube current in the scan parameters if this is technically possible. Other considerations apply for low-dose CT.
•Slice thickness: The detector configuration should provide for a reconstructed slice thickness of 1 to 1.5 mm. But that does not apply to CT scanners with a limited row count, for which a compromise has to be made between the minimum slice thickness possible and the scan duration. A limiting factor for the slice thickness in such cases is the maximum length of breath suspension that can be maintained before breathing artifacts degrade the image quality. There does not appear to be much benefit in selecting a slice thickness of substantially less than 1 mm in the thoracic region because of the ensuing rise in image noise; a reduced slice thickness is unlikely to confer any additional diagnostic insights of relevance.
•Image reconstructions recommended for routine examinations:
– 5 mm axial for quick orientation also for the referring physician (soft-tissue and lung kernel).
– Axial thin-slice reconstructions (1.5–3 mm) with soft-tissue kernel, in CTA possibly reduced slice thickness.
– Axial thin-slice reconstructions (1–1.5 mm) with lung kernel to allow for volumetric measurements.
– 3–5 mm coronal and sagittal.
•Overlapping of thin-slice reconstructions: To achieve a good image quality for 3D (three-dimensional) reformatting of image data and precise volumetry, overlapping reconstruction of the thin-slice series by at least 20% of slice thickness is recommended.
•IV contrast: If IV contrast administration is indicated, a fixed delay of 40 s may be used for most diagnostic purposes. Alternatively, a bolus tracking procedure could be employed. Here the arrival of the contrast bolus in the descending aorta triggers the scan. An additional delay of a few seconds is advisable, for example, to accentuate the contrast between a tumor and its surrounding tissues. The use of CTA for diagnostic exploration of pulmonary embolisms requires bolus tracking or a test bolus in the pulmonary trunk or right ventricle.
•Scanning direction: Examination is performed in deep inspiration. A caudocranial scanning direction helps to reduce breathing artifacts. First, the basal lung regions most susceptible to breathing artifacts are scanned, followed by the less susceptible apical regions. Furthermore, with appropriate contrast medium timing, beam hardening artifacts caused by highly concentrated contrast material in the superior vena cava and brachiocephalic veins can be reduced.
1.3.1 High-Resolution Computed Tomography
The term “high-resolution computed tomography” (HRCT) dates back to the early 1980s.10 While that term has proved immutable over the past some 30 years, the underlying examination technology has undergone rapid development. Back then the body region to be scanned could only be visualized in sequential single slices, and acquisition of slices of 10-mm thickness represented the normal standard. Since each individual slice was acquisitioned in a separate breath-hold phase, imaging the entire lung took a lot of time.
Due to its low spatial resolution in the z-direction, the thick-slice CT was of limited value for differential diagnosis of diffuse lung parenchymal diseases. This differential diagnosis requires the assignment of pathologic changes to the structures of the pulmonary lobule, which is not possible with a 10-mm slice thickness. The key driver of HRCT was thus to generate thin slices of the lung parenchyma (slice thickness: around 1 mm) to improve such assignment. However, sequential 1-mm slices were not suitable for continuous imaging of the entire lung at that time. The only remedy here was therefore to acquisition discontiguous slices at greater distances apart (e.g., 10 mm). This inevitably results in incomplete visualization of the lung. For diagnosis of diffuse lung diseases, a number of representative slices suffice; however, thanks to the higher spatial resolution, it has been possible to achieve a diagnostic gain but there was a risk of focal changes being overlooked.
The term HRCT was thus normally understood as an examination technique which permits maximum spatial resolution11:
• Reduced slice thickness (maximum 1.5 mm) at greater distances apart (e.g., 10 mm).
• High radiation dose for the single slice (high tube voltage and high tube current).
• Edge-enhancing reconstruction kernel for maximum spatial resolution in the slice plane.
• Maximum image matrix (at least 512 × 512 pixels).
Since 1998, multidetector CT has been available providing for spiral imaging of the entire lung in 1-mm slices during a single-breath hold. This marked the advent of an alternative to the discontiguous thin single slices afforded by conventional HRCT. Its main advantage derives from the ability to display the entire lung in a slice thickness that hitherto had only been possible with HRCT. The problem of incomplete visualization of the lung parenchyma had now been resolved, albeit at the expense of higher radiation exposure and a minimally poorer image quality. Follow-up examinations became more precise since identical slice planes were always available for comparison of the previous and follow-up examinations. As such, in recent years thin-slice multidetector CT has just about fully supplanted the classic sequential HRCT.12 Nowadays, sequential HRCT plays a limited role for follow-up examination of diffuse lung diseases in young patients13 because of its lower radiation dose.
Note
Today, using modern scanners the entire lung can be imaged in continuous 1-mm slices in a few seconds. Hence, examination results of relatively good quality can be obtained even for severely dyspneic patients.
1.3.2 Low-Dose Computed Tomography
Many pathologic changes in the lung parenchyma contrast sharply with their surroundings. That means there is considerable potential for dose reduction in CT provided that the clinical issue of diagnostic interest is limited to detection or exclusion of high contrast objects. Typical examples of such clinical questions are early detection of lung cancer in the context of lung cancer screening, or detection of fungal pneumonia in immunocompromised patients. Both examinations are aimed at detection of foci of soft-tissue opacity in the aerated lung. Dose reduction causes considerably higher image noise (▶Fig. 1.5) but this does not adversely affect detection of relevant findings.14
At a technical level, dose reduction in low-dose CT is generally achieved by reducing the tube current. To further reduce the dose (ultralow-dose CT), a lower tube voltage (80–100 kVp) is sometimes used.15 The use of automatic exposure control is not generally recommended for low-dose CT.16 Scanogram-adapted methods of tube current modulation are thought to be errorprone due to eccentric patient positioning. Online modulation of the tube current may be overregulated in the region of the shoulders and upper abdomen because of higher radiation absorption. Both present a risk of unnecessarily high radiation exposure or inadequate image quality when the tube current is too low. A more robust approach entails the use of a weight-adapted, fixed tube current. Several lung cancer screening trials used a variety of low-dose CT protocols, which generally achieved an effective dose of approximately 1.5 mSv.16,17 These provide for a dose saving of over 80% compared with standard CT; with ultralow-dose protocols, radiation exposure similar to a chest radiograph in two views can even be achieved.15
Fig. 1.5 Low-dose CT compared with standard CT. Higher image noise of low-dose CT, but good visualization of the pulmonary structures and of left posterior pleural plaque (arrows). (a) Standard CT with CTDIVol of 6.5 mGy. (b) Low-dose CT with CTDIVol of 1.5 mGy.
There are limitations with regard to the detection of subtle ground-glass opacities and early forms of pulmonary emphysema since these findings induce only minor changes of CT density compared to their surroundings.18
1.3.3 Special CT Examination Techniques
Expiratory CT scan
Many diseases of the small airways are associated with obstruction of the bronchioles. Standard CT inspiratory images may yield normal results. Only on an expiratory scan can the disease be detected through pronounced air trapping (▶Fig. 1.6).
Two examination techniques are available:
•Sequential expiratory scans: A few sequential expiratory scans, in addition to the inspiratory spiral scan, yield just slightly higher radiation exposure. Even severely dyspneic patients generally tolerate the very short breath-hold times for sequential expiratory scans. One drawback is the sampling error since only a small part of the lung parenchyma is displayed. Besides, interpretation of the findings with regard to air trapping may be difficult at times.
•Expiratory volume acquisition: In addition to an inspiratory spiral CT scan, a second expiratory spiral scan is obtained across the entire thorax. Its advantage is that it displays the whole of the lung and focal air trapping is not overlooked. But this involves higher radiation exposure, although the expiratory scan can be obtained in low-dose technique. Besides, patients cannot hold their breath in expiration for as long as in inspiration. If a very fast CT scanner is not available, a compromise must be reached between slice thickness and scan duration since otherwise breathing artifacts would adversely affect image interpretation.
Note
Visualization of the trachea on CT images helps to verify whether the image was obtained in expiration. In the latter case, the posterior wall of the trachea, the membranous part, will protrude anteriorly. This sign is particularly useful if there is massive diffuse air trapping and there is essentially no difference between the expiratory and inspiratory images. This shows whether air trapping was really present or whether the patient had not correctly implemented the breathing command. At times, such examination results are very difficult to interpret. Breathing dynamics imaging will help in cases of doubt (see below).
Expiratory CT in addition to an inspiratory CT scan is also recommended for differential diagnosis of lung fibrosis—in particular, for differentiation between usual interstitial pneumonia and chronic hypersensitivity pneumonitis.19
Dynamic CT of the Ventilation Cycle
Dynamic CT of the ventilation cycle is indicated if there are difficulties in interpreting the expiratory scans or because of suspected dynamic respiratory tract stenosis which cannot be identified in inspiration.20,21
The easiest approach for this examination is to use the bolus tracking feature implemented in many CT scanners and to set the threshold value to start the scan high enough so that it is never reached. To begin with, the patient takes a few normal breaths under bolus tracking, followed by a few forced breaths. Eventually, the bolus tracking mode must be stopped manually. An imaging frequency of one image per second suffices for interpretation of the findings.
Fig. 1.6 Expiratory CT for visualization of small airway disease. (a) Hardly any abnormalities in inspiration. (b) In expiration greater evidence of air trapping (darker areas) in the diseased lung parenchyma.
For evaluation, lung parenchymal opacity is measured at the same site on all images using a region of interest of several centimeters, thus demonstrating how lung density changes in the course of the breathing cycles. These values can be displayed as graphs with the evaluation software present in many CT scanners (▶Fig. 1.7). The measurements are to be performed in both lungs.
Note
It is advisable to acquisition dynamic CT scans in different lung levels; at least three measurements are recommended in the upper, middle, and lower field.
A change of at least 50 HU (Hounsfield units) in lung parenchymal density during a breathing cycle is normal. Lower values are interpreted as air trapping (see ▶Fig. 1.7). In the presence of severe unilateral respiratory tract stenosis, a paradoxical increase in the density of the diseased lung may be identified in inspiration.
Imaging in the Prone Position
Occasionally, dependent opacities in the posterior segments of the lower lobes may manifest as a diffuse increase in lung parenchymal density. They make it more difficult to evaluate the subpleural space and, at times, are misinterpreted as an early form of diffuse parenchymal lung disease. If differentiating physiologic dependent opacities from incipient parenchymal lung disease is of clinical relevance, this can be done by obtaining an additional CT scan with the patient in the prone position. Whereas lung parenchymal disease will persist, dependent opacities disappear in the prone position (▶Fig. 1.8). It is important to make this distinction, for example, when evaluating occupational lung diseases (see Chapter 18).
Fig. 1.7 Dynamic CT of the ventilation cycle. Visualization of lung density during several breathing cycles. Illustrated in each case are measurements in the right (curve 1) and in the left lung (curve 2). (a) Normal results for the left lung (2). Density changes in one breathing cycle of more than 50 HU (Hounsfield units). On the right (1), mild air trapping with lower density amplitude. (b) Extensive air trapping. Only minor changes in lung parenchymal density; in the left lung (2) more massive air trapping than on the right (1).
Fig. 1.8 Dependent opacities in both lungs. CT images. (a) In supine position: Subpleural densities in the posterior lower lobes. (b) In the prone position: complete resolution of findings (image rotated by 180°).
A few sequential CT scans are generally sufficient for reliable differential diagnosis. There is no need for an additional spiral scan to display the lungs in their entirety.
Dynamic Contrast Enhancement
Dynamic contrast enhancement may be useful in differential diagnosis of pulmonary nodules (see Chapter 21) in certain clinical situations. This technique is based on the observation that the absence of contrast enhancement by a nodule makes its malignancy very unlikely. One advantage of this method is its high predictive value of benignity of around 96%.22 But a drawback is its low specificity (58%) since, apart from malignant, many benign nodules also exhibit contrast enhancement.
First, a short unenhanced thin-slice spiral CT scan of the nodule is obtained. Then IV contrast is injected (110 mL with 3 mL/s flow rate) and the scan is repeated after 60, 120, 180, and 240 seconds. Nodule density is measured with a region of interest comprising around two-thirds of the nodule (▶Fig. 1.9). An increase in density by less than 15 HU in all four spiral scans following contrast administration compared with unenhanced examination is considered predictive of benignity.22 The procedure is suitable for nodules with at least 8 mm diameter.
1.3.4 Dual-Energy Computed Tomography
Dual-energy CT (DECT) scans the body region to be examined utilizing X-rays of two different energy levels. The usual practice is to use two energy levels of approximately 140 and 80 kVp. Depending on the CT scanner manufacturer and equipment features, different technical solutions are employed:
• One scan, synchronous imaging with two X-ray tubes, of different tube voltage, which are offset by approximately 90°.
• One scan, quasi-synchronous imaging using very fast voltage switching in one X-ray tube, thus providing for acquisition of alternating projections with high and low tube voltage.
• One scan, synchronous imaging using one X-ray tube and detectors of different spectral sensitivity.
• Two scans, asynchronous imaging with acquisition in rapid succession of two spiral scans with different tube voltages.
The data thus acquisitioned provide additional information and postprocessing possibilities beyond conventional CT imaging23:
•Iodine maps: Utilizing an algorithm for material decomposition the iodine content of each voxel is determined and displayed in a parametric image (▶Fig. 1.10). This shows contrast enhancement, which can be used as a surrogate parameter for lung perfusion.
•Spectral imaging: From the DECT dataset, monoenergetic images with different virtual tube voltages can be calculated. The standard CT image acquisitioned with a tube voltage of 120 kVp corresponds to the image impression of a monoenergetic image at 70 kV. Monoenergetic images with a lower virtual tube voltage exhibit higher radiation absorption of the iodinated contrast material. Accordingly, for example, a CTA with poor vascular contrast can be subsequently improved when interpreting the monoenergetic images at lower virtual kV levels (e.g., 50 kV).
•Virtual unenhanced imaging: From the primary CT dataset acquisitioned with IV contrast, virtual unenhanced images can be calculated for better evaluation of contrast enhancement by pulmonary nodules. However, in certain cases there may not be reliable concordance between density measurement on virtual unenhanced CT images and the actual unenhanced CT density.
•Xenon-enhanced ventilation visualization: Pulmonary ventilation can be visualized with DECT by using inhaled xenon similarly as for the iodine maps described above.24
1.4 Magnetic Resonance Imaging
Jürgen Biederer
1.4.1 Introduction
Thanks to the latest developments in equipment and pulse sequence technology, magnetic resonance imaging (MRI) is set to become the third most important modality, together with radiography and CT, for diagnostic imaging of the lung. The state of the art permits its widespread deployment not just as a radiation-free alternative for young patients and pregnant women: more than any other imaging modality, MRI offers the combined advantage of insights into morphology and functional information (on lung perfusion, breathing mechanics) within a single examination. Notwithstanding the current state of the technology, many potential users continue to have reservations about utilizing lung MRI, mainly because of the widespread assumption that a reliable and reproducible image quality is difficult to achieve in the everyday routine setting. Essentially, there are two hurdles that reinforce these reservations:
Fig. 1.9 Benign nodule in left lower lobe. Dynamic CT contrast enhancement. (a) Unenhanced CT: Mean nodule density on CT: 18 HU. (b) 60 s after IV contrast injection: No significant contrast enhancement (CT density: 26 HU). (c) Visualization of low contrast enhancement on parametric image.
Fig. 1.10 DECT for visualization of contrast enhancement. (a) Parenchymal image. (b) Parametric image with visualization of iodine content of each voxel, “iodine map.”
• First, MRI is much more complex than other modalities. Trying to get to grips with this technology at one’s own initiative using noncustomized product sequences can be tedious and disappointing. For a successful start, it is therefore recommended to use as far as possible standardized and preset sequence packets, as offered by some MRI scanner manufacturers.25 The aim of this present section is to give an overview of the sequence techniques, diagnostic facilities, and sequence packets tailored to the most commonly encountered clinical problems.
• The second hurdle relates to the interpretation and evaluation of the images. Experienced thoracic radiologists are not often familiar with the contrasts and poorer spatial resolution of MRI compared with CT, and may need time to get used to the new modality. In addition to attending courses and studying the pertinent literature, new users are therefore advised to arrange guest visits to radiology institutes already using lung MRI.
Unlike radiography and CT, MRI is not based on ionizing radiation but rather on excitation of the rotating hydrogen nuclei in water and organic compounds. The specific anatomic and physiologic nature of the lung is therefore challenging for MRI: in the ventilated lung, the large organ volume contains only a small amount of tissue and fluids which, due to the low proton density, exhibits little signal, with an unfavorable signal-to-noise ratio. This is further compounded by magnetic field inhomogeneities at the air–water interfaces causing decay of the weak signal within milliseconds. Therefore, modern sequence techniques with short echo times are needed in order to at all be able to detect the low signal emitted by the lung tissue. Other interfering factors are the continuous, often irregular movements of the chest caused by breathing and heartbeat. Hence, the healthy, ventilated lung tissue exhibits no, or at most only low, signal which is at times obscured by pulsation artifacts. The majority of pathologic findings are now known to be associated with a higher density of tissue or fluid collections. As such, thanks to their characteristic high signal and good soft-tissue contrast, clinically relevant MRI findings can be distinguished from the intact, dark lung tissue (▶Fig. 1.11).26
Fig. 1.11 Adenocarcinoma in posterior upper lung lobe. MR image. The tumor has areas of variable signal intensity, reflecting tumor portions with different histopathologic differentiation.
1.4.2 Equipment Technology
In principle, MRI of the lung can be performed at either low field strengths (1.0 T and lower) or also in high-field scanners at 3 T. Modern 1.5 T MRI scanners are equipped with gradient strengths of more than 40 mT/m and gradient rise times of more than 200 mT/(m × ms), permitting echo times of less than 1.5 ms. Therefore, thanks to superior magnetic field homogeneity, higher lung signal and less susceptibility to artifacts, low-field strength scanners tend to be more suitable than their high-field strength counterparts. However, modern 3 T MRI scanners are typically equipped with powerful gradient systems that offset the undesirable effects of higher field strengths coming into play in the lung (reduced lung signal, increased fluid artifacts in certain sequences). At the other side of the spectrum, low-field strength scanners have an altogether less powerful gradient system, which means that the potential benefits of lung MRI cannot be fully exploited at low-field strength.26 The following recommendations for the sequence protocol are thus intended for 1.5 T scanners but can also be applied at 3 T.27
Multichannel coil systems and parallel imaging techniques play a crucial role in enhancing the performance of modern MRI scanners. In parallel imaging, the spatial arrangement of multiple coil elements is exploited to gain additional spatial information from the differences in the sensitivity profiles of the various elements. With parallel imaging, the imaging time can be shortened or, alternatively, a higher spatial resolution can be achieved in the same imaging time. Besides, parallel imaging at higher field strengths (e.g., 3 T) can help to reduce energy deposition in the patient and remain within the limits of the specific absorption rate.
Note
Since the gain in imaging speed or spatial resolution comes at the expense of slight signal loss, the acceleration factors should not exceed 2 or 3 for lung examination. Otherwise, there would be a marked increase in the noise level. Because of lung movement calibration of the sensitivity profile should be integrated into the sequence (e.g., GRAPPA, auto SENSE, FLEX). If that is not the case, there is a risk of interfering artifacts arising from the spatial incongruence between the sensitivity scan and the actual imaging phase.26
For routine practice, the use of dedicated multielement body coils in combination with the scanner’s back or spinal coil has proved beneficial. To optimize image quality at the apex of the lung (superior thoracic aperture, brachial plexus), it can be helpful to use additionally at least the posterior element of the neck coil if that combination is possible.
There are various techniques available to control motion artifacts,26 the easiest and most robust being fast images in the breath-hold technique. Where appropriate, lung imaging can be divided into several breath-hold phases (multi-breath-hold technique). This is the most practical and fastest technique for the clinical setting. For acquisition of high-resolution images or examination of patients who are unable to hold their breath long enough (in general several breath-hold phases of 15–20 s are needed), respiratory-triggered sequences can also be used. Here, the respiratory signal is generated either mechanically (by means of a pneumatic respiratory belt or a belt showing changes in electrical impedance) using the navigator technique or, alternatively, an MR-compatible spirometer.28 In the navigator technique, a small examination volume is positioned on an element subject to respiratory motion, e.g., the dome of the diaphragm; movement of the contrasting structure is automatically analyzed in the breathing phase. In respiratory-triggered sequences, images are then acquisitioned only in the defined inspiratory or expiratory phases.
The main disadvantage of any triggered technique is the additional time needed.25 Triggered images of the thorax can take as long as 3 to 5 min. If an extra triggering step is included after the cardiac phase (double-trigger technique), the imaging time is further increased by several minutes. Therefore, respiratory-triggered sequences play only a minor role in routine practices.
Currently, the most common protocol recommendations are based on fast sequences in the breath-hold technique. With these sequences, a routine examination of the chest without contrast medium administration can be executed in 15 min, and with contrast in 20 min.25 Respiratory-triggered sequences are offered as an alternative to patients who are unable to hold their breath long enough, or as an option for children whose cooperation throughout the examination procedure cannot be expected.29 Inclusion of additional fast sequences in free breathing will complete the protocol with information about the patient’s impaired breathing mechanics and gross cardiac function.
In principle, the examination can be performed in the breath-hold technique in either inspiration or expiration. Image acquisition in expiration can be used to visualize the lung parenchymal signal since on expiratory images the proton density per volume fraction is higher and the signal yield greater.26 However, for most diagnostic purposes the positive contrast of pathologic lung changes against the dark signal exhibited by the lung tissue is exploited, hence inspiratory images are suitable.
Note
Since other standard thoracic imaging techniques are predominantly conducted in inspiration (chest radiographs, CT), comparison of previous examination results with MRI is facilitated when using inspiratory scans.25
1.4.3 Pulse Sequences for Diagnostic Imaging
With parallel imaging, large volumes, such as the chest, can be imaged in high detail resolution, with high signal-to-noise ratio and in one breath hold. Typically, fast gradient-echo (GE) sequences, steady-state GE sequences, and fast spin-echo (SE) sequences are used for this purpose.
Fast Gradient-Echo Sequences
Fast GE sequences (FLASH, SPGR, FFE) are part of the standard protocol presets of modern MRI scanners and very robust in practice. With parallel imaging and slice volume interpolation (e.g., volumetric interpolated breath-hold acquisition), volume acquisition of the entire thorax with 5-mm slice thickness is possible in one breath-hold phase.30 Whereas unenhanced images can typically be obtained without fat signal suppression (good delineation of the mediastinal lymph nodes against the unenhanced bright fatty tissue), fat signal suppression is routinely recommended after contrast medium administration since the contrast-enhanced lymph nodes stand out clearly against the dark background of the suppressed fatty tissue signal.31
Steady-State Gradient-Echo Sequences
Steady-state GE sequences (bSSFP, TrueFISP, FIESTA, BFE) are used to achieve very short scanning times; hence, they are commonly used for MRI of the heart but are also advantageous for imaging the lung. Flip angles of generally more than 50° provide for T2w/T1w (T2- to T1-weighted) image contrast and visualize fluids and blood with high signal intensity thanks to long T2 constants. Steady-state GE sequences are therefore suitable for examining the pulmonary vessels without application of contrast medium.32
Fast Spin-Echo Sequences
After initial excitation, fast spin-echo (FSE) sequences (RARE/HASTE, Turbo-FSE, TSE) utilize multiple 180° refocusing pulses to expedite signal readout. In extreme cases, a single excitation pulse after multiple refocusing pulses is enough to obtain information for a single slice (RARE sequence). Armed with the knowledge that the image information is contained in redundant form in the k-space (mirrored), the imaging time can be further shortened by performing only partial readout (partial or half-Fourier sequences, e.g., HASTE). Because of the 180° refocusing pulses, the acquisition times of FSE sequences are essentially longer than those of GE or steady-state GE sequences. At the same time, energy deposition is higher, hence the limits of the specific absorption rate are also reached more quickly. FSE sequences are typically acquired in the multislice 2D mode.26 However, acquisition of single slices, e.g., with only half-Fourier readout (HASTE), can be so fast that heartbeat motion is fully compensated. Therefore, HASTE sequences are a good option if evaluating chest organs in proximity to the heart.31
FSE sequences offer an option where, instead of constant parallel orientation of all slices, by using rotating phase encoding (PROPELLER/BLADE) the impact exerted by heartbeat and blood flow artifacts in the phase encoding direction can be considerably reduced.26
Diffusion-weighted imaging (DWI) sequences are also performed with fat signal suppression. These comprise different basic SE sequences on which a signal is superimposed, making the signal emitted by fluid-containing images susceptible to restricted brownian motion of the water molecules (diffusibility). With low diffusion weighting, the image is like that of a fat-signal suppressed T2w SE sequence, whereas with higher diffusion weighting tumor tissue, in particular with greater cellularity, reduced extracellular space, large nuclei, dense intracellular protein deposition, and, in all cases, resulting restricted brownian molecular motion, is visualized with high signal intensity.33,34 Furthermore, DWI sequences are particularly useful for the detection of mediastinal lymph nodes which are depicted with high signal intensity.
Contrast-Enhanced Sequences
For most clinical diagnostic purposes (e.g., tumor staging), basic manual intravenous contrast injection, followed by fat-saturated fast GE sequences, is sufficient (▶Fig. 1.12). Pulmonary angiograms with excellent image quality can be obtained using fast GE sequences and automated intravenous injection of a T1 time-shortening contrast agent (typically gadolinium chelates). Taking full advantage of a breath-hold time of around 20 s, an image quality on a par with that of CT can be achieved (▶Fig. 1.13).
As an alternative, modern scanners and sequence techniques also offer a faster variant of contrast-enhanced MRA (magnetic resonance angiography) for time-resolved 3D visualization of pulmonary circulation. At the expense of slightly poorer detail resolution, the volume data of the entire thorax can be acquired at an interval of 1 to 2 s. The time resolution of this 4D perfusion sequence is enough for separation of arterial, parenchymal, and venous phases.28,35 The parenchymal phase is particularly suitable for detection of discrete perfusion deficits or, with the aid of suitable software, for calculation of parameter maps of regional lung perfusion, regional blood volume, and transit times.
Fig. 1.12 Cystic fibrosis. MR images. Inflammatory thickening of bronchial walls, bronchiectasis and secretory retention, pronounced in bilateral upper lung lobes. (a) Coronal, fat-signal suppressed T1w GE sequence following contrast injection. (b) Fat-signal suppressed T2w FSE sequence.
Fig. 1.13 MRA (magnetic resonance angiography) optimized to parenchymal phase of the thorax for exclusion of pulmonary embolism. (a) MIP (maximum intensity projection). (b) Coronal, single slice without any evidence of intravasal thrombi or parenchymal perfusion deficits.
The most expedient approach for combination of both techniques may be to first perform a time-resolved perfusion sequence with a small amount of contrast medium. In addition to providing data on regional lung perfusion, this can also help identify the optimal time point for contrast medium injection (typically up to 0.2 mmol/kg body weight) for subsequent acquisition of high resolution MRA.36,37
Functional Magnetic Resonance Imaging of the Lung
More than any other modality used for diagnostic imaging of the thorax and lungs, MRI has the potential to combine morphologic and functional information. The best known techniques involve visualization of the breathing mechanics (movements of the chest wall, diaphragm, mediastinum, lung tissue, and airways; ▶Fig. 1.14) as well as contrast-enhanced diagnostic evaluation of lung perfusion with fast GE and steady-state free-precession sequences.
1.4.4 Recommendations for Examination Protocols
Protocol recommendations have been published that are able to match the different generic sequence designations to the various scanner configurations.25 The following recommendations are tailored to that basic concept.
To gain acceptance in routine practice, a sequence protocol for MRI of the lung must be easy to apply, be robust, and endowed with reproducible image quality and high diagnostic power at the most commonly used field strength (1.5 T). More complex components such as an electrocardiogram, placement of a respiratory belt, or IV contrast administration should be avoided as far as possible. Practical solutions should be devised for common problems such as shortness of breath or for young children.
It is proposed to have one common basic protocol for all important clinical problems which permits modular supplementation for specific purposes, e.g., for tumor staging or evaluation of pathologies related to the pulmonary vessels and lung perfusion. For emergency situations, e.g., acute pulmonary artery embolism, fast and efficient procedures should be available which, when warranted, can also be incorporated into a tight routine MRI schedule or can be implemented by night on-call personnel with only limited MRI experience.
The modular design of the sequence protocols presented below should also enable users to put together customized packets, with additional sequences, for example, for heart MRI during cardiopulmonary imaging or for combination with modules for other applications.
