Presentation slides on Chest CT imaging

1. Chest CT
Dr OPEYEMI

2. Outline
• Introduction
• Principle of Computer Tomography
• Indications for Chest CT
• Risks associated with Computer Tomography
• Types of Chest CT
• Assessment of Chest CT
– Planes/Views
– Windows
• Normal Chest CT
• Pathological Chest CT
• Conclusion

3. Introduction
• CT, or CAT scans, are special X-ray tests that
produce cross-sectional images of the body using
X-rays and a computer.
• CT was developed independently by a British
engineer named Sir Godfrey Hounsfield and Dr.
Alan Cormack.
• It has become a mainstay for diagnosing medical
diseases.
• For their work, Hounsfield and Cormack were
jointly awarded the Nobel Prize in 1979

4. Introduction
• CT scanners first began to be installed in 1974.
• CT scans takes "pictures" of slices of the body
so doctors can look right at the area of
interest
• CT has revolutionized medicine because it
allows doctors to see diseases that, in the
past, could often only be found at surgery or
at autopsy

5. Principle of Computer Tomography
• A motorized table moves
the patient through a
circular opening in the CT
imaging system
• An X-ray source and a
detector assembly within
the system rotate around
the patient

6. Principle of Computer Tomography
• Detectors in rows
opposite the X-ray source
register the X-rays that
pass through the patient's
body as a snapshot in the
process of creating an
image.
• Many different
"snapshots" (at many
angles through the
patient) are collected
during one complete
rotation

7. Principle of Computer Tomography
• For each rotation of the
X-ray source and
detector assembly, the
image data are sent to a
computer to
reconstruct all of the
individual "snapshots"
into one or multiple
cross-sectional images
(slices) of the internal
organs and tissues

8. Axial CT image shows opacity in the posterior part of the lung which could represent
dependent opacity or pulmonary inflammation. The prone images shows complete
resolution of the opacity suggesting dependent atelectasis.
8

9. Persistent opacity in the posterior lung in a patient
with pulmonary fibrosis.
9

10. Indication for Computer Tomography
• A CT scan of the chest may be performed to
assess the chest and its organs for tumors and
other lesions, when another type of examination,
such as X-rays or physical examination, is not
conclusive.
• A CT scan of the chest may also be used to
evaluate the effects of treatment of thoracic
tumors.
• Another use of chest CT is to provide guidance for
biopsies and/or aspiration of tissue from the
chest

11. Risks associated with Computer
Tomography
• Radiation exposure and cancer risk
• Pregnancy
• Kidney diseases and contrast media
• Allergic diseases
• Metallic objects within the chest, such as
surgical clips or a pacemaker

12. Radiation dose
• Annual background radiation ----- --- 2.5 mSv
• PA CHEST Radiograph ----- ----- ----- 0.05 mSv
• Spaced axial HRCT (10mm space) ----- 0.7 mSv ( 14 X ray)
• Spaced axial HRCT (20 mm space) ------ 0.35 mSv ( 7 X ray)
• Low Dose Spaced axial HRCT -------- 0.02 mSV
• MD-HRCT ---- ------- 4 - 7 msv ( 60-80 x ray)
12

13. Types of Chest CT
• Standard Non-contrast
– Assess lung parenchyma
• Standard Contrast
– Specifically to assess mediastinum/vascular structures
& chronic pleural diseases
• High resolution CT chest (HRCT)
– Very thin cuts of 1-1.5mm thick
– Excellent spatial resolution
– Excellent to clarify lung parenchyma & airways
– Specifically useful for ILD

14. There are approximately 23 generation
of dichotomous branching
From trachea to the alveolar sac
HRCT can identify upto 8th order central
bronchioles
14

15. Planes/Views of Computer
Tomography
• CT produce cross-sectional images that appear
to open the body up, allowing the doctor to
look at it from the inside
• CT scan images allow the doctor to look at the
inside of the body just as one would look at
the inside of a loaf of bread by slicing it

16. Planes/Views of Computer
Tomography
• Axial view
– Bottom to top view
– Most common view

17. Planes/Views of Computer
Tomography
• Coronal view
– Front to back view
– Usually a reconstruction
of the axial view

18. Planes/Views of Computer
Tomography
• Sagittal view
– Usually a reconstruction
of axial view

19. Chest CT windows
• Chest CT windows
– A setting of attenuation/radiation dose used to
delineate different tissues & organs according to their
densities
• 3 Chest CT windows
– Mediastinal
• Heart, thyroid, lymph nodes, vascular structures
– Lung
• Lung parenchyma & vasculature
– Bone
• Clavicle, scapula, ribs

20. Mediastinal window

21. Mediastinal window

22. Mediastinal window

23. Mediastinal window

24. Assessment
of Chest CT

25. Important Parameters
• Name
• Age
• Sex
• Date
• Orientation
• Contrast/Noncontrast

26. Step 1: Identify the level using
anatomical landmarks
• Stenoclavicular joint – T1
• Sternal angle, 2nd rib, aortic arch – T4
• Carina of trachea – T5
• Bifurcation of pulmonary trunk – T5/T6
• Inferior pulmonary veins entering LA – T7/T8

28. Step 2: Systematic assessment
• A – air
• B – bone
• C – cardiac & great vessels
• D – digestive
• E – extras
• S – soft tissue

29. Q.1. What is the dominant HR-pattern ?
Q.2. Where is it located within the secondary lobule
(centrilobular, Perilymphatic or random) ?
Q.3. Is there an upper versus lower zone or a central versus
peripheral predominance ?
Q.4. Are there additional findings (pleural fluid,
lymphadenopathy, traction bronchiectasis) ?
STRUCTURED APPROACH
29

31. Pathological CT Chest patterns
• Reticular
– Septal thickening
• Smooth or Nodular
• Nodular
– Centrilobular
– Perilymphatic
• High attenuation
– Ground glass opacity
– Consolidation
• Low attenuation
– Emphysema
– Cystic lung disease
– Honeycomb lung

32. HRCT PATTERN
INCREASED LUNG
ATTENUATION
LINEAR AND
RETICULAR
OPACITIES
NODULES AND
NODULAR
OPACITIES
PARENCHYMAL
OPACIFICATION
consolidation
Ground glass
DECREASED LUNG
ATTENUATION
CYSTIC LESIONS,
EMPHYSEMA, AND
BRONCHIEACTASIS
MOSAIC
ATTENUATION
AND PERFUSION
AIR TRAPPING ON
EXPIRATORY
SCANS
32

35. Septal thickening
• Thickening of the lung interstitium by
– Fluid
– Fibrous tissue
– Infiltration by cells
• Results in pattern of reticular opacities due to
thickening of the interlobar septa

37. Lymphangitis carcinomatosa

39. Peribronchovascular Interstitial Thickening
PBIT
Smooth
Pulmonary
edema/
hemorrhage
Lymphoma /
leukemia
Lymphangitic
spread of
carcinoma
Nodular
Sarcoidosis
Lymphangitic
spread of
carcinoma
Irregular
Due to
adjacent lung
fibrosis
Sarcoidosis,
silicosis, TB
and talcosis
Venous, lymphatic
or infiltrative
disease
lymphatic or
infiltrative
diseases
39

40. Nodules

41. Size, Distribution, Appearance
Nodules and Nodular Opacities
Size
Small Nodules: <10 mm Miliary - <3 mm
Large Nodules: >10 mm Masses - >3 cms
Appearance
Interstitial opacity:
 Well-defined, homogenous,
Soft-tissue density
Obscures the edges of vessels or adjacent structure
Air space:
Ill-defined, inhomogeneous.
Less dense than adjacent vessel – GGO
small nodule is difficult to identify
41

44. Perilymphatic nodules: D/D
 Sarcoidosis
 Lymphangitic carcinomatosis
 Lymphocytic interstitial
pneumonia (LIP)
 Lymphoproliferative disorders
 Amyloidosis
44

45. Tree-in-bud sign

46. Tree-in-bud: helps narrow the
differential of Centrilobular nodules

47. 47
Centrilobular nodules with or without tree-in-bud opacity: D/D :
With tree-in-bud opacity
 Bacterial pneumonia
 Typical and atypical
mycobacteria infections
 Bronchiolitis
 Diffuse panbronchiolitis
 Aspiration
 Allergic bronchopulmonary
aspergillosis
 Cystic fibrosis
 Endobronchial-neoplasms
(particularly
 Bronchioloalveolar
carcinoma)
Without tree-in-bud opacity
 All causes of centrilobular
nodules with tree-in-bud
opacity
 Hypersensitivity
pneumonitis
 Respiratory bronchiolitis
 Cryptogenic organizing
pneumonia
 Pneumoconioses
 Langerhans’ cell
histiocytosis
 Pulmonary edema
 Vasculitis
 Pulmonary hypertension

48. 48
Random nodules: D/D
1. Haematogenous metastases
2. Miliary tuberculosis
3. Miliary fungal infection
4. Disseminated viral infection
5. Silicosis or coal-worker’s pneumoconiosis
6. Langerhans’ cell histiocytosis

49. Parenchymal Opacification
Ground-glass opacity
Consolidation
Lung calcification &
high attenuation
opacities.
49

50. GROUND GLASS OPACITIES
• Hazy increased attenuation of lung, with
preservation of bronchial and vascular
margins
• Pathology : it is caused by
# partial filling of air spaces,
# interstitial thickening,
# partial collapse of alveoli,
# normal expiration, or
# increased capillary blood volume
• D/t volume averaging of morphological
abnormality too small to be resolved by
HRCT
50

53. IMPORTANCE OF GGO
• Can represent - microscopic interstitial disease
(alveolar interstitium)
- microscopic alveolar space disease
- combination of both
 In the absence of fibrosis, mostly indicates the presence
of an ongoing, active, potentially treatable process
 NB :: Ground Glass opacity should be diagnosed only on
scans obtained with thin sections : with thicker sections
volume averaging is more - leading to spurious GGO,
regardless of the nature of abnormality
53

54. DIFFERENTIAL DIAGNOSIS : GGO
54

56. The location of the abnormalities in ground glass pattern
can be helpful:
• Upper zone predominance:
Respiratory bronchiolitis
PCP.
• Lower zone predominance: UIP, NSIP, DIP.
• Centrilobular distribution:
Hypersensitivity pneumonitis,
Respiratory bronchiolitis
56

57. GGO with few cystic and reticular lesion in
HIV + ve patient -- PCP
Combination of GGO with fibrosis
and tractional bronchiectasis-- NSIP
57

58. CRAZY PAVING PATTERN
• It is scattered or diffuse ground-glass attenuation
with superimposed interlobular septal thickening
and intralobular lines.
• Causes:
58

59. Combination of ground glass
opacity and septal thickening :
Alveolar proteinosis.
59

60. 60
CONSOLIDATION: High attenuation density
• Consolidation is defined as increased attenuation, which results in
obscuration of the underlying vasculature, usually producing air
bronchogram.
• The presence of consolidation implies that the air within affected
alveoli has been replaced by another substance, such as blood, pus,
oedema, or cells.
• When consolidation is evident on a chest radiograph, HRCT does
not usually provide additional diagnostically useful information.

61. D/D on the basis of
presentation
Acute consolidation is seen in:
- Pneumonias (bacterial, mycoplasma , PCP)
- Pulmonary edema due to heart failure or ARDS
- Hemorrhage
- Acute eosinophilic pneumonia
Chronic consolidation is seen in:
- Organizing Pneumonia
- Chronic eosinophilic pneumonia
- Fibrosis in UIP and NSIP
- Bronchoalveolar carcinoma or lymphoma
61

62. 62
Patchy ground-glass opacity, consolidation,
and nodule mainly with peribronchovascular
distribution with reversed halo signs (central
ground-glass opacity and surrounding air-
space consolidation)
Peripheral consolidations with
upper lobe predominance (photo
negative of pulmonary edema)

64. Lung calcification: high attenuation
opacities
Multifocal lung calcification
• Infectious granulomatous ds - TB, histoplasmosis,
and varicella, pneumonia;
• Sarcoidosis , silicosis, Amyloidosis
• Fat embolism associated with ARDS
Diffuse & dense lung calcification
• Metastatic calcification,
• Disseminated pulmonary ossification, or
• Alveolar microlithiasis
64

65. 65

66. Low attenuation patterns
• Honeycombing: small
cystic spaces with
irregularly thickened
walls of fibrosis.
Usually in peripheral &
subpleural part
irrespective of cause
• Bronchiectasis is xter by
localised bronchial
dilation

67. HRCT findings manifesting as decreased
lung opacity
Lung Cysts,
Emphysema,
and
Bronchiectasis
67

68. Lung cysts
• Thin walled (less than 4mm) , well defined and
circumscribed air containing lesions
• They are lined by cellular epithelium, usually fibrous
or epithelial in nature.
• Common cause are : 1. Lymphangiomyomatosis
2. Langerhans Histiocytosis
3. Lymphoid interstitial
pneumonia
They need to be differentiated from emphysematous
bullae, blebs and pneumatocele.
68

69. Axial HRCT image through the upper
lobes shows multiple bilateral bizarre-
shaped cysts and small centrilobular
nodules in a smoker with Langerhans’
cell histiocytosis.
Axial HRCT image through the
upper lobes shows multiple bilateral
uniform, thin-walled cysts.
69

70. BRONCHIECTASIS
Bronchiectasis is defined as localized, irreversible dilation of the
bronchial tree.
HRCT findings of the bronchiectasis include
# Bronchial dilatation
# Lack of bronchial tapering
# Visualization of peripheral airways.
70

71. BRONCHIAL DILATATION
# The broncho-arterial ratio (internal diameter of the
bronchus /pulmonary artery) exceeds 1.
# In cross section it appears as “Signet Ring
appearance”
LACK OF BRONCHIAL TAPERING
# The earliest sign of cylindrical bronchiectasis
# One indication is lack of change in the size of an airway
over 2 cm after branching.
VISUALIZATION OF PERIPHERAL AIRWAYS
# Visualization of an airway within 1 cm of the costal
pleura is abnormal and indicates potential bronchiectasis
71

73. A NUMBER OF ANCILLARY FINDINGS ARE ALSO RECOGNIZED:
# Bronchial wall thickening : normally wall of bronchus should
be less than half the width of the accompanying pulmonary
artery branch.
# Mucoid impaction
# Air trapping and mosaic perfusion
Extensive, bilateral mucoid impaction
Mosaic perfusion caused by large and small
airway obstruction.
Small centrilobular nodules are visible in the
right lower lobe
73

74. Low attenuation patterns
• Lung cysts are defined
as radioluscent areas
with cavity wall
thickness <4mm
• Cavities: wall thickness
>4mm

75. HONEYCOMBING
• Defined as - small cystic spaces with irregularly thickened
walls composed of fibrous tissue.
• Predominate in the peripheral and subpleural lung regions
• Subpleural honeycomb cysts typically occur in several
contiguous layers. D/D- paraseptal emphysema in which
subpleural cysts usually occur in a single layer.
• Indicates the presence of “END stage” disease regardless
of the cause.
75

76. Causes
Lower lobe predominance :
1. UIP or interstitial fibrosis
2. Connective tissue disorders
3. Hypersensitivity pneumonitis
4. Asbestosis
5. NSIP (rare)
Upper lobe predominance :
1. End stage sarcodosis
2. Radiation
3. Hypersensitivity Pneumonitis
4. End stage ARDS
76

77. EMPHYSEMA
• Permanent, abnormal enlargement of air
spaces distal to the terminal bronchiole and
accompanied by the destruction of the walls
of the involved air spaces.
77

78. Centrilobular (proximal or centriacinar)
emphysema
• Found most commonly in the upper lobes
• Manifests as multiple small areas of low attenuation without a
perceptible wall, producing a punched-out appearance.
• Often the centrilobular artery is visible within the
centre of these lucencies.
78

79. PANLOBULAR EMPHYSEMA
• Affects the entire secondary pulmonary lobule
and is more pronounced in the lower zones
• Complete destruction of the entire pulmonary
lobule.
• Results in an overall decrease in lung attenuation
and a reduction in size of pulmonary vessels
79

80. Paraseptal (distal acinar) emphysema
• Affects the peripheral parts of the secondary
pulmonary lobule
• Produces subpleural lucencies.
80

81. Cicatricial Emphysema/ irregular air
space enlargement
• previously known as irregular or cicatricial emphysema
• can be seen in association with fibrosis
• with silicosis and progressive massive fibrosis or
sarcoidosis
BULLOUS EMPHYSEMA :
• Does not represent a specific histological abnormality
• Emphysema characterized by large bullae
• Often associated with centrilobular and paraseptal
emphysema
81

82. Paraseptal Emphysema vs
Honeycombing
Paraseptal emphysema Honeycomb cysts
occur in a single layer at the
pleural surface
may occur in several layers in the
subpleural lung
predominate in the upper lobes predominate at the lung bases
unassociated with significant
fibrosis
Asso with other findings of fibrosis.
Associated with other findings of
emphysema
Absent
82

83. Bullae
A sharply demarcated area of emphysema ≥ 1 cm
in diameter
a thin epithelialized wall ≤ 1 mm.
uncommon as isolated findings, except in the lung
apices
Usually asso with evidence of extensive
centrilobular or paraseptal emphysema
When emphysema is associated with
predominant bullae, it may be termed bullous
emphysema
83

84. Pneumatocele
• Defined as a thin-walled, gas-filled space within the lung,
• Associated with acute pneumonia or hydrocarbon
aspiration.
• Often transient.
• believed to arise from lung necrosis and bronchiolar
obstruction.
• Mimics a lung cyst or bulla on HRCT and cannot be
distinguished on the basis of HRCT findings. 84

85. CAVITARY NODULE
• Thicker and more irregular
walls than lung cysts
• In diffuse lung diseases -
LCH, TB, fungal infections,
and sarcoidosis.
• Also seen in rheumatoid lung
disease, septic embolism,
pneumonia, metastatic
tumor, tracheobronchial
papillomatosis, and Wegener
granulomatosis
Cavitary nodules or cysts in
tracheobronchial papillomatosis.
fungal pneumonia
85

86. Mosaic attenuation & perfusion
• Lung density and attenuation depends partially on amount
of blood in lung tissue.
• The term 'mosaic attenuation' is used to describe density
differences between affected and non-affected lung areas.
• It is seen as inhomogeneous attenuation of lung
parenchyma with focal region of lucency which show
smaller size of vessels
• May be due to vascular obstruction, abnormal ventilation
or airway disease/
86

87. Mosaic attenuation due to small airway disease
# Air trapping and bronchial dilatation commonly seen.
# Areas of increased attenuation have relatively large
vessels, while areas of decreased attenuation have small
vessels.
# Causes include: Bronchiectasis, cystic fibrosis and
bronchiolitis obliterans.
Mosaic attenuation due to vascular disease
# common in patients with acute or chronic pulmonary
embolism (CPE), and
# decreased vessel size in less opaque regions is often
visible
87

88. MOSIAC PATTERN
DEPENDENT LUNG ONLY
PRONE
POSITION
RESOLVE
PLATE
ATELECTASIS
NOT
RESOLVE
GROUND
GLASS
NONDEPENDENT LUNG
EXPIRATION
NO AIR
TRAPPING
VESSEL SIZE
DECREASED
VASCULAR
NORMAL
GROUND
GLASS
AIR TRAPPING
AIRWAYS
DISEASE
88

89. Inhomogeneous lung
opacity: mosaic
perfusion in a patient
with bronchiectasis.
central bronchiectasis with
multifocal, bilateral
inhomogeneous lung opacity.
The vessels within the areas of
abnormally low attenuation are
smaller than their counterparts
in areas of normal lung
attenuation.
89

90. Air trapping on expiration
• Most patients with air trapping seen on expiratory
scans have inspiratory scan abnormalities, such as
bronchiectasis, mosaic perfusion, airway thickening,
or nodules suggest the proper differential diagnosis.
• Occasionally, air trapping may be the sole abnormal
finding on an HRCT study.
• The differential diagnosis include ---
bronchiolitis obliterans; asthma; chronic
bronchitis; and hypersensitivity pneumonitis
90

91. Air trapping on expiratory imaging
in the absence of inspiratory scan
findings in a patient with
bronchiolitis obliterans.
(A) Axial inspiratory image through
the lower lobes shows no clear
evidence of inhomogeneous lung
opacity.
(B) Axial expiratory image shows
abnormal low attenuation
(arrows) caused by air trapping,
representing failure of the
expected increase in lung
attenuation that should normally
occur with expiratory imaging.
91

92. Head cheese sign
• It refers to mixed densities which includes presence
of-
# consolidation
# ground glass opacities
# normal lung
# Mosaic perfusion
• Signifies mixed infiltrative and obstructive disease
• Common cause are : Hypersensitive pneumonitis
Sarcoidosis
DIP
92

93. Axial HRCT image in a patient with
hypersensitivity pneumonitis shows a
combination of ground-glass opacity, normal
lung, and mosaic perfusion (arrow) on the same
inspiratory image.
93

94. Distribution within the lung
Upper lung zone preference is seen in:
1.Inhaled particles: pneumoconiosis (silica or
coal)
2.Smoking related diseases (centrilobular
emphysema
3. Respiratory bronchiolitis (RB-ILD)
4.Langerhans cell histiocytosis
5.Hypersensitivity pneumonitis
6.Sarcoidosis
Lower zone preference is seen in:
1. UIP
2. Aspiration
3. Pulmonary edema 94

95. Central vs peripheral zone
• Central Zone Peripheral
zone
1. Sarcoidosis 1. COP
2. Cardiogenic pulmonary 2. Ch Eosinophilic
Pneumonia
edema 3. UIP
3. Bronchitis 4. Hematogenous
mets
95

96. Additional findings
Pleural effusion is seen in:
• Pulmonary edema
• Lymphangitic spread of carcinoma - often
unilateral
• Tuberculosis
• Lymphangiomyomatosis (LAM)
• Asbestosis
96

97. Hilar and mediastinal lymphadenopathy
# In sarcoidosis the common pattern is right
paratracheal and bilateral hilar adenopathy ('1-2-
3-sign').
# In lung carcinoma and lymphangitic
carcinomatosis adenopathy is usually unilateral.
#'Eggshell calcification' in lymph nodes occurs in ----
Silicosis and coal-worker's pneumoconiosis and is
sometimes seen in sarcoidosis, post irradiation
Hodgkin disease, blastomycosis and scleroderma .
97

98. Sarcoidosis: 1-2-3 Sign

99. Conclusion
• A thorough knowledge of the basic anatomy is of
utmost importance.
 When attempting to reach a diagnosis or differential
diagnosis of lung disease using HRCT, the overall
distribution of pulmonary abnormalities should be
considered along with their morphology, HRCT
appearance, and distribution relative to lobular
structures.
Correlation of the radiological findings with patients
clinical and laboratory findings to reach a likely diagnosis
•
99

100. 100

101. Conclusion
• Chest computer tomography has become an
important tool in diagnosis and evaluation of
my lung diseases
• Interpretation involves the identification of
dominant pattern & distribution of lung
densities within the lung and/or secondary
lobules