Different tissues in our body absorb X-rays at different extents:
| Air | fat | soft tissue | bone | metal |
|---|---|---|---|---|
| Least opaque | to | to | to | most opaque |
| Most lucent | least lucent | |||
| Black | white |
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Relative Densities
The images seen on a chest radiograph result from the differences in densities of the materials in the body.
The hierarchy of relative densities from least dense (dark on the radiograph) to most dense (light on the radiograph) include:
- Gas (air in the lungs)
- Fat (fat layer in soft tissue)
- Water (same density as heart and blood vessels)
- Bone (the most dense of the tissues)
- Metal (foreign bodies)
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Four major view of chest radiograph
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Postero-anterior (PA)
Antero-posterior (AP)
Lateral view
Other- Apical lordotic view
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Postero-anterior position (PA View)
- The standard position for obtaining a routine chest radiograph.
- Patient stands upright with anterior wall of the chest placed against the film
- The shoulders are rotated forward enough to touch the film, ensuring that the scapulae does not obscure a portion of the lung fields.
- Usually taken with the patient in full inspiration.
- The PA film is viewed as the patient is standing in front of you.
- Patient and X-Ray tube distance is 6 ft (180 cm).
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PA View
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Antero-posterior (AP View)
- Used when patient is debilitated, immobilized or unable to cooperate with the PA procedure.
- Film is placed behind the patient's back with the patient in a supine position.
- Heart is at greater distance from the film hence appear more magnified than in the PA.
- The scapulae are visible because they are not rotated out of the view as they are in a PA.
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AP View
PA vs. AP Films
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Accurate Size
Exaggerated Size
Anterior
Posterior
Posterior
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Anterior
X-rays
PA Film
AP Film
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PA vs. AP Films
PA Film
AP Film
Same Patient
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Lateral view
- Patient stands upright with the left/right side of the chest against the film and arm raised over the head.
- Allow the viewer to see behind the heart and diaphragmatic dome.
- Typically used in conjunction with PA view of the same side of chest to help determine the three dimensional position of organs or abnormal densities.
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Lateral View
Lateral decubitus
- The patient lies on either left or right side than in the standing position as with the regular lateral radiograph.
- Often used to differentiate between loculated and non loculated pleural effusion, since the non loculated effusion will collect in the dependent position
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Apical Lordotic View
- Used to observe pathology of apex that not clearly visible in PA view.
- In this view X-Ray beam is angled towards the head.
Apical Lordotic View
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- Three Main Factors Determine the Technical Quality of the Radiograph
- Inspiration
- Penetration
- Rotation
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Assessment of Adequate Inspiration
In a patient with normal lung volumes, on a chest X-ray taken during full inspiration:
- 9-10 posterior ribs should be visible
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Assessment of Adequate Inspiration
In a patient with normal lung volumes, on a chest X-ray taken during full inspiration:
- 9-10 posterior ribs should be visible
- 6-7 anterior ribs should be visible, with the 7th rib “piercing” the diaphragm
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Penetration
On a properly exposed chest radiograph:
- The lower thoracic vertebrae should be visible through the heart
- The bronchovascular structures behind the heart (trachea, aortic arch, pulmonary arteries, etc.) should be seen
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1----Underexposure
In an underexposed chest radiograph,
- The cardiac shadow is? opaque,
- With little or no visibility of the thoracic vertebrae.
- The lungs may appear much denser and whiter, much as they might appear as with infiltrates present.
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2-----Overexposure
With greater exposure of the chest radiograph, the
- Heart becomes more radiolucent and
- Lungs become proportionately darker.
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In an overexposed chest radiograph, the air-filled lung periphery becomes extremely radiolucent, and often gives the appearance of lacking lung tissue, as would be seen in a condition such as emphysema.
Assessing Exposure/Penetration
Good quality film
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Too bright (Underexposed)
Too much contrast (Overexposed)
Rotation
Patient rotation can be assessed by observing the clavicular heads and determining whether they are equal distance from the spinous processes of the thoracic vertebral bodies.
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Relationship Between Clavicle and Vertebral Spinous Processes
The spinous processes will be closer to the clavicle on the side that is rotated forward.
Anatomy - Bones
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Anatomy – Cardiac Silhouette and Mediastinum
Anatomy – Diaphragm and Pleura
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Anatomy – Lungs
Fissures
Anatomy – Lungs
Right Upper Lobe
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Anatomy – Lungs
Right Middle Lobe
Anatomy – Lungs
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Right Lower Lobe
Anatomy – Lungs
Left Upper Lobe
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Anatomy – Lungs
Left Lower Lobe
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The ABCDEF System
(Assess the technical quality)
A – Airways
B - Bones (and soft tissue)
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C - Cardiac silhouette (and mediastinum)
D - Diaphragm (and gastric bubble)
E – Effusions (i.e. Pleura)
F – “Fields” (i.e. Lung Fields)
(Lines, Tubes, Devices, Surgeries)
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Airway Deviation
| Abnormalities deviating trachea away from affected side | Abnormalities deviating trachea towards the affected side |
|---|---|
| Pneumothorax | Marked atelectasis / collapsed lung |
| Pleural effusion | Lobectomy / Pneumonectomy |
| Large mass | Pleural fibrosis |
| Pulmonary fibrosis (rarely unilateral) |
Airway Deviation
High pressure in left hemithorax
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?
Massive left pleural effusion
Low pressure in left hemithorax
?
Total collapse of left lung (no pneumothorax)
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Airway Deviation
Rightward deviation of trachea due to mediastinal mass
Splaying of the right and left main bronchi (carinal angle > 90°)
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B- Bone and soft tissues
- Look at each rib in turn
- Clavicles
- Scapula and humerus if visible
- Lower cervical and thoracic spine
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Sclerosis – ? Density of bone.
Can be focal or diffuse
Etiologies include:
- Osteoblastic metastasis
- Primary bone tumor
- Various benign tumor-like bone lesions
- Paget's disease
- Chronic osteomyelitis
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Sclerosis
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Lytic Lesions
Lytic lesions -? Density of bone.
Can be solitary or multiple
Etiologies include:
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- Osteolytic metastasis
- Multiple myeloma
- Various benign cyst-like bone lesions
- Paget's disease
- Acute osteomyelitis
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Scoliosis vs. Kyphosis
Scoliosis
Spine curves from side to side.
Seen on PA/AP views.
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Kyphosis
Exaggerated front to back curvature of upper spine. Seen on lateral views.
"Barrel Chest"
Refers to specific thoracic deformity that occurs in advanced COPD:
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- Kyphosis
- Increased AP diameter
Rib Notching
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Rib Notching
Rib notching is focal deformation of one or more ribs.
Etiologies depend upon whether the superior or inferior surface is affected:
| Superior Surface | Inferior Surface |
|---|---|
| Osteogenesis imperfecta | Coarctation of the aorta |
| Connective tissue diseases | Subclavian or SVC obstruction |
| Local pressure | s/p Blalock Taussig shunt (only 2 upper ribs) |
| Hyperparathyroidism |
Subcutaneous Emphysema
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Air within the subcutaneous tissues can occur due to:
Air introduced internally
- Pneumothorax
- Pneumomediastinum
- Pulmonary interstitial emphysema
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Air introduced externally
- Penetrating chest wall trauma
- Post-surgical
- Complications from chest tube
Air produced locally
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- Necrotizing infection with gas producing organisms ("gas gangrene")
Cervical Ribs
- Anatomic variant
- Prevalence ~ 0.5 – 1%
- Can by unilateral or bilateral
- Usually an incidental finding
- Can cause thoracic outlet syndrome
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C-Cardia
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- Two third of the heart lie on the left with one third on the right.
- The heart should take less than half of the thoracic cavity.
- Left atrium, left ventricle create left heart border.
- Right heart border is entirely created by right atrium
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Cardiothoracic ratio
CT ratio= CR+CL/T
CR+CL= Transverse Cardiac Diameter
T= Transverse Thoracic Diameter
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CTR is more than 50% but heart is normal
Spurious causes of cardiac enlargement
- Portable AP films
- Obesity
- Pregnant
- Ascites
- Straight back syndrome
- Pectus excavatum
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RVH v/s LVH
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RV Hypertrophy
LV Hypertrophy
Left Atrial Enlargement
Findings include:
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- Splaying of the carinal angle > 90°
- Double density sign
Left Atrial Enlargement
Left sided heart failure (any cause)
Mitral valve disease (e.g. mitral stenosis, mitral regurgitation, mitral valve prolapse)
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Right Ventricular Enlargement
Findings include:
- Filling of retrosternal space (on lateral view)
Right Ventricular Enlargement
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Pulmonary hypertension (any cause)
Pulmonary valve disease (e.g. pulmonic stenosis, pulmonic regurgitation)
Normal
Right Ventricular Enlargement
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Pericardial Effusion
Classic water bottle shape of a large effusion
D-Diaphragm
Both diaphragm should form sharp margin with lateral chest wall
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Both diaphragm contour should be clearly visible medially to the spine
Mediastinal Masses
Anterior / Superior
Lymphoma
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Thyroid
Thymus
Teratoma
Aortic aneurysm (superior only)
Middle
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Lymphadenopathy
Aortic aneurysm
Pericardial cysts
Dilated esophagus
Hiatal hernia
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Posterior
Neurogenic tumors
Extension of spinal masses (e.g. tumors, infection)
Mediastinal Masses
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Aortic Aneurysms
Hilar Enlargment
Pneumothorax
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Deep Sulcus Sign
Pneumothorax
Primary pneumothorax (a.k.a. "spontaneous pnuemothorax)
Secondary pneumothorax
Iatrogenic (e.g. thoracentesis, lung biopsy, central line placement)
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COPD
Cystic fibrosis
Pneumonia
Pneumothorax
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Giant Emphysematous bulla
Minimal Pleural Effusion:
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Pleural Effusions
Free Flowing vs. Loculated
Free flowing effusion
Loculated effusion
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Free Flowing vs. Loculated
Lateral Decubitus View
Free flowing effusion
Loculated effusion
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"Pseudotumor"
Term most commonly used to refer to a fluid collection trapped within a fissure, which can give the appearance of a lung mass.
Suspicion for trapped fluid is based on:
- Location at a fissure (most occur in the horizontal fissure)
- Smooth lenticular contour
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Hydropneumothorax
- Air in pleural cavity
- Lung margin visible
- Bilateral fluid level: Any time you see a horizontal fluid level, it means that there is air and fluid in the pleural space
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F- Lung fields
- Normally there is a visible markings throughout the lungs due to the pulmonary artery and veins, continuing all the way to the chest wall.
- Both lungs should be scanned, starting at the apices and working downwards, comparing the left and right lung fields at the same level.
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Lung fields
Elevated Hemidiaphragm
Elevated Hemidiaphragm
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Diminished lung volume (e.g. atelectasis)
Phrenic nerve paralysis
Eventration of the diaphragm
Subphrenic abscess
Hepatomegaly or splenomegaly
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Pneumomediastinum
Pneumomediastinum
Trauma
Esophageal rupture
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Vomiting
Asthma
Post-neck or chest surgery
Barotrauma (e.g. diving, positive pressure ventilation)
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Pneumopericardium
Pneumopericardium
Trauma
Bacterial pericarditis secondary to gas-producing organism
Post-cardiac surgery or pericardial drain
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Fistula between pericardium and either lung, stomach, or esophagus.
Pulmonary Embolism
Hampton's sign
Westermark sign
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Fleischner sign
Pulmonary Edema
Pulmonary Edema
Acute Diffuse Alveolar
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- Bilateral
- Diffuse
- Butterfly pattern
- Soft fluffy lesions
- Coalescing
- Air bronchogram
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Differentiating Cardiogenic From Non-Cardiogenic Edema
- Air Bronchograms
- Peribronchial Cuffing
- Kerley Lines
- Cephalization
- Bat's Wing Pattern
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Air Bronchograms
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- Bronchi are usually not visible on X-ray.
- Opacification of alveoli adjacent to bronchi results in the dark, air-filled bronchi becoming identifiable.
Peribronchial Cuffing
- Bronchi are usually not visible on X-ray.
- Interstitial edema can accumulate around bronchi, making the bronchial walls thick.
- Appears like a ring when seen in cross section, and like tram tracks when seen longitudinally.
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Kerley A and B Lines
Kerley A Lines
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Diagonal, unbranching lines, 2-6cm long, extending from the hilum. Represent channels between peripheral and central lymphatics.
Kerley B lines
Faint, thin horizontal lines, 1-2cm long, at the lung periphery, usually at the bases. Represent interlobular septa.
Cephalization
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- Increased visibility of pulmonary vessels at the lung apices as compared to the bases.
- Suggestive of increased left atrial pressure.
- Highly subjective with relatively poor interobserver agreement.
"Bat's Wing" Pattern
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Bilateral, perihilar concentration of opacification.
"Bat's Wing" Pattern
Cardiogenic Pulmonary Edema
Pneumonia: Viral, PCP, Aspiration
Inhalational Injury
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Pulmonary Alveolar Proteinosis
Pulmonary Hemorrhage
Cardiogenic vs. Non-Cardiogenic Pulmonary Edema
| Cardiogenic | Non-Cardiogenic (e.g. ARDS) |
|---|---|
| Cardiac size typically enlarged | Cardiac size typically normal |
| Regional distribution of opacities relatively homogeneous | Regional distribution of opacities relatively patchy |
| Air bronchograms uncommon | Air bronchograms common |
| Peribronchial cuffing common | Peribronchial cuffing uncommon |
| Concurrent pleural effusion(s) and Kerley B lines more common | Concurrent pleural effusion(s) and Kerley B lines less common |
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Radiographic Patterns of Pneumonia
| Subtype of Pneumonia | Radiographic Features | Classic Causative Organisms | |
|---|---|---|---|
| Lobar Pneumonia | Homogenous consolidation Air bronchograms common Sharp borders corresponding to fissures | Streptococcus pneumoniae | Klebsiella pneumoniae |
| Segmental Pneumonia (a.k.a. Bronchopneumonia) | Patchy opacification Air bronchograms uncommon Vague borders Frequently bilateral | Staphylococcus aureus | Haemophilus influenzae |
| Interstitial Pneumonia | Reticular pattern No air bronchograms Often develops into airspace disease | Mycoplasma pneumoniae | Viral pneumonia Pneumocystis pneumonia |
| Round Pneumonia | Spherical opacification Easily mistaken for tumor or other lung mass Much more common in children than adults | Haemophilus influenza This download link is referred from the post: MBBS Lecture Notes for all subjects (updated for 2021 syllabus) - All universities |
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