thoracic imaging

What are the main diagnostic imaging options for the thorax?

Plain X-ray, CT, MRI, ultrasound, and nuclear medicine imaging.

Why do solid tissues appear white on X-ray and CT?

They absorb more X-rays than air-filled spaces.

How do air-filled spaces appear on X-ray and CT?

Dark, because they absorb little X-ray radiation.

How do MRI images form?

Magnets and radiofrequency pulses.

How does ultrasound form images?

High-frequency sound waves reflect from tissues.

How does nuclear medicine imaging work?

A radioactive tracer is injected, inhaled, or swallowed and detected by a gamma camera.

Name common reasons for thoracic imaging.

Chest infection, respiratory failure, ARDS, pulmonary embolism, trauma, and lung or pleural disease.

What are common diseases assessed with thoracic imaging?

CF, bronchiectasis, COPD, cancer, congenital disease, pleural disease, and pneumoconiosis.

What are common uses of a chest X-ray (CXR)?

Diagnose conditions, pre-operative assessment, check lines/tubes, and assess treatment effectiveness.

What are key limitations of CXR?

It provides a 2D view of 3D anatomy and may require multiple views.

What is the standard CXR projection?

Posteroanterior (PA), usually with a lateral view; interpret the views together.

How is a PA chest X-ray taken?

X-rays pass from posterior to anterior, with the detector in front of the patient.

Why is PA the preferred standard CXR view?

It reduces magnification of the heart compared with an AP view.

How is a CXR displayed to the viewer?

As if the patient faces you: the patient's left appears on your right.

Why is a lateral CXR useful?

It can reveal findings hidden on the frontal view and improves anatomical assessment of the heart.

How is the patient positioned for a lateral CXR?

Usually with the left chest against the detector.

When is an AP/mobile CXR used?

When the patient cannot stand or attend radiology, e.g. in ICU or ED.

How may an AP/mobile CXR be taken?

Sitting upright in bed or supine.

What is the first step when reading a CXR?

Check patient identifiers, date/time, side marker, and projection.

How do you assess CXR rotation?

The medial ends of the clavicles should be equidistant from the spinous processes.

What indicates adequate inspiration on a CXR anteriorly?

About 5–6 anterior ribs intersect the right hemidiaphragm; roughly one rib fewer on the left.

What indicates adequate inspiration on a CXR posteriorly?

About 9–10 posterior ribs intersect the right hemidiaphragm; roughly one rib fewer on the left.

What indicates adequate CXR exposure?

Intervertebral disc spaces should be just visible through the heart shadow.

What are signs of an overexposed CXR?

Whiter image; disc spaces behind the heart are hard to see; opacities may be over-interpreted.

What are signs of an underexposed CXR?

Darker image with reduced visible lung markings; abnormalities may be missed.

Which extra-thoracic structures should be checked on a CXR?

Clavicles, scapulae, soft tissues/breast shadows, abdomen, and subdiaphragmatic gas.

What should be assessed in the thoracic spine and ribs on CXR?

Spinal curvature and rotation, rib shape, and rib-space crowding or widening.

What should normal diaphragms look like on CXR?

Clearly outlined and domed, with clear acute costophrenic and cardiophrenic angles.

Which hemidiaphragm is normally higher, and by approximately how much?

The right, by about 2 cm.

What can cause an elevated hemidiaphragm?

Phrenic nerve/diaphragm paralysis, lower-lobe collapse, or low lung volumes/poor inspiration.

What can cause a lowered, flattened diaphragm?

Hyperinflation (e.g. asthma or emphysema); pneumothorax may also lower it.

Where should the trachea normally lie on CXR?

Approximately midline.

At what level does the trachea usually bifurcate?

At the carina around T5–T7.

What structures are found in the hilar regions?

Pulmonary arteries and veins, bronchi, and lymph nodes.

What is the normal relative height of the hila?

The left hilum is usually higher than the right.

What is the normal position of the heart on CXR?

About one-third to the right and two-thirds to the left of midline.

What is the normal cardiothoracic ratio on an adult PA CXR?

Less than 50% of the internal thoracic diameter.

What may an enlarged cardiac silhouette indicate?

Cardiomegaly, although projection and technique must be considered.

What may loss of the left heart border indicate?

A lingular abnormality, such as consolidation.

What may loss of the right heart border indicate?

A right middle lobe (RML) abnormality, such as consolidation.

What should normal lung fields look like on CXR?

Mostly dark, with fine white vascular markings extending towards the periphery.

What does absence of peripheral lung markings suggest?

Pneumothorax, especially when a visible pleural line is present.

What can extra lung-field opacity indicate?

Consolidation/pneumonia, atelectasis/collapse, or a mass/tumour.

What is CT chest imaging?

Computer-processed X-rays create cross-sectional slices and can reconstruct 3D views.

What are the three main types of chest CT in these notes?

Standard chest CT, CT pulmonary angiography (CTPA), and high-resolution CT (HRCT).

What is standard chest CT commonly used for?

Detailed assessment of thoracic structures; contrast may highlight mediastinal structures.

What is CTPA designed to assess?

Pulmonary blood vessels and suspected pulmonary embolism.

What is the gold-standard imaging test for pulmonary embolism in these notes?

CT pulmonary angiography (CTPA).

What is high-resolution CT (HRCT) used for?

Suspected interstitial lung disease and detailed assessment of lung parenchyma.

What are typical HRCT section characteristics in these notes?

Very thin, approximately 1 mm sections; usually no contrast.

What are advantages of chest CT over CXR?

Cross-sectional/3D views, better localisation and accuracy, and improved assessment of small airways, mediastinum, pleura, and parenchyma.

What are disadvantages of chest CT?

Cost/access, much higher radiation than CXR, contrast-related kidney risk, and possible movement artefact.

What is the silhouette sign?

Loss of a normally visible border where adjacent structures have similar radiographic density.

Why does consolidation or collapse cause a silhouette sign?

The affected lung becomes denser/whiter and obscures the adjacent heart, mediastinal, or diaphragmatic border.

Loss of the left heart border localises disease to which region?

The lingula of the left lung.

Loss of the right heart border localises disease to which region?

The right middle lobe.

Loss of the diaphragm border may indicate disease in which region?

The adjacent lower lobe.

What is an air bronchogram?

Dark, air-filled bronchi outlined by surrounding opaque alveoli.

What conditions can produce air bronchograms?

Alveolar processes such as pneumonia, ARDS, or pulmonary oedema, where alveoli fill with fluid, pus, or blood.

What is atelectasis?

Collapse of part or all of a lung due to loss of air, with reduced volume and increased density.

What are key CXR features of atelectasis/collapse?

Opacity, reduced lung volume, and possible shift of structures towards the collapsed area; ± silhouette sign or air bronchogram.

Which way do mediastinal structures shift with volume-loss collapse?

Towards the side of collapse.

What other CXR changes may occur with lung collapse?

Elevated diaphragm, narrowed intercostal spaces, and ribs sloping/crowding towards the affected side.

What is pulmonary consolidation?

Alveoli filled with material, commonly fluid/pus in pneumonia, making the lung appear opaque.

What are key CXR features of consolidation?

Increased opacity, usually without volume loss; ± silhouette sign and air bronchograms.

How can lobar pneumonia differ from bronchopneumonia on CXR?

Lobar pneumonia may be anatomically delineated; bronchopneumonia may appear patchy.

How does consolidation differ from atelectasis in volume?

Consolidation usually has no volume loss; atelectasis causes volume loss.

What is pulmonary hyperinflation?

Increased lung volume from excess air, such as with air trapping.

What are key CXR features of hyperinflation?

Increased lucency, reduced vascular markings, low flat diaphragms, widened rib spaces, more horizontal posterior ribs, and an elongated heart.

What conditions commonly cause hyperinflation?

COPD/emphysema and acute asthma.

What are pulmonary bullae?

Thin-walled, air-filled spaces within the lung.

What is acute pulmonary oedema?

Fluid accumulation in the extravascular lung spaces, including interstitium and/or alveoli.

What are cardiogenic causes of pulmonary oedema?

Left-sided heart failure and other causes of elevated pulmonary venous pressure.

What are non-cardiogenic causes of pulmonary oedema?

Examples include sepsis, drowning, and ARDS.

What are CXR features of acute pulmonary oedema?

Diffuse bilateral opacity, sometimes a batwing pattern, Kerley B lines, cardiomegaly, and pleural effusions.

What are Kerley B lines associated with?

Interstitial fluid/septal thickening, commonly in pulmonary oedema.

What is a pleural effusion?

Fluid accumulation in the pleural space.

What are CXR features of pleural effusion?

Increased opacity, blunted costophrenic angle with a meniscus, and possible ovoid/elliptical opacity on lateral view.

Can pleural effusions be unilateral or bilateral?

Yes; laterality depends on the underlying cause.

What is a pneumothorax?

Air in the pleural space between visceral and parietal pleura.

What are key CXR features of pneumothorax?

Increased lucency, absent peripheral lung markings, and a visible visceral pleural line.

Where does a small pneumothorax often appear on an upright CXR?

At the lung apex, where pleural air rises.

What is a tension pneumothorax?

Progressive pleural air accumulation that raises pressure and can compromise breathing and circulation.

Why is tension pneumothorax life-threatening?

It can compress intrathoracic structures and impair venous return and cardiac output.

Which way does the mediastinum shift in tension pneumothorax?

Away from the affected side when pressure is sufficient.

How urgently must tension pneumothorax be managed?

It requires immediate emergency decompression; do not delay for imaging if clinically suspected.

Why is clinical diagnosis important in tension pneumothorax?

Radiology may underestimate its size, and treatment is time-critical.

What is subcutaneous emphysema?

Air trapped in subcutaneous soft tissues, such as skin and muscle layers.

What are CXR features of subcutaneous emphysema?

Lucent/black streaks or pockets of air in extra-thoracic soft tissues.

What is bronchiectasis?

Abnormal, persistent dilation of bronchi; it may occur with cystic fibrosis or other causes.

What is interstitial lung disease?

A group of disorders affecting lung interstitium and often causing diffuse interstitial abnormalities.

What is a lung abscess?

A localised collection of pus in the lung that forms a cavity, usually with a thick wall.

What is malignant mesothelioma?

An aggressive malignancy of mesothelial tissue, most often arising from the pleura.

What are key mesothelioma facts from these notes?

Rare; most common primary pleural neoplasm; about 80% are asbestos-related.

What may mesothelioma look like on CXR?

Pleural opacity encasing and contracting the affected hemithorax, sometimes with pleural effusion.

How does an infant's chest differ on imaging?

Different chest-wall shape, more horizontal ribs, and a proportionally larger heart.

Why must attachments and foreign structures be checked on CXR?

To assess the position and course of lines, tubes, catheters, implants, and other devices.

Name examples of internal devices visible on CXR.

Endotracheal tube, internal jugular catheters, Port-a-Cath, and pulmonary artery catheter.

Why is a lateral CXR interpreted together with the PA view?

The lateral view may reveal abnormalities not visible on the frontal view.

What does an opacity generally represent on CXR?

A whiter region caused by increased density or reduced air content.