Ch02: Chest Radiology — Technique & Normal Anatomy（胸部影像技术与正常解剖）

# Ch02: Chest Radiology — Technique & Normal Anatomy（胸部影像技术与正常解剖）

Preparatory Mindset

Chest imaging techniques include X-ray, CT, radionuclide lung scanning, PET/CT, ultrasound and MRI (a very small role). Chest X-ray is the first-line test for most chest problems; CT is used for detailed evaluation. When interpreting any chest film, develop a routine: check the film label (left/right, patient, date), assess inspiration, then read the ABCs — Airway, Breathing (lung fields), Circulation (heart and mediastinum), Diaphragm and the chest wall.

Core Concepts

Imaging techniques

• Chest X-ray: PA view (standard) + lateral view. Full inspiration is essential. The image is two-dimensional with overlap of structures.
• Chest CT: contiguous sections; intravenous contrast to visualize the mediastinum, hila and pulmonary vessels; display in lung window, soft-tissue (mediastinal) window and bone window.
• Radionuclide lung scan: perfusion (99mTc-labelled macroaggregates of albumin trapped in pulmonary capillaries → reflects blood flow) and ventilation scans; used to diagnose/exclude pulmonary embolism (largely superseded by CT pulmonary angiography).
• FDG-PET/CT: FDG is taken up by many tumors (primary lung cancers, metastases, active lymphoma); used to stage lung cancer/lymphoma and diagnose recurrence; inflammation also concentrates FDG → not entirely specific.
• Ultrasound: absorbed by air in lung → confined to processes in contact with the chest wall (pleural effusions, pleural masses, selected mediastinal masses); excellent for ultrasound-guided thoracentesis and needle biopsy of chest-wall-contacting masses.

How to analyze an imaging examination

Ask three questions in order: Location (where is the abnormality?), Extension (how extensive is it?), Differentiation (what is it?).

Normal anatomy of the chest X-ray

• Imagine the patient is always facing you (the viewer).
• Normal pulmonary vascular pattern: arteries and veins branching vertically to the upper and lower lobes; the lower zone vessels are larger than the upper zone ones (gravity).
• The right hemidiaphragm is normally up to 2.5 cm higher than the left (liver beneath it).
• On a good inspiratory film, the dome of the right hemidiaphragm is at the level of the anterior end of the sixth rib.
• Hilar shadows represent the pulmonary arteries and veins; the left hilum is usually slightly higher than the right. Hilar enlargement is usually due to lymphadenopathy or enlarged vessels.
• The trachea is central; deviation suggests mass, collapse or thyroid disease (narrowing of the trachea by an enlarged thyroid).
• Thymus (children): may produce a "sail sign" — normal in infants.
• A normal chest CT shows the lung anatomy in lung window and mediastinal structures in soft-tissue window.

Key normal measurement points

• Right hemidiaphragm at ~6th anterior rib on good inspiration.
• Right hemidiaphragm up to 2.5 cm higher than left.
• Left hilum slightly higher than right.
• Lower-zone vessels larger than upper-zone vessels (normal; reversed = cephalization = pulmonary venous hypertension).

High-Yield Points

• Key Point: PA view is standard; always check the film label (left/right).
• Key Point: Right hemidiaphragm is up to 2.5 cm higher than the left; at the level of the 6th anterior rib on good inspiration.
• Key Point: Left hilum is slightly higher than the right; hila = pulmonary arteries/veins.
• Key Point: Chest CT needs at least lung + soft-tissue windows; IV contrast for mediastinum/hila/vessels.
• Key Point: Thoracic US is confined to chest-wall-contacting lesions; used to guide thoracentesis.
• Key Point: FDG-PET is used for lung cancer staging but is not specific (inflammation also lights up).

Topic Summary

Chest imaging begins with a well-taken PA + lateral CXR, with CT (lung + mediastinal windows, ± IV contrast) for detail. Reading a CXR systematically (label → inspiration → ABCs → heart → hila → diaphragm → bones) prevents misses. Key normal landmarks: right hemidiaphragm ~2.5 cm higher than left and at the 6th anterior rib on inspiration; left hilum higher than right; lower-zone vessels larger than upper. US and PET/CT serve specific roles (pleural-guided procedures; lung cancer staging).