CT Chest

Question 1

Describe chest CT

Answer 1

Chest computed tomography (CT) is a valuable imaging technique used to evaluate the chest region for various pathologies. It provides detailed cross-sectional images that help in diagnosing and assessing conditions affecting the lungs, heart, blood vessels, and surrounding structures.

Question 2

Describe units of density in CT and list tissues in order of least to most dense

Answer 2

Density
Measured by the Hounsfield scale:
- Air -1000 –black
- Fat -40
- Water 0
- Organs 40
- Bone 500
- Metal 1000 –white

Question 3

List the four types of CT chest scans most commonly performed

Answer 3

• Routine CT chest
• High resolution CT
• CT thoracic angiogram
• CT pulmonary angiogram

Question 4

Describe routine CT

Answer 4

This scan may or may not involve the use of contrast medium and is used to examine the chest area from the shoulders to the upper abdomen.
- contrast medium helps delineate vascular structures
- 50mL of Isovue (2mL / second)
- 22g IVC is acceptable
- large variety of indications
- from shoulders to upper abdomen (include adrenals)

Question 5

Describe high resolution CT

Answer 5

It is a non-contrast scan specifically used for diagnosing interstitial lung disease. Special reconstruction filters are applied to enhance spatial resolution.
Sub-types:
- inspiratory
- expiratory
- prone imaging

Question 6

Describe CT thoracic angiogram

Answer 6

It involves a non-contrast CT followed by a contrast-enhanced CT angiogram. The scan assesses the thoracic aorta from above the aortic arch to the aortic bifurcation.
- uses 50-75cc of Isovue (4-6mL / second) followed by a 50cc saline flush
- NOTE: cannot pick up small pulmonary embolus

Question 7

Describe CT pulmonary angiogram

Answer 7

This scan uses strong contrast medium to opacify the pulmonary arteries and identify pulmonary embolism. It also helps in detecting co-existing pulmonary pathologies.
- uses 50-75cc of Isovue (4-6mL / second) followed by a 50cc saline flush
Procedure
- Lie down in the doughnut
- Girth and weight limitation ^[improved with years]
- Requires breath holding
- 3D acquisition

Intravenous Contrast medium
- Iodinated contrast. Isovue 300 / 370
- Injected via a peripheral cannula.
- Largely cannot use PICC lines and central lines.
- “Contraindications”
- Renal impairment
- Allergic reaction
- Iodine sensitive cancer
- Not contraindicated in pregnancy/breastfeeding

Question 8

Describe risk of radiation with CT chest

Answer 8

Chest CT scans involve exposure to ionizing radiation. The effective dose is approximately 8.00mSv, equivalent to about 160 chest x-rays or 3.6 years of background radiation.

The benefits of the scan in diagnosing and managing conditions largely outweigh the associated radiation risks.

Dose reduction techniques and alternative imaging studies can be considered when appropriate.
- Follow-up with radiographs instead of CT
- Alternative diagnostic study e.g. Nuclear Medicine V/Q Scan
- Dose reduction techniques
- Limited field of view
- Machine / operator controlled

Question 9

Describe common pathologies identified by CT chest scans

Answer 9

CT chest scans can help identify and evaluate various pathologies, including:

• Consolidation
• Pneumothorax with bronchiectasis
• Pleural effusion
• Lung cancer
• Rib fracture
• Emphysema
• Pulmonary metastases
• Cavitating pulmonary lesions
• Lung abscess
• Pulmonary embolism including saddle pulmonary embolus
• Aortic dissection
• Pancoast tumor
• Sarcoidosis
• Breast cancer ‘peau d’orange’
• Thoracic spine fracture