How to interpret High-Resolution Computed Tomography (HRCT) images?

How to Interpret High-Resolution Computed Tomography (HRCT) Images

HRCT interpretation requires systematic evaluation of specific anatomical landmarks and recognition of key fibrotic patterns, with side-by-side comparison of baseline and follow-up images at corresponding anatomical levels to accurately assess disease progression. 1

Technical Requirements for Optimal HRCT Imaging

• Acquisition protocol must include:

  • No contrast media (lung parenchyma naturally has high contrast)
  • Volumetric scanning at full inspiration in supine position
  • Thin section reconstruction (≤1.5 mm)
  • High spatial frequency algorithm for lung parenchyma 2
  • Shortest rotation time (0.5s) and highest pitch to minimize motion artifacts 2

• Additional views when needed:

  • Prone position imaging to differentiate gravity-dependent changes from true interstitial abnormalities 2, 1
  • Expiratory acquisition to identify air trapping in conditions like hypersensitivity pneumonitis 2

Systematic Approach to HRCT Interpretation

1. Evaluate Five Key Anatomical Levels

For baseline quantification of disease extent, assess these specific regions 2, 1:

• Region 1: Aortic arch level
• Region 2: 1 cm below carina
• Region 3: Right pulmonary venous confluence
• Region 4: Midpoint between regions 3 and 5
• Region 5: 1 cm above right hemidiaphragm

2. Identify Key Fibrotic Patterns

Look specifically for these features 2, 1:

• Traction bronchiectasis/bronchiolectasis (dilated airways due to surrounding fibrosis)
• Honeycombing (clustered cystic airspaces with well-defined walls)
• Ground-glass opacities (hazy increased opacity without obscuring vessels)
• Fine reticulation (network of fine linear opacities)
• Lobar volume loss (reduced lung volume with displacement of fissures)

3. Assess Distribution Pattern

Note the predominant distribution 1, 3:

• Peripheral vs. central
• Upper vs. lower lung predominance
• Patchy vs. diffuse involvement

4. Quantify Disease Extent

• Calculate percentage of lung involvement globally across both lungs 2
• Document coexistence of emphysema (report as <15% or ≥15% of total lung volume) 2
• Use multiplanar reconstructions (sagittal and coronal) to increase diagnostic confidence 2, 1

Evaluating Disease Progression

For follow-up scans, systematically assess for 2, 1:

• Increased extent or severity of traction bronchiectasis
• New ground-glass opacities with traction bronchiectasis
• New fine reticulation
• Increased extent or coarseness of reticular abnormality
• New or increased honeycombing
• Increased lobar volume loss

Critical technique: Perform side-by-side comparison of baseline and follow-up images at corresponding anatomical levels to reduce variability and increase reproducibility 2

Reporting Requirements

A comprehensive HRCT report should include 2, 1:

• Definition of disease pattern according to established guidelines
• Quantification of fibrosis extent as percentage of lung involvement
• Classification of follow-up as improved, stable, or progressive
• Integration with clinical and functional data

Common Pitfalls to Avoid

• Misinterpreting dependent atelectasis: Always consider prone imaging when suspicious changes are seen in dependent regions 2, 1
• Inadequate inspiration: Suboptimal inspiration can mimic ground-glass opacity 2
• Motion artifacts: Can simulate interstitial abnormalities 2
• Comparing non-corresponding levels: Always ensure anatomical landmarks match when comparing serial scans 2
• Isolated radiological interpretation: HRCT findings should always be integrated with clinical and functional data 2, 1

Optimizing Follow-up Evaluation

• Ideally perform follow-up scans at the same facility using the same scanner 2
• Follow-up within 12 months is advisable for patients with progressive pulmonary fibrosis 2
• Consider earlier follow-up if clinical or functional decline occurs 2

Remember that expert chest radiologists play a key role in ensuring high-quality visual assessment of complex disease patterns and monitoring disease changes 2, 1.