High-Resolution CT (HRCT) is the Best Type of CT Scan for Evaluating Pulmonary Fibrosis
High-resolution computed tomography (HRCT) is the recommended type of CT scan for evaluating pulmonary fibrosis, as it provides the most detailed assessment of lung parenchyma and fibrotic changes. 1, 2
Technical Requirements for HRCT in Pulmonary Fibrosis
HRCT for pulmonary fibrosis evaluation should include:
Mandatory Components:
- No injection of contrast medium
- Inspiratory apnoea slices
- Axial contiguous or non-reconstructed slices separated by ≤2 cm
- Slice thickness ≤2 mm
- Reconstruction field focused on lungs
- Image acquisition complying with radiation safety norms
- Archiving of millimetric slices on digital media for further reading 1
Optional Components:
- Multiplanar reconstruction on sagittal and coronal planes to increase diagnostic confidence 1
- Images in the prone position if gravity-dependent opacities hamper analysis in supine position
- Expiration slices to exclude lobular air trapping 1
Standardized Assessment Protocol
For consistent evaluation of pulmonary fibrosis on HRCT, a standardized approach is recommended:
Baseline quantification of disease extent should be performed by visual scoring of five preselected regions:
- Region 1: The aortic arch
- Region 2: 1 cm below the level of the carina
- Region 3: The right pulmonary venous confluence
- Region 4: The midpoint between Regions 3 and 5
- Region 5: 1 cm above the cupola of the right hemidiaphragm 1
Visual scoring should consider:
- Extent and severity of traction bronchiectasis
- Ground-glass opacities with traction bronchiectasis
- Fine reticulation
- Extent and coarseness of reticular abnormality
- Honeycombing
- Lobar volume loss 1
Coexistence of emphysema must be reported and quantified as <15% or ≥15% 1
Diagnostic Value of HRCT in Pulmonary Fibrosis
HRCT has significantly improved the diagnostic evaluation of pulmonary fibrosis by:
- Allowing detailed assessment of lung parenchyma
- Enabling earlier diagnosis
- Reducing differential diagnosis based on tomographic pattern
- Identifying associated conditions like emphysema 2
The accuracy of a confident diagnosis of usual interstitial pneumonia (UIP) made by HRCT by a trained observer is approximately 90%, making it vastly superior to conventional chest radiography 2.
Follow-up Assessment
For monitoring disease progression:
- Follow-up HRCT should be classified as improved, progressive, or stable
- All features must be compared on corresponding anatomical levels
- The longitudinal assessment should ideally be performed on serial images acquired in the same radiology facility with the same scanner 1
- Follow-up timing is typically recommended at 24 months, though this may vary based on clinical presentation 1
Multidisciplinary Approach
The HRCT chest examination report should:
- Contain a definition of the disease pattern according to guidelines
- Include quantification of the extent of fibrosis by percentage at baseline and follow-up
- Be validated by an experienced thoracic radiologist and discussed among specialists
- Include a recommendation for patient referral to an expert center with multiple specialists for confirmed fibrotic interstitial disease 1
Pitfalls and Caveats
- A normal chest radiograph does not rule out microscopic evidence of UIP pattern on lung biopsy, underscoring the importance of HRCT 2
- While automated quantitative assessment methods are developing, visual assessment by expert chest radiologists remains essential for accurate evaluation 1
- The interpretation of HRCT findings should always be integrated with clinical and functional data for optimal diagnosis and management 1
- Complex cases should be referred to expert centers or pulmonology departments experienced in interstitial lung diseases 1
By following these standardized protocols for HRCT acquisition and interpretation, clinicians can optimize the evaluation of pulmonary fibrosis, leading to more accurate diagnosis and appropriate management decisions.