HRCT Protocol, Secondary Pulmonary Lobule, and Distribution Analysis

High-resolution chest CT is not merely a reconstruction label. It combines thin sections, high spatial resolution, and selected inspiratory, expiratory, or prone images according to the clinical question. Pattern analysis uses location within the secondary pulmonary lobule together with craniocaudal and central-peripheral predominance.

Volumetric inspiratory imaging is the basis of most examinations. Expiratory images can reveal air trapping, while prone images can separate dependent posterior density from true interstitial abnormality. Additional series are chosen for the question rather than acquired automatically, with radiation exposure considered.

Assessment framework

• Check section thickness, reconstruction kernel, and inspiratory adequacy.
• Describe upper-lower, central-peripheral, and anterior-posterior distribution.
• Localize nodules as centrilobular, perilymphatic, or random within the secondary lobule.
• Record reticulation, traction bronchiectasis, honeycombing, ground glass, and consolidation separately.
• For mosaic attenuation, assess vessel caliber and expiratory images together.

What the report should contain

• State the technique and whether expiratory or prone images were obtained.
• Describe the dominant pattern and distribution before assigning a diagnostic label.
• When fibrosis is present, record traction and architectural distortion.
• Compare pattern and extent with prior imaging.
• Use a guideline category only when technical and clinical scope are appropriate.

Common errors

• Calling every thin-section chest CT an HRCT protocol.
• Mistaking dependent atelectasis for early fibrosis.
• Calling mosaic attenuation air trapping without expiratory and vascular confirmation.

Example report wording

Example impression: Mild lower-lobe and subpleural reticulation with traction bronchiolectasis is present in both lungs. There is no honeycombing. Posterior opacities persist on prone images. Expiratory imaging shows no substantial lobular air trapping. The findings support a fibrotic interstitial lung disease pattern; final classification requires clinical and multidisciplinary correlation.

For a nodular pattern, continue with the HRCT approach to diffuse pulmonary nodules.

References

1. American College of Radiology. Practice Parameter for Thoracic CT. Source (opens in a new tab)
2. Fleischner Society. Glossary of Terms for Thoracic Imaging. Source (opens in a new tab)

Clinical note: This material is for radiology education. Do not generate an automatic diagnosis or management decision without checking guideline scope, patient factors, and local policy.