HRCT chest - prone (protocol)

Prone high-resolution CT (HRCT) chest corresponds to an additional CT acquisition performed as part of an HRCT chest protocol. It represents a scan performed with the patient in a prone position and images obtained in full inspiration. 

This additional imaging is particularly useful for detecting subtle or early interstitial lung disease (ILD). The rationality behind it is to differentiate it from dependent lung atelectasis, which commonly presents as subpleural densities or lines.

Indications

Some institutions routinely acquire prone slices during every initial HRCT chest; in others, the radiologist reviews the supine CT with the patient still on the table to determine if an additional prone series might be helpful. 

Patients with unknown or early interstitial lung disease are the ones that most benefit from it. When there is advanced interstitial lung diseaseILD, dependent opacities are unlikely to pose a diagnostic dilemma and, therefore, additional prone images are of uncertain relevance¹.

Prone HRCT can also be useful in assessing potential fungal balls (aspergillomas) as they are mobile and are dependent in both supine and prone positions ⁴.

Technique

• sequential-spaced acquisition is preferred over a volumetric acquisition in view of a reduction in the radiation dose that the patient is exposed to
• slice gap of 2-4 cm
• no intravenous contrast is required
• postprocessing: high-spatial-frequency or sharpening algorithm (bone algorithm)