Is a low-dose (LD) computed tomography (CT) scan suitable for diagnosing interstitial lung disease (ILD)?

From the Guidelines

Low-dose CT scanning is not the preferred diagnostic tool for interstitial lung disease (ILD) due to its compromised image quality and potential to miss subtle lung parenchymal changes. The diagnosis of ILD requires a multidisciplinary assessment of clinical, laboratory, imaging, functional, and sometimes histologic features, with high-resolution computed tomography (HRCT) being the primary imaging tool used to detect ILD and outline its extension and pattern 1.

Key Considerations for ILD Diagnosis

• HRCT is the gold standard for ILD diagnosis, providing the necessary spatial resolution to evaluate interstitial abnormalities.
• HRCT typically uses thin slices (1-2 mm) and high-spatial-frequency reconstruction algorithms to enhance detail visualization.
• Low-dose CT (LDCT) scanning compromises image quality by increasing noise and reducing resolution of fine anatomical details, which may lead to missed diagnoses of subtle lung parenchymal changes, including ground-glass opacities, reticular patterns, honeycombing, and traction bronchiectasis.
• A volumetric HRCT scan should be acquired on full inspiration, complemented at baseline with an additional acquisition in ventral decubitus and a non-contiguous acquisition on expiration, as recommended by the Portuguese Pulmonology Society, the Portuguese Rheumatology Society, and the Portuguese Radiology and Nuclear Medicine Society 1.

Clinical Practice Recommendations

• For patients with suspected ILD, a complete history and physical examination, including a search for clinical features suggestive of connective tissue disease (CTD), should be performed.
• Pulmonary function tests (PFTs) are a reliable tool for early ILD detection and provide the most accurate measurement of disease severity.
• Patients diagnosed with ILD should undergo a multidisciplinary evaluation of disease severity, associated symptoms, pulmonary function impairment, and disease extent on HRCT.
• While dose-reduction techniques may be employed in clinical practice, complete low-dose protocols are generally reserved for lung cancer screening rather than ILD evaluation, and standard HRCT techniques should be used for the initial diagnostic evaluation to ensure accurate diagnosis and classification of the specific ILD pattern.

From the Research

Low-Dose CT Scan for Interstitial Lung Disease

• A low-dose (LD) computed tomography (CT) scan can be suitable for diagnosing interstitial lung disease (ILD), but its effectiveness depends on various factors such as radiation dose and image quality 2, 3.
• Studies have shown that reducing the radiation dose can affect the detectability of interstitial lung changes, particularly for subtle changes such as ground-glass opacities (GGO) and reticulations 2.
• However, a minimum dose is needed to maintain diagnostic accuracy in chest CT for suspected ILD, and additional dose reduction beyond a certain point may not significantly change the percentage agreement (PA) for detecting these changes 2.
• The use of low-dose CT protocols with a combination of reduced tube current and increased slice thickness can compensate for noise-associated image quality degradation and allow for accurate assessment of ILD-specific features 3.

Diagnostic Accuracy and Image Quality

• The diagnostic accuracy of low-dose CT scans for ILD can be affected by factors such as image noise and radiation dose, but studies have shown that it is still possible to achieve high diagnostic accuracy with low-dose protocols 2, 3.
• High-resolution CT (HRCT) is the preferred imaging technique for evaluating ILD, and low-dose CT protocols can be optimized to provide high-quality images with minimal radiation exposure 3, 4.
• The correlation of CT findings with clinical data and other diagnostic tests, such as pulmonary function tests and bronchoalveolar lavage, is essential for accurate diagnosis and management of ILD 5, 4.

Clinical Applications and Management

• ILD is a complex group of conditions that require a multidisciplinary approach to diagnosis and management, including the use of low-dose CT scans as a diagnostic tool 5, 4.
• The management of ILD involves a range of treatments, including antifibrotic therapy, immunomodulatory therapy, and lung transplantation, and low-dose CT scans can play a crucial role in monitoring disease progression and response to treatment 5, 4.
• A holistic approach to the care of patients with ILD is essential, taking into account their high symptom burden and considerable palliative care needs 4.