High-resolution computed tomography remains central to the assessment of diffuse lung disease, with recommendations varying according to whether disease is suspected, acutely worsening or clinically stable. The 2026 American College of Radiology Appropriateness Criteria update addresses initial imaging, suspected acute exacerbation or deterioration and surveillance of confirmed diffuse lung disease. Diffuse lung disease can involve inflammation, fibrosis or both, with imaging patterns that may overlap across conditions. Multidisciplinary discussion involving pulmonologists, radiologists, pathologists and other clinical specialists remains the standard for diagnosis, risk stratification and monitoring, while imaging supports diagnosis and treatment decisions across these clinical settings.
HRCT Leads Initial Assessment
For adults with suspected diffuse lung disease, high-resolution CT (HRCT) of the chest without intravenous contrast is considered usually appropriate for initial imaging. Chest radiography is also usually appropriate, but its role differs. It can provide an initial assessment for alternative diagnoses that may present similarly, while a normal radiograph does not exclude clinically important diffuse lung disease. CT has greater sensitivity and specificity than radiography for detecting and characterising these disorders.
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HRCT supports a pattern-based assessment of disease distribution and morphology and can narrow the differential diagnosis or provide a confident diagnosis. Its interpretation also contributes to multidisciplinary discussion and can help identify sites for tissue sampling when diagnostic confidence remains low. Initial HRCT protocols should use thin-section imaging, with prone and expiratory acquisitions recommended when feasible. Prone imaging can improve assessment of dependent lung and fibrosis, while expiratory imaging can assist evaluation of small-airways disease. Volumetric CT acquisition also enables multiplanar thin-section reconstructions for assessing disease distribution.
Routine chest CT without contrast may be appropriate in some settings when thin-slice imaging and lung reconstruction kernels are used, but HRCT is favoured. Typical HRCT protocols do not require intravenous contrast. MRI is usually not appropriate for initial imaging because supporting research remains limited, while FDG-PET/CT is also usually not appropriate despite possible secondary roles in selected diffuse lung diseases.
CT Supports Evaluation of Acute Deterioration
When confirmed diffuse lung disease is accompanied by suspected acute exacerbation or acute clinical deterioration, chest CT without intravenous contrast and HRCT without contrast are usually appropriate alternatives. CT can identify new airspace abnormalities associated with acute worsening and can also help assess alternative or concurrent causes of deterioration, including pulmonary oedema, pneumothorax, infection or malignancy. In suspected acute exacerbation of idiopathic pulmonary fibrosis, new opacities on CT are a required diagnostic feature. The distribution and extent of CT findings may also have prognostic value.
In the acute setting, prone and expiratory acquisitions may not be feasible and can generally be omitted. Standard chest CT without contrast is therefore favoured over a full HRCT protocol when thin-section imaging is performed. Chest radiography remains usually appropriate as an initial examination, particularly for detecting other causes of acute symptoms, although it is less sensitive and specific than CT for diffuse lung disease.
CT with intravenous contrast may be appropriate in selected situations when overlapping or concurrent diagnoses need evaluation. CT angiography may also be appropriate when pulmonary embolism is a concern, particularly when risk factors are present and the clinical presentation is ambiguous or not explained by CT findings. MRI is usually not appropriate for acute deterioration because the available research does not support its use, and FDG-PET/CT is likewise not supported for this indication.
HRCT Remains the Main Surveillance Tool
For confirmed diffuse lung disease without acute clinical deterioration, HRCT of the chest without intravenous contrast is usually appropriate for surveillance. Serial examinations can support assessment of disease stability, progression or reversibility and may improve diagnostic accuracy as imaging appearances evolve over time. Several conditions can show temporal evolution that becomes more specific on follow-up imaging. In several diffuse lung diseases, expert recommendations support surveillance HRCT at annual to biennial intervals, with shorter intervals potentially appropriate when clinical progression is suspected or in selected conditions.
HRCT is favoured over routine CT because its higher spatial resolution improves assessment of fine parenchymal abnormalities and interval changes. Routine CT without contrast may still be appropriate when thin-slice imaging and lung kernels are used. Prone and expiratory sequences are optional during follow-up rather than routinely required.
Chest radiography may be useful in certain clinical contexts as a complementary examination, but CT is more sensitive and specific for parenchymal changes. MRI is usually not appropriate for surveillance because supporting research remains limited, although small studies show concordance with HRCT and pulmonary function and suggest potential functional information from specialised sequences. FDG-PET/CT has a more limited surveillance role. It can assist assessment of disease extent, activity and treatment response in sarcoidosis, while evidence is more restricted for other fibrotic and nonfibrotic diffuse lung diseases.
The updated recommendations place non-contrast chest CT, particularly HRCT, at the centre of imaging across suspected disease, acute deterioration and surveillance. Chest radiography retains a role in initial assessment and in selected follow-up contexts, while contrast-enhanced CT or CT angiography may be appropriate for particular clinical questions such as alternative diagnoses or possible pulmonary embolism. MRI and FDG-PET/CT generally have limited roles in routine evaluation. Imaging protocols should be tailored to the clinical situation, with adjunct HRCT sequences used selectively and multidisciplinary discussion continuing to guide diagnosis, risk assessment and monitoring.
Source: Journal of the American College of Radiology
Image Credit: iStock
References:
Chelala L, Walker C, Little B et al. (2026) ACR Appropriateness Criteria® Diffuse Lung Disease: 2026 Update. Journal of the American College of Radiology: In Press.
