Is a CT (Computed Tomography) scan with or without contrast best for visualizing fluid in the lungs?

From the Guidelines

A CT scan with contrast is the preferred method for visualizing fluid in the lungs, as it provides superior visualization of vascular structures and helps differentiate between various types of fluid collections. This is based on the most recent and highest quality study available, which recommends the use of CT chest with IV contrast in cases of suspected parapneumonic effusion or empyema 1. The use of contrast-enhanced CT allows for better visualization of the pleura and helps to identify features such as pleural enhancement, pleural thickening, and loculation, which are commonly associated with the diagnosis of empyema 1.

Some key points to consider when using CT scans to visualize fluid in the lungs include:

• The typical contrast agent used is an iodinated compound administered intravenously at a dose of 1-2 mL/kg body weight immediately before scanning.
• The decision between contrast and non-contrast CT should be made based on the specific clinical question, the patient's renal function (with eGFR preferably above 45 mL/min/1.73m²), and history of allergic reactions to contrast media.
• Non-contrast CT can still effectively detect fluid in the lungs and may be preferred for patients with contraindications to contrast agents, such as those with kidney dysfunction or severe contrast allergies.
• Acquiring the CT scan 60 seconds after the IV contrast bolus optimizes visualization of the pleura 1.

It's worth noting that the British Thoracic Society guidelines also recommend the use of CT scans with contrast enhancement for the investigation of pleural effusions, as it can help to differentiate between benign and malignant disease 1. However, the most recent and highest quality study available is the 2024 study published in the Journal of the American College of Radiology, which provides more specific guidance on the use of CT scans with contrast in the diagnosis of parapneumonic effusions and empyema 1.

From the Research

CT Scan for Visualizing Fluid in Lungs

• A CT scan can be used to visualize fluid in the lungs, and the use of contrast may depend on the specific condition being diagnosed 2.
• For pulmonary edema, CT can detect acinar shadows and air-bronchograms more clearly than conventional radiography, and can image the specific pattern of distribution of edema in cross-section 2.
• In cases of pleural disease, CT can be used to assess empyema and loculated pleural fluid collections prior to drainage, and to evaluate benign and malignant pleural tumors 3.
• Contrast-enhanced CT can be used to assess regional pulmonary perfusion, as well as nodule and tumor perfusions in various pulmonary diseases 4.
• The use of contrast in CT scans for pulmonary diseases can provide additional information on perfusion and can be useful in routine clinical practice 4.

Use of Contrast in CT Scans

• The use of iodinated contrast material is generally preferred for CT scans, but may be contraindicated in patients with renal failure or allergy to iodinated contrast material 5.
• In such cases, alternative imaging techniques such as ventilation-perfusion scintigraphy or MRI may be used 5, 6.
• Contrast-enhanced CT can provide both structural and functional information, and can be used to quantify pulmonary perfusion 6, 4.

Comparison with Other Imaging Modalities

• CT is generally preferred over other imaging modalities such as MRI for the diagnosis of pulmonary embolism 5.
• However, MRI may have a limited but important role in the evaluation of focal pleural tumors and in determining the extent of malignant mesothelioma prior to therapy 3.
• Ultrasound has been traditionally used for the assessment of pleural disease, but CT has found increasing utility in this area 3.