Should a Pulmonary Embolism (P.E) Computed Tomography (CT) scan be performed with contrast or without contrast?

From the Guidelines

For a pulmonary embolism (PE) CT scan, contrast is necessary and should be performed with intravenous contrast, not without. The standard protocol is a CT pulmonary angiogram (CTPA) with contrast, which allows visualization of the pulmonary arterial tree to detect filling defects caused by blood clots 1. According to the most recent guidelines, there is no relevant literature to support the use of CT chest without and with IV contrast to assess PE in patients with low or intermediate probability with positive D-dimer 1.

Key Points to Consider

• The contrast medium (typically iodinated) is injected intravenously and timed to opacify the pulmonary arteries during the scan.
• Without contrast, a CT scan cannot reliably detect pulmonary emboli as the clots themselves have similar density to surrounding structures and become visible only when contrasted against the bright, contrast-filled vessels.
• Before proceeding with the contrast study, patients should be screened for contraindications including severe renal impairment (eGFR < 30 ml/min), history of severe contrast reactions, and pregnancy.
• Adequate hydration before and after the scan is recommended to reduce the risk of contrast-induced nephropathy.
• If contrast is absolutely contraindicated, alternative diagnostic approaches such as ventilation-perfusion (V/Q) scanning or MRI may need to be considered, though these have limitations compared to CTPA for PE diagnosis 1.

Diagnostic Approach

• The American College of Radiology (ACR) recommends CTPA as the primary imaging modality for evaluating patients suspected of having acute PE 1.
• CTPA has played an increasingly significant role in the diagnosis of PE since the first major clinical study in 1992 by Remy-Jardin et al 1.
• Technological advancements in CT—from helical to multidetector—have led to improved resolution of the pulmonary arteries, large and small 1.

From the FDA Drug Label

The decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological, and unenhanced CT findings. Contrast enhancement appears to be greatest immediately after bolus administration (15 seconds to 120 seconds). Utilization of a continuous scanning technique (ie, dynamic CT scanning) may improve enhancement and diagnostic assessment of tumor and other lesions such as abscess, occasionally revealing unsuspected or more extensive disease

The use of contrast in a P.E CT scan should be determined on a case-by-case basis, considering the potential benefits and risks.

• The decision to use contrast should be based on a careful evaluation of clinical and radiological findings.
• Contrast enhancement can improve the diagnostic assessment of certain lesions, but it may also be associated with risk and increased radiation exposure 2.

From the Research

CT Scan for Pulmonary Embolism

• The use of contrast material in CT scans for pulmonary embolism is a common practice, as it helps to improve image quality and diagnostic accuracy 3, 4, 5, 6, 7.
• Studies have shown that the use of contrast material can increase the sensitivity and specificity of CT scans in detecting pulmonary embolism 3, 4, 6.
• However, there are certain situations where the use of contrast material may be contraindicated, such as in patients with renal failure or allergy to iodinated contrast material 3, 4.
• In such cases, alternative imaging modalities such as ventilation-perfusion scintigraphy or MRI may be used 3, 4, 6.

Image Quality and Contrast Material

• The image quality of CT scans can be affected by the type and amount of contrast material used 5, 7.
• Studies have shown that higher iodine delivery rates can improve image quality and reduce the number of non-sufficient scans 5.
• The use of high concentration and high iodine delivery rate contrast material protocols can provide the best image quality of both CTPA and perfusion map images of the lung 7.

Diagnostic Algorithms and Imaging Modalities

• The diagnosis of pulmonary embolism typically involves a combination of clinical evaluation, laboratory tests, and imaging modalities 4, 6.
• CT pulmonary angiography is the recommended imaging technique for patients with a high clinical probability of pulmonary embolism 4.
• Other imaging modalities such as ventilation-perfusion scans and lower extremity ultrasound may be used in patients with contraindications to CT or in certain clinical situations 4, 6.