When to Order Imaging for Suspected Pulmonary Embolism: ACR Appropriateness Decoded
When to Order Imaging for Suspected Pulmonary Embolism: ACR Appropriateness Decoded
It’s late in a busy shift, and you have a patient with pleuritic chest pain, tachycardia, and a concerning story. Suspected pulmonary embolism (PE) is high on the differential, but the next step is critical. Do you order a CT Angiography (CTA) of the pulmonary arteries, a ventilation/perfusion (V/Q) scan, or something else entirely? The American College of Radiology (ACR) Appropriateness Criteria provide an evidence-based framework for these decisions, balancing diagnostic yield with risks like radiation exposure and contrast-induced nephropathy. This guide decodes the official ACR recommendations for suspected PE, helping you choose the right initial imaging study for your patient’s specific clinical context.
What Does the ACR Guideline for Suspected Pulmonary Embolism Cover?
The ACR Appropriateness Criteria for Suspected Pulmonary Embolism focus on the initial diagnostic imaging for adult and pediatric patients presenting with acute signs or symptoms suggestive of PE. The guidelines are structured around pretest probability—typically determined using a validated clinical decision rule like the Wells’ score or the revised Geneva score—and, in some cases, D-dimer results. The scenarios address common clinical situations, including patients with low, intermediate, and high pretest probability, as well as the unique considerations for pregnant patients.
These criteria do not apply to the evaluation of chronic thromboembolic pulmonary hypertension (CTEPH), surveillance imaging after a PE diagnosis, or the workup of incidental pulmonary emboli found on imaging performed for other reasons. The focus is strictly on the acute, initial diagnostic pathway for a suspected first-time PE event.
What Imaging Should I Order for Suspected Pulmonary Embolism? Recommendations by Clinical Scenario
The optimal imaging strategy for suspected pulmonary embolism hinges on the patient’s pretest probability and specific clinical factors. The ACR provides clear guidance for several common scenarios.
For a patient with a low or intermediate pretest probability and a negative D-dimer, the ACR states that any form of imaging is Usually Not Appropriate. In this context, the negative predictive value of the D-dimer is sufficiently high to effectively rule out PE, making the risks associated with imaging unnecessary.
When the patient has a low or intermediate pretest probability but a positive D-dimer, imaging is warranted. Both CTA pulmonary arteries with IV contrast and a V/Q scan are rated as Usually Appropriate. CTA is often preferred for its speed and ability to identify alternative diagnoses, while a V/Q scan is an excellent alternative for patients with severe contrast allergies or renal impairment. A “triple rule-out” CTA, which also evaluates for aortic dissection and coronary artery disease, is rated May be Appropriate (Disagreement), reflecting a lack of consensus on its routine use for this indication.
In a patient with a high pretest probability, diagnostic imaging is indicated without a preceding D-dimer test. Similar to the scenario above, both CTA pulmonary arteries with IV contrast and a V/Q scan are considered Usually Appropriate. In this high-risk group, some clinicians may start with a lower extremity ultrasound to look for deep vein thrombosis (DVT). The ACR rates US duplex Doppler lower extremity as May be Appropriate (Disagreement); if positive for DVT, it confirms the need for anticoagulation and can sometimes obviate the need for chest imaging.
For a pregnant patient with suspected pulmonary embolism, the algorithm is different to minimize fetal radiation exposure. The first step is often a US duplex Doppler lower extremity, which is rated Usually Appropriate and involves no ionizing radiation. If the ultrasound is negative, further imaging is necessary. A chest radiograph is also Usually Appropriate to assess for other causes of symptoms. If PE is still suspected, both CTA pulmonary arteries and a V/Q scan are rated Usually Appropriate. The choice involves a nuanced discussion with the patient about the trade-offs: CTA delivers a higher radiation dose to the maternal breast tissue, while a V/Q scan results in a slightly higher dose to the fetus.
ACR Imaging Recommendations Table for Suspected Pulmonary Embolism
| Clinical Scenario | Top Procedure | ACR Rating | Adult RRL | Pediatric RRL |
|---|---|---|---|---|
| Low or intermediate pretest probability with a negative D-dimer. Initial Imaging. | No Imaging Indicated | Usually Not Appropriate | N/A | N/A |
| Low or intermediate pretest probability with a positive D-dimer. Initial imaging. | CTA pulmonary arteries with IV contrast | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
| Low or intermediate pretest probability with a positive D-dimer. Initial imaging. | V/Q scan lung | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ 0.3-3 mSv [ped] |
| High pretest probability. Initial Imaging. | CTA pulmonary arteries with IV contrast | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
| High pretest probability. Initial Imaging. | V/Q scan lung | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ 0.3-3 mSv [ped] |
| Pregnant patient. Initial Imaging. | US duplex Doppler lower extremity | Usually appropriate | O 0 mSv | O 0 mSv [ped] |
| Pregnant patient. Initial Imaging. | Radiography chest | Usually appropriate | ☢ <0.1 mSv | ☢ <0.03 mSv [ped] |
| Pregnant patient. Initial Imaging. | CTA pulmonary arteries with IV contrast | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
| Pregnant patient. Initial Imaging. | V/Q scan lung | Usually appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ 0.3-3 mSv [ped] |
Adult vs. Pediatric Suspected Pulmonary Embolism Imaging: Radiation Dose Tradeoffs
While PE is less common in children than in adults, the diagnostic principles are similar, but with a heightened emphasis on radiation safety. The ACR provides distinct pediatric relative radiation levels (RRLs) to guide decision-making, reflecting the increased radiosensitivity of developing tissues and the longer life expectancy over which potential stochastic effects of radiation could manifest. This aligns with the ALARA (As Low As Reasonably Achievable) principle.
For example, a V/Q scan in a pediatric patient carries an RRL of ☢ ☢ ☢ (0.3-3 mSv), which is a full tier lower than the adult RRL of ☢ ☢ ☢ (1-10 mSv) for the same study. Conversely, a CTA of the pulmonary arteries is rated ☢ ☢ ☢ ☢ (3-10 mSv) in children, a higher tier than the adult rating of ☢ ☢ ☢ (1-10 mSv), highlighting the greater relative dose concern. These differences underscore the importance of carefully considering the risks and benefits of each modality and tailoring the imaging choice to the individual pediatric patient, often favoring non-ionizing or lower-dose options when diagnostically equivalent.
Imaging Protocol Details for Suspected Pulmonary Embolism
Once you’ve decided on the right study based on the ACR criteria, ensuring it is performed correctly is paramount for diagnostic accuracy. The specific details of the imaging protocol—from contrast timing in a CTA to the type of radiotracer used in a V/Q scan—can significantly impact image quality. Our protocol guides cover technique, contrast, and interpretation principles for the studies recommended above:
Tools to Help You Order the Right Study for Suspected Pulmonary Embolism
Navigating imaging guidelines at the point of care can be challenging. To streamline this process, GigHz provides several integrated tools designed for busy clinicians and trainees.
For clinical scenarios beyond suspected PE, the ACR Appropriateness Criteria Lookup tool offers a quick, searchable interface to the full library of ACR guidelines, covering thousands of clinical variants across all organ systems.
To ensure the chosen study is executed to the highest standard, the Imaging Protocol Library provides detailed, institution-level protocols for hundreds of common and advanced imaging procedures, including CT, MRI, and ultrasound.
When discussing radiation exposure with patients or tracking cumulative dose, the Radiation Dose Calculator can translate the mSv values of different scans into relatable analogies, supporting shared decision-making and informed consent.
What is the first-line imaging test for suspected PE in a non-pregnant patient?
For most non-pregnant patients with an intermediate or high pretest probability (or a low probability with a positive D-dimer), CT pulmonary angiography (CTA) is the first-line imaging test. It is fast, widely available, and highly sensitive and specific for PE. It also provides the added benefit of potentially identifying alternative diagnoses for the patient’s symptoms, such as pneumonia, aortic dissection, or pericardial effusion.
When is a V/Q scan preferred over a CTA for suspected PE?
A V/Q scan is preferred over a CTA in several situations. The most common reasons include severe allergy to iodinated contrast media, significant renal insufficiency (where contrast-induced nephropathy is a concern), or in younger patients, particularly females, to reduce radiation dose to the breast tissue. A V/Q scan is most useful in patients with a normal baseline chest radiograph.
Is a D-dimer test always necessary before imaging for PE?
No. A D-dimer test is most useful in patients with a low or intermediate pretest probability for PE. In this group, a negative D-dimer can reliably rule out PE and avoid the need for imaging. However, in patients with a high pretest probability, the D-dimer test has poor negative predictive value and is not recommended. These patients should proceed directly to diagnostic imaging.
How should suspected PE be evaluated in a pregnant patient?
The evaluation in pregnant patients is stepwise to minimize radiation. The first step is typically a lower extremity venous compression ultrasound. If positive for DVT, the diagnosis is confirmed, and treatment can begin without further imaging. If the ultrasound is negative, a chest radiograph is often performed. If PE is still suspected, either a V/Q scan or a CTA is performed, with the choice depending on a discussion of the relative radiation risks to the mother and fetus.
Can MRI/MRA be used to diagnose pulmonary embolism?
Magnetic resonance angiography (MRA) of the pulmonary arteries is rated as “May be appropriate” by the ACR in some scenarios. While it avoids ionizing radiation, it is less sensitive than CTA, particularly for smaller, subsegmental emboli. MRA is also more susceptible to motion artifact, is less widely available, and takes longer to perform. It is typically reserved for patients who have a contraindication to both CTA and V/Q scanning.
What is a “triple rule-out” CTA, and when is it used?
A “triple rule-out” CTA is a specialized CT angiography protocol designed to simultaneously evaluate for three major causes of acute chest pain: pulmonary embolism, aortic dissection, and acute coronary syndrome. The ACR rates it as “May be appropriate (Disagreement)” for the primary indication of suspected PE. Its use is controversial because it requires a higher radiation dose and a larger contrast bolus than a standard PE study, and it may not be necessary if the clinical suspicion for aortic or coronary disease is low.
Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 12, 2026
