Pulmonary Angiography: Uses, Procedure, and Findings

Pulmonary angiography is an imaging technique used to evaluate the pulmonary arteries and identify abnormalities affecting blood flow through the lungs. It is especially important in the diagnosis of pulmonary embolism, although it may also be used to detect pulmonary artery stenosis, aneurysms, and arteriovenous malformations.

Modern evaluation of the pulmonary circulation relies heavily on computed tomography angiography, while conventional pulmonary angiography is generally reserved for cases in which noninvasive testing is inconclusive.

Understanding how these techniques work is important for interpreting pulmonary vascular disease and selecting appropriate diagnostic studies.

What Is Pulmonary Angiography?

Pulmonary angiography refers to imaging techniques that visualize the pulmonary arterial circulation after contrast material is introduced into the bloodstream. The contrast makes the pulmonary arteries stand out from surrounding structures so that clinicians can evaluate the vessels for obstruction, narrowing, abnormal dilation, or other structural abnormalities.

Under normal conditions, contrast material flows through the pulmonary arteries and their branches, creating a visible branching vascular pattern. When a blood vessel is obstructed, contrast may fail to fill the vessel normally. This can produce a filling defect or abrupt interruption in the expected vascular pattern.

Pulmonary angiography is most commonly associated with the diagnosis of pulmonary embolism, a condition in which material obstructs one or more pulmonary arteries. Most pulmonary emboli are caused by thrombi that form in the deep veins of the lower extremities or pelvis and then travel through the venous circulation to the lungs.

Two major forms of pulmonary angiographic imaging are used:

• Computed tomography pulmonary angiography, commonly called CTPA or CTA
• Conventional catheter-based pulmonary angiography

Note: CTA has become the primary imaging test for most patients with suspected pulmonary embolism because it is fast, noninvasive, widely available, and capable of directly visualizing pulmonary arterial obstruction.

Pulmonary Vascular Anatomy

Understanding pulmonary angiography requires a basic understanding of pulmonary vascular anatomy.

Blood returning from the systemic circulation enters the right atrium and then passes into the right ventricle. The right ventricle pumps blood into the main pulmonary artery. The main pulmonary artery then divides into right and left pulmonary arteries, which carry blood to the corresponding lungs.

These arteries divide into progressively smaller vessels:

• Main pulmonary arteries
• Lobar arteries
• Segmental arteries
• Subsegmental arteries
• Smaller peripheral branches

Note: Pulmonary angiography evaluates these vessels to determine whether blood is flowing normally. Large emboli may involve the main or lobar pulmonary arteries, while smaller emboli may lodge in segmental or subsegmental branches. The ability to detect small peripheral emboli depends partly on the resolution of the imaging system.

Pulmonary Embolism

Pulmonary embolism is one of the most important conditions evaluated with pulmonary angiography.

A pulmonary embolus is material that travels through the circulation and becomes lodged within a pulmonary artery. Although several types of embolic material are possible, most clinically significant pulmonary emboli are caused by blood clots.

A thrombus typically forms in the deep veins of the legs or pelvis. Part or all of the thrombus may break free, travel through the inferior vena cava, enter the right side of the heart, and then pass into the pulmonary arteries. Once the embolus becomes lodged in a pulmonary artery, it partially or completely obstructs pulmonary blood flow.

This can produce:

• Ventilation-perfusion mismatch
• Increased pulmonary vascular resistance
• Hypoxemia
• Increased right ventricular workload
• Reduced cardiac output in severe cases
• Pulmonary infarction in some patients

Note: Large emboli can cause severe hemodynamic instability, while smaller emboli may produce more subtle symptoms.

Clinical Presentation of Pulmonary Embolism

The symptoms of pulmonary embolism are often nonspecific, which is one reason imaging is so important.

Common findings may include:

• Sudden shortness of breath
• Pleuritic chest pain
• Tachypnea
• Tachycardia
• Hypoxemia
• Cough
• Hemoptysis
• Anxiety
• Syncope
• Unexplained hypotension in severe cases

Note: Pulmonary embolism may resemble pneumonia, myocardial infarction, pneumothorax, heart failure, or other cardiopulmonary disorders. Because symptoms alone cannot reliably confirm the diagnosis, clinical probability assessment and diagnostic testing are typically used together.

Computed Tomography Pulmonary Angiography

Computed tomography pulmonary angiography is the most commonly used imaging examination for suspected pulmonary embolism.

Modern CT scanners can obtain detailed images of the chest within seconds. During CTPA, iodinated contrast material is injected intravenously at a relatively high rate. Images are acquired while the contrast is concentrated within the pulmonary arteries.

This produces bright contrast-filled vessels that can be evaluated for intravascular filling defects. CTPA provides detailed cross-sectional images of the pulmonary arteries while also allowing visualization of the lungs, pleura, mediastinum, chest wall, and other thoracic structures.

How CT Pulmonary Angiography Is Performed

The patient first requires adequate intravenous access. Because the contrast must enter the circulation rapidly, a large-bore peripheral intravenous catheter is commonly placed in an antecubital vein. Certain central vascular devices may also be suitable if they are approved for high-pressure contrast injection.

Contrast material is then injected rapidly into the vein. The contrast travels through the venous circulation, enters the right side of the heart, and moves into the pulmonary arteries.

CT scanning is timed so that images are obtained while the pulmonary arterial system contains a high concentration of contrast. Accurate timing is important. If images are obtained too early or too late, the pulmonary arteries may not be adequately opacified, reducing diagnostic quality.

Appearance of Normal Pulmonary Arteries

On a properly performed CT pulmonary angiogram, contrast-filled pulmonary arteries appear bright. The main pulmonary artery and its branches can be followed outward into progressively smaller vessels. The contrast column should generally be smooth and uninterrupted.

Radiologists evaluate the vessels in multiple planes and may use reconstructed images to examine complex areas of the pulmonary circulation. Normal pulmonary arteries should not contain dark intravascular defects interrupting the contrast column.

Appearance of Pulmonary Embolism on CTA

A pulmonary embolus commonly appears as a filling defect within a contrast-enhanced pulmonary artery. The contrast within the artery appears bright, while the thrombus appears relatively dark. The appearance depends on the position of the embolus.

A clot may appear centrally within the vessel, surrounded by contrast, or it may partially contact the arterial wall.

An embolus that completely obstructs an artery may create abrupt termination of contrast filling beyond the obstruction. These findings allow clinicians to determine both the location and extent of embolic disease.

Saddle Pulmonary Embolus

A saddle embolus is a large pulmonary embolus located near the bifurcation of the main pulmonary artery. The clot may extend into both the right and left pulmonary arteries. Because of its location, a saddle embolus may obstruct a large portion of the pulmonary circulation.

However, the anatomical size of a clot does not always directly predict the patient’s hemodynamic status. Clinical severity depends on several factors, including the degree of vascular obstruction, right ventricular function, and underlying cardiopulmonary disease.

CTA can clearly demonstrate a saddle embolus and help define the extent of pulmonary arterial involvement.

Pulmonary Infarction

Pulmonary embolism can sometimes lead to pulmonary infarction. Pulmonary infarction occurs when obstruction of pulmonary blood flow causes ischemic injury and tissue death within part of the lung.

Because the lungs receive blood from both the pulmonary and bronchial circulations, pulmonary infarction does not occur with every embolus.

When infarction develops, CT imaging may show a peripheral wedge-shaped opacity.

The base of the wedge is often located near the pleural surface, while the apex points toward the obstructed vessel. Pulmonary infarction may be associated with pleuritic chest pain and hemoptysis.

Image Slice Thickness

CT scanners create images in thin sections or slices. Chest CT images may be reconstructed using slice thicknesses of approximately 1 to 5 mm, depending on the purpose of the study.

Pulmonary embolism studies frequently use very thin slices, sometimes around 1 mm. Thin slices improve spatial resolution, allowing structures located close together to be distinguished more clearly. This is especially useful when evaluating smaller segmental and subsegmental pulmonary arteries.

The disadvantage is that thinner slices create substantially more images. A pulmonary embolism study using very thin sections may generate hundreds or even around 1,000 images that must be interpreted. Thin images may also have more image noise.

Multiplanar Reconstruction

CT data can be reconstructed into different imaging planes.

Traditional axial images display the chest in horizontal sections, but reconstructed images may also be produced in:

• Coronal planes
• Sagittal planes
• Oblique planes

Multiplanar reconstruction can help radiologists follow pulmonary arteries along their natural course. For example, a coronal reconstruction may make it easier to see thrombus extending through upper- and lower-lobe pulmonary arterial branches.

These reconstructions do not necessarily require another scan. They are created from the original CT data.

Diagnostic Accuracy of CT Pulmonary Angiography

CTPA has high diagnostic accuracy for pulmonary embolism, although performance varies depending on several factors. Reported sensitivity has ranged widely, while specificity is generally high.

Factors that affect diagnostic performance include:

• CT scanner technology
• Image resolution
• Contrast timing
• Patient movement
• Respiratory motion
• Body size
• Size and location of the embolus
• Experience of the interpreting radiologist

Note: CTPA performs particularly well for emboli located in the main and lobar pulmonary arteries. Smaller peripheral emboli can be more difficult to detect, although modern multidetector CT systems have significantly improved visualization of smaller vessels.

PIOPED II and CT Pulmonary Angiography

The Prospective Investigation of Pulmonary Embolism Diagnosis II, commonly called PIOPED II, evaluated multidetector CT angiography in patients with suspected acute pulmonary embolism.

After inconclusive examinations were excluded, CT angiography demonstrated a sensitivity of approximately 83% and a specificity of approximately 96%. When venous-phase imaging was included, sensitivity increased.

One of the important findings from the study was that imaging results should be interpreted in relation to the patient’s clinical probability of pulmonary embolism. A CTA result that agrees with the clinical assessment has greater diagnostic value than a result that strongly conflicts with the patient’s clinical presentation.

Clinical Probability and Imaging

Imaging should not be interpreted in isolation. Before CTA is obtained, clinicians often estimate the likelihood that the patient has pulmonary embolism. Clinical prediction tools such as the Wells criteria may be used to classify patients according to their probability of disease.

Factors considered may include:

• Signs of deep vein thrombosis
• Tachycardia
• Previous venous thromboembolism
• Recent surgery or immobilization
• Hemoptysis
• Malignancy
• Whether pulmonary embolism is considered more likely than another diagnosis

Note: The results of this clinical assessment help determine which diagnostic tests are appropriate.

Role of D-Dimer Testing

D-dimer testing may be used in patients who are considered unlikely to have pulmonary embolism. D-dimer is a breakdown product produced when cross-linked fibrin is degraded.

Elevated D-dimer levels can occur when significant clot formation and breakdown are present. However, D-dimer is not specific for pulmonary embolism. Levels may also increase in many other conditions.

A normal D-dimer in an appropriately selected low-risk patient may help exclude pulmonary embolism without the need for CT imaging. An elevated result does not confirm pulmonary embolism but may lead to further testing, including CTPA.

Advantages of CT Pulmonary Angiography

CTPA offers several important advantages. First, the procedure is noninvasive compared with conventional pulmonary angiography. Although intravenous access is required, a catheter does not need to be advanced directly into the pulmonary arteries.

Second, scanning is rapid. This is particularly valuable when evaluating patients with acute shortness of breath or chest pain.

Third, modern CT scanners are widely available in many hospitals. Fourth, CTPA directly visualizes pulmonary arterial obstruction. Finally, CT imaging can reveal alternative explanations for a patient’s symptoms.

For example, CTA may identify:

• Pneumonia
• Pneumothorax
• Pleural effusion
• Pulmonary mass
• Atelectasis
• Aortic abnormalities
• Other thoracic pathology

Note: This ability to identify alternative diagnoses is particularly valuable because pulmonary embolism may present with nonspecific symptoms.

Limitations of CT Pulmonary Angiography

CTPA also has limitations. Iodinated contrast must be administered intravenously, which may present problems in certain patients.

Potential concerns include:

• Contrast hypersensitivity
• Renal dysfunction
• Inadequate vascular access
• Poor contrast timing
• Motion artifacts
• Inability to cooperate with breath-holding
• Radiation exposure

Note: A technically inadequate examination may fail to clearly visualize the pulmonary arteries. If the test is nondiagnostic and clinical suspicion remains high, additional testing may be necessary.

Iodinated Contrast

Iodinated contrast is essential for conventional CT pulmonary angiography because it allows blood vessels to be distinguished from surrounding tissue. Before administering contrast, clinicians should consider whether the patient has a history of significant contrast reactions.

Severe hypersensitivity reactions can occur, although they are uncommon. Renal function is also an important consideration because iodinated contrast may contribute to kidney injury in susceptible patients. The risks and benefits of contrast administration should therefore be considered in relation to the clinical need for the examination.

Radiation Exposure

CT pulmonary angiography exposes the patient to ionizing radiation. Radiation dose varies according to scanner type, imaging protocol, patient size, and other technical factors.

For comparison, a standard chest CT may deliver an effective radiation dose in the range of several millisieverts, while a routine chest radiograph delivers far less radiation. The diagnostic value of CTPA must therefore be considered together with the patient’s overall clinical situation. Unnecessary repeat imaging should be avoided when possible.

Ventilation-Perfusion Scanning

Ventilation-perfusion scanning is another important imaging method used to evaluate pulmonary embolism. A V/Q scan assesses ventilation and pulmonary blood flow rather than directly visualizing thrombus within the pulmonary arteries.

During the ventilation portion, the patient inhales a radiolabeled gas or aerosol. During the perfusion portion, radiolabeled particles are injected intravenously and travel through the pulmonary circulation. The distribution of ventilation and perfusion is then compared.

Ventilation-Perfusion Mismatch

Pulmonary embolism decreases or eliminates blood flow to affected lung regions while ventilation may remain relatively preserved. This creates a ventilation-perfusion mismatch.

A region of lung that receives ventilation but has reduced perfusion may raise suspicion for pulmonary embolism. Multiple segmental perfusion defects without matching ventilation abnormalities increase the probability of pulmonary embolism. However, V/Q scan findings must be interpreted with the clinical presentation and other available information.

When V/Q Scanning May Be Used

V/Q scanning is often considered when CTA cannot be performed. Examples may include patients with:

• Significant iodinated contrast allergy
• Severe renal dysfunction
• Other contraindications to iodinated contrast

A normal or very low probability V/Q scan in a patient with low clinical probability may effectively exclude clinically significant pulmonary embolism. Intermediate or indeterminate findings may require additional testing.

Single-photon emission computed tomography may also improve the ability of nuclear medicine imaging to identify perfusion abnormalities.

Conventional Pulmonary Angiography

Conventional pulmonary angiography was historically considered the definitive imaging examination for pulmonary embolism.

It is now used much less frequently because CTPA provides high-quality pulmonary vascular imaging without requiring catheterization of the pulmonary arteries. Conventional pulmonary angiography remains valuable when noninvasive testing does not provide a definitive diagnosis.

How Conventional Pulmonary Angiography Is Performed

Conventional pulmonary angiography requires vascular catheterization. A catheter is introduced through a vascular access site and advanced through the venous circulation toward the right side of the heart and pulmonary arteries.

Contrast material is then injected directly into the pulmonary arterial circulation. Rapid X-ray imaging records the movement of contrast through the pulmonary vessels. This produces an angiogram showing the pulmonary arterial tree.

Because contrast is injected directly into the pulmonary arteries, the procedure can provide detailed visualization of vascular abnormalities.

Angiographic Findings of Pulmonary Embolism

Pulmonary emboli on conventional angiography may appear as:

• Intraluminal filling defects
• Abrupt vessel cutoffs
• Failure of distal vessels to fill normally
• Abnormal contrast flow around an obstruction

Note: A normal pulmonary artery should fill uniformly with contrast. When thrombus occupies part of the vessel lumen, the contrast flows around the clot, producing a visible filling defect. Complete obstruction may cause contrast flow to stop suddenly at the point of occlusion.

Risks of Conventional Pulmonary Angiography

Conventional pulmonary angiography is invasive and carries greater procedural risk than CTPA.

Potential complications include:

• Bleeding from the vascular access site
• Hematoma formation
• Contrast reactions
• Vascular injury
• Cardiac arrhythmias
• Hemodynamic instability
• Kidney injury related to contrast

Note: Because a catheter must pass through the cardiovascular system, careful patient monitoring is required. The procedure may be inappropriate in certain patients with severe bleeding abnormalities, severe uncontrolled hypertension, or shock, depending on the clinical circumstances.

Post-Procedure Monitoring

After catheter-based angiography, the vascular access site should be monitored for bleeding. The patient may be required to remain in bed for a period of time, particularly if a femoral vascular approach was used.

Monitoring may include assessment of:

• Blood pressure
• Heart rate
• Oxygen saturation
• Distal circulation
• Access-site bleeding
• Hematoma formation
• Pain
• Signs of contrast reaction

Note: Clinical teams should also monitor renal function when appropriate.

Other Pulmonary Arterial Abnormalities

Pulmonary angiography is not limited to pulmonary embolism. It may also help identify several other abnormalities affecting the pulmonary arterial circulation.

Pulmonary Artery Stenosis

Pulmonary artery stenosis refers to abnormal narrowing of part of the pulmonary arterial system. The narrowing may reduce blood flow to the affected region of the lung. Angiography can help determine the location and severity of the stenosis.

Pulmonary Artery Aneurysm

A pulmonary artery aneurysm is an abnormal dilation of a pulmonary artery. Angiographic imaging can demonstrate enlargement of the vessel and help define the surrounding vascular anatomy.

Pulmonary Arteriovenous Malformations

A pulmonary arteriovenous malformation is an abnormal direct connection between pulmonary arteries and veins. These abnormal vessels allow blood to bypass the normal pulmonary capillary bed.

Angiography can be used to define the feeding arteries and draining veins associated with the malformation. This information may be important when planning catheter-based treatment.

Chronic Thromboembolic Disease

Pulmonary vascular imaging is also important in patients with chronic thromboembolic pulmonary hypertension. In this disorder, organized thrombotic material remains within the pulmonary arteries and causes persistent obstruction. Over time, pulmonary vascular resistance increases and pulmonary hypertension may develop.

Evaluation may involve:

• Ventilation-perfusion scanning
• CT pulmonary angiography
• Conventional pulmonary angiography
• Right-heart catheterization
• Echocardiography
• Pulmonary function testing

Note: A normal V/Q scan makes chronic thromboembolic pulmonary hypertension much less likely. Angiographic imaging may be used to define the location and extent of chronic vascular obstruction.

Pulmonary Hypertension Evaluation

Pulmonary angiography may also contribute to the evaluation of pulmonary hypertension. Pulmonary hypertension has many possible causes, including left-sided heart disease, chronic lung disease, chronic thromboembolic disease, and pulmonary arterial hypertension.

Pulmonary vascular imaging helps determine whether chronic thromboembolic obstruction is contributing to elevated pulmonary artery pressure. When thromboembolic disease is excluded, clinicians may focus on other potential causes.

Right-heart catheterization may then be used to directly measure pulmonary arterial pressures and other hemodynamic variables.

CTA vs. Conventional Pulmonary Angiography

CTA and conventional pulmonary angiography both visualize the pulmonary arteries, but they differ significantly in how they are performed. CTPA uses intravenous contrast and CT imaging. It is relatively rapid, noninvasive, and capable of evaluating the entire chest.

Conventional angiography requires catheterization of the pulmonary arterial circulation and direct contrast injection. Because of the greater invasiveness of catheter angiography, CTPA is generally preferred for initial evaluation.

Conventional angiography is typically reserved for selected situations in which other tests are nondiagnostic or when detailed vascular information is required.

CTA vs. V/Q Scanning

CTPA directly shows thrombus within the pulmonary arteries. V/Q scanning evaluates the physiological consequences of pulmonary arterial obstruction by comparing ventilation and perfusion. Both tests can contribute to pulmonary embolism diagnosis, but they are useful in different circumstances.

CTPA is commonly selected when iodinated contrast can be safely administered and a high-quality CT examination can be obtained. V/Q scanning may be preferred when contrast administration is undesirable or contraindicated.

Note: The choice of study depends on patient factors, clinical probability, available resources, and previous testing.

Relationship to Other Thoracic Imaging

Pulmonary angiography is one component of thoracic imaging. Standard chest CT provides detailed anatomical information about the lungs, pleura, mediastinum, chest wall, and other thoracic structures.

MRI can evaluate selected cardiovascular structures without ionizing radiation, although it has technical limitations and may not be appropriate for every patient. Thoracic ultrasound is useful for detecting pleural fluid and pneumothorax and for guiding procedures such as thoracentesis.

Nuclear medicine techniques provide functional information about pulmonary ventilation and perfusion. Each technique answers a different clinical question. Pulmonary angiography is selected when detailed evaluation of the pulmonary vascular system is required.

Role of the Respiratory Therapist

Respiratory therapists may encounter patients undergoing evaluation for pulmonary embolism in emergency departments, intensive care units, and other acute-care settings. The respiratory therapist should recognize clinical findings that may indicate significant pulmonary vascular obstruction.

Important findings may include sudden hypoxemia, unexplained tachypnea, pleuritic chest pain, increased oxygen requirements, and acute respiratory distress. Respiratory therapists may also be involved in oxygen therapy and monitoring before and after imaging.

A patient with severe pulmonary embolism may require advanced respiratory support if gas exchange or hemodynamic stability deteriorates. However, respiratory treatment does not replace definitive evaluation and treatment of the vascular obstruction.

Key Takeaways

• Pulmonary angiography is primarily used to visualize the pulmonary arteries.
• CT pulmonary angiography has become the main imaging test for suspected acute pulmonary embolism.
• Pulmonary emboli usually appear as dark filling defects within contrast-enhanced pulmonary arteries.
• CTA can also reveal alternative causes of cardiopulmonary symptoms.
• Clinical probability should be considered together with imaging results.
• V/Q scanning remains useful when CT angiography cannot be performed or produces inconclusive results.
• Conventional pulmonary angiography is invasive and is generally reserved for selected cases.
• Iodinated contrast reactions, renal function, radiation exposure, and vascular access should be considered when angiographic studies are planned.

Pulmonary Angiography Practice Questions

1. What is pulmonary angiography?
Pulmonary angiography is an imaging technique used to visualize the pulmonary arteries after contrast material is introduced into the vascular system.

2. What is the most common reason for performing pulmonary angiographic imaging?
The most common reason is to evaluate a patient for pulmonary embolism.

3. What does a pulmonary embolus typically look like on CT pulmonary angiography?
A pulmonary embolus typically appears as a dark filling defect within a bright, contrast-enhanced pulmonary artery.

4. Where do most thrombi that cause pulmonary embolism originate?
Most originate in the deep veins of the lower extremities or pelvis.

5. What imaging test is generally considered the primary imaging modality for suspected pulmonary embolism?
CT pulmonary angiography (CTPA) is generally the primary imaging modality for suspected pulmonary embolism.

6. Why has CT pulmonary angiography largely replaced conventional pulmonary angiography for the initial evaluation of pulmonary embolism?
CT pulmonary angiography is noninvasive, rapidly performed, widely available, and highly accurate for evaluating the pulmonary arteries.

7. Why is a large-bore intravenous catheter commonly used during CT pulmonary angiography?
A large-bore intravenous catheter allows contrast material to be injected rapidly enough to adequately opacify the pulmonary arteries.

8. Where is a peripheral intravenous catheter commonly placed for CT pulmonary angiography?
It is commonly placed in an antecubital vein.

9. Why is contrast timing important during CT pulmonary angiography?
The CT images must be obtained while a high concentration of contrast is present within the pulmonary arteries for the vessels to be adequately visualized.

10. What is a filling defect on pulmonary angiography?
A filling defect is an area within a contrast-filled pulmonary artery where contrast is displaced or interrupted by material such as a thrombus.

11. What angiographic finding may indicate complete obstruction of a pulmonary artery?
An abrupt cutoff or termination of contrast within the artery may indicate complete obstruction.

12. What is a saddle pulmonary embolus?
A saddle pulmonary embolus is a large embolus located near the bifurcation of the main pulmonary artery that may extend into both the right and left pulmonary arteries.

13. What pulmonary finding may develop when an embolus causes ischemic injury to lung tissue?
Pulmonary infarction may develop.

14. How may pulmonary infarction appear on CT imaging?
It may appear as a peripheral, wedge-shaped opacity with its base near the pleural surface.

15. Why are thin CT slices useful when evaluating the pulmonary arteries?
Thin slices improve spatial resolution and help visualize smaller segmental and subsegmental pulmonary arteries.

16. What is one disadvantage of using very thin CT slices during a pulmonary embolism study?
Very thin slices increase the number of images that must be interpreted and may also increase image noise.

17. What is multiplanar reconstruction in CT pulmonary angiography?
Multiplanar reconstruction uses CT data to create images in different planes, such as coronal, sagittal, or oblique views.

18. Why can multiplanar reconstruction be useful when evaluating pulmonary embolism?
It can make it easier to follow pulmonary arteries along their course and visualize thrombi extending through multiple arterial branches.

19. For which pulmonary arterial locations is CT pulmonary angiography particularly effective at detecting emboli?
It is particularly effective for emboli involving the main and lobar pulmonary arteries.

20. What factors can reduce the diagnostic quality of CT pulmonary angiography?
Poor contrast timing, patient movement, respiratory motion, inadequate vascular access, image noise, and small distal emboli can reduce diagnostic quality.

21. Why should clinical probability be considered along with CT pulmonary angiography findings?
The diagnostic value of the imaging result is stronger when it agrees with the patient’s estimated clinical probability of pulmonary embolism.

22. What clinical prediction tool may be used to estimate the probability of pulmonary embolism?
The Wells criteria may be used to estimate the clinical probability of pulmonary embolism.

23. What laboratory test may help exclude pulmonary embolism in an appropriately selected patient with a low clinical probability?
A D-dimer test may help exclude pulmonary embolism when the result is normal in an appropriately selected low-risk patient.

24. Does an elevated D-dimer level confirm pulmonary embolism?
No. An elevated D-dimer is nonspecific and may occur in many conditions, so additional testing may be required.

25. What is an important advantage of CT pulmonary angiography besides detecting pulmonary embolism?
It can identify alternative thoracic abnormalities that may explain the patient’s symptoms, such as pneumonia, pneumothorax, pleural effusion, or other chest pathology.

26. What is ventilation-perfusion scanning used to evaluate in a patient with suspected pulmonary embolism?
It evaluates the relationship between ventilation and pulmonary blood flow to identify regions where perfusion is reduced despite preserved ventilation.

27. What type of V/Q abnormality may suggest pulmonary embolism?
A ventilation-perfusion mismatch in which ventilation is preserved but perfusion is reduced or absent may suggest pulmonary embolism.

28. When is V/Q scanning commonly considered instead of CT pulmonary angiography?
It is commonly considered when CTA is contraindicated, such as in patients with significant iodinated contrast allergy or severe renal dysfunction.

29. What does the ventilation portion of a V/Q scan assess?
It assesses the distribution of inhaled radiolabeled gas or aerosol throughout the lungs.

30. What does the perfusion portion of a V/Q scan assess?
It evaluates the distribution of pulmonary blood flow after intravenous administration of radiolabeled particles.

31. What does a normal or low-probability V/Q scan suggest in a patient with low clinical probability for pulmonary embolism?
It can help exclude a clinically significant pulmonary embolism.

32. Why can an intermediate-probability V/Q scan be problematic?
It may not reliably confirm or exclude pulmonary embolism, so additional diagnostic testing may be needed.

33. What nuclear medicine technique may improve the sensitivity of V/Q imaging?
Single-photon emission computed tomography, or SPECT, may improve sensitivity and visualization of perfusion abnormalities.

34. When is conventional pulmonary angiography generally used today?
It is generally reserved for cases in which noninvasive imaging does not provide a definitive diagnosis.

35. How is contrast delivered during conventional pulmonary angiography?
Contrast is injected directly into the pulmonary arteries through a vascular catheter.

36. What imaging method is used during conventional pulmonary angiography?
Rapid X-ray imaging is used to visualize contrast flowing through the pulmonary arterial system.

37. What is one angiographic sign of an acute pulmonary embolus on conventional pulmonary angiography?
An intraluminal filling defect is one common sign.

38. What other angiographic sign may indicate pulmonary arterial obstruction?
An abrupt cutoff of a pulmonary artery may indicate obstruction.

39. Why is conventional pulmonary angiography considered invasive?
It requires vascular access and advancement of a catheter through the circulation into the pulmonary arterial system.

40. What vascular complication may occur after conventional pulmonary angiography?
Bleeding or hematoma formation may occur at the vascular access site.

41. Why should the access site be monitored after catheter-based pulmonary angiography?
Monitoring helps detect post-procedure bleeding, hematoma formation, or other vascular complications.

42. What hemodynamic complication may occur during invasive pulmonary angiography?
Hemodynamic instability may occur, particularly in critically ill patients.

43. Why can cardiac rhythm monitoring be important during conventional pulmonary angiography?
Catheter advancement through the cardiovascular system can provoke cardiac arrhythmias.

44. What pulmonary vascular abnormality besides pulmonary embolism may be detected with angiography?
Pulmonary artery stenosis may be detected.

45. What is pulmonary artery stenosis?
Pulmonary artery stenosis is an abnormal narrowing of a pulmonary artery or one of its branches.

46. What is a pulmonary artery aneurysm?
A pulmonary artery aneurysm is an abnormal dilation or enlargement of a pulmonary artery.

47. What is a pulmonary arteriovenous malformation?
It is an abnormal direct connection between pulmonary arteries and veins that allows blood to bypass the normal pulmonary capillary bed.

48. How can pulmonary angiography assist in evaluating an arteriovenous malformation?
It can define the feeding arteries and draining veins associated with the abnormal vascular connection.

49. What chronic pulmonary vascular condition may be evaluated with angiographic imaging?
Chronic thromboembolic pulmonary hypertension may be evaluated with angiographic imaging.

50. Why is pulmonary vascular imaging important in chronic thromboembolic pulmonary hypertension?
It helps identify persistent organized thrombotic obstruction within the pulmonary arteries and defines the location and extent of the disease.

51. What is chronic thromboembolic pulmonary hypertension?
Chronic thromboembolic pulmonary hypertension is a form of pulmonary hypertension caused by persistent organized thrombotic obstruction within the pulmonary arteries.

52. What imaging study can help exclude chronic thromboembolic disease when the result is normal?
A normal ventilation-perfusion scan can help exclude chronic thromboembolic disease.

53. What invasive test may be used to measure pulmonary artery pressures during the evaluation of pulmonary hypertension?
Right-heart catheterization may be used to directly measure pulmonary artery pressures.

54. Why is CT pulmonary angiography useful beyond the pulmonary arteries themselves?
It can also evaluate surrounding thoracic structures, including the lungs, pleura, mediastinum, and chest wall.

55. What contrast agent is commonly used for CT pulmonary angiography?
An iodinated contrast agent is commonly used.

56. Why should a history of contrast hypersensitivity be reviewed before CT pulmonary angiography?
Patients with prior significant reactions may be at increased risk for another hypersensitivity reaction to iodinated contrast.

57. Why is renal function considered before administration of iodinated contrast?
Iodinated contrast can contribute to kidney injury in susceptible patients.

58. What type of radiation is used during CT pulmonary angiography?
CT pulmonary angiography uses ionizing radiation.

59. Why should unnecessary repeat CT pulmonary angiography be avoided?
Repeated studies increase cumulative radiation exposure and may also require additional contrast administration.

60. What is one reason CT pulmonary angiography may be nondiagnostic?
Inadequate opacification of the pulmonary arteries can make the examination nondiagnostic.

61. How can patient movement affect CT pulmonary angiography?
Movement can create artifacts that reduce image clarity and make the pulmonary arteries more difficult to evaluate.

62. Why can respiratory motion interfere with CT pulmonary angiography?
Respiratory motion can blur pulmonary vascular structures and reduce the ability to identify small emboli.

63. What may be considered if CT pulmonary angiography is inconclusive and clinical suspicion for pulmonary embolism remains high?
Additional testing, such as V/Q scanning or conventional pulmonary angiography, may be considered.

64. What does specificity describe when evaluating the accuracy of CT pulmonary angiography?
Specificity describes the ability of the test to correctly identify patients who do not have pulmonary embolism.

65. What does sensitivity describe when evaluating CT pulmonary angiography?
Sensitivity describes the ability of the test to correctly identify patients who do have pulmonary embolism.

66. What sensitivity was reported for CT angiography in the PIOPED II study after inconclusive examinations were excluded?
The reported sensitivity was approximately 83%.

67. What specificity was reported for CT angiography in the PIOPED II study?
The reported specificity was approximately 96%.

68. What happened to sensitivity when CT angiography was combined with venous-phase imaging in the PIOPED II study?
Sensitivity increased to approximately 90%.

69. Why can the same CT pulmonary angiography result have different clinical significance in different patients?
Its significance depends partly on the patient’s pretest clinical probability of pulmonary embolism.

70. What does a discordant relationship between clinical probability and CTA findings mean?
It means the imaging result does not fit well with the expected likelihood of pulmonary embolism based on the clinical assessment.

71. What may be necessary when CT pulmonary angiography findings and clinical probability strongly disagree?
Additional diagnostic evaluation may be necessary.

72. Why is pulmonary embolism considered a perfusion problem?
It obstructs pulmonary arterial blood flow and reduces perfusion to affected regions of the lung.

73. How can pulmonary embolism affect pulmonary vascular resistance?
Obstruction of pulmonary arteries can increase pulmonary vascular resistance.

74. What effect can a large pulmonary embolism have on the right ventricle?
It can increase right ventricular workload and may contribute to right ventricular strain or failure.

75. How can a severe pulmonary embolism affect cardiac output?
A severe embolism can reduce cardiac output by significantly obstructing pulmonary blood flow and impairing right ventricular function.

76. Why can pulmonary embolism cause hypoxemia?
Pulmonary embolism can cause hypoxemia by creating areas of the lung that are ventilated but poorly perfused, resulting in ventilation-perfusion mismatch.

77. What symptom is commonly associated with pulmonary infarction caused by pulmonary embolism?
Pleuritic chest pain is commonly associated with pulmonary infarction.

78. What respiratory symptom may occur when pulmonary infarction causes bleeding into lung tissue?
Hemoptysis may occur.

79. Why can pulmonary embolism be difficult to diagnose based on symptoms alone?
Its symptoms are nonspecific and may resemble conditions such as pneumonia, myocardial infarction, pneumothorax, or heart failure.

80. What is the main pulmonary artery?
The main pulmonary artery is the large vessel that carries deoxygenated blood from the right ventricle toward the lungs.

81. Into which two major vessels does the main pulmonary artery divide?
It divides into the right and left pulmonary arteries.

82. What vessels come after the lobar pulmonary arteries?
The lobar pulmonary arteries divide into segmental pulmonary arteries.

83. Why may subsegmental pulmonary emboli be more difficult to detect?
They occur in smaller peripheral vessels that are harder to visualize than the main or lobar pulmonary arteries.

84. How has modern multidetector CT improved pulmonary embolism detection?
It has improved spatial resolution and visualization of smaller peripheral pulmonary arteries.

85. What does pulmonary arterial opacification mean during CT pulmonary angiography?
It refers to the pulmonary arteries becoming clearly visible because they are filled with contrast material.

86. What can happen if CT images are obtained before adequate contrast reaches the pulmonary arteries?
The arteries may be poorly opacified, making pulmonary emboli more difficult to detect.

87. What can happen if CT images are obtained too late after contrast injection?
Contrast concentration in the pulmonary arteries may decrease, reducing image quality.

88. Why can an antecubital vein be useful for contrast administration during CTA?
It can accommodate a large-bore intravenous catheter and allows rapid delivery of contrast into the central circulation.

89. What does an uninterrupted contrast column suggest in a pulmonary artery?
It suggests that the vessel lumen is patent without an obvious intravascular filling defect.

90. What is meant by pulmonary artery patency?
Pulmonary artery patency means that the artery is open and allows blood to flow through it.

91. How does a partially occlusive embolus differ from a completely occlusive embolus on angiographic imaging?
A partially occlusive embolus allows some contrast to pass around the clot, while a completely occlusive embolus may stop distal contrast filling.

92. Why may coronal CT reconstructions be helpful in pulmonary angiography?
They can provide a longer view of pulmonary arterial branches and help show thrombus extending through multiple vessels.

93. What is one reason CTA is useful when the diagnosis is uncertain?
It can evaluate the pulmonary arteries while also revealing other thoracic abnormalities that could explain the patient’s symptoms.

94. What alternative diagnosis associated with infection may be identified on CTA when pulmonary embolism is absent?
Pneumonia may be identified.

95. What pleural emergency may be identified on CTA as an alternative cause of acute chest symptoms?
Pneumothorax may be identified.

96. What pleural abnormality involving excess fluid may be detected during CTA?
Pleural effusion may be detected.

97. Why is conventional pulmonary angiography used less often than in the past?
Modern noninvasive imaging, especially CT pulmonary angiography, can provide a definitive diagnosis in many patients without pulmonary arterial catheterization.

98. What is one reason severe bleeding abnormalities may be a concern before conventional pulmonary angiography?
Vascular puncture and catheterization can increase the risk of hemorrhage.

99. Why may severe uncontrolled hypertension increase the risk of conventional pulmonary angiography?
Marked hypertension can increase the risk of vascular complications during an invasive catheter-based procedure.

100. What is the overall purpose of combining clinical assessment with pulmonary vascular imaging?
The purpose is to determine whether pulmonary vascular obstruction is present while interpreting imaging findings in the context of the patient’s symptoms, risk factors, and pretest probability.

Final Thoughts

Pulmonary angiography provides direct information about the structure and patency of the pulmonary arterial circulation. CT pulmonary angiography is now the primary imaging method used for suspected pulmonary embolism because it is rapid, widely available, and capable of demonstrating both vascular obstruction and alternative thoracic abnormalities.

Ventilation-perfusion scanning remains useful when CTA is unsuitable, while conventional pulmonary angiography continues to have a role when noninvasive tests cannot provide a definitive answer.

Accurate interpretation depends on combining imaging findings with clinical probability, patient risk factors, and other diagnostic information to determine whether pulmonary vascular obstruction is present.