Certified Respiratory Therapist Practice Exam

Which imaging modality is least helpful in diagnosing a pulmonary embolism?

1. CT Angiography

2. V/Q Scanning

3. Transthoracic Ultrasound

4. AP Chest X-Ray

The correct answer is: AP Chest X-Ray

When diagnosing a pulmonary embolism (PE), certain imaging modalities are specifically better suited for this purpose. An AP (anteroposterior) chest X-ray is least helpful because it primarily evaluates the structural and functional aspects of the lungs and heart but does not provide direct visualization of blood vessels. While it can help to exclude other conditions or suggest the presence of problems, such as pleural effusions or lung opacities, it lacks the sensitivity and specificity necessary for detecting a PE. In contrast, CT angiography is the gold standard for diagnosing pulmonary embolisms due to its high sensitivity in visualizing the pulmonary arteries and detecting clots. V/Q (ventilation-perfusion) scanning is also a valuable tool, particularly in patients who may not be suitable for CT due to contraindications such as renal impairment or allergies to contrast agents. Transthoracic ultrasound can assess right heart strain or visualize thrombi in some cases, although it is not typically the first-line choice for diagnosing PE. In summary, while other modalities provide targeted and effective means for diagnosing a pulmonary embolism, the AP chest X-ray merely offers broad information that is insufficient for confirming the presence of a pulmonary embolism specifically.