**10. Pulmonary angiography**

**8. Computed tomography pulmonary angiography (CTPA)**

Jardin 2007) and IV contrast.

126 Pulmonary Hypertension

study 1990)

**9. Ventilation/perfusion scanning (V/Q scan)**

presence of PE in this group (Calvo-Romero 2005). (Table 3)

**V/Q Scan Probability Clinical Probability of Pulmonary Embolism**

High 96 88 56 Intermediate 66 28 16 Low 40 16 4 Normal or near normal 0 6 2

**Table 3.** Likelihood of pulmonary embolism according to scan category and clinical probability (based on PIOPED

**High Intermediate Low**

Over the last several decades, CTPA has become the first-line imaging modality for the assessment of PE. When compared with V/Q scanning in a randomized, single-blinded noninferiority clinical trial involving 1417 patients, CTPA was found to be non-inferior to V/Q scanning (Anderson 2007). CTPA is readily available and offers a high level of sensitivity and specificity for acute PE (Huisman 2013). PIOPED II found CTPA to be 83% sensitive and 96% specific for PE (Stein 2006). The newer generation multi-detector CTPA sensitivity is over 95% for segmental, lobar and centrally located PE (Huisman 2013) and is an extremely useful test to exclude PE (van Beek 2001). As with all other imaging modalities for pulmonary thromboembolism, CTPA should be used as part of an integrated approach in the evaluation of PE (Rathbun 2000, Van Strijen 2005) utilizing risk assessment tools to determine the appropriateness of proceeding to CTPA as this test does expose patients to radiation (Remy-

An alternative diagnostic study to CTPA is V/Q scanning. V/Q scanning involves imaging of pulmonary perfusion and ventilation to evaluate for areas of mismatch that suggest the presence of PE. The average radiation exposure for a V/Q scan is 1.2 mSv. PIOPED evaluated the accuracy of V/Q scanning in the assessment of pulmonary embolism compared with the gold standard pulmonary angiogram (PIOPED 1990). Patients with a high clinical probability of PE and a high probability V/Q had a 95% likelihood of truly having a PE. Patients with a low clinical probability of PE and a low probability VQ scan had a 4% likelihood of having a PE (Gottschalk 2007). A normal V/Q scan virtually excluded PE (PIOPED 1990). Unfortunately, in patients with other combinations of clinical risk and V/Q results, the diagnostic accuracy of V/Q ranged from 15-86%. Therefore, additional diagnostic testing is required to determine the Pulmonary angiography is an invasive test that requires catheter placement in the pulmonary artery and directed IV contrast infusion to detect intraluminal vascular filling defects that might be caused by PE. This test requires performance and interpretation expertise and carries a risk of intracardiac catheter placement, radiation, and contrast exposure. In 1992, Stein et al (Stein 1992) reported 0.5% mortality, 1% nonfatal complications and 5% minor complications associated with this test in the 1,111 patients who underwent angiography in PIOPED. In most centers, pulmonary angiography has been replaced by CTPA as the standard for the diagnosis of PE (Hogg 2006). Currently, pulmonary angiography is only employed when other less invasive attempts at diagnosis are inconclusive.
