Spiral computed tomography for acute pulmonary embolism

Pulmonary embolism (PE) is a common condition with considerable morbidity and mortality. Although previous imaging algorithms were widely employed, a definitive diagnosis was often not attained. The ability to directly visualize emboli using spiral computed tomography (CT) angiography has led to its widespread implementation. The recommended acquisition parameters for single row spiral CT scanners include 3 mm or narrower collimation, pitch 1.7-2.0, reconstruction spacing 2 mm or less, standard algorithm, and 60% contrast injected at 3-5 mL/s. Images must be reviewed on a workstation for optimal diagnostic accuracy. Preliminary studies indicate that multirow CT scanners offer improved accuracy for distal segmental and subsegmental PE. Published studies using optimal techniques have found sensitivity and specificity of approximately 90%, with a 20%-30% prevalence of PE. Previous imaging algorithms offered limited diagnostic value for the 70%-80% of patients without PE. It has been shown that spiral CT identifies an alternate diagnosis in approximately 70% of these patients with clinically significant chest symptoms but without PE. Additionally, a resource utilization study comparing the rate of confident diagnosis following a screening examination for acute PE showed a significantly (p < 0.05) increased rate of confident diagnosis using spiral CT compared with ventilation perfusion scintigraphy. Meta-analysis studies of the existing data regarding spiral CT in acute PE have shown deficiencies in study designs, indicating that further research is required. However, at this time, we believe that spiral CT is useful in those patients suspected of acute PE.