Detection of pulmonary embolism by D-Dimer assay, spiral computed tomography, and magnetic resonance imaging

Pulmonary embolism (PE) remains difficult to diagnose. Ventilation perfusion lung scan, the standard diagnostic test for PE, has poor overall sensitivity. The gold standard examination, pulmonary angiography, is invasive and has some risk, making clinicians reluctant to refer patients. In recent years, new diagnostic modalities have been investigated, including D- Dimer assays, spiral computed tomography (CT), and magnetic resonance imaging (MRI). The authors reviewed the literature and noted that the D-Dimer assays by ELISA or rapid ELISA design are approximately 90% to 95% sensitive, but are not specific for the diagnosis of pulmonary embolism. Spiral CT has been studied with conflicting results; however, in the largest studies the reported sensitivities are greater than approximately 85%. Electron beam CT is an alternative technique, which has not been as extensively studied. MRI is also useful for imaging the pulmonary arterial vasculature, but remains experimental. Although a more accurate assessment of the sensitivity of these new modalities will need to wait until a large angiographically controlled study, such as the planned PIOPED II, can be done, D-Dimer assay and spiral CT are often useful in the detection of pulmonary embolism. The authors make recommendations for their use in a diagnostic algorithm, as alternatives to the standard ventilation perfusion lung scan.