Pulmonary embolism is a common condition that often escapes diagnosis in life. The mortality attributable to pulmonary embolism depends on many factors but can be up to 30% in untreated patients, more than 10 times the annual mortality for patients treated with anticoagulant drugs (2.5%).1 Balanced against the danger of underdiagnosis are the risks of treatment with anticoagulants.2 Investigation is often haphazard and treatment empirical, reflecting the relative insensitivity and poor specificity of traditional non-invasive diagnostic tests such as ventilation/perfusion (V/Q) scintigraphy.3 In an attempt to improve diagnostic precision, many studies have recommended combinations of tests.4 5 6 Pulmonary arteriography is justly regarded as the final arbiter, but it is underused and is available in only a third of hospitals in the United Kingdom.7

Spiral computed tomography images the pulmonary vessels directly. It is non-invasive and increasingly available. During a scan, which is performed in a single breath hold, intravenous contrast medium is given, and …