Electron beam computed tomography and ventilation perfusion scintigraphy in the diagnosis of pulmonary embolism

The purpose of this study, performed in patients with suspected pulmonary embolism (PE), was to compare V/Q scans and electron beam computed tomography (CT) scans on a patient-by-patient and segment-by-segment basis. Both a segment-based and a lobe-based analysis was performed in those patients positive for PE. The diagnosis of PE was assumed on the basis of a mismatch at V/Q scanning or a filling defect in a pulmonary vessel at contrast-enhanced electron beam CT. In 37/45 patients (24 female, 21 male, 58±16 years) with suspected PE, the diagnosis of PE was confirmed or excluded by both modalities, resulting in a correlation of 82% between electron beam CT and V/Q scanning. In the 28 patients positive for PE according to one or both modalities, 504 segments were evaluated. Of these 504 segments, 248 (nearly 50%) showed perfusion defects on V/Q scans, of which only 90 (36%) displayed emboli at electron beam CT. Overall, a total of only 135 of the 504 segments (27%) were abnormal at electron beam CT. More than 50% of the patients with discrepant results did not show an embolus at electron beam CT. It is concluded that there is a good correlation (82%) between V/Q scanning and electron beam CT on a patient-by-patient basis but a markedly less good correlation (62%) in a segment-based analysis.