Comparison of 133Xe single-breath and washout imaging in the scintigraphic diagnosis of pulmonary embolism.

To compare the utility of 133Xe single-breath (SB) and prolonged washout (WO) imaging in the scintigraphic diagnosis of pulmonary embolism, ventilation and perfusion studies of 66 patients who had pulmonary angiography within 48 hours were reviewed. The single-breath-perfusion (SB-P) and washout-perfusion (WO-P) studies agreed in 59 of 66 patients (89%). Each of the seven patients with disparate interpretations had an SB-P interpretation with a high probability for pulmonary embolism and a WO-p reading of low probability, with 133Xe retention in areas which appeared normal on the SB image. Single-breath images with 133Xe are not suitable as the sole determinant of ventilation-perfusion (V-P) match or mismatch, especially when subsegmental perfusion defects are present. Prolonged washout imaging improves the specificity of V-P imaging in patients with suspected pulmonary embolism.