The Diagnosis of Pulmonary Embolism

Izzie Boxen, MD, FRCDC
JAMA. 1990;264(20):2623-2624. doi:10.1001/jama.1990.03450200031013.
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To the Editor.—  The PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) study,1 being a large, multicenter study, will undoubtedly have an effect on the use of lung ventilation/perfusion scans by many other physicians. However, the conclusions of the study are seriously flawed. All ventilation imaging was done only in posterior view and with xenon 133.Ventilation imaging is best done in the views that show perfusion defects. If aerosol is used, then the same six views as on perfusion imaging can be obtained. The drawback to this is the limitation of aerosol imaging to assessing only early or wash-in ventilation.Xenon 127 gives images with much better resolution than does xenon 133 and, unlike xenon 133, can be used after perfusion imaging without interference from technetium Tc 99m photons. Computer subtraction of the perfusion images is therefore not necessary, as it is if xenon 133 is used after technetium


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