This is a Phase 3 within-subject trial of Technegas Ventilation SPECT and Tc-99m MAA perfusion imaging compared to xenon (Xe-133) Ventilation Planar and Tc-99m MAA perfusion imaging for the diagnosis of PE. Diagnosis of PE provided by review of the subjects' documented clinical information after 30 days of follow-up. Primary assessments of efficacy will be based on an independent blind reads of the Technegas V/Q SPECT images by three different readers and the independent blind reads of Xe 133 V/Q planar images by three different readers.