The standard test to diagnose PE is the Pulmonary Computed Tomography Angiogram (CTA). This can be prohibitive with some patients due to the amount of radiation exposure as well as the complications associated with the need to use intravenous (IV) contrast. In patients not eligible for CTA, the other option for diagnosis is a ventilation-perfusion (V/Q) single photon emission computed tomography (SPECT) scan. Though this is often prohibitive due to transport to Nuclear Medicine dept., prolonged test time, no test during off hours, etc. In this study the investigators are looking at an alternative method of diagnosing PE's in the Emergency Department where the investigators look at the breathing and blood flow to the lungs thru respiratory gated non-contrast CT (commonly called 4DCT).