Lung Ultrasound Safety in Humans

The purpose of this study is to investigate if diagnostic ultrasound as it is routinely performed in humans causes lung hemorrhage significant enough to appear on thoracic CT. The investigators' hypothesis is that diagnostic lung ultrasound will not cause lung hemorrhage in humans. Damage to the lung in animal models has been shown to be mechanical rather than thermal in nature and evidence suggests that this injury is likely not from inertial cavitation but from alveolar resonance. Models of the alveolar resonance theory predict that hemorrhage should not happen in adult human lungs if the ultrasound frequency is higher than 1.69 MHz and mechanical index (MI) is less than 1.9 which is maintained with standard scanning protocol for thoracic ultrasound. A previous human study showed no gross macroscopic lung hemorrhage in patients undergoing transesophageal echocardiography with pressures of 2.4 MPa and MI 1.3 with exposure durations ranging 7-68 minutes. The investigators propose to perform a routine lung ultrasound exam on patients who are scheduled to undergo chest computed tomography evaluation for pulmonary embolus as part of their routine care. The ultrasound will be performed immediately prior to CT imaging and markers will be placed on the patients chest to ensure the correct lung tissue is being evaluated. There will be two sham markers so the radiologist will be blinded to which tissue had ultrasound applied and which did not. The CT scan will then be evaluated per routine and also to see if there are signs of microscopic or macroscopic hemorrhage under the skin markers.