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
This is a prospective, observational cohort study of emergency department patients designed
to assess for radiographic changes suggestive of lung hemorrhage after thoracic ultrasound.
The investigators will only approach patients scheduled for CT scan as part of their routine
care in the emergency department for enrollment. Only patients > 18 years old. Patients who
are not english speaking will only be consented if there is a medical interpreter
immediately available who can be approached for informed consent.
Patients who have given informed consent will have a lung ultrasound performed by a study
physician immediately prior to CT scan - after the patient has been transported to the ED
radiology area but before the CT scan is performed. The lung ultrasound will be performed
using a low frequency probe (2-5 MHz). Of the four standard positions used in lung
ultrasonography (Zone 1, 4, 5, 8; see Image 1 below), study ultrasonography will be
performed on only two.
The two positions selected for use will be chosen immediately prior to ultrasound
performance by the performing physician using a simple binary random number generator for
each lung. This will ensure that one zone is subjected to ultrasound on each lung. A small
radio-opaque button will be placed overlying all four zones (i.e., those exposed and those
not exposed) in the standard position of the ultrasound footprint (ie where the ultrasound
was or would have been performed) and then the patient will undergo the CT scan according to
standard radiology department protocols.
The CT scan will then be reviewed for signs of alveolar hemorrhage in the lung tissue
immediately adjacent to the radio-opaque button. Radiologists will be blinded as to which
buttons abut zones exposed to ultrasound or not exposed. Any findings will be immediately
reported to the patient's care team and the patient and standard protocols for treatment and
observation will be followed.
The investigators have calculated the need to enroll 200 patients to observe a 7% range
above and below previously published numbers of incidental findings on chest CT scan.
- All patients greater than 18 years of age scheduled to receive chest tomography scans
for pulmonary embolus.