Inclusion Criteria:

• Adults aged 18 years or older. For retrospective PE cases: patients with acute pulmonary embolism confirmed by CT pulmonary angiography, with completed pulsatile electrical impedance tomography examination, adequate image data, and available clinical information.

For retrospective healthy controls: adults without evidence of lower-extremity venous thrombosis, with normal D-dimer levels, simplified Wells score ≤1, and no pulmonary embolism-related symptoms or history.

For prospective PE patients: patients newly diagnosed with pulmonary embolism by CT pulmonary angiography or CT pulmonary angiography plus CT venography, with body mass index less than 50 kg/m², who voluntarily participate and provide written informed consent.

For prospective non-PE controls: patients with suspected acute pulmonary embolism who undergo CT pulmonary angiography or CT pulmonary angiography plus CT venography, but in whom pulmonary embolism is not confirmed, who voluntarily participate and provide written informed consent.

Exclusion Criteria:

• Previous diagnosis of chronic pulmonary embolism or idiopathic pulmonary arterial hypertension.

Acute exacerbation of chronic obstructive pulmonary disease, acute heart failure, acute myocardial infarction, or other severe cardiopulmonary diseases that may interfere with study assessment.

Pregnancy or lactation. Thoracic deformity. Contraindications to EIT examination, including automatic implantable cardioverter defibrillator, chest wounds limiting electrode belt placement, implanted pumps, or other conditions unsuitable for EIT electrode belt placement.

Participation in another clinical trial during the same period, for prospective participants.

Unstable vital signs requiring emergency rescue, leaving no time to complete EIT examination, for prospective participants.

Any other condition considered unsuitable for participation by the investigators.