What imaging modalities can be used to detect pulmonary emboli?

V/Q scan: Assesses for diminished pulmonary perfusion in the setting of preserved ventilation as a sign of PE. V/Q scanning is the best validated technique for detection of PE.
CTPA: Detects emboli within pulmonary arterial branches rather than detecting effects of emboli on perfusion. Also a well-validated technique for detection of PE.
MRPA: Used in patients who are not candidates for CTPA due to allergies to iodinated contrast agents. Like CTPA, it detects filling defects rather than perfusion defects.
Angiography: The gold standard for the diagnosis of PE, but its invasiveness and cost make it unsuitable as a screening test