TABLE 1

Ventilation, Perfusion, and Radiographic Interpretive Criteria for Pulmonary Embolism

PIOPED	Modified PIOPED II	Perfusion-only modified PIOPED II	Perfusion-only PISAPED
High LR	High LR	PE present	PE present
>2 large mismatched (V:Q) segmental defects^*	≥2 large mismatched (V:Q) segmental defects^*	≥2 large mismatched (Q:CXR) segmental defects^*	≥1 wedge-shaped Q defects
Borderline high LR
2 large mismatched (V:Q) segmental defects^*
Intermediate LR	Nondiagnostic	Nondiagnostic	Nondiagnostic
2 moderate or 1 large mismatched (V:Q) defect^*Difficult to categorize as high or low	All other findings	All other findings	Cannot classify as PE-present or PE-absent
Borderline low LR
1 matched (V:Q) defect, CXR-negative
Low LR
Nonsegmental perfusion defects^†
Q defect substantially < CXR defect
Matched (V:Q) defects, CXR-negativeAny number of small Q defects^*
Normal	Very low LR	PE absent	PE absent
No Q defects^‖	Nonsegmental^†Q defect < CXR lesion1–3 small segmental^* defectsSolitary matched (V:Q:CXR) defect (≤1 segment) in mid or upper lungStripe sign^‡Solitary large pleural effusion^§≥2 matched (V:Q) defects, regionally normal CXR	Very low probabilityNonsegmental^†Q defect < CXR lesion1–3 small segmental^* defectsSolitary matched (Q:CXR) defect (≤1 segment) in mid or upper lungStripe sign^‡Solitary large pleural effusion^§	Non–wedge-shaped Q defectContour defect caused by enlarged heart, mediastinum, or diaphragmNear-normal QNormal Q
	Normal
	No Q defects

↵* Or equivalent where large segmental defect, >75% of segment, equals 1 segmental equivalent; moderate defect, 25%–75% of segment, equals 0.5 segmental equivalent; small defect, <25%, is not counted.
↵† For example, prominent hilum, cardiomegaly, elevated diaphragm, linear atelectasis, or costophrenic angle effusion with no other perfusion defect in either lung and no other radiographic lesion.
↵‡ Peripheral perfusion in a defect (best seen on tangential view).
↵§ Pleural effusion in at least one third of pleural cavity, with no other perfusion defect in either lung.
↵‖ Perfusion defects exactly match shape of CXR.
V:Q = ventilation–perfusion; CXR = chest radiograph; PE = pulmonary embolism; LR = likelihood ratio.