Table 4: PIOPED I Criteria in the assessment of PE [22].

Normal	Normal perfusion
Very low probability	One to three small^a perfusion defects; normal chest radiograph; ventilation irrelevant
Low probability	Non-segmental^b perfusion defects Single moderate^c & perfusion defect; chest radiograph normal; ventilation irrelevant Any perfusion defect substantially smaller than chest film defect; ventilation irrelevant Ventilation/perfusion match ≤50% of lung including ≤75% of 1 lung zone^d with normal or almost normal chest radiograph More than 3 small^a perfusion defects; chest film and ventilation irrelevant 3 or fewer small perfusion/chest film matches; ventilation irrelevant
Indeterminate or intermediate	Abnormality that is not defined clearly by other criteria
High probability	2 or more large^e & perfusion defects; ventilation and chest film normal 2 or more large^e & perfusion defects in which perfusion defect is substantially larger than either matching ventilation or chest film defect 2 or more moderate^c perfusion defects and one large perfusion defect; ventilation and chest film normal 4 or more moderate^c perfusion defects; ventilation and chest film normal

^aSmall is 25% or less of an anatomic segment.

^bNon-segmental means very small effusion, cardiomegaly, hila, etc.

^cModerate means >25% and <75% of a segment.

^dLung zone means upper, middle, or lower third of the lung.

^eLarge means >75% of a segment.