What are the modified PIOPED criteria for a high-probability scan?

Two or more large mismatched segmental defects or any combination of mismatched defects equivalent to two large segmental defects (all moderate and large defects may be added; therefore, two moderate defects equal one large).
Perfusion defect unaccompanied by a radiographic abnormality; if one is present, the perfusion defect must be substantially larger.