To calculate the CTOI, the arterial tree of each lung was considered to have 10 segmental arteries (three in the upper lobes, two in the middle lobe and in the lingula, and five in the lower lobes). The presence of an embolus in a segmental artery was scored 1 point. Central or paracentral emboli were scored a value equal to the number of segmental arteries arising distally. Depending on the degree of vascular obstruction a weighting factor was assigned to each value (0, no thrombus; 1, partial occlusion; and 2, total occlusion). Isolated subsegmental embolus was considered as a partially occluded segmental artery and was assigned a value of 1. Thus, the CTOI could vary from 1 to 40 points per patient. Dividing the patient score by the maximal total score and multiplying the result by 100 calculated the percentage of vascular obstruction. Based on the percentage of vascular obstruction, patients were then divided into three groups (<15% versus 15–50% versus >50%).