Example of calculation of the Qanadli obstruction index from CTPA. Axial CT scan shows a proximal completely occlusive thrombus (long arrow) in the right main pulmonary artery, and partial thrombus in the left main pulmonary artery (short arrow). The Qanadli score index would therefore be [(10 x 2) + (10 x 1) = 30/40] = 75%.