Validation of an Automated Technique for Quantification of Pulmonary Perfusion Territories Using Computed Tomography Angiography.

Background: Computed tomography pulmonary angiography (CTPA) is the primary modality for the detection and diagnosis of pulmonary embolism (PE) while the stratification of PE severity remains challenging using angiography. Hence, an automated minimum-cost path (MCP) technique was validated to quantify the subtended lung tissue distal to emboli using CTPA. Methods: A Swan-Ganz catheter was placed in the pulmonary artery of seven swine (body weight: 42.6 +/- 9.6 kg) to produce different PE severities. A total of 33 embolic conditions were generated, where the PE location was adjusted under fluoroscopic guidance. Each PE was induced by balloon inflation followed by computed tomography (CT) pulmonary angiography and dynamic CT perfusion scans using a 320-slice CT scanner. Following image acquisition, the CTPA and the MCP technique were used to automatically assign the ischemic perfusion territory distal to the balloon. Dynamic CT perfusion was used as the reference standard (REF) where the low perfusion territory was designated as the ischemic territory. The accuracy of the MCP technique was then evaluated by quantitatively comparing the MCP-derived distal territories to the perfusion-derived reference distal territories by mass correspondence using linear regression, Bland-Altman analysis, and paired sample t-test. The spatial correspondence was also assessed. Results: The MCP-derived distal territory masses ( MassMCP, g) and the reference standard ischemic territory masses (MassREF, g) were related by MassMCP =1.02MassREF - 0.62 g (r=0.99, paired t-test P=0.51). The mean Dice similarity coefficient was 0.84 +/- 0.08. Conclusions: The MCP technique enables accurate assessment of lung tissue at risk distal to a PE using CTPA. This technique can potentially be used to quantify the fraction of lung tissue at risk distal to PE to further improve the risk stratification of PE.