Dual Energy CT Evaluation of the Severity of Pulmonary Thromboembolism: Correlation of Pulmonary Perfusion Score with CT

Pulmonary thromboembolism (PTE) is an important cause of morbidity and mortality in hospitalized patients and computed tomographic angiography (CTA) has become the gold standard diagnostic examination for suspected PTE. Dual energy computed tomography (DECT) not only detects thromboembolic filling defects but also provides functional perfusion information by generating iodine distribution maps.

The objective of the study is to determine the value of perfusion defect score (P score) in detection of the severity of acute pulmonary thromboembolism (PTE) and to correlate it with pulmonary obstruction score (Qanadli score), other CTA parameters and clinical findings.

Fifty five patients, with acute PTE who underwent DECT were reviewed. We calculated P score, Qanadli score, ratio of the right ventricle diameter to the left ventricle (RV/LV ratio) and the main pulmonary artery (PA) diameter by using the dual energy CTA images. The correlation between CTA parameters and clinical- echocardiographic data was investigated.

Correlation analysis showed a significant positive correlation between the P score and Qanadli score (r = 0.748, P < 0.001). There was also a significant positive correlation between P score and RV/LV ratio (r = 0.432 P = 0.001) and between Qanadli score and RV/LV ratio (r = 0.424 P = 0.001). Echocardiographic data was present in 39 patients (70.9 %). P score was significantly higher in patients with RV dilatation (P = 0.022) and RV dysfunction (P = 0.001) on echocardiography. Likewise, similar interaction was present in between Qanadli score and RV dilatation (P = 0.023) and RV dysfunction (P = 0.003). No correlation was present between P score and blood gas analysis [partial pressure of oxygen in arterial blood (PaO2) , partial pressure of arterial carbon dioxide ( PaCO2),(PaO2)/fraction of inspired oxygen (FiO2), oxygen saturation] and hemodynamic data (blood pressure, and pulse).

P score is seen as a good adjunctive tool to other CTA parameters and echocardiography in detection of PTE severity. Addition of perfusion changes to clinical risk assessment will help in the management of patients.