New CT index to quantify arterial obstruction in pulmonary embolism: Comparison with angiographic index and echocardiography

OBJECTIVE. This study was designed to define and evaluate a specific index to quantify arterial obstruction with helical CT in acute pulmonary embolis m. MATERIALS AND METHODS. Fifty-four patients (mean age, 56 years) with proven pulmonary emboli among 158 consecutive patients, who had undergone both CT and pulmonary angiography for clinically suspected pulmonary embolism, wer e eligible for the study. The CT obstruction index was defined as Sigma (n - d) (n, value of the proximal clot site, equal to the number of segmental branches arising distally; d, degree of obstruction scored as partial obstr uction [value of 1] or total obstruction [value of 2]). We compared the CT obstruction index with pulmonary arterial obstruction on angiography (asses sed by the Miller index), using linear regression, and correlated it with f indings on echocardiography. Interobserver variability was determined for b oth CT and pulmonary angiography indexes. RESULTS. The CT obstruction index (29% +/- 17%) and the Miller index (43% /- 25%) were well correlated (r = 0.867, p < 0.0001) with an excellent conc ordance between investigators for both the CT index (r = 0.944, p < 0.0001) and the Miller index (r = 0.904, p < 0.0001). A CT obstruction index great er than 40% identified more than 90% of patients with right ventricular dil atation. CONCLUSION. The degree of arterial obstruction in pulmonary embolism may be quantified by a specific CT index that appears reproducible and highly cor related to the previously described index with pulmonary angiography. Furth er evaluations are needed to investigate the usefulness of the CT obstructi on index for stratification of patient risk and determining therapeutic opt ions.