Diagnostic accuracy in quantitative evaluation of attenuation of pulmonary thrombus on noncontrast computed tomography scan

Abstract

Objectives: The objective is to assess the role of noncontrast computed tomography (NCCT) in the identification of pulmonary thromboembolism (PTE) using the difference in attenuation value between thrombus and blood pool and to establish its diagnostic accuracy. Methods: A single-center retrospective analysis was carried out for 1 year among the patients of all age groups who were referred for imaging workup with clinical suspicion of pulmonary embolism (PE). A standard protocol was followed for all the patients undergoing computed tomography pulmonary angiography (CTPA). The diagnosis of PE was based on the direct visualization of the intraluminal thrombus as complete/partial filling defect on CTPA. The average attenuation value of the thrombus on NCCT was measured retrospectively after referring to its position on the corresponding enhanced scans. The difference in attenuation of the pulmonary vessels with and without the thrombus was calculated on NCCT. The data was utilized in the generation of receiver operator characteristic curve to obtain the best cut off level for attenuation differences of the vessels and its accuracy in detecting PTE was determined. Results: Among the study population of 50 subjects, the mean age was found to be 42 years in our study with male sex (72%) having more preponderance to PTE than female sex (28%). The average blood pool range was between 20 and 60 Hounsfield unit (HU). The mean of differences in attenuation between thrombus and blood pool was 34.07 HU. The optimal cut off level for PE affection proved to be difference in attenuation of the pulmonary arteries of more than 20 HU. The sensitivity and specificity were 89.47% and 83.33%, respectively. Conclusion: In clinically suspected cases of PTE, CTPA is the most reliable diagnostic tool. However, with plain computed tomography itself, considering the difference in attenuation values, the thrombus can be identified in majority of the cases thereby reducing the exposure to radiation and contrast to the patients.

Keywords

• computed tomography pulmonary angiography
• pulmonary thromboembolism
• non contrast computed tomography scan