The accuracy of the Hounsfield unit in pulmonary embolism diagnostics.

Objective: Pulmonary embolism (PE) is a vascular disease that is most frequently diagnosed using the radiological imaging technique computed tomography pulmonary angiography (CTPA). In this study, we aimed to demonstrate the diagnostic accuracy of the Hounsfield unit (HU) for PE based on the hypothesis that acute thrombosis causes an increase in HU value on CT.

Methods: This research was a single-center, retrospective study. Patients presenting to the emergency department diagnosed with PE on CTPA were enrolled as the study group. Patients admitted to the same emergency department who were not diagnosed with PE and had noncontrast CT scans were included as the control group. A receiver operating curve was produced to determine the diagnostic accuracy of HU values in predicting PE.

Results: The study population (n=74) consisted of a study group (n=46) and a control group (n=28). The sensitivity and specificity of the HU value for predicting PE on thoracic CT were as follows: for the right main pulmonary artery, 61.5% and 96.4% at a value of 54.8 (area under the curve [AUC], 0.690); for the left main pulmonary artery, 65.0% and 96.4% at a value of 55.9 (AUC, 0.736); for the right interlobar artery, 44.4% and 96.4% at a value of 62.7 (AUC, 0.615); and for the left interlobar artery, 60.0% and 92.9% at a value of 56.7 (AUC, 0.736).

Conclusion: HU may exhibit high diagnostic specificity on CT for thrombi up to the interlobar level. An HU value exceeding 54.8 up to the interlobar level may raise suspicion of the presence of PE.