Retrospective study demonstrates a 125 Hounsfield unit threshold for acute pulmonary embolism on CT scans, indicating high density differentiates artifacts from clots.
Key Points
To determine the CT attenuation profile of acute pulmonary embolism and establish an upper Hounsfield unit threshold to reliably differentiate true thrombi from imaging artifacts.
Retrospective analysis of 60 patients (2018–2023) with acute pulmonary embolism who also had a negative CT pulmonary angiogram within the preceding 2 weeks.
Measured attenuation across 105 acute clots and 41 artifacts, evaluating technical predictors such as tube voltage and vessel density using ANOVA and linear regression.
Mean attenuation for acute pulmonary embolism was 50 ± 40 HU compared to 110 ± 146 HU for imaging artifacts.
A threshold of ≤125 HU achieved 97% sensitivity (102/105) for acute pulmonary embolism and 37% specificity (15/41), with values above 125 HU exhibiting 97% specificity for artifact.
Subsegmental clots demonstrated lower attenuation than larger clots, while tube voltage and proximal vessel attenuation were poor predictors of clot density.