Background <p>Acute central pulmonary embolism (ACPE) is associated with poor prognosis and higher mortality rates, emphasizing the importance of early detection to improve patient outcomes. The symptoms of ACPE present with non-specificity, and unenhanced chest CT may be employed prior to CTPA for the diagnosis of pulmonary diseases such as pneumonia. In such scenarios, early identification of ACPE is of paramount importance.</p> Objectives <p>This study aimed to evaluate the diagnostic utility of unenhanced CT in ACPE involving thrombosis locted in the main pulmonary artery or the right or left pulmonary artery, as well as to develop a convenient and rapid tool for assessing the risk of ACPE on unenhanced CT.</p> Methods and materials <p>This retrospective study developed a diagnostic tool based on variables identified from unenhanced CT images acquired within 12&#xa0;h prior to computed tomography pulmonary angiography (CTPA) in 122 patients. A stepwise logistic regression approach was employed to construct the diagnostic modeland utilized to designed a nomogram suitable for clinical application. Subsequently, this Nomogram was validated in another cohort of 24 patients.</p> Results <p>Unenhanced CT model comprising abnormal density signs, main pulmonary artery and aorta ratio&gt;0.83 and Azygos vein were predictive indicators for ACPE in both the derivation (AUC 0.877; 95% CI 0.805 to 0.930) and validation cohorts (AUC 0.844; 95% CI 0.638 to 0.958) and superior to D-dimer (AUC 0.799; 95% CI 0.717 to 0.866).&#xa0;</p> Conclusion <p>Unenhanced CT is valuable for diagnosing ACPE, especially in patients with non-specificity symptoms.</p>