Objective To optimize the virtual monoenergetic imaging (VMI) energy level for pulmonary computed tomography (CT) angiography (PCTA) based on image quality and thrombus visualization and evaluate its impact on the confidence of radiological technologists in detecting pulmonary embolism (PE).

Methods Patients who underwent PCTA because of clinical suspicion of PE at our hospital between February 2025 and March 2025 were prospectively screened. All examinations were performed using dual-source dual-energy CT, and the images were reconstructed into 120 kVp equivalent polyenergetic imaging (PEI) and VM images at energy levels of 70, 60, 50, and 40 keV. One radiological technologist conducted objective measurements to assess the ascending aorta, main pulmonary artery, left pulmonary artery branch, right pulmonary artery branch, right lower lobe pulmonary artery branch, left lower lobe pulmonary artery branch, liver parenchyma, and erector spinae muscle to obtain CT values (Hounsfield units HU) and their standard deviations (SD) to calculate the signal-to-noise ratio (SNR). The contrast-to-noise ratio (CNR) was calculated using the SD value of the erector spinae muscle as the background noise. Two radiological technologists evaluated the images of 23 patients with thrombi using a 5-point scale to assess their confidence in alerting them to PE. A score of 5 denoted a high certainty of thrombus presence, necessitating immediate notification to the diagnostic physician for review and issuance of a critical value, whereas a score of 1 denoted no thrombus detection, requiring no prior review by the diagnostic physician. Differences in objective and subjective assessments between the different image groups were compared.

Results The study included 98 patients, with a mean age of 72.06±13.41 years, comprising 47 male and 51 female patients; 23 had thrombi and 75 did not. Objective measurements revealed that in the 40, 50, and 60 keV VMI images, as the VMI energy level decreased, the corresponding CT values increased, providing improved tissue contrast. However, the SD values also increased, indicating higher noise levels (P < 0.005). In the 40 and 50 keV VMI images, the CNR values for the vessels and thrombi were higher than those in the PEI images (P < 0.005). Subjective assessment showed that the two technologists detected almost all thrombi (225/230, 97.8%), but had greater confidence in alerting PE when observing 50 keV VMI images than when observing PEI images (4.41±0.88 vs. 4.72±0.58, P < 0.001).

Conclusion For the clinical task of detecting PE using PCTA, 50 keV VMI images are preferred to enhance the confidence of radiological technologists in alerting patients with PE, facilitating timely physician review and issuance of critical values, with the potential to improve clinical diagnoses and the treatment process for patients.