The investigators aimed to compare the image quality and diagnostic performance of DECTPA using lower concentration iodine contrast materials and using normal concentration iodine contrast materials in the evaluation of suspected pulmonary embolism.

All patients met the inclusion and exclusion criteria will be given written informed consensus. The enrolled patients will randomly receive one of the three injection protocols: A: 30mL Iomeprol (Iomeron 300, Bracco Imaging, Milano, Italia) injected at a flow rate of 4mL/s; B: 50mL Iomeprol (Iomeron 300, Bracco Imaging, Milano, Italia) injected at a flow rate of 4mL/s; C: 50mL Ioversol (Ioversol 350, Hengrui, Jiansun, China) injected at a flow rate of 4mL/s. A and B groups are both lower concentration iodine contrast material groups, with different total iodine loads.

Inclusion Criteria:

• Age greater than 18 years old
• Clinical suspicion of pulmonary embolism suggests CTPA examination (Wells score>4 or D-2 polymer elevation)
• Patient's general physical condition tolerates CTPA examination

Exclusion Criteria:

• Allergy to iodine contrast agents
• Hyperthyroidism
• Pregnancy
• Weight greater than 80kg
• Heart failure patients, NYHA heart function level III or IV

patients who will undergo CT pulmonary angiography due to clinical suspicion of pulmonary embolism

index that measuring image quality and pulmonary embolism CTPA diagnostic results for each individual

After the main paper is published.

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