The goal of this clinical trial is to evaluate the diagnostic effcacy and safety of ultrasound elastography guided pleural biopsy in the differential diagnosis of benign and malignant pleural effusion. The main question it aims to answer are: the effectiveness and safety of ultrasound elastography guided pleural biopsy in the differential diagnosis of benign and malignant pleural effusion.

Participants will undergo ultrasound elastography guided pleural biopsy or traditional ultrasound-guided pleural biopsy.

Inclusion Criteria:

1. Patients with unexplained pleural effusion (patients with pleural effusion with negative aspiration)
2. Sign the informed consent form
3. The patient must have chest CT, biochemical examination of pleural fluid, cytological examination of pleural fluid and other data before operation

Exclusion Criteria:

1. The cytological examination of pleural fluid indicates "highly suspicious" patients (unless the cytological examination results of patients are inconsistent with clinical manifestations and CT examination). The pleural fluid cytology proved to be malignant. Patients with severe pleural adhesion who cannot undergo medical thoracoscopic examination will not be randomly selected, and elastic ultrasound-guided biopsy can be performed after informed consent, as a subgroup of population analysis. Those who cannot tolerate closed pleural biopsy due to severe cardiopulmonary dysfunction and poor general condition Coagulation dysfunction. Leakage. The age is less than 18 years old.
2. The pleural fluid cytology proved to be malignant.
3. Patients with severe pleural adhesion who cannot undergo medical thoracoscopic examination will not be randomly selected, and elastic ultrasound-guided biopsy can be performed after informed consent, as a subgroup of population analysis.
4. Those who cannot tolerate closed pleural biopsy due to severe cardiopulmonary dysfunction and poor general condition
5. Coagulation dysfunction.
6. transudate
7. The age is less than 18 years old.