The purpose of the study is to describe confocal laser endomicroscopy (CLE) interpretation criteria for different types of peripheral pulmonary lesions (PPLs), with histopathological correlation, and to perform the validation of these criteria.

CLE is a modern imaging technique that uses an excitation laser light to create real-time microscopic images of tissues. During transbronchial lung biopsy, CLE has the potential to provide real-time non-invasive diagnosis of PPLs ("optical biopsy"). In this study, we will obtain CLE images within the target lesion before taking a biopsy during transbronchial lung biopsy of PPLs. We will compare the results of the "optical biopsy" with the corresponding histopathological results and develop CLE interpretation criteria for different types of PPLs. In addition, we will perform the validation of these criteria to evaluate the ability of CLE to discriminate between benign and malignant PPLs.

Inclusion Criteria:

1. Patients older than 18 years.
2. Chest CT shows peripheral pulmonary lesions (peripheral pulmonary lesions are lesions beyond the segmental bronchi that are invisible during bronchoscopy), and transbronchial biopsy is considered necessary and feasible.
3. Patients who have good compliance and sign informed consent.

Exclusion Criteria:

1. Patients with known allergy for fluorescein.
2. Pregnant or lactating women.
3. Patients with contraindications of bronchoscopy.
4. The investigators believe that patient has other conditions that are not suitable for the study.

Patients with peripheral pulmonary lesions scheduled for transbronchial lung biopsy.