Abstract: Miniature catheter-based ultrasound transducers are used to image peritracheal or bronchial structures including masses, lymph nodes, and vessels. Most preferably, a 6.2 French catheter containing either a 12.5 or 20 MHz ultrasound transducer coupled with an ultrasound unit is passed through the working channel of a flexible bronchoscope and directed to the region of interest. Patients with pulmonary masses detected by X-ray or computed tomography were studied and it was found that characteristic ultrasound patterns of masses, lymph nodes and blood vessels could be distinguished. Thus, catheter-based ultrasound transducers are useful to evaluate a variety of bronchopulmonary abnormalities. This approach was found to be valuable in the selection of the appropriate site for biopsy. In accordance with the present invention, an improved ultrasound catheter that incorporates a biopsy brush is therefore disclosed.