Development and clinical evaluation of a 10MHz ultrasound linear array catheter for endobronchial imaging

Applying endoscopic ultrasound to image external part of bronchial tubes is of great interest and complementary with other imaging methods. In continuation with our previous work [1], this paper presents the design and acoustical testing of a catheter array for endobronchial imaging completed by results of the clinical study performed with this probe. The transducer is a 64 elements ultrasound array included in a 7 Fr (2.3 mm Outer Diameter) catheter in order to be used in an existing bronchofiberscope. The array has a 200 µm pitch, a 1.5 mm elevation, and operates at 10 MHz center frequency. The piezoelectric material is based on 1-3 piezo-composite technology and the front layer is selected to act both as a matching and barrier layer. The probe is interfaced to a commercial ultrasound system. It was used in 25 patients without any inconvenience for the patient (in terms of discomfort and time duration which is limited to 10 minutes at the maximum) or the clinicians (easy use, perfect visualization of the area of interest). The only limitation encountered concerns the presence of air bubbles on bronchial walls which could limit the visualization of structures. This allowed the characterization of chest tumors (hypoechoic tissue) with possible adjacent lymph nodes (minimal size of 3 mm) which were not described on CT-scan. This identified clearly some underlying vessels to be spared during biopsy. This helps in identifying some regions of tumours which appeared as vascularized to guide the site of biopsy. In conclusion this specific probe is of great value to better image bronchial structures, to depict extension of tumours as well as possible sentinel lymph nodes for a more complete initial diagnosis and guidance of biopsies. This will be used to improve diagnosis and safety of biopsy.