Photoacoustic endoscopy with hollow structured lens-focused polyvinylidine fluoride transducer.

Currently, most transducers in photoacoustic endoscopy (PAE) are ceramic based, which are complicated to fabricate and are expensive. In this work, we have for the first time presented a hollow structured epoxy lens-focused transducer that was based on a 52 μm thick polyvinylidine fluoride (PVDF) film for the purpose of PAE imaging. Intensive field characteristic tests were performed on transducers with different lens curvatures, and results show that with the 6 mm fixed aperture, a lateral resolution less than 0.5 mm can be obtained with a focal length around 19 mm, which is close to the theoretical calculations. The PAE application of the built transducer was also demonstrated with phantom experiments. Compared with the commonly used ceramic-based transducers, the proposed method has greatly reduced the design and fabrication cost of the hollow structured focused transducer as required in PAE, and facilitated the development of the PAE system in lab conditions. The built transducer may play an important role in the PAE imaging of some relatively large human structures and organs, such as the gastrointestinal tract and the cervical canal.