A photoacoustic imaging system with variable gain at different depths

We established a photoacoustic imaging (PAI) system that can provide variable gain at different depths. The PAI system consists of a pulsed laser with an optical parametric oscillator working at a 728nm wavelength and an imaging-acquisition-and-processing unit with an ultrasound transducer. A voltage-controlled attenuator was used to realize variable gain at different depths when acquiring PAI signals. The proof-of-concept imaging results for variable gain at different depths were achieved using specific phantoms. Both resolution and optical contrast obtained through the results of variable gain for a targeted depth range are better than those of constant gain for all depths. To further testify the function, we imaged the sagittal section of the body of in vivo nude mice. In addition, we imaged an absorption sample embedded in a chicken breast tissue, reaching a maximum imaging depth of ∼4.6cm. The results obtained using the proposed method showed better resolution and contrast than when using 50dB gain for all depths. The depth range resolution was ∼1mm, and the maximum imaging depth of our system reached ∼4.6cm. Furthermore, blood vessels can be revealed and targeted depth range can be selected in nude mice imaging.