Photoacoustic-only preamplification in simultaneous photoacoustic and ultrasound imaging using switchable preamplifier

Sharing the same acoustic imaging principle, photoacoustic (PA) imaging is available to be done simultaneously with ultrasound (US) imaging, while still discrepancy between two modalities exists as PA imaging relatively suffers with higher depth attenuation and low signal contrast compared to the US imaging. In order to balance the PA to the level of US, we designed an application-specific integrated circuit (ASIC) preamplifier built in with selective switching protocol to amplify only the PA signal. The preamplifier accepts two distinct triggers: synchronized to the Q-switch trigger given with actual beam emission, preamplifier switches and amplifies the PA signal with customized gain. On the other hand, within the flashlamp trigger given before the Q-switch trigger (approx. 300 μs), the preamp is switched off and the US acquisition bypasses amplification. The preamp affords single channel, and we implemented the designed preamplifier to the acoustic-resolution 3D PAUS scanner installed with 5-MHz single-element focused transducer. The signal-to-noise ratio (SNR) and according penetration depth enhancement was well validated by imaging both carbon leads and wire phantoms under optically turbid media (5% diluted milk), measured to be ~ 16.8 dB at 25 mm and 10.6 dB at 33.7 mm, respectively. To fully demonstrate the improvement of PA images under practical circumstance, the bimodal whole-body image of a healthy anesthetized nude Balb/c mouse was acquired with and without the preamplifier. As a result, the organs (spleen, liver, cecum) and vasculatures lying down in the deeper region were unveiled from preamplifier-applied PA images. Above all, our proposed switchable preamplifier well preserved PA signal of weak level against sequentially acquired with high intensity US signals, extending the penetration depth and increasing the PA image contrast. Further extension toward multichannel application would be helpful to translate array US transducer-based simultaneous PA/US imaging toward clinical practice.