Abstract
Photoacoustic (PA) imaging is a hybrid imaging technique that can provide both structural and functional information of biological tissues. Due to limited permissible laser energy deposited on tissues, highly sensitive PA imaging is required. Here, we developed a 20 MHz lead zirconium titanate (PZT) transducer (1.5 mm × 3 mm) with front-end amplifier circuits for local signal processing to achieve sensitivity enhanced PA imaging. The electrical and acoustic performance was characterized. Experiments on phantoms and chicken breast tissue were conducted to validate the imaging performance. The fabricated prototype shows a bandwidth of 63% and achieves a noise equivalent pressure (NEP) of 0.24 mPa/√Hz and a receiving sensitivity of 62.1 μV/Pa at 20 MHz without degradation of the bandwidth. PA imaging of wire phantoms demonstrates that the prototype is capable of improving the detection sensitivity by 10 dB compared with the traditional transducer without integrated amplifier. In addition, in vitro experiments on chicken breast tissue show that structures could be imaged with enhanced contrast using the prototype and the imaging depth range was improved by 1 mm. These results demonstrate that the transducer with an integrated front-end amplifier enables highly sensitive PA imaging with improved penetration depth. The proposed method holds the potential for visualization of deep tissue structures and enhanced detection of weak physiological changes.
Highlights
Photoacoustic (PA) imaging has drawn much attention worldwide during the last two decades with its compelling advantage of combining the high-contrast of pure optical imaging with the deep penetration depth of ultrasound (US) imaging [1,2,3,4,5]
PA imaging has been demonstrated to be capable of high resolution structural imaging such as mapping of subcutaneous micro-vessels [9,10,11,12,13], anatomic features discrimination [14,15,16], and detection of atherosclerotic plaques based on the Sensors 2020, 20, 766; doi:10.3390/s20030766
As the laser energy increases, the enhancement of PA signal is eventually limited by the optical absorption saturation and the maximum permissible exposure specified by American National Standards Institute (ANSI) [39]
Summary
Photoacoustic (PA) imaging has drawn much attention worldwide during the last two decades with its compelling advantage of combining the high-contrast of pure optical imaging with the deep penetration depth of ultrasound (US) imaging [1,2,3,4,5]. Since the signal attenuation caused by the scattering of light and the attenuation of the acoustic waves is more than one order of magnitude per centimeter at 10 MHz [35], the acoustic pressure of the PA signals arriving at the transducer is in the Pa or sub-Pa range depending on the depth [36]. When high frequency transducers (≥ 20 MHz) are used to achieve high spatial resolutions, signals become extremely weak considering the frequency-dependent attenuation on the order of 0.5 dB·cm-1 ·MHz-1 in biological tissues [37]. For a given absorption contrast, the detection sensitivity of PA imaging mainly depends on the incident light exposure and the efficiency of the detector [38]. As the laser energy increases, the enhancement of PA signal is eventually limited by the optical absorption saturation and the maximum permissible exposure specified by American National Standards Institute (ANSI) [39]
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