Photoacoustic (PA) imaging (PAI) is a burgeoning modality within the realm of biomedical imaging that harnesses the dual benefits of rich optical contrast and high spatial resolution in deep scattering tissue, overcoming the optical diffusion limit by converting light to sound.¹ PAI relies on the PA effect, facilitating the discernment of signals from within deep tissue layers. As shown in Fig. 1(a), a typical PAI system include a nanosecond pulse laser source for light illumination and ultrasound transducer for PA signal detection. In addition, a low-noise-preamplifier and a data acquisition (DAQ) device are used for PA signal amplification and conversion into a digital signal for post-processing and display.

Photoacoustic computed tomography (PACT) combines the optical contrast of optical imaging and the penetrability of sonography. In this work, we develop a novel PACT system to provide real-time imaging, which is achieved by a 120-elements ultrasound array only using a single data acquisition (DAQ) channel. To reduce the channel number of DAQ, we superimpose 30 nearby channels’ signals together in the analog domain, and shrinking to 4 channels of data (120/30 = 4). Furthermore, a four-to-one delay-line module is designed to combine these four channels’ data into one channel before entering the single-channel DAQ, followed by decoupling the signals after data acquisition. To reconstruct the image from four superimposed 30-channels’ PA signals, we train a dedicated deep learning model to reconstruct the final PA image. In this paper, we present the preliminary results of phantom and in-vivo experiments, which manifests its robust real-time imaging performance. The significance of this novel PACT system is that it dramatically reduces the cost of multi-channel DAQ module (from 120 channels to 1 channel), paving the way to a portable, low-cost and real-time PACT system.

Photoacoustic tomography (PAT) combining both optical absorption and ultrasound detection, is a unique and emerging technology in the field of medical imaging developed in recent years. PAT is based on the generation and detection of high-frequency pulsed PA signals. Therefore, a multi-channel data acquisition (DAQ) system with high sampling rate is crucial to simultaneously receive the multiway PA signals for real-time imaging. However, the cost of a high-speed multi-channel DAQ is quite high. In this brief, a multiway PA signal delay-line module for PAT was proposed, which merges four channels of PA signals in one channel that significantly reduces DAQ's channel number needed for PAT system. Specifically, an analog circuit design is proposed to accurately delay four-channel PA signals and sum them into one channel before digitization, which records both timing and amplitude of the raw PA signals. Additionally, we reconstruct the four PA waveforms from the recorded signal for image reconstruction by delay-and-sum (DAS) algorithm. To verify the feasibility of the delay-line module in the PAT system, we conducted both simulations and experiments with promising results.

This paper reports broadened bandwidth aluminum nitride (AlN) piezoelectric micromachined ultrasound transducers (BB-PMUT) for photoacoustic imaging (PAI). PMUT based on micro-electromechanical systems (MEMS) technology gains significant attention for PA endoscopic imaging inside colorectal and even blood vessel due to its miniature size, high sensitivity and versatility. Broadened bandwidth, resulting from variable membrane cavity size during the fabrication process, provides benefit to imaging spatial resolution improvement. Moreover, AlN thin film is a non-toxic material, which makes it harmless for biomedical applications with potential of CMOS-MEMS integration. In this work, a BB-PMUT is designed and fabricated. The vibration modes, impedance and bandwidth are analyzed. The BB-PMUT provides a wider fractional bandwidth (65%) for signal detection, which significantly increases the resolution compared with traditional single frequency PMUT design. We have conducted experimental validation on an agar sample to present the sensor's performance in improving axial resolution.

Photoacoustic imaging (PAI) is a fast-developing non-invasive imaging technique, which provides optical contrast in deep scattering tissue with high spatial resolution. Conventional photoacoustic (PA) imaging has been widely studied based on linear PA effect, which is induced by single short laser pulse. Recently, nonlinear photoacoustic effect has been proposed by using two consecutive laser pulses with two laser sources. In this paper, we report a dual-contrast nonlinear photoacoustic (dNPA) sensing and imaging technique by single high-repetition-rate laser induced nonlinear PA effect. Using the high-repetition-rate pulsed laser, two different kinds of imaging contrasts can be extracted: optical and thermal contrasts. Unlike conventional PA imaging that exhibits optical absorption only, we could extract thermal contrast that is reflected by the rising slope/trend of temperature and consequent PA signals. In this paper, the high-repetition-rate nonlinear PA effect and dual-contrast mechanism were proposed in theory with detailed mathematical modelling. The dual-contrast PA sensing and imaging were demonstrated by experimental results with both in vitro phantom and ex vivo porcine tissues. The results indicate both optical absorption and thermal accumulation properties of different samples, which could enhance the image contrast significantly.

Photoacoustic tomography (PAT) is an emerging technology for biomedical imaging that combines the superiorities of high optical contrast and acoustic penetration. In the PAT system, more PA signals are preferred to be detected from full field of view to reconstruct the PA images with higher fidelity. However, the requirement for more PA signals’ detection leads to more time consumption for single-channel scanning-based PAT system or higher cost of data acquisition (DAQ) module for an array-based PAT system. To address this issue, we proposed a programmable acoustic delay-line (PADL) module to reduce DAQ cost and accelerate imaging speed for PAT system. The module is based on bidirectional conversion between acoustic signals and electrical signals, including ultrasound transmission in between to provide sufficient time delay. The acoustic delay-line module achieves tens or hundreds of microseconds’ delay for each channel and is controlled by a programmable control unit. In this work, it achieves to merge four inputs of PA signals into one output signal, which can be recovered into original four PA signals in the digital domain after DAQ. The imaging experiments of pencil leads embedded in agar phantom are conducted by the PAT system equipped with the proposed PADL module, which demonstrated its feasibility to reduce the cost of the PAT system. An in vivo study of human finger PAT imaging with delay-line module verified its feasibility for biomedical imaging applications.