Real-time photoacoustic_fluorescence bimodal small animal imaging

Real-time photoacoustic/fluorescent bimodal small animal imaging

“Recently, the Li Changhui Research Group of the Department of Biomedical Engineering of Peking University designed a photoacoustic fluorescence (PA-FL) imaging system that can provide real-time bimodal imaging. The half-loop ultrasonic array is used for high-quality PA tomography, and the specially designed optical window allows simultaneous whole-body fluorescence imaging. The performance of this bimodal system has been demonstrated in live animal studies, including real-time monitoring of the perfusion and metabolic processes of fluorescent dyes. Studies have shown that the PA-FL imaging system has unique potential in the study of live small animals. The related results were published in Photoacoustics, a top journal of photoacoustics, under the title “Real-time dual-modal photoacoustic and fluorescence small animal imaging” (District 1, Chinese Academy of Sciences, with an impact factor of 7.9 in 2022), with Sun Yu, Department of Biomedical Engineering, School of Future Technology, Peking University, as the first author and Li Changhui as the corresponding author. ”

Photoacoustic imaging (PAI) breaks through the barriers of high-resolution optical imaging in depth by combining light absorption contrast and sound resolution. At the same time, fluorescence imaging (FLI) has the advantages of high sensitivity and specificity, and is rich in fluorescent agents and fluorescent proteins, which have been playing a key role in live animal research. Based on different optical comparison mechanisms, PAI and FLI can provide important complementary information to each other.

The PAI-FLI system consists of two subsystems: the FLI subsystem and the PAI subsystem. As shown in Fig. 1, the PAI system uses a customized 256-element half-ring ultrasound transducer array (ULSO TECH Inc, China) with a center frequency of 5.0 MHz and a unidirectional bandwidth of 80%. The diameter of the described half-ring was 100 mm, and each array element was cylindrically focused in the elevation direction with a focal length of 40 mm.

Figure 1 Bimodal imaging system. (a) The three-dimensional schematic diagram of the system; (b) The diagram of the optical path and the acoustic path

In order to maximize the signal-to-noise ratio (Snr) of the ultrasonic transducer array, a self-developed 256-channel preamplifier (40db gain) is directly connected to the ultrasonic transducer array. The amplified PA signal is then received in parallel by the 256-channel data acquisition system DAQ (Marsonics: DAQ, Tsingpai Tech-Co, China, 6db gain) at a 40mhz sampling rate. The sound amplification signal is Optical parametric oscillator by an OPO pulse laser (INNOLAS SpitLight 600, Germany) at a repetition rate of 10hz. The laser is coupled into 1 ~ 10 fiber bundles, each of which is a rectangle of 1 × 7 mm. The branching ends are evenly distributed around the imaging target, forming an approximately uniform circular illumination pattern, as shown in Figure 1.

A 10 Hz OPO laser with a repetition period of 100 ms is used to excite the PA signal, and a 785 nm continuous wave laser is used to excite the FL signal. When the photodetector detects a pulsed laser from the OPO laser, it emits a pulsed signal to trigger the fluorescence camera and data acquisition system (DAQ). Once the trigger is received, the PA's DAQ system captures 2048 data points at 40 MHz and completes within 51.2 µs. However, the fluorescent camera will delay the start of exposure by 10ms. This is to avoid fluorescence imaging from being affected by a strong OPO laser. The principle is shown in Figure 2.

Figure 2.

Schematic diagram of dual-mode synchronous operation

Figure 3.

Photoacoustic imaging of mouse body

In this work, a real-time PA-FL bimodal imaging system was developed, using a semi-annular ultrasonic array to achieve real-time two-dimensional imaging PAI combined with full-body FLI through an optical window. The imaging system successfully realized real-time imaging of the perfusion and metabolic processes of fluorescent dyes in mice. The system combines the advantages of FLI and PAI. Among them, FLI has a large field of view and high sensitivity for real-time full-body coverage, and PAI has high resolution in deep tissue imaging and provides tissue structure information. The real-time simultaneous imaging capabilities of bimodal fluorescence and photoacoustic systems have opened up new avenues for small animal research and preclinical research.

DOI:
10.1016/j.pacs.2024.100593.

Literature source：Photoacoustics, 2024.

Beijing Qingpai Technology provided a data acquisition system for this research-MarsonicsDAQ (click for details). MarsonicsDAQ series products are special data acquisition equipment designed for high-end photoacoustic imaging, thermoacoustic imaging, magnetoacoustic imaging and other acoustic scientific research work. This series of products is based on 128 channels and 256 channels, and at the same time supports customers to customize more channels, higher performance, and some specialized functions as needed. The product adopts high-precision data acquisition hardware design and user-friendly and easy-to-use efficient software workflow design. The equipment sampling rate is as high as 80MSPS, and the specially customized DAQxxx-S48 model product sampling rate can be as high as 125MSPS, the sampling depth is 14bit, the maximum gain is 80dB and multi-stage adjustable. All channels can achieve synchronous acquisition, and support integrated imaging of multiple device channels.

In related applications such as acoustic signal acquisition, data acquisition with extremely high signal-to-noise ratio can be realized, which provides a basic guarantee for further improving image and signal quality.

Figure 4.

Data acquisition system (Marsonics DAQ, Beijing Qingpai Technology)

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