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Microwave-induced thermoacoustic imaging, as an emerging biomedical imaging technique, combines the high contrast of microwave imaging with the high spatial resolution of ultrasound imaging. Microwave-induced thermoacoustic microscopy, as an important branch of this technology, retains these advantages while possessing the ability to visualize finer tissue characteristics. However, traditional raster scanning mechanisms introduce interference into microwave field distribution due to mechanical motion, thus necessitating multiple signal average to maintain signal-to-noise ratio. Additionally, the idle time during motor movement results in extended single-scan durations, limiting its practical applications. To address these limitations, this work proposes a rapid imaging system based on one-dimensional galvanometer scanning. The system employs a hybrid galvanometer-translation stage architecture and an optimized scanning strategy to minimize microwave field interference, reduce the number of signal averages and shortens the idle time, ultimately achieving more than a tenfold improvement in imaging speed. A specially designed timing control algorithm ensures the precise synchronization of microwave excitation, galvanometer motion, and ultrasound detection, while the reconstruction algorithm suitable for the optimizing scanning method effectively corrects distortions generated in the scanning process. The system performance is assessed through phantom and ex vivo tissue experiments. Resolution tests show hundred-micrometer resolution along all three axes (332 μm × 324 μm × 79 μm), while contrast and depth imaging experiments confirm its ability to clearly distinguish targets with different conductivities, achieving an effective detection depth of at least 10 mm in tissue. Early tumor mimicking experiments further demonstrate the ability of the system to identify lesion boundaries, preliminarily revealing its potential for rapid tumor margin assessment. This approach maintains the imaging quality of microwave-induced thermoacoustic microscopy while enhancing imaging efficiency and system stability, thereby laying a crucial foundation for advancing the technology from laboratory research to clinical applications.
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Keywords:
- microwave-induced thermoacoustic imaging /
- microwave-induced thermoacoustic microscopy /
- galvanometer scanning /
- imaging speed
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图 1 CST仿真模型及电场分布结果 (a)传统栅型扫描机制下的仿真模型; (b)对应(a) 的组织内电场分布; (c)振镜-平移台混合扫描机制下的仿真模型; (d)对应(c)的组织内电场分布
Figure 1. CST simulation models and electric field (E-field) distribution results: (a) Simulation model under the conventional raster-scanning mechanism; (b) E-field distribution within the tissue corresponding to (a); (c) simulation model under the galvanometer-translational stage hybrid scanning mechanism; (d) E-field distribution within the tissue corresponding to (c).
图 2 快速微波热声显微成像系统示意图
Figure 2. Schematic of fast microwave-induced thermoacoustic microscopy imaging system.
图 3 快速微波热声显微成像系统时序图
Figure 3. Timing diagram for fast microwave-induced thermoacoustic microscopy system.
图 4 铜丝分辨率测试实验 (a)直径为90 μm的铜丝实物图; (b)三维热声图像; (c) X轴分辨率测试时沿Z轴方向投影的1号和2号铜丝的二维热声显微图像; (d) (c)图中沿白色虚线的热声信剖面图; (e) Y轴分辨率测试时沿Z轴方向投影的1号和2号铜丝的二维热声显微图像; (f) (e)图中沿白色虚线的热声信剖面图; (g) Z轴分辨率测试时2号与3号铜丝沿Y轴方向投影的二维热声显微图像; (h) (g)图中沿白色虚线的热声信剖面图
Figure 4. Copper wire experiment: (a) Photograph of 90 μm-diameter copper wires; (b) 3D FTAM image; (c) 2D FTAM images of copper wires 1 and 2 along the z-axis for X-axis resolution testing; (d) thermoacoustic signal profile along the white dashed line in (c); (e) 2D FTAM images of copper wires 1 and 2 along the Z-axis for Y-axis resolution testing; (f) thermoacoustic signal profile along the white dashed line in (e); (g) 2D FTAM images of copper wires 2 and 3 along the Y-axis for Z-axis resolution testing; (h) thermoacoustic signal profile along the white dashed line in (g).
图 5 盐水管对比度测试实验 (a)内径0.2 mm的盐水管实物图; (b)二维热声显微图像; (c) (b)图中选中区域像素值的统计结果以及与2%, 3%浓度盐水管的理论电导率对比图
Figure 5. Saline tube experiment: (a) Photograph of saline tubes with 0.2 mm inner diameter; (b) 2D FTAM image; (c) statistical results of pixel values in the selected region from (b), with theoretical electrical conductivity values for 2% and 3% saline concentration tubes.
图 6 深度成像 (a)置于空气中的样品实物图; (b) (a)图中样品对应的三维及二维微波热声图像; (c)嵌入脂肪中的样品实物图; (d) (c)图中样品对应的三维及二维微波热声图像
Figure 6. Depth imaging: (a) Photograph of the sample placed in air; (b) corresponding 3D and 2D microwave-induced thermoacoustic images of the sample in (a); (c) photograph of the sample embedded in fat; (d) corresponding 3D and 2D microwave-induced thermoacoustic images of the sample in (c).
图 7 早期肿瘤模拟成像 (a)实物图; (b)二维超声显微图像; (c)二维热声显微图像; (d)二维热声/超声显微融合图像; (e)三维超声显微图像; (f)三维热声显微图像; (g)三维热声/超声显微融合图像
Figure 7. Early-stage tumor simulation imaging: (a) Photograph of the phantom; (b) 2D ultrasound image; (c) 2D TAM image; (d) 2D thermoacoustic-ultrasound image; (e) 3D ultrasound image; (f) 3D TAM image; (g) 3D thermoacoustic-ultrasound image.
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