Anti-jamming thermoacoustic imaging based on fiber Bragg grating ultrasonic detection and photoelectric conversion...

Thermoacoustic Imaging (TAI) combines the high contrast of microwave imaging with the high resolution of ultrasound imaging, establishing itself as a novel, non-invasive medical diagnostic technique. However, the high-power (peak power: 5∼100 kW; pulse width: 10∼1000 ns) used in TAI often cause remarkable interference with thermoacoustic signal acquisition systems and traditional piezoelectric ultrasound transducers. This interference leads to degraded thermoacoustic image quality and a pronounced "near-field dead zone" (NFDZ), which severely restricts the clinical application and development of TAI.

To address these challenges, this paper proposes using fiber Bragg grating (FBG) for thermoacoustic signal detection. The high sensitivity and strong resistance to electromagnetic interference offered by FBG are leveraged to achieve interference-resistant signal acquisition. Additionally, a photoelectric conversion synchronous triggering method is adopted to prevent strong coupling of spatially distributed pulse microwave signals to the data acquisition system due to excessively long coaxial cables. This approach ensures more reliable and interference-resistant data acquisition for TAI.

Utilizing FBG with their high sensitivity and electromagnetic interference resistance, the system replaces traditional piezoelectric transducers for thermoacoustic signal detection. Additionally, a photoelectric conversion triggering method was implemented to avoid microwave pulse coupling interference caused by long coaxial cables. Experimental validation included comparisons between FBGs and traditional transducers in terms of signal-to-noise ratio (SNR), as well as noise measurements using both coaxial bayonet nut connector (BNC) cable and photoelectric trigger configurations to contrast test noise levels. Furthermore, the distance between the microwave antenna and data acquisition system was adjusted to validate the attenuation pattern of electromagnetic interference. TAI experiments used soy sauce tubes for their controllable composition/morphology. Systems imaging the tube also apply to human arms and ex vivo porcine liver (similar microwave absorption to tumors). This standardized, cost-efficient, and ethical approach provides a reliable basis for biological tissue imaging research.

Experimental results show FBG with photoelectric triggering achieves SNR values of 28.32 (70.2% improvement) and 30.74 dB (66.3% improvement) compared to traditional transducers at 16.64 and 18.48 dB, respectively, representing an overall SNR enhancement of 64.0%∼88.0%. Furthermore, the photoelectric conversion triggering method reduces noise levels, which means shortening the NFDZ, leading to improved imaging quality and an extended effective detection range. Additionally, it was found that increasing the distance between the microwave antenna and the data acquisition system effectively reduced the noise amplitude, with the attenuation of direct spatial coupling interference conforming to the electric field intensity attenuation law (1/r attenuation).

This study establishes that the FBG-based thermoacoustic imaging system, leveraging FBG's high sensitivity and electromagnetic interference resistance combined with photoelectric triggering, enhances signal quality and effectively suppresses near-field artifacts, enabling reliable clinical imaging. Validation through noise, signal, and spatial analyses confirms FBG's utility in advancing TAI. In summary, the method proposed in this article can be used for thermoacoustic endoscopy (especially for intravascular thermoacoustic endoscopy), thyroid and breast ablation TAI monitoring, as well as multimodal imaging combined with MRI and TAI.