Fabry–Pérot interference principle-based non-contact thermoacoustic imaging system for breast tumor screening

Microwave-induced thermoacoustic imaging (MTAI) is a potential nonionizing candidate for breast tumor detection due to its high contrast of tissue dielectric absorption and high resolution of ultrasonography. However, conventional MTAI systems need to contact the imaging targets through the ultrasound-coupling medium for the efficient transmission of thermoacoustic signals. This is a major drawback for potential applications such as navigation of open surgeries, burns, and ulcer testing. In this paper, we report a Fabry–Perot (FP) interference principle-based non-contact thermoacoustic imaging system (NCTAIS). The system can infer the ultrasonic intensity by detecting the changes of the acoustically induced refractive index in the FP cavity. The miniaturized FP interferometer with a diameter of 5 mm achieves outstanding imaging sensitivity with a frequency response up to 1 MHz. An adaptive Stolt migration-based imaging reconstruction algorithm is proposed to solve the MTAI image distortion caused by the significant difference in sound velocity between air and a biological tissue. The NCTAIS is capable of achieving an axial resolution of 0.95 mm and a lateral resolution of 1.91 mm. The technical feasibility for breast tumor screening is validated with an in vitro simulated breast tumor model. The results demonstrate that the proposed NCTAIS offers high imaging sensitivity, high contrast, and deep imaging depth and will have more application scenarios than the conventional MTAI system, requiring the ultrasonic coupling medium to contact ultrasonic transducers.