Microwave-induced Thermoacoustic and Ultrasonic Dual-Modal Endoscopy for Rectum Tumor Detection

Accurate detection of deeply invasive rectal cancer remains a major clinical challenge: conventional optical endoscopy is limited to superficial mucosal visualization, while endoscopic ultrasound lacks sufficient functional contrast to distinguish malignant from benign tissues. Herein, we developed an integrated endoscopic microwave-induced thermoacoustic/ultrasound dual-modal imaging system. Its core is a miniaturized coaxial probe integrating a 3.05 GHz circularly polarized omnidirectional antenna and a 15 MHz focused ultrasound transducer, with FPGA timing synchronization to achieve precise co-registration of dual-modal signals. The system provides intrinsic functional contrast by exploiting the dielectric property differences between tumor and normal tissues, achieving thermoacoustic imaging over a 3 cm axial scanning range with radial penetration exceeding 1.5 cm in tissue-mimicking phantoms. Meanwhile, it enables precise anatomical localization via high-resolution ultrasound imaging. Ex vivo porcine rectum experiments successfully resolved the layered structure of the rectal wall including the mucosa, submucosa, and muscularis propria, with measured conductivity and acoustic impedance values in good agreement with theoretical predictions. T1-T3 staged tumor phantom experiments demonstrated that ultrasound imaging could accurately localize tumor invasion depth within each tissue layer, while thermoacoustic signal intensity increased progressively with the conductivity gradient associated with tumor progression. This system can simultaneously provide complementary functional and structural information without ionizing radiation, offering a novel technical approach for early rectal cancer diagnosis, accurate T-staging, and treatment response monitoring.