Enhanced in vivo thermoacoustic imaging of intracerebral hemorrhage in rat models through an optimal microwave illumination strategy

We present a novel metal reflector based illumination strategy for optimized thermoacoustic tomography (TAT) of intracerebral hemorrhage (ICH). The strategy can capture stray microwave energy from the imaging area, redirects it synchronously to brain tissues, disrupts original electric (E)-field boundary conditions, and reshapes the E-field distribution into uniformity. This renders TAT more dependent on inherent dielectric property differences of brain tissues than external E-field variations, thereby enhancing image quality. Numerical simulations were performed to evaluate the reflector dimensions, and it was determined that a half-wavelength diameter reflector provided an optimal performance, achieving minimal E-field intensity deviation, optimal energy absorption density in brain tissue, and superior lesion-to-tissue contrast. Based on the optimal parameters from the simulations, a metal reflector was fabricated and integrated into the TAT system for in vivo detection in normal and ICH rats. Imaging of rat brain was then conducted and demonstrated that the reflector enhanced TAT significantly improved tissue boundary definition, hemorrhage/edema visibility, image sharpness/contrast and intergroup symmetry differences. The TAT image quality is further improved when an image reconstruction algorithm integrating logarithmic depth weighting with multi-scale Retinex is used. Anatomical photographs and HE-stained pathological examinations and MRI scans of the brain tissue imaged proved these TAT imaging findings. The reflector-optimized strategy has low cost and high system compatibility. This study suggests that our reflector-based TAT may offer a new yet practical tool for in vivo dielectric brain research and auxiliary diagnostics of neurological diseases.