Feasibility study of robotically tracked photoacoustic computed tomography

Photoacoustic imaging (PA) is becoming a promising modality for pre-clinical and clinical application by providing functional information with high penetration depth. In particular, PA computed tomography (PACT) aims to visualize the photoacoustic source distribution by scanning ultrasound transducers around a surface of the structure. Placing transducers around the subject or rotating the subject with fixing transducer position are two major approaches to scan in circular arc trajectory, but both are not flexible and have their drawbacks. To resolve the problem, we propose a new scanning method based on the robotic tracking technique. High flexibility of the scanning geometry is available because the trajectory of the tracked transducer generated by robot motion will be regarded as the scanning path. A simulation study of proposed method is conducted, assuming a 6cm array ultrasound transducer was used as receivers. To replicate the scenario that the probe is moved by robot, the probe is placed at two positions across a designated rotation angle, and received signals at both positions are used to generate an image. Compared to the result without robot motion, the lateral resolution of the target drastically improved due to aperture extension. In addition, the effect of error in one of the pose in lateral and axial direction was also simulated. Finally, an experiment was conducted to demonstrate the feasibility of the system. The result indicates that the ultrasound calibration is required to the system, and the robotically tracked PACT has a huge potential to be a new scanning strategy.