A hybrid simulation phase correction method for endoscopic trans-osseous ultrasound imaging

Due to the high risk of neurological or vascular injuries related to cortical perforation during pedicle screw insertion, the endoscopic ultrasound imaging shows potential for radiation-free intraoperative navigation, capable of providing real-time guidance for the insertion. To ensure penetration depth, low-frequency ultrasound is often selected. However, the quality of trans-osseous ultrasound imaging is affected by the limited resolution as well as the bone-induced aberration. To improve the image quality, a virtual source synthetic aperture focusing and coherence factor weighting method (VSSAF-CFW) was adopted for imaging, and a hybrid simulation method was applied to correct phase aberration. This paper proposed a hybrid analytical-numerical simulation phase correction method based on intermediate virtual points (HAN-IVP). This method is based on a simplification of the conventional full-wave model. The agreement of the proposed HAN-IVP method and conventional method was assessed by 12 sets of comparative simulations under various conditions. The simulation results indicate that the mean error of Time-of-Flight (TOF) is -0.003 μs and the average Pearson correlation coefficient is 0.915. The performance of the proposed HAN-IVP-based VSSAF-CFW method was evaluated through in vitro experiments using both plate and ring bone specimens. In the plate bone experiment, the proposed method reduced the center positional shift by 0.385 mm, reduced the -6 dB lateral beam width by 1.13 mm, and increased the peak-to-sidelobe contrast ratio by a factor of 1.26. The ring bone experiment further validated the applicability of the proposed method under a curved bone geometry closer to the trans-osseous endoscopic imaging scenario. The HAN-IVP method achieved precise phase correction while reducing the computational cost. The combination of HAN-IVP and VSSAF-CFW effectively improved the quality of rotational scanned trans-osseous ultrasound imaging, demonstrating its potential for future clinical translation.