Transcranial Ultrasound Super-Resolution Imaging Using Chirp-Coded Excitation With Adaptive Attenuation Mismatched Filter and Multilayer Correlation Phase Correction

Cerebral microvasculature imaging is crucial in the diagnosis of various cerebrovascular diseases. Ultrasound localization microscopy (ULM) enables microvascular imaging at microscopic resolution through the localization of injected microbubbles (MBs). However, the strong attenuation of transcranial ultrasound limits the sensitivity of vascular detection, and phase aberration caused by mismatched speed of sound in different tissues reduces the resolution of transcranial ULM (TULM). In this study, a chirp-coded excitation signal was transmitted, and an adaptive attenuation mismatched filter (AMF) was constructed based on the attenuation of each frequency component to improve the signal-to-noise ratio (SNR) and resolution of the compressed signal. Moreover, a multilayer correlation phase correction (MCor) method was proposed for precision TULM, independently correcting phase aberration in different fields of view. The simulation results confirm that the chirp-coded excitation and AMF increase the SNR by 11.31 dB and the axial resolution by 0.08λ compared with those of the single-pulse excitation under strong attenuation conditions. For phase aberration, the MCor improves the lateral and axial resolutions to 0.77 and 0.19λ, respectively. Additionally, the advanced phase correction method enhances the refocusing ability, improving the contrast by 2.46 dB. For in vivo TULM, the proposed method was more robust, which can reconstruct richer microvascular structures than the conventional method, with a 15.68% increase in saturation. Moreover, the resolution of the microvasculature improved by 7.19 µm (27.24%). These results validate the advantages of the proposed method in achieving rich microvascular reconstruction with higher resolution than conventional methods under transcranial imaging conditions. Thus, the proposed method has application potential in ultrasound imaging of small vessels in the brain.