Contrast-Free Super-Resolution microvascular imaging through high frequency ultrasound imaging

An imaging technique called ultrasound localization microscopy (ULM) has emerged as a means of achieving super-resolution microvascular imaging through localization and tracking of microbubbles (MBs) in blood vessels. However, the use of ULM in preclinical and clinical applications has presented challenges such as prolonged data acquisition times and specific MB injection requirements. To address this drawback, in the present study, erythrocyte ULM (eULM), a contrast-free method for microvascular imaging with a high spatiotemporal resolution that is based on ultra-high-frequency ultrasound (HFUS), was proposed. This technique involves localizing and tracking erythrocytes rather than MBs to achieve super-resolution cerebrovascular imaging. To assess its performance, we conducted two conventional ULM procedures under identical conditions, comparing the image resolution and ability to the measure cerebrovascular hemodynamics of the conventional and proposed ULM procedures. The estimated spatial resolutions for eULM and conventional ULM were 7.3 μm and approximately 10-13 μm, respectively. eULM yielded satisfactory results with just 30-s data accumulation, whereas most ULM techniques typically require 1-10 min for data acquisition. eULM is an in vivo contrast-free ultrasound microvascular imaging method capable of achieving microscopic resolution for live organ imaging. This innovation holds promise as an invaluable diagnostic tool for various diseases that involve changes in microvascular blood flow, making it suitable for both preclinical and clinical applications due to its contrast-free imaging capabilities. Keywrods: high frequnecy ultrasound imaging, super-resolution imaging, microvascular imaging, Doppler ultrasound, brain flow imaging.