Ultrasound super-resolution microvascular imaging of kidney microvascular alterations in acute kidney injury on a clinical ultrasound scanner

BACKGROUND: Early assessment of acute kidney injury (AKI) is critical to the prognosis of patients. Kidney microcirculation hemodynamic changes are pivotal to AKI pathogenesis. This study aims to evaluate the feasibility of ultrasound resolution microvascular (URM) imaging in evaluating kidney microvascular alterations in ischemia-reperfusion induced AKI using a clinical ultrasound scanner, with qualitative and quantitative microvascular analysis. METHODS: Sprague Dawley rats were randomly divided into ischemia-reperfusion injury (IRI), sham and control groups. Kidney microvascular characteristics were captured using URM. URM images were compared with color Doppler and superb microvascular imaging (SMI). In addition, URM was capable of providing quantitative information on blood density and velocities. After ultrasound examination, kidney tissues were fixed for pathological sectioning and examination. RESULTS: Compared to color Doppler and SMI techniques, interlobar, arcuate, cortical radial vessels, and part of the medullary organization were more visible on URM density maps. URM identified vessels 4-7 times thinner compared with color Doppler and SMI. The average URM smallest analyzable vessel was 0.11 ± 0.01 mm. Furthermore, quantitative findings demonstrated significant differences in kidney cortical mean vessel ratio, mean density and perfusion index between the IRI group and both control and sham groups (p < 0.0001, = 0.0237, = 0.0028). These parameters correlated significantly with CD31 immunohistochemistry (r = 0.62-0.68). CONCLUSIONS: This study demonstrates the feasibility of URM in AKI using a conventional clinical ultrasound scanner, with simple examination procedure and post-processing tools. Hence, this technique could be a promising diagnostic tool for qualitative and quantitative kidney microvascular assessment.