REVIEW ARTICLE 129 2576-2508/ C AUDT 2022·http://www.AUDT.org This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed. Renal Contrast-enhanced Ultrasound: Clinical Applications and Emerging Research Felipe Velasquez-Botero, MD a , Ananya Balasubramanya a , Ying Tang, MD b , Qiang Lu, MD c , Ji-Bin Liu, MD a , John R. Eisenbrey, PhD a, * a Department of Radiology, Thomas Jefferson University, Philadelphia, PA, USA; b Department of Ultrasound, Tianjin Frist Central Hospital, Tianjin, China; c Department of Ultrasound, West China Hospital of Sichuan University, Chengdu, China Received September 14, 2022; revision received October 5, 2022; accepted October 14, 2022 Abstract: Contrast-enhanced ultrasound (CEUS) is an imaging modality that has achieved considerable relevance in various clinical settings including the assessment of renal disease. CEUS is performed by injecting microbubble-based ultrasound contrast agents (UCAs) that create signals to display the microvasculature, allowing quantitative and qualitative assessment of parenchymal perfusion and real-time visualization of the renal anatomy. In recent years, CEUS has been widely accepted and applied for the assessment of kidney perfusion and the characterization of indeterminate renal masses, primarily due to its diagnostic efficacy, availability, low cost, reproducibility, and absence of nephrotoxicity. CEUS provides a higher spatial and temporal resolution than other cross-sectional imaging, resulting in high sensitivity and specificity for its applications in a variety of renal conditions including cancer monitoring following ablation, detection of transplant complications, hypoperfusion, acute traumatic injury, renal artery stenosis, parenchymal infection, and kidney intervention guidance. Additionally, the continuous investigation and development of new technologies surrounding this imaging technique have shown encouraging preliminary results for the use of CEUS in the evaluation of molecular expression in several disease processes, the dynamic analysis of blood flow kinetics, and the implementation of super-resolution imaging systems. The purpose of this article is to provide an overview of the current and potential clinical applications of renal CEUS. Key words: Contrast-enhanced ultrasound; Renal disease; Renal CEUS; Emerging spplications; CEUS applications Advanced Ultrasound in Diagnosis and Therapy 2022; 04: 129-146 DOI: 10.37015/AUDT.2022.220036 * Corresponding author: 796 Main, 132 S. 10 th Street, Department of Radiology, Thomas Jefferson University, Philadelphia, PA 19107, USA email: john.eisenbrey@jefferson.edu C ontrast-enhanced ultrasound (CEUS) is an advanced type of ultrasound that involves the intravenous injection of gas microbubbles that allow real-time visualization of the vascular architecture of the organ of interest. This technique was initially intended to study the cardiovascular system but later demonstrated potential in evaluating various abdominal viscera. CEUS has been documented to be of great clinical utility in the assessment of kidney pathology due to its diagnostic performance and safety profile [1]. Ultrasound Contrast Agents (UCAs) are composed of gas microbubbles (1-8 µm) surrounded by a protein, lipid, or polymer shell. Microbubbles (MBs) contain a core gas (generally sulfur hexafluoride or octafluoropropane) that has low diffusibility and solubility in water, as well as high vapor pressure, resulting in UCAs persisting inside the intravascular space. In response to ultrasound waves MBs contract and expand, reflecting the transducer with improved acoustic energy than passive reflectors and enabling increased backscattering signals (up to 30 dB) [1,2]. The non-linear oscillation pattern of MBs generates harmonic signals that help differentiate contrast signals from background tissues [3]. Microbubbles are cleared from the vascular space approximately five to fifteen minutes following the injection of UCA. The internal gas is exhaled through the lungs, and the shell particles