Kidney disease is prevalent in cats, affecting up to 80% of senior cats, and has significant impacts on their health. Given the large reserve functional capacity of kidneys, blood and urine tests do not detect kidney disease at early stages when treatments would be most effective. In people, studies have demonstrated the ability of two advanced ultrasound technologies, power Doppler (PDI) and microvascular flow (MVF), to detect changes in renal cortical perfusion in patients with kidney disease. To date, these technologies have not been implemented in feline medicine. This study will translate and apply these findings to cats with chronic kidney disease. The study aims to establish the clinical utility for ultrasound-based renal cortical perfusion measurements in the diagnosis and staging of chronic kidney disease, and to determine the precision of each technique (PDI or MVF) for assessing renal cortical perfusion in cats in a clinical setting. Our primary hypothesis is that alterations in renal cortical perfusion detected by power Doppler imaging (PDI) and microvascular flow (MVF) imaging will be associated with International Renal Interest Society (IRIS) staging of chronic kidney disease in cats. Additionally, we hypothesize that precise measurements can be achieved with both power Doppler imaging (PDI) and microvascular flow (MVF) imaging in assessing renal cortical perfusion. To test these hypotheses, we propose a 24-month, prospective, case-control study to enroll 150 cats, consisting of 120 Disease cats and 30 Control cats without kidney disease. Full lab work and indirect blood pressure measurements will be performed to diagnose and stage kidney disease. An abdominal ultrasound (including PDI and MVF kidney imaging) will be completed, with blinded review of the kidney ultrasound studies by a board-certified radiologist. In a subset of the enrolled cats (n=30) two observers (radiologist and radiology resident) will each acquire two sets of PDI and MVF images for evaluation of intra-operator repeatability and inter-operator reproducibility. Renal cortical perfusion parameters from PDI (perfusion intensity %) and MVF imaging (vascular index %) will be calculated using computer software programs. Comparisons of ultrasound findings will be made between Disease vs. Control groups, Disease sub-groups, PDI vs MVF measurements, and within and between operators. This will be the first study to investigate the application of advanced ultrasound technologies for the evaluation of renal cortical perfusion in cats. It will fill an ongoing need for the development of new methods for diagnosing and characterizing feline kidney disease.