Super-resolution Ultrasound Imaging of the Renal Microvasculature in Rats with Metabolic syndrome

Super-resolution Ultrasound imaging (SRI) can visualize and quantify changes in the microvasculature. Metabolic syndrome is associated with hypertension and hyperlipidemia that affects different organs, including the kidneys. Ex vivo studies have shown glomerular injury in Obese Zucker rats (OZR) over time. If in vivo SRI can diagnose renal disease earlier than currently possible, treatment can be initiated in time to postpone the onset of renal complications in persons with metabolic syndrome. The overall aim of this study was to investigate whether SRI can detect early microvascular changes in the kidneys of rats with metabolic syndrome. The rats presented in this work were scanned at an early age to get a baseline scan prior to further studies. An 11-week-old OZR and a healthy age-matched Zucker rat were investigated. During open surgery, the left kidney was scanned for 10 min using a modified BK5000 scanner (BK Medical, Denmark) and a fixated X18L5s transducer. SonoVue (Bracco, Italy) was injected intravenously (1:10 dilution). Contrast images were obtained using a pulse amplitude modulation sequence and interleaved B-mode images were obtained for tissue motion correction (focused beam transmission, 6 MHz, 50 Hz, MI: 0.2). An in-house tool was used to track microbubble (MB) movements between frames to estimate the MB velocities measured in a large region of the cortex and the outer medulla. Both the cortex and the medulla were well-perfused with MBs, and no morphological differences in the microvasculature were found between the two rats. The thickness of the cortex and the medulla was almost identical; cortex 1.8 mm, medulla 8 mm, craniocaudal length 2.0 vs. 1.9 cm (healthy vs. OZR). The same was true regarding the MB velocities (median (IQR; difference between upper and lower quartiles = Q3 - Q1) in mm/s) for healthy vs. OZR; cortex 0.75 (3.51) vs. 0.65 (2.64) and medulla 0.75 (0.32) vs. 0.62 (0.30). This is the first time SRI has been used on the kidneys of rats with metabolic syndrome. The results will be used as the foundation for further investigations of the renal microvascular changes, which occur in the course of metabolic syndrome.