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 hyperlipidemia that affect 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 before it becomes evident with current measures, earlier treatment can be initiated to postpone the onset of renal complications in persons with metabolic syndrome.

The overall aim of this study is 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. In this work an 11-week-old OZR and a healthy agematched Zucker rat were investigated.

During open surgery, the left kidney was scanned for 10 min using a modified BK5000 scanner (BK Medical, Denmark), a fixed X18L5s transducer and intravenously administered SonoVue (1:10). Images were obtained using interleaved contrast (amplitude modulation) and B-mode sequences with focused beam transmission (6 MHz, 50 Hz, MI: 0.2).

An in-house tool was used to track microbubble (MB) movements between frames, in order to estimate the MB velocities, which were measured in a large region of the cortex and the outer medulla. This is the first time SRI has been used on the kidneys of rats with Metabolic syndrome. 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) 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).

The results show that SRI can visualize the renal microvasculature of a young OZR. Therefore, the method can be used for further investigations of the renal microvascular changes that occur in the course of Metabolic syndrome.