Color Doppler energy--a new technique to study tissue perfusion in renal transplants

Information on renal tissue perfusion after transplantation remains important for renal allograft monitoring. Findings obtained by conventional Doppler sonography are limited to vascular resistance (RI). The new technique color Doppler energy (CDE) is Doppler angle independent, omits flow velocity and direction, and is proportional to the returning signal strength. The aim of our study was to standardize the application of this technique and to analyze the information obtained. Forty-six CDE studies were performed with an Acuson 128XP in 28 children (mean age 12.4+/-5.3 years) between 4 days and 10 years after renal transplantation. The most-reproducible information was obtained with a 5-MHz linear probe and a constant area of 2x3 cm (log compression 40 dB, filter 3). CDE provided a high-resolution cross-sectional display of perfused cortical tissue vessels. According to the density of signals, the perfusion could be grouped into six perfusion scores (PS). The interobserver concordance was more than 85%. No correlation was found between PS and RI or blood pressure. However, there was a significant correlation between PS and glomerular filtration rate (r=-0.78, P<0. 001). These first results demonstrate a significant relationship between PS and chronic rejection. Non-rejection-related functional impairment exhibited no decrease in PS. We conclude that our proposed standardized CDE renal study is observer independent. CDE is a promising new technique that provides information on renal allograft dysfunction that is different from classical color Doppler findings. Further studies will clarify its role in renal transplant monitoring and its ability to replace more-invasive techniques.