**2. Ultrasound**

Standard care in detection of AR includes (Doppler-) ultrasound examination. Typical ultra‐ sound findings in cases of AR are rejection-related graft enlargement (swelling, more globular shape), reduction of corticomedullary differentiation, increased echogenicity, prominent me‐ dullary pyramids, or irregularities in the graft perfusion (reversed plateau of diastolic flow), but its specificity and sensitivity for AR is limited, even when echo enhancers are applied [14;15]. Elevated resistance indices can occur in the presence of acute as well as chronic rejec‐ tion. However, values lower than 0.8 are expected and usually values above 0.8 indicate in‐ creased intrarenal pressure as it occurs for example in acute tubular necrosis (ATN) or AR and is linked to a poor longterm renal allograft function [16-18]. Notably, sensitivity and reliability of this method mainly depend on the investigators experience. A comprehensive overview of "What ultrasound can do and cannot do" in diagnostics of renal transplant pathologies was published by Cosgrove and Chan [16]. Using contrast agent or targeted ultrasound in the future, this method might offer significant potential, whereas at present studies are at best at experimental stage and are completely lacking in patients with renal AR.
