[Imaging after kidney transplantation in childhood and adolescence].

The ultrasound (US) examination is the most important imaging procedure in the clinical care of children with chronic kidney disease, the assessment before kidney transplantation and in the acute and chronic phase after successful kidney transplantation. In trained hands, particularly with experience in Doppler sonography, US ensures that vascular complications, such as occlusions, thrombosis, stenosis as well as non-vascular complications, e.g., urinary tract dilatation, abscesses, hematomas, urine leaks or lymphoceles, are cost-effectively and rapidly diagnosed at any time. For the diagnosis of acute rejection, the US signs in the intraindividual course are only suggestive, but not specific. The gold standard for the diagnosis of acute rejection is a kidney biopsy. In these cases, US serves to exclude other causes. The use of multimodal techniques, various Doppler techniques and microvascular procedures, such as superb microvascular imaging (SMI) or B‑flow and contrast-enhanced ultrasonography (CEUS), optimizes the imaging in the context of transplantations in children. Magnetic resonance imaging with diffusion-weighed imaging (DWI), magnetic resonance angiography (MRA) and magnetic resonance urography (MRU) as well as functional MRU (fMRU) performed with the administration of gadolinium-containing contrast agents, are part of the extended diagnostics and possibly necessary for surgical planning in the early phase after kidney transplantation and for long-term assessment after transplantation. Excretory urography is associated with ionizing radiation and intravenous administration of iodine-containing contrast medium and is obsolete in children. Computed tomography (CT) using age-adapted and weight-adapted dose protocols is an alternative in emergencies if MRI is not available.