Ultrasound contrast agents allow the display of the excretory urinary tract and the demonstration of vesicoureteral reflux of urine from the bladder up to the kidney in children.

For the assessment of urinary reflux the bladder is filled with physiological saline solution and a small amount of microbubble contrast agent is added to make the fluid in the bladder echogenic. The distribution and potential reflux of the bladder content can be assessed after instillation and during subsequent micturition, creating an increased pressure in the bladder.

The urine reflux can be graded using the scale below:

grade I: reflux into the ureter, not reaching the renal pelvis

grade II: reflux reaches renal pelvis, without dilatation of the ureter

grade III: mild dilatation of the renal pelvis, with no significant changes of the renal calix

grade IV: moderate dilatation of the renal pelvis, renal fornix blunted but papillary impressions still visible

grade V: strong dilatation of the ureter with kinking, pelvicalyceal system highly dilated, loss of papillary impressions

The advantage of CEUS is the possibility of a dynamic examination in realtime. Bladder filling, microbubble distribution and potential reflux and micturition can be assessed continuously and repeated multiple times. The examination does not include ionising radiation and administration of radioactive or viscous solutions. Usually no sedation and/or fixation of the child is required and the parents can stay in the examination room. The prolonged stability of modern ultrasound contrast agents provides sufficient time for a thorough examination of both sides of the urinary tract.