Introduction Diagnostic imaging for vesicoureteric reflux (VUR) is a common procedure in children. Currently, three modalities are available for reflux diagnosis, namely voiding cystourethrography (VCUG), radionuclide cystography (RNC) and voiding urosonography (VUS). The last of these is carried out using US in combination with intravesical administration of US contrast agent (UCA). This allows the use of ionizing radiation to be avoided, which is not the case in RNC and VCUG. However, in VCUG a marked reduction in radiation dose has been achieved with the introduction of digital pulsed fluoroscopy. 1 2 3 4 6 7 8 10 11 15 16 17 23 24 25 26 US contrast agent 27 d 8 28 29 Concentration 28 13 15 30 13 30 15 31 Dosage 4 5 13 1 12 28 32 21 15 18 33 34 Physicochemical properties 35 Interaction with normal saline solution 36 2 2 27 37 Interaction with urine 38 Ascent of microbubbles in the ureter 39 Procedural details 28 40 US scan modalities Fundamental imaging 1 Fig. 1 a c b d a b arrow c d b d  Colour Doppler US 32 31 41 11 14 31 41 42 41 42 15 Harmonic imaging 43 43 44 2 17 18 33 17 18 33 Fig. 2 a c b d a b dotted circle c d arrow b d  Dedicated high-MI contrast imaging with multiple display options 3 4 45 Fig. 3 arrow a b c  Fig. 4 arrow a b arrowhead  Procedural steps Precontrast scans of the bladder, ureters and kidneys 28 Intravesical administration of normal saline and US contrast agent 13 28 21 40 28 Postcontrast scan of the bladder, ureters and kidneys 28 23 Postcontrast scan of the bladder, ureters and kidneys during and after voiding 28 Postcontrast scan of the urethra during voiding (urethrosonography) 46 47 16 19 48 51 19 48 49 48 49 19 50 51 16 5 48 49 48 47 19 49 Fig. 5 a b a a B pU aU arrow b  49 Cyclical filling of the bladder 52 53 54 56 54 55 54 55 6 56 Fig. 6 At the end of VUS and bladder emptying there can still be a “layer” of UCA lining the mucosa of the empty bladder. The configuration of the bladder in transverse section in combination with the remaining echogenic UCA resembles the mouth part of a “smile sign”. This sign indicates that there is still sufficient UCA in the bladder and if considered necessary a second filling with normal saline only would suffice to carry out cyclical VUS  Grading of reflux 13 57 58 59 60 1 60 Table 1 Reflux grading in contrast-enhanced VUS Grade Definition I Microbubbles only in the ureter II Microbubbles in the renal pelvis; no significant renal pelvic dilatation III Microbubbles in the renal pelvis + significant renal pelvic dilatation + moderate calyceal dilatation IV Microbubbles in the renal pelvis + significant renal pelvic dilatation + significant calyceal dilatation V Microbubbles in the renal pelvis + significant renal pelvic dilatation and calyceal dilatation + loss of renal pelvis contour + dilated tortuous ureters Duration of VUS examination 12 28 31 42 12 28 31 42 61 55 VUS with a second-generation US contrast agent (SonoVue) 62 63 67 6 62 63 64 67 67 7 65 65 67 Fig. 7 a THI b arrow  Contraindications and adverse events from intravesical administration of US contrast agents 12 20 28 41 42 12 28 42 68 37 29 69 64 67 Conclusion 70