Apart from physical preparation, psychological preparation is necessary for both, patients and parents as they may be anxious due to fear of pain and unknown, urethral catheterization, and radiation use (Fig. 2) (1). To help both patients and parents relieve the anxiety from the VCUG, providing a translated explanatory pamphlet provided by The Image Gently Campaign of The Alliance for Radiation Safety in Pediatric Imaging (https://www.imagegently.org) can be used as a solution (110). In addition, introducing the procedure to the patients and the parents is also recommended just before the examination (1). Mild sedation can be considered in case of uncooperative patients; however, alert state is preferred for physiologic voiding (1112).

Before the examination, the supplies should be prepared (Fig. 3A). The contrast for VCUG at our institute is prepared by mixing 30 mL of iodine-containing contrast (300 or 350 mg I/mL, Iohexol; BONOREX, Central Medical Service, Seoul, Korea) with 100 mL saline. A tip for contrast is to keep concentration under 30% to avoid chemical irritation (12). Five-French feeding tubes for infants, 8-French feeding tubes for children, or a catheter larger than 8-French feeding tube for adolescents should be used (4). Also, few chlorhexidine balls for skin sterilization, sterile lubricant gel for coating catheter, a plastic extension tubing, a syringe for regurgitating urine bladder, one inch of tape for anchoring catheter to the skin, and sterile surgical drape having a hole are used. A warmer for maintaining body temperature of infant and light for better visibility during catheter insertion are also helpful (Fig. 3B).

Parents are recommended to stand beside their children for comforting them during the procedure. If the patient's mother is pregnant, she is advised to be with the patient only during catheter insertion. For girls, sterilization of perineal skin and interlabial area with chlorhexidine balls is the first step. Next, a surgical drape having a hole should be secured and a catheter coated with lubricant gel should be inserted gently. Anchoring a catheter with tape on the inner thigh is recommended in girls. Often, the labial adhesion is encountered. Unless the urethral opening is exposed, VCUG can be performed after treating labial adhesion and reassessing the need for VCUG (1).

For boys, sterilization of perineal and penile skin including penile tip after retracting foreskin with chlorhexidine balls is the first step. The next step is to secure a surgical drape having a hole, followed by insertion of a catheter coated with lubricant gel, and anchoring catheter with tape to lower abdominal skin and penis. The foreskin is common in an infant, which makes it difficult to insert a catheter. Therefore, retracting the foreskin and exposing the urethral opening is a tip for successful insertion of catheter in boys (1). After finishing catheterization, the foreskin should be reduced. If foreskin is retracted unnecessarily for a longer time, it gets trapped behind the glans, causing edema of the glans (4). Insert the catheter as much as you need by winding it, once inside the urinary bladder. Excessive catheter insertion can trigger knotting within the urinary bladder and may need longer removal time (4). Then, drain naturally or regurgitate urine with a syringe to empty the urinary bladder (12).

Contrast and saline mixture is hanged about 1 m above the table to naturally instill it into the emptied bladder. Do not squeeze plastic bag containing contrast and saline mixture to instill faster because manual pressure can produce artificial VUR. Instill contrast and saline mixture to near full capacity. The estimate of the near full capacity of the urinary bladder is different in children of different ages. Approximate volume of the urinary bladder can be calculated by the formulas (1):

(Kg × 7) mL in an infant

[(age + 2) × 30] mL in children

For example, approximate volume of the urinary bladder is 35 mL in 5 kg infants, 70 mL in 10 kg infant, and 100 mL in 1.5-year-old children. When the bladder is full, the infants begin crying and flexing their toes.

Under the ‘ALARA’ principle, performers should store focused images of critical areas and conditions. Pulsed fluoroscopy with last image hold technique and adjustment of collimators are key strategies to avoid unnecessary exposure to radiation (9). Continuous fluoroscopy should be avoided during filling of urinary bladder; brief and intermittent fluoroscopy is sufficient. Increasing the distance between the child and the X-ray source and removing the antiscatter grid for small patients are also recommended (13). Antiscatter grid itself is source of scattered radiation and is less useful in small patients, because smaller patient leads to less scattered radiation. Moreover, reducing patient dose is closely related to staff protection by reducing scattered radiation from a patient which is proportional to staff radiation.

A standardized evaluation of critical areas and conditions should be ensured and are categorized into anteroposterior (AP) projection of urinary bladder during early filling phase (Fig. 4A), full filling phase of urinary bladder (Fig. 4B), the oblique projection of urinary bladder focusing both UVJs (Fig. 4C, D), an AP projection of urinary bladder during voiding (Fig. 4E), renal collecting system with or without presence of reflux (Fig. 4F), an AP projection of urinary bladder post voiding (Fig. 4G), and lateral projection for urethra during voiding in boys. A scout image is not a significant image in the management decision although its dose is low (14). Therefore, obtaining a routine scout image is not recommended. In the early filling phase, the AP image of urinary bladder demonstrates ureteroceles (Fig. 5). If any abnormality is observed, oblique projections of the urinary bladder to evaluate further distal ureters should be used (Fig. 6A). The presence of ureteroceles with or without eversion, or diverticulum is demonstrated on oblique images clearly (Fig. 6B, C). To grade VUR using VCUG, focused images targeting renal collecting system are essential. In the absence of VUR, capturing images at renal collecting system is recommended for the evidence of negative VUR. Images for the urethra, especially in boys, are easy to be missed, however, it is important. To evaluate urethra, lateral projection during voiding is standardly used. The fluoroscopic time and dose-area product are documented on the last image of study (Fig. 4G). Dimming of room lights, being patient and calm, erect positioning, the sound of flowing water, instilling water on the toes or perineum, and encouragement can be helpful when older girls or adolescents hesitate to void (1). Occasionally, infants void after removal of catheter (11).

The cyclic VCUG is refilling the bladder following voiding in multiple times within the catheter in place and is valuable in infant to avoid missing significant reflux and potential ectopic ureter (Fig. 7) (151617). Refluxed contrast medium is diluted by unopacified urine in the first session. But refluxed contrast medium is better demonstrated on the second session for less dilution. In our institution, two sessions of cyclic VCUG are performed in infants to maximize detection of VUR.

The grading for severity of VUR is according to the International Reflux Study in Children and is based on VCUG (Table 2) (12). The higher the grade and the prolonged the morbidity, worse is the prognosis. Although, mild VUR (grade I and II) resolves spontaneously with age in the first decade of life, timely detection and immediate intervention of severe VUR (grade Ⅲ, IV, and V) is critical to prevent sequels such as renal scarring, hypertension, and end-stage renal diseases (236). To achieve the ultimate goal of VCUG, acquaintance with VUR grading system and appropriate reporting of VUR is essential. Although, the degree of ureteral dilatation depicted in the grading system, criteria for mild, moderate and severe dilatation are not clear (12). The reflux nephropathy (renal scarring) is characterized by atrophy, tubular destruction, and interstitial fibrosis, and almost always accompanies blunting or distortion of the calyx (318). Therefore, it is important to examine calyceal blunting clearly.

In key features, grade I reflux does not reach the renal pelvis and has a questionable clinical impact (Fig. 8) (23). Grade II reflux reaches the renal pelvis but does not dilate fornices (Fig. 9). Grade III reflux does not or minimally deform fornices (Fig. 10). It is borderline grade between grade II and grade IV reflux. Grade IV reflux presents blunt fornices, but the impression of papillae is not visible in majority of papillae (Fig. 11). Grade V reflux is characterized by loss of papillary impression (Fig. 12). In reporting, the maximal degree of VUR is described (12).

On VCUG, the inner wall of urinary bladder on AP projection is smooth and its contour is round. The interureteric ridge which is the elevated border of trigone in cephalad, is visible on the lateral projection at about distal one-quarter of the posteroinferior urinary bladder (Fig. 13). Any other space occupying lesions, fistulous or diverticular structures suggesting mass, urachal remnant, or diverticulum observed during VCUG should be reported.

Urethral evaluation is critical in boys (Fig. 13). Therefore, it is better to prepare the field of view and lateral position to demonstrate optimal view of urethra (4). Posterior urethral valve is the result of remaining and fused anterior mucosal folds which should be absorbed during normal development. Posterior urethral valve may lead to decompensation of the urinary bladder, distal ureteral obstruction, and end-stage renal disease (1). Oligohydramnios, bladder distention, bilateral hydroureteronephrosis, and occasionally fetal ascites are the manifestation of the severe obstruction of posterior urethral valve (12). Normal fold at posterior urethra is often seen, therefore, along with flap-like filling defect, disproportional dilatation of posterior urethra during voiding is also observed in posterior urethral valve (1). Removal of the catheter during voiding is recommended for proper evaluation of posterior urethral valve (1).