CAKUT is far from rare. The anomalies, which arise when the ureteric bud fails to develop normally from the Wolffian duct or when it interacts defectively with the metanephric blastema during organogenesis, affect more than one percent of live births and account for thirty to fifty percent of all malformations detected before birth. They represent a leading cause of chronic kidney disease in children, and a substantial proportion of affected patients progress toward renal failure if the underlying problems are not identified and managed early. Because some anomalies remain silent while others quietly destroy nephrons, accurate and timely imaging is the linchpin of pediatric nephro-urology, guiding decisions about when to operate, when to monitor, and when to leave well enough alone.

Until now, the diagnostic backbone has been a pairing of ultrasound and dynamic renal scintigraphy. Ultrasound, the universal first-line tool, is safe and widely available but operator-dependent and often imprecise in complex anatomical variants. Dynamic renal scintigraphy using the radiotracer 99mTc-MAG3 has long been considered the gold standard for quantifying split renal function and urinary drainage, but it delivers a dose of ionizing radiation to patients who, in many cases, will need serial follow-up throughout childhood. Vesicoureteral reflux, meanwhile, is assessed separately with voiding cystourethrography or contrast-enhanced voiding urosonography. The result is a piecemeal diagnostic pathway that the Genoa team describes as ripe for consolidation.

Functional MRU collapses that pathway into a so-called one-stop-shop. In a single session, dynamic contrast-enhanced sequences combined with dedicated post-processing software deliver detailed anatomical imaging alongside quantitative measurements of differential renal function, urinary drainage, excretory patterns and urinary flow. Comparative studies cited in the review show that MRU-derived volumetric split renal function estimates, calculated with both area-under-the-curve and Rutland-Patlak kinetic methods, agree well with scintigraphy while demonstrating excellent intra- and inter-reader repeatability. Drainage curve classifications also correspond closely, although the authors note that differences in diuretic timing protocols between the two modalities explain some borderline discrepancies. Crucially, the technique achieves this without a single photon of ionizing radiation, an advantage that compounds over the many follow-up scans a child with CAKUT may require.

The practical protocol described in the review unfolds in three phases: preparation, acquisition and post-processing. Children younger than five are generally studied under sedation, although neonates needing only morphological assessment can be imaged awake using the feed-and-wrap swaddling technique, in which a sleeping, recently fed infant is gently secured in a folded sheet. Cooperative older children may be accompanied by a screened parent. Preparation includes peripheral venous access, intravenous hydration with ten to twenty milliliters per kilogram of saline, and bladder management, catheterization in sedated patients and simple voiding in cooperative ones. Because gadolinium-based contrast agents are cleared exclusively by glomerular filtration, renal function must be verified beforehand through serum creatinine and an estimated glomerular filtration rate calculated with the Schwartz formula.

Acquisition begins with morphology: axial and coronal T2-weighted turbo spin echo sequences with and without fat suppression map the parenchyma, the collecting system and anatomical variants such as duplex systems, while diffusion-weighted imaging flags areas of parenchymal inflammation and three-dimensional heavily T2-weighted sequences hunt for ectopic ureteral insertions. The functional phase then follows a tightly choreographed script. Furosemide at 0.5 to 1 milligram per kilogram, capped at 20 milligrams, is injected immediately before dynamic T1-weighted gradient echo acquisition using the F0 technique. The dynamic sequence runs continuously for twelve to fifteen minutes at high temporal resolution of three to five seconds during the first five minutes, then every thirty seconds, with a 0.1 millimole per kilogram gadolinium bolus delivered after the first three cycles. A three-dimensional angiographic breath-hold study, using a cumulative contrast dose of up to 0.3 millimole per kilogram, follows, and delayed urographic images are captured at five-minute intervals up to twenty minutes to characterize the renal pelvis, ureters and bladder.

The quantitative magic happens in post-processing. The review highlights a new analysis pipeline in which artificial intelligence models automatically segment the kidneys, renal pelvis and abdominal aorta across both morphological and functional volumes, with the operator retaining the ability to review and correct each mask. From these segmentations the software computes absolute and relative renal volumes, percentage-enhancement curves normalized to the pre-contrast baseline, and a battery of functional indices. Drainage curves are classified as normal, borderline or accumulating depending on whether signal intensity falls steadily after its peak, plateaus, or keeps rising, a distinction that directly informs whether hydronephrosis reflects true obstruction requiring surgery or benign stasis. Differential renal function is quantified twice, through the area under the filtration-phase curve and through Rutland-Patlak kinetic modeling referenced to a suprarenal aortic input function, with both measures weighted by parenchymal volume. Two transit-time biomarkers, calyceal transit time and renal transit time, complete the panel, with prolonged values serving as sensitive early indicators of urodynamic impairment.

The clinical payoffs are illustrated condition by condition. In ureteropelvic junction obstruction, the most common cause of upper urinary tract blockage in children, MRU distinguishes intrinsic stenosis from extrinsic compression by a crossing accessory renal artery, a distinction that determines whether surgeons perform a standard Anderson-Hynes dismembered pyeloplasty or a Hellström vascular hitch procedure. A quantitative scoring system proposed in 2022 standardizes MRU-based diagnosis and management of this condition, and postoperative scans can document functional recovery through improving transit times and filtration parameters. In megaureter and ureterovesical junction obstruction, where many cases resolve spontaneously by age two to five, MRU supports conservative surveillance and identifies the minority of children whose declining differential renal function warrants ureteral reimplantation, increasingly performed with robotic assistance.

The technique also excels where scintigraphy struggles. In dysplastic and hypoplastic kidneys, including multicystic dysplastic kidney, precise MR segmentation separates enhancing parenchyma from cysts and collecting systems, and the degree of dysplasia correlates negatively with residual function. In duplex systems, which follow the Weigert-Meyer rule with an obstructed upper moiety and a reflux-prone lower moiety, MRU characterizes each moiety’s separate functional contribution while defining complex anatomy that ultrasound and reflux-only studies cannot. For ectopic, malrotated and fused kidneys such as the horseshoe kidney, dynamic sequences separate harmless urinary stasis from genuine obstruction and reveal aberrant vessels that may compress the ureter. The authors close with a proposal for a structured reporting model intended to standardize MRU interpretation across centers. With sedation requirements low, no adverse events reported, and new AI-driven software interfacing directly with hospital PACS systems, the review positions functional MRU as a cornerstone of personalized, radiation-free care for the most common group of fetal anomalies encountered in modern medicine.

Subject of Research: Functional magnetic resonance urography for evaluating congenital anomalies of the kidney and urinary tract in children

Article Title: How we do it: functional magnetic resonance urography in congenital anomalies of the kidney and urinary tract

Article References: Anfigeno, L., Basso, L., Gnocchi, G., Barbieri, L., Minetti, E., Olivi, B., Verrina, E., Mattioli, G., & Damasio, M. B. (2026). How we do it: functional magnetic resonance urography in congenital anomalies of the kidney and urinary tract. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06745-5

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06745-5

Keywords: functional MR urography, CAKUT, pediatric radiology, kidney anomalies, differential renal function, renal scintigraphy, hydronephrosis, gadolinium contrast, AI segmentation, ureteropelvic junction obstruction, duplex kidney, chronic kidney disease