Pediatric magnetic resonance urography

Abstract

Magnetic resonance urography (MRU) is a powerful clinical tool that fuses anatomic information with functional data in a single test without the use of ionizing radiation. This article provides an overview of the technical aspects, as well as common clinical applications with an emphasis on the evaluation of hydronephrosis. A fluid challenge is an essential part of our MRU protocol and enables the definition of compensated or decompensated kidneys within the spectrum of hydronephrosis. This classification may have prognostic implications when surgery is being considered. In addition, underlying uropathy can be identified on the anatomical scans and renal scarring can be seen on both the anatomical and dynamic scans. MRU can identify and categorize dysmorphic kidneys in vivo and may provide insight into congenital abnormalities seen in conjunction with vesicoureteric reflux. MRU is still in its infancy and as the technique develops and becomes widely available, it seems likely that it will supplant renal scintigraphy in the evaluation of renal tract disorders in children. MAGNETIC RESONANCE UROGRAPHY (MRU) represents the next step in the evolution of uroradiology in children because it fuses superb anatomic and functional imaging in a single test that does not use ionizing radiation. MRU has advantages over other modalities in that it generates tissue contrast from a variety of sources. In addition to spin echo T1 and T2 images, dynamic imaging is performed in conjunction with the injection of a gadolinium-based contrast agent (GBCA) in order to assess the concentrating and excretory functions of the kidney. The evaluation of the contrast dynamics is similar to renal scintigraphy but with the important distinction that the signals originating from the renal parenchyma can be separated from those originating from the collecting system. While MR is not used routinely to assess the degree of vesicoureteric reflux (VUR), it can detect the anatomical consequences of VUR in terms of dilated ureters, distorted anatomy of the collecting system and renal scarring, and the functional consequences of renal scarring.We have performed MR urograms on close to 2000 children over the last 8 years and have found that meticulous attention to patient preparation and scanning technique is essential if high-quality images are to be reliably obtained, with appropriate hydration and sedation being key factors in the success of the examination. There have been several publications assessing the ability of MRU to reliably quantify the glomerular filtration rate (GFR) using an arterial input function (AIF) derived from the aorta and the signal curves measured in the renal parenchyma (1-3); however, there are still a number of problems to be addressed before this becomes a clinical reality (4). Thus, we have based our approach on deriving measures that can be thought of as indices of renal function in that they are correlated with, but not necessarily equal to, the GFR. We use these to derive several measures of differential renal function...

Chronic Urinary Obstruction: Evaluation of Dynamic Contrast-enhanced MR Urography for Measurement of Split Renal Function

“…The Patlak-Rutland plot method must take into account the input function estimated from heart and lung ROI measurements at RS (7) and from an ROI in the abdominal aorta at DCE MR urography (22,28). Other functional criteria at DCE MR urography have been published (1,5,11,(14)(15)(16), such as the slope of the uptake curve, the volume of contrast-enhancing renal parenchyma, the transit time between the cortex and the upper ureter and the 2-3-minute ratio of uptake as functional parameters.…”

“…Dynamic pulse sequences performed after injection of an intravenous bolus of gadolinium chelates (ie, dynamic contrast material-enhanced [DCE] MR urography) have been used to calculate the percentage of SRF from time-intensity curves. Investigators (1,5,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) have reported significant correlation of DCE MR urographic results with SRF derived from radioscintigraphy in a number of single-center studies. Two methods have been developed to calculate the SRF from the time-intensity curve: (a) the area under the curve (AUC) method (18)(19)(20) and (b) the Patlak-Rutland method, which is currently the reference method used with RS (7).…”

Renal parenchyma impairment characterization in partial unilateral ureteral obstruction in mice with intravoxel incoherent motion‐MRI

“…The indication for surgery generally depends on imaging criteria, requiring a few months of follow‐up of the patients. Renal function and kidney morphology data are evaluated by renal ultrasound, renal scintigraphy and, more recently, uro‐magnetic resonance imaging (uro‐MRI) . These investigations are non‐invasive, but poorly predict the optimal timing of surgery and renal recovery after surgical repair.…”

Dynamic MR urography in children with uropathic disease with a combined 2D and 3D acquisition protocol—comparison with MAG3 scintigraphy

“…Other protocols currently proposed 15 favour 3D spoiled gradientecho sequences providing higher spatial resolution. However, longer acquisition times of repetitive 3D measurements are more susceptible to breathing artefacts, which are particularly evident in older children.…”