Renal transit time with MR urography in children

Magnetic resonance urography: a practical approach to preparation, protocol and interpretation

Magnetic resonance urography (MRU) is an important MRI application that provides noninvasive comprehensive morphological and functional evaluation of the kidneys and urinary tract. It can be used to assess congenital anomalies of the kidney and urinary tract, which often present as urinary tract dilation. In children, MRU allows for high tissue contrast and high spatial resolution without requiring ionizing radiation. Magnetic resonance urography requires patient preparation in the form of pre-examination intravenous hydration, placement of a urinary catheter, and the administration of diuretics at the time of the exam. The imaging protocol is based on T2-weighted images for anatomical assessment and dynamic post-contrast images for functional evaluation. These images are then used to generate quantitative and graphic results including contrast transit and excretion time as well as to calculate differential renal function. This review focuses on a simple approach to pediatric MRU acquisition and interpretation based on clinical cases and the authors' experience.

Quantitative renal magnetic resonance imaging: magnetic resonance urography

The goal of functional renal imaging is to identify and quantitate irreversible renal damage and nephron loss, as well as potentially reversible hemodynamic changes. MR urography has evolved into a comprehensive evaluation of the urinary tract that combines anatomical imaging with functional evaluation in a single test without ionizing radiation. Quantitative functional MR imaging is based on dynamic contrast-enhanced MR acquisitions that provide progressive, visible enhancement of the renal parenchyma and urinary tract. The signal changes related to perfusion, concentration and excretion of the contrast agent can be evaluated using both quantitative and qualitative measures. Functional evaluation with MR has continued to improve as a result of significant technical advances allowing for faster image acquisition as well as the development of new tracer kinetic models of renal function. The most common indications for MR urography in children are the evaluation of congenital anomalies of the kidney and urinary tract including hydronephrosis and renal malformations, and the identification of ectopic ureters in children with incontinence. In this paper, we review the underlying acquisition schemes and techniques used to generate quantitative functional parameters including the differential renal function (DRF), asymmetry index, mean transit time (MTT), signal intensity versus time curves as well as the calculation of individual kidney glomerular filtration rate (GFR). Visual inspection and semi-quantitative assessment using the renal transit time (RTT) and calyceal transit times (CTT) are fundamental to accurate diagnosis and are used as a basis for the interpretation of the quantitative data. The importance of visual assessment of the images cannot be overstated when analyzing the quantitative measures of renal function.

The Emerging Role of MR Urography in Imaging Megaureters in Children

INTRODUCTION

Megaureter, described as ureter dilatation more than 7 mm in diameter, commonly associated with other anomalies, is still a diagnostic and therapeutic challenge. Magnetic resonance urography (MRU) appears as a promising method in urinary tract imaging, providing both anatomical and functional information. There are several postprocessing tools to assess renal function (including differential renal function) and severity of ureteral obstruction based on MRU. Still, the place of this method in the diagnostic algorithm of ureteropelvicalyceal dilatation with megaureter remains underestimated. Analysis of imaging findings in a group of children diagnosed with megaureter was done.

MATERIAL AND METHODS

A retrospective analysis of magnetic resonance urography (MRU) was performed in 142 consecutive patients examined from January 2013 to September 2019. Twenty-five patients meeting the criteria of megaureter (dilatation more than 7 mm) in MRU were included in the further analysis. The MRU, ultrasound (US), and scintigraphy results were compared and analyzed together and compared with clinical data.

RESULTS

The sensitivity and specificity of US was comparable to the MRU in the assessment of upper urinary tract morphology (p > 0.05). In five out of 25 children, megaureter was found in each kidney; in a single case, both poles of a duplex kidney were affected. In the diagnosis of ureter ectopia, the MRU was superior to the US for which sensitivity did not exceed 16%. The US showed limited value in the diagnostics of segmental ureter dysplasia as a cause of primary megaureter when compared with MRU. Four cases were visualized in MRU studies, whereas the US examination was negative (all confirmed during surgery). There was a moderate correlation between relative renal function between fMRU and scintigraphy (t = 0.721, p = 0.477) and in the severity of obstruction assessment between both methods (r = 0.441, p < 0.05). However, in 10 kidneys with megaureter, the results in scintigraphy were inconclusive due to the signal from the megaureter imposing on the renal field.

CONCLUSIONS

MRU seems to be a preferred method in the diagnostic algorithm for megaureter, providing both anatomical and functional information. MRU is superior to US and scintigraphy in diagnosing urinary tract anomalies with megaureter.

Potential benefits of functional magnetic resonance urography (fMRU) over MAG3 renal scan in children with obstructive uropathy

INTRODUCTION

Functional renal imaging, most commonly with MAG3 nuclear medicine renal scan, is recommended in the evaluation of children with urinary tract dilation (UTD) suspected of obstructive uropathy. Alternatively, renal function can be evaluated with functional Magnetic Resonance Urography (fMRU), which has superior anatomic detail. However, there are not enough data comparing both methods' equivalency. In this study, we compare the functional and obstruction parameters of fMRU and MAG3 in a pediatric cohort presenting with obstructive uropathy.

STUDY DESIGN

This is an IRB-approved retrospective review of all children undergoing fMRU at a single, free-standing children's hospital between May 2008 and September 2017. Patients who also underwent a MAG3 renal scan within 6 months and who had no interval surgical intervention were included in the study. Bladder catheterization was performed prior to both imaging studies.

RESULTS

735 children had 988 fMRU studies performed during the study period. 37 unique patients (13 girls and 24 boys) with median age of 6 months (range: 2 mo-19 y) were included in the final sample. Median time interval between studies was 70 days (range 6-179 days). The majority of participants (26/37, 70.3%) presented with UTD P3 and had diagnosis of uretero-pelvic junction obstruction (UPJO) in 21/37. Differential renal function (DRF) was used to group 10 fMRU and 9 MAG3 patients as normal; 9 fMRU and 11 MAG3 as mild; 11 fMRU and 6 MAG3 as moderate; and 7 fMRU and 6 MAG3 as severe; Wilcoxon signed-rank test (p = 0.5106). Results were similar for DRF among patients with and without duplex kidneys. In the analysis of obstruction, using reference standard T½ MAG3 ≥ 20 min, a greater or equal than 6 min renal transit time (RTT) from fMRU showed a specificity of 94%, a sensitivity of 62%, and an AUC of 0.827.

DISCUSSION AND CONCLUSIONS

The differential renal function determined by MAG3 and fMRU in children was not statistically different, therefore we concluded that it was similar and potentially equivalent. Better correlation was shown in patients who had normal split kidney function. While the tests are clinically equivalent, the variability of DRF within each clinical category (i.e., normal, mild, moderate, severe) is not surprising, because MAG3 does not clearly differentiate the dilated collecting system from the functional parenchymal tissue, while fMRU does. Using MAG3 as the gold standard, fMRU was 94.74% specific and 5% more sensitive in detecting UPJO with a RTT of 6min vs. 8min.

Febrile Urinary Tract Infections in Children with Primary Non-Refluxing Megaureter: A Systematic Review and Meta-Analysis

BACKGROUND

Knowledge of the baseline risk of febrile urinary tract infections in patients with primary non-refluxing megaureter can help clinicians to make informed decisions for offering continuous antibiotic prophylaxis.

OBJECTIVE

The primary objective of this systematic review was to determine the pooled prevalence of febrile urinary tract infections in patients with primary non-refluxing megaureter selected for primary non-surgical management independent of associated attributed risk factors at initial presentation in order to assess the value of continuous antibiotic prophylaxis.

METHODS

MEDLINE, EMBASE, and Cochrane Controlled Trials Register electronic databases were searched for eligible studies without language and time restriction. The systematic review was carried out following the recommendations of the Cochrane Collaboration and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. (PROSPERO registration number CRD42018104752).

RESULTS

Of 25 871 records, 16 studies (n=749 patients) were eligible for inclusion. The overall pooled prevalence of febrile urinary tract infections in patients with primary non-refluxing megaureter was 14.35% (95% confidence interval: 8.8-22.6). The calculated number needed to treat for patients on continuous antibiotic prophylaxis to prevent one single febrile urinary tract infection over the course of 1-2 years would be 4.3.

CONCLUSION

Based on the current available evidence the use of continuous antibiotic prophylaxis for children with PM selected for primary non-surgical treatment should be taken into consideration, at least in patients with urinary outflow impairment, higher grade of ureteral dilatation, and for children in the first months of life.

Color Doppler Ultrasonography in Evaluating the Outcomes of Pyeloplasty in Ureteropelvic Junction Obstruction

Purpose

To evaluate the accuracy of Color Doppler ultrasonography for diagnosing post pyeloplasty elimination of obstruction in Ureteropelvic Junction Obstruction patients.

Methodology

Patients with the diagnosis of UPJO enrolled in the study and underwent open pyeloplasty. Three to 6 months after the operation, patients were recalled and underwent isotope scan as the gold standard test and renal color Doppler ultrasonography to assess the success rate of pyeloplasty.

Results

A total of 39 patients were evaluated and analyzed. The average follow-up time for patients was 9.1 months. The success rate of surgery in the study population was 100%. The mean RI of the affected side before the operation was 0.69 ± 0.01 and after the pyeloplasty, it reached to 0.65 ± 0.01. The difference between the mean RI of the affected side before and after the operation is 0.04 (P < 0.001). Age, type and severity of obstruction and the technique of surgery did not have any impact on these parameters. The difference between the RI of the affected and healthy side was termed ΔRI. ΔRI before and after the operation was 0.084 and 0.014, respectively. The decrease of ΔRI in the case of pyeloplasty is 0.07 on average (P < 0.001), which can be predicted for pyeloplasty success.

Discussion

Color Doppler ultrasonography can be used as a non-invasive, fast, non-expensive, and available modality for evaluating the outcome of pyeloplasty instead of the nuclear scan or IVP.

State-of-the-Art Renal Imaging in Children

Imaging modalities for diagnosing kidney and urinary tract disorders in children have developed rapidly over the last decade largely because of advancement of modern technology. General pediatricians and neonatologists are often the front line in detecting renal anomalies. There is a lack of knowledge of the applicability, indications, and nephrotoxic risks of novel renal imaging modalities. Here we describe the clinical impact of congenital anomalies of the kidneys and urinary tract and describe pediatric-specific renal imaging techniques by providing a practical guideline for the diagnosis of kidney and urinary tract disorders.

Morphologic and functional evaluation of duplicated renal collecting systems with MR urography: A descriptive analysis

PURPOSE

To describe the morphology and function of duplicated collecting systems in pediatric patients undergoing functional MR urography (fMRU).

METHODS

This is a HIPAA compliant IRB approved retrospective study of all patients with duplicated renal collecting systems undergoing fMRU at our institution between 2010 and 2017. Two pediatric radiologists evaluated the studies to determine the presence, morphology and function of duplicated collecting systems using both T2-weighted and dynamic post-contrast fat saturated T1-weighted images. Assessed morphologic features included pelvic and calyceal dilation, partial or complete ureteral duplication, ureteral dilation, ectopic ureteral insertion and ureteroceles. Functional analysis was carried out per moiety.

RESULTS

A total of 86 examinations (63 girls; 23 boys), median age 2.6 years (Standard Deviation 6.4 years, interquartile range: 0.4-10.3 years) and 107 kidneys (39 right; 30 left and 19 bilateral), which yielded 214 evaluable moieties, were included in the final sample. One hundred and sixty-three (76.1%) of the moieties had normal morphological features and normal functional results (average calyceal transit time and renal transit time of 2 min 28 s and 3 min 16 s, respectively). The remaining 51 moieties (23.8%) were hypoplastic or dysplastic. Seventy-seven (35.9%) had pelvic and calyceal dilation. Slightly more than half of the kidneys had complete ureteral duplication (60/107; 56%); 50 (50/107, 46.7%) had ectopic ureters (23 intra- and 27 extravesical) and 9 (9/107, 8.4%) had ureteroceles.

CONCLUSION

fMRU provides comprehensive information regarding the morphology and function of duplicated renal collecting systems in children. In particular, fMRU is useful for assessing barely or non-functioning renal poles and ectopic ureters.

Prenatal Urinary Tract Dilatation

Urinary tract dilatation (UTD) is the most common congenital anomaly detected on prenatal ultrasonography (US), affecting 1% to 3% of all pregnancies. This article focuses on the prenatal detection of UTD and the postnatal evaluation and management based on the UTD grading system risk assessment. Prophylactic antibiotics and postnatal imaging are discussed. The recent management trend is for a more conservative approach to minimize unnecessary testing and exposures to the fetus and neonate while detecting those who may have clinically significant disorder. The renal bladder US remains a critical part of the evaluation and helps guide further investigations.

Dynamic MRI and isotope renogram in the functional evaluation of pelviureteric junction obstruction: A comparative study

OBJECTIVE

The aim of this study was to evaluate and compare the diagnostic accuracy of dynamic contrast- enhanced magnetic resonance imaging (dMRI) and isotope renogram in the functional evaluation of pelviureteric junction obstruction (PUJO).

MATERIAL AND METHODS

Forty-two patients included in the study were investigated with isotope renogram and subsequently, subjected to dMRI. Time-activity curves were generated for both isotope renogram and dMRI. Out of the 42 cases, 9 cases were conservatively managed. Thirty-three cases were taken up for surgical intervention.

RESULTS

Of 33 patients taken up for surgical intervention, 12 underwent laparoscopic nephrectomy and 21 of them pyeloplasty. The mean glomerular filtration rates (GFRs) as measured by isotope renogram and dMRI were 22.5+4.2 mL/min and 23.8+3.1 mL/min respectively. The calculation of GFR by isotope renogram, showed good correlation with that of dMRI with correlation coefficient of 0.93. The dMRI was able to reveal the functional status of the renal unit accurately. dMRI did not yield false positive results with 20 of 21 patients scheduled for pyeloplasty and 11 of 12 patients scheduled for nephrectomy. Isotope renogram had a false positive result in 3 cases compared with surgical diagnosis.

CONCLUSION

Analysis of renal function using dMRI yielded results comparable to those of renal scintigraphy, with superior spatial and contrast resolution. It was also better in prompting management decisions with respect to the obstructed systems. dMRI can be used as a "one stop imaging examination" that can replace different imaging methods used for morphological, etiological and functional evaluation of PUJO.

Imaging in children with unilateral ureteropelvic junction obstruction: time to reduce investigations?

The objective of the study was the development of an abridged risk-stratified imaging algorithm for the management of children with unilateral ureteropelvic junction obstruction (UPJO). Data on timing, frequency and duration of diagnostic imaging in children with unilateral UPJO was extracted retrospectively. Based on these findings, an abridged imaging algorithm was developed without changing the intended management by the clinicians and the outcome of the individual patient. The potential reduction of imaging studies was analysed and stratified by risk and management groups. The reduction in imaging studies, seen for ultrasound (US) and functional imaging (FI), was 45% each. On average, this is equivalent to 3 US and 1 FI studies less for every patient within the study period. The change was more pronounced in the low-risk groups. Progression of UPJO never occurred after 2 years of age and all secondary surgeries were carried out until the age of 3.

CONCLUSIONS

Although our findings need to be validated by further prospective research, the developed imaging algorithm represents a risk-stratified approach towards less imaging studies in children with unilateral UPJO, and a follow-up beyond 3 years of age should be considered only in selected cases at the discretion of the clinician. What is Known: • ultrasound and functional imaging represent an integral part of therapeutic decision-making in children with unilateral ureteropelvic junction obstruction • imaging studies cannot accurately assess which patients are in need of surgical intervention, therefore close, serial imaging is preferred What is New: • a new, risk-stratified imaging algorithm was developed for the first 3 years of life • applying this algorithm could lead to a considerable reduction of imaging studies, and also the associated risks and health-care costs.

Automatic renal segmentation for MR urography using 3D-GrabCut and random forests

PURPOSE

To introduce and evaluate a fully automated renal segmentation technique for glomerular filtration rate (GFR) assessment in children.

METHODS

An image segmentation method based on iterative graph cuts (GrabCut) was modified to work on time-resolved 3D dynamic contrast-enhanced MRI data sets. A random forest classifier was trained to further segment the renal tissue into cortex, medulla, and the collecting system. The algorithm was tested on 26 subjects and the segmentation results were compared to the manually drawn segmentation maps using the F1-score metric. A two-compartment model was used to estimate the GFR of each subject using both automatically and manually generated segmentation maps.

RESULTS

Segmentation maps generated automatically showed high similarity to the manually drawn maps for the whole-kidney (F1 = 0.93) and renal cortex (F1 = 0.86). GFR estimations using whole-kidney segmentation maps from the automatic method were highly correlated (Spearman's ρ = 0.99) to the GFR values obtained from manual maps. The mean GFR estimation error of the automatic method was 2.98 ± 0.66% with an average segmentation time of 45 s per patient.

CONCLUSION

The automatic segmentation method performs as well as the manual segmentation for GFR estimation and reduces the segmentation time from several hours to 45 s. Magn Reson Med 79:1696-1707, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Detection of obstructive uropathy and assessment of differential renal function using two functional magnetic resonance urography tools. A comparison with diuretic renal scintigraphy in infants and children

AIM

After detection of obstructive uropathy (OU), the indication for or against surgery is primarily based on the differential renal function (DRF). This is to compare functional magnetic resonance urography (fMRU) with dynamic renal scintigraphy (DRS) to assess OU and DRF in infants and children.

PATIENTS, METHODS

Retrospective analysis in 30 patients (female: 16; male: 14; median age: 5.5 years [0.2-16.5]), divided into subgroup A (age: 0-2 years; n = 16) and B (> 2-17 years; n = 14). fMRU was assessed by measuring renal transit time (RTT) and volumetric DRF with CHOP fMRU tool (CT) and ImageJ MRU plug-in (IJ). OU detection by fMRU was compared with DRS (standard of reference) using areas under the curves (AUC) in ROC analyses. Concordant DRF was assumed if absolute deviation between fMRU and DRS was ≤ 5 %.

RESULTS

DRS confirmed fixed OU in 4/31 kidneys (12.9 %) in subgroup A. AUC of CT was 0.94 compared with 0.93 by IJ. Subgroup B showed fixed OU in 1/21 kidneys (4.8 %) with AUCs of 0.98 each. RTT measured neither by CT nor by IJ in confirmed fixed OU was < 1200 s - resulting in negative predictive values of 1.0 each. In subgroup A, DRF was concordant in 81.3 % of the kidneys for CT and DRS compared with 75.0 % for IJ and DRS. In subgroup B, CT and DRS were concordant in 91.7 %, and IJ and DRS in 45.8 % of the kidneys.

CONCLUSION

fMRU accurately excluded fixed OU in infants and children, independent from the software used for quantification. However, assessment of DRF with fMRU deviated from DRS especially in infants who may profit most from early intervention. Thus, fMRU cannot fully replace DRS as primary functional examination. If, for clinical reasons, fMRU is performed in first place and it cannot exclude fixed OU, it should be followed by DRS for validation and DRF quantification.

Comparison of intravenous urography and magnetic resonance urography in preoperative evaluation of pelvi-ureteric junction obstruction in children

Aims:

To compare intravenous urography (IVU) and magnetic resonance urography (MRU) in the preoperative evaluation of pelvi-ureteric junction obstruction (PUJO) in children.

Materials and Methods:

A total of 35 children up to 10 years of age in whom unilateral or bilateral PUJO were suspected on ultrasonography were enrolled in this prospective study. All children underwent IVU and MRU, and the findings were compared.

Results:

Of the 70 kidneys evaluated, 14 (20%) were not visualized on IVU because of nonexcretion of contrast, whereas all the 70 (100%) kidneys were visualized on MRU. On IVU, nephrogram was not visualized in 66 (94.2%) of the 70 kidneys, whereas MRU showed prompt and homogeneous nephrogram in 68 (97.1%) of the 70 kidneys. No evidence of PUJO was seen in 31 (44.2%) kidneys on both IVU and MRU. IVU showed PUJO in 26 (37.1%) kidneys, whereas MRU showed it in 38 (54.2%) kidneys. MRU detected two duplex systems that were missed on IVU. A focal renal lesion and two incidental extra renal abnormalities were detected on MRU, which were not visualized on IVU.

Conclusion:

MRU is better than IVU, especially in case of poorly functioning kidneys which are not visualized on IVU. MRU also provides anatomic details of the ureter and vessels with better evaluation of renal parenchyma. It also has an additional advantage of detecting incidental extra renal abnormalities, if present.

MR urography in children and adolescents: techniques and clinical applications

Renal and urinary tract imaging is commonly performed in the pediatric population, particularly in the setting of suspected or known congenital anomalies. In most cases, adequate anatomic assessment can be achieved using ultrasound and fluoroscopic techniques, and evaluation of differential renal function and urinary tract drainage can be accomplished with renal scintigraphy. However, in a subset of children, anatomic or functional questions may remain after this routine evaluation. In this setting, magnetic resonance imaging (MRI) tailored to evaluate the kidneys and urinary tract, known as MR urography (MRU), can be used to depict the kidneys, ureters, and urinary bladder in detail and to determine differential renal function and assess urinary tract drainage. The objectives of this review article are to (1) describe pediatric-specific MRI techniques for assessment of the kidneys and urinary tract and (2) present common clinical applications for pediatric MRU where imaging can "add value" in terms of diagnosis and patient management.

Detailed evaluation of the upper urinary tract in patients with prune belly syndrome using magnetic resonance urography

INTRODUCTION

Magnetic resonance urography (MRU) has proven to be useful in the setting of complex urologic anatomy. Prune belly syndrome (PBS) patients are known to have malformed and highly variable urinary tract anatomy due to significant dilation and renal dysplasia.

OBJECTIVE

To further characterize the renal and ureteral anatomy and renal function in patients with PBS via MRU.

STUDY DESIGN

Children with PBS undergoing MRU (2006-2011) were identified. Studies were performed to evaluate severe hydronephrosis in all patients. Demographics, previous imaging, and MRU findings were collected. A single radiologist reviewed all studies.

RESULTS

MRU was performed on 13 boys, with a median age of 29.3 months (IQR 6-97). Two patients underwent >1 study for ureteropelvic junction obstruction (UPJ obstruction) and calyceal diverticulum with a solitary kidney, respectively. Hydroureteronephrosis (HUN) was identified in 12 boys (92%), while one (8%) did not have ureteral dilation. All patients demonstrated morphologic abnormalities beyond HUN as follows: five (38%) renal dysplasia; five (38%) scarring; four (31%) calyceal diverticula; and three (23%) thickened bladder. The median renal transit time (RTT) was 6 min (IQR 3.5-10.5), and >8 min (range 8.5-35) in six patients; one patient was ultimately diagnosed with obstruction. The mean serum creatinine was 0.5 ± 0.3 mg/dl. This summary figure is a coronal excretory phase T1 MRU image demonstrating absence of well-defined calyces and a 5-cm calyceal diverticulum (white arrow).

DISCUSSION

This study reports significant anatomic and functional findings on MRU that were not readily apparent when using standard imaging for children with PBS. The high-resolution images and functional data obtained with MRU allowed for visualization of calyceal diverticula and abnormal renal pelvic anatomy not previously described in PBS. In addition, renal dysplasia could be identified with MRU, which is badly characterized in the PBS population outside of renal biopsy studies. Potential limitations of the study included its nature as a small retrospective case series, which limited the ability to compare imaging modalities. Imaging modalities were based on individual clinical needs; therefore, comparison with diuretic renal scintigraphy was limited.

CONCLUSION

MRU provided anatomic and functional details of the urinary tract in children with PBS that allowed for characterization of new renal anatomic abnormalities, including the incidence of calyceal diverticula and renal dysplasia, which have not been previously described. While renal scarring, dysplasia and calyceal diverticula were easily discerned on MRU in ten patients, their clinical significance requires longer follow-up in a larger patient population.

High temporal resolution dynamic MRI and arterial input function for assessment of GFR in pediatric subjects

PURPOSE

To introduce a respiratory-gated high-spatiotemporal-resolution dynamic-contrast-enhanced MRI technique and a high-temporal-resolution aortic input function (HTR-AIF) estimation method for glomerular filtration rate (GFR) assessment in children.

METHODS

A high-spatiotemporal-resolution DCE-MRI method with view-shared reconstruction was modified to incorporate respiratory gating, and an AIF estimation method that uses a fraction of the k-space data from each respiratory period was developed (HTR-AIF). The method was validated using realistic digital phantom simulations and demonstrated on clinical subjects. The GFR estimates using HTR-AIF were compared with estimates obtained by using an AIF derived directly from the view-shared images.

RESULTS

Digital phantom simulations showed that using the HTR-AIF technique gives more accurate AIF estimates (RMSE = 0.0932) compared with the existing estimation method (RMSE = 0.2059) that used view-sharing (VS). For simulated GFR > 27 mL/min, GFR estimation error was between 32% and 17% using view-shared AIF, whereas estimation error was less than 10% using HTR-AIF. In all clinical subjects, the HTR-AIF method resulted in higher GFR estimations than the view-shared method.

CONCLUSION

The HTR-AIF method improves the accuracy of both the AIF and GFR estimates derived from the respiratory-gated acquisitions, and makes GFR estimation feasible in free-breathing pediatric subjects.

Congenital midureteric stricture: challenges in diagnosis and management

Background. Congenital midureteric stricture (MUS) is a rare malformation. We report our experience with five cases seen over a period of 4 years from 2010 to 2014. Materials and Methods. The study was based on the retrospective analysis of five patients diagnosed as having MUS. Diagnosis was suspected after fetal ultrasonography (USG) in one patient and magnetic resonance urography (MRU) in four patients. Retrograde pyelography (RGP) was performed on three patients. The final diagnosis was confirmed during surgical exploration in all the patients. Results. MRU was found to be a good investigation method. It showed the site of obstruction in the ureter in all instances. Intravenous urography detected proximal ureteric dilatation present in two of the patients. RGP delineates the level of stricture and the course of ureter, as shown in our cases. All patients had significant obstruction on the affected side. Four patients underwent ureteroureterostomy, all of whom had satisfactory results. In one patient, ureteric reimplantation was carried out due to distal small ureteric caliber. Conclusion. This rare entity is often misdiagnosed initially as pelviureteric junction obstruction. MRU is an excellent option for the anatomical location and functional assessment of the involved system. At the time of surgical correction of a ureteral obstruction, RGP is a useful adjunct for delineating the stricture level and morphology.

Magnetic resonance urography for diagnosis of pediatric ureteral stricture

PURPOSE

Ureteral stricture is a rare cause of hydronephrosis in children and is often misdiagnosed on ultrasound (US) and diuretic renal scintigraphy (DRS), requiring intraoperative diagnosis. We evaluated ureteral strictures diagnosed by magnetic resonance urography (MRU) at our institution.

MATERIALS AND METHODS

Children with ureteral stricture who underwent MRU were identified. Patient demographics, prior imaging, MRU findings, and management were assessed. The efficacy of MRU in diagnosis of stricture was compared with US and DRS. Patients with ureteropelvic or ureterovesical junction obstruction were excluded.

RESULTS

Twenty-eight ureteral strictures diagnosed by MRU between 2003 and 2013 were identified; 22% of strictures were diagnosed by DRS ± US. The mean age at MRU diagnosis was 2.4 years (range 4 weeks-15 years). Hydronephrosis was the most common presentation, accounting for 20 (71%) cases. Other etiologies included pain (3), incontinence (2), and urinary tract infection, cystic kidney, and absent kidney, present in one case each. A mean of 2.7 imaging studies was obtained prior to MRU diagnosis. Twenty-one (75%) ureteral strictures required surgical intervention, with the approach dependent upon location.

CONCLUSIONS

MRU provides excellent anatomic and functional detail of the collecting system, leading to accurate diagnosis and management of ureteral stricture in children.

Comparison of magnetic resonance imaging with radionuclide methods of evaluating the kidney

Nuclear medicine and MRI provide information about renal perfusion, function (glomerular filtration rate), and drainage. Some tracers that are used in nuclear medicine (technetium-diethylene triamine pentaacetic acid ([(99m)Tc-DTPA] and (51)chromium-EDTA) and some contrast media (CM) that are used for MRI (gadolinium-DTPA for instance) share the same pharmacokinetic properties, though, detection techniques are different (low-spatial resolution 2-dimensional projection with a good concentration-to-signal linearity for nuclear medicine and high-resolution 3-dimensional localization with nonlinear behavior for MRI). Thus, though based on the same principles, the methods are not the same and they provide somewhat different information. Many MRI perfusion studies have been conducted; some of them were compared with nuclear medicine with no good agreement. Phase contrast can reliably assess global renal blood flow but not perfusion at a tissular level. Arterial spin labeling has not proven to be a reliable tool to measure renal perfusion. Techniques using CM theoretically can assess perfusion at the tissular level, but they have not proven to be precise. To assess renal function, many models have been proposed. Some MRI techniques using CM, both semiquantitative (Patlak) and quantitative, have shown ability to roughly assess relative function. Some quantitative methods (Annet's and Lee's methods) have even showed that they could roughly estimate absolute renal function, with better results than estimated glomerular filtration rate. Quantification of drainage has not been much studied using MRI.

New magnetic resonance imaging methods in nephrology

Established as a method to study anatomic changes, such as renal tumors or atherosclerotic vascular disease, magnetic resonance imaging (MRI) to interrogate renal function has only recently begun to come of age. In this review, we briefly introduce some of the most important MRI techniques for renal functional imaging, and then review current findings on their use for diagnosis and monitoring of major kidney diseases. Specific applications include renovascular disease, diabetic nephropathy, renal transplants, renal masses, acute kidney injury, and pediatric anomalies. With this review, we hope to encourage more collaboration between nephrologists and radiologists to accelerate the development and application of modern MRI tools in nephrology clinics.

Magnetic resonance urography in evaluation of duplicated renal collecting systems

Duplex renal collecting systems are common congenital anomalies of the upper urinary tract. In most cases they are incidental findings and not associated with additional pathologies. They demonstrate, however, higher incidences of hydroureteronephrosis, ureteroceles, and ectopic ureters. The most comprehensive morphologic and functional evaluation of duplex systems can be achieved using magnetic resonance urography. Functional magnetic resonance urography allows better separation of the renal poles, thus more accurate calculation of the differential renal functions compared with renal scintigraphy. Magnetic resonance urography is the study of choice when upper urinary tract anatomy is complex or when functional evaluation is needed.

MR urography: Anatomical and quantitative information on congenital malformations in children

Background and Aim:

Magnetic resonance urography (MRU) is considered to be the next step in uroradiology. This technique combines superb anatomical images and functional information in a single test. In this article, we aim to present the topic of MRU in children and how it has been implemented in Northern Greece so far. The purpose of this study is to demonstrate the potential of MRU in clinical practice. We focus both on the anatomical and the quantitative information this technique can offer.

Materials and Methods:

MRU was applied in 25 children (ages from 3 to 11 years) diagnosed with different types of congenital malformations. T1 and T2 images were obtained for all patients. Dynamic, contrast-enhanced data were processed and signal intensity versus time curves were created for all patients from regions of interest (ROIs) selected around the kidneys in order to yield quantitative information regarding the kidneys function.

Results:

From the slopes of these curves we were able to evaluate which kidneys were functional and from the corticomedullary cross-over point to determine whether the renal system was obstructed or not.

Conclusion:

In all 25 cases MRU was sufficient, if not superior to other imaging modalities, to establish a complete diagnosis.

Functional MRI of the kidneys

Renal function is characterized by different physiologic aspects, including perfusion, glomerular filtration, interstitial diffusion, and tissue oxygenation. Magnetic resonance imaging (MRI) shows great promise in assessing these renal tissue characteristics noninvasively. The last decade has witnessed a dramatic progress in MRI techniques for renal function assessment. This article briefly describes relevant renal anatomy and physiology, reviews the applications of functional MRI techniques for the diagnosis of renal diseases, and lists unresolved issues that will require future work.

Magnetic resonance urography in children - when and why?

BACKGROUND

The aim of the study was to determine the potential of magnetic resonance urography (MRU) in evaluation of paediatric urinary tract pathologies. PATIENTS AND METHODS.: Twenty-one paediatric urological patients were evaluated with T1, T2 prior and after and 3D gradient echo sequences after the contrast administration. Results were compared with findings obtained with ultrasound which was performed to all of patients, intravenous urography performed to 14 patients with the diagnosis of hydronephrosis and voiding cystouretrography performed to 6 patients where hydronephrosis was suspected to be caused by vesicoureteral reflux (VUR).

RESULTS

MRU not only established the cause of hydronephrosis in all 14 cases (5 ureteropelvic junction (UPJ) stenosis, 1 functional stenosis, 3 residual hydronephrosis, 1 combination of UPJ and vesico-ureteric junction (VUJ) stenosis with hydromegaureter, 2 fetal ureters and 3 insufficient broad ureteral orifices), but gave additional information about existing pathological conditions in all of patients compared to other previously performed examination (1 caliceal lithiasis, 4 UPJ stenosis, 1 VUJ stenosis, 1 neurogenic bladder, 1 hypotonic ureter, 1 urinary infection, 1 duplication of pelvis and ureter, 1 urinary retention and 1 fetal ureter). Other MRU findings were: 3 polycystic kidney disease, 1 caliceal cyst, 2 simple renal cysts, 1 long hypotonic twisted ureters and 1 hypertrophied column of Bertini.

CONCLUSIONS

Because of the ability to acquire high contrast and spatial resolution images of the whole urinary tract in any orthogonal plane, MRU enables a precise detection and differentiation of pathological urological conditions. We believe that in the future, because of its advantages, MRU will replace traditional methods in the evaluation of urinary tract pathologies.

[Imaging evaluation of renal function: principles and limitations]

The kidney performs multiple functions. Glomerular filtration is the most studied of these functions. In clinical practice, the surgical indication for patients with unilateral uropathy is frequently based on the split renal function as demonstrated by scintigraphy. MRI is not yet validated as a technique but nonetheless offers an interesting non-radiating alternative to achieve both morphological and functional renal evaluation. Recent pulse sequences such as diffusion, arterial spin labeling, and blood oxygenation dependent imaging may also provide additional information. CT and US remain of limited value for the evaluation of renal function.

Pediatric uroradiology: state of the art

Recent years have witnessed major strides in imaging modalities, including US and contrast-enhanced voiding urosonography, fluoroscopy, CT and MRI, and these have significantly impacted paediatric uroradiology. The trend is towards reduced or no radiation exposure and combined morphological and functional imaging. This review presents the currently available and recommended modalities in modern paediatric uroradiology practice.

Synthesis and evaluation of nanoglobule-cystamine-(Gd-DO3A), a biodegradable nanosized magnetic resonance contrast agent for dynamic contrast-enhanced magnetic resonance urography

Dynamic contrast-enhanced magnetic resonance imaging has been recently shown to be effective for diagnostic urography. High-resolution urographic images can be acquired with T1 contrast agents for the kidney and urinary tract with minimal noise in the abdomen. Currently, clinical contrast agents are low molecular weight agents and can rapidly extravasate from blood circulation, leading to slow contrast agent elimination through kidney and consequently providing limited contrast enhancement in urinary tract. In this study, a new biodegradable macromolecular contrast agent, nanoglobule-G4-cystamine-(Gd-DO3A), was prepared by conjugating Gd-DO3A chelates on the surface of a generation 4 nanoglobule, poly-l-lysine octa(3-aminopropyl)silsesquioxane dendrimer, via a disulfide spacer, where the carrier had a precisely defined nanosize that is far smaller than the renal filtration threshold. The in vivo contrast enhancement and dynamic imaging of the urinary tract of the agent was evaluated in nude mice using a low molecular weight agent Gd(DTPA-BMA) as a control. The agent eliminated rapidly from blood circulation and accumulated more abundantly in urinary tract than Gd(DTPA-BMA). The fast elimination kinetics is ideal for functional evaluation of the kidneys. The morphology of the kidneys and urinary tract was better visualized by the biodegradable nanoglobular contrast agent than Gd(DTPA-BMA). The agent also resulted in low liver contrast enhancement, indicating low nonspecific tissue deposition. These features render the G4 nanoglobule-cystamine-(Gd-DO3A) conjugate a promising contrast agent for magnetic resonance urography.

Obstructive diseases of the urinary tract in children: lessons from the last 15 years

Imaging urinary tract obstruction is a common query in paediatric uroradiology. With the advent of a more conservative treatment approach, the task of imaging today is to distinguish as early as possible those kidneys that do not require surgery, from those that will deteriorate and lose function and/or growth potential and thus benefit from surgery. At present, in spite of significant advancements in imaging and the introduction of diuretic paediatric MR-urography, there is still no reliable a-priori pro-futuro assessment. Thus, repeated follow-up imaging is often necessary for monitoring. Imaging usually starts with US; the major additional complementary and more function-oriented tools are diuretic renal scintigraphy and MR-urography. The frequency and timing as well as the detailed protocol vary within institutions, partly because of differences in the criteria that are used for indicating surgery. Intra-venous urography (IVU) for obstruction has practically vanished apart from for a few exceptions, and the "Whitaker" test is today seldom performed, being reserved for complicated cases.

The Society for Fetal Urology consensus statement on the evaluation and management of antenatal hydronephrosis

The evaluation and management of fetuses/children with antenatal hydronephrosis (ANH) poses a significant dilemma for the practitioner. Which patients require evaluation, intervention or observation? Though the literature is quite extensive, it is plagued with bias and conflicting data, creating much confusion as to the optimal care of patients with ANH. In this article, we summarized the literature and proposed recommendations for the evaluation and management of ANH.

MR urography in children. Part 2: how to use ImageJ MR urography processing software

MR urography (MRU) is an emerging technique particularly useful in paediatric uroradiology. The most common indication is the investigation of hydronephrosis. Combined static and dynamic contrast-enhanced MRU (DCE-MRU) provides both morphological and functional information in a single examination. However, specific post-processing must be performed and to our knowledge, dedicated software is not available in conventional workstations. Investigators involved in MRU classically use homemade software that is not freely accessible. For these reasons, we have developed a software program that is freely downloadable on the National Institute of Health (NIH) website. We report and describe in this study the features of this software program.

Renal measurements, including length, parenchymal thickness, and medullary pyramid thickness, in healthy children: what are the normative ultrasound values?

OBJECTIVE

The objective of our study was to develop, by use of ultrasound, nomograms of renal parenchymal thickness, medullary pyramid thickness (height), renal length, and the ratio of medullary pyramid thickness to parenchymal thickness in healthy children.

SUBJECTS AND METHODS

This prospective study included 292 consecutive children (136 boys and 156 girls) who were referred between October 2008 and March 2009 for problems other than urinary tract symptoms or underlying kidney disorders. The children were between 1 month and 18 years old (mean age, 6.1 +/- 5.9 years). Real-time gray-scale sonography was performed with a linear or curved array transducer. All examinations were performed by the same experienced radiologist (16 years of experience in pediatric sonography at the time the study began). All the children were well hydrated and had full bladders at the time of examination. Renal length measurements were performed in the sagittal view, and the maximum length of each kidney was measured. Measurements of parenchymal thickness and medullary pyramid thickness were performed on the same image on which length measurements were made. Parenchymal thickness and medullary pyramid thickness were measured at the middle third portion of the kidney. The Wilcoxon's signed rank test was used for statistical analysis.

RESULTS

Nomograms of renal parenchymal thickness, medullary pyramid thickness, renal length, and the ratio of medullary pyramid thickness to parenchymal thickness were developed. When all age groups were pooled together, statistically significant differences were observed between right and left kidneys in terms of parenchymal thickness (p < 0.001), medullary pyramid thickness (p < 0.001), and renal length (left kidneys were longer, with thicker medullary pyramids and parenchyma; p < 0.001). A slight but significant difference in the ratio of medullary pyramid thickness to parenchymal thickness was observed (p = 0.045).

CONCLUSION

By use of renal sonography, nomograms of renal parenchymal thickness, medullary pyramid thickness, renal length, and the ratio of medullary pyramid thickness to parenchymal thickness were established in healthy children.

Functional analysis in MR urography - made simple

MR urography (MRU) has proved to be a most advantageous imaging modality of the urinary tract in children, providing one-stop comprehensive morphological and functional information, without the utilization of ionizing radiation. The functional analysis of the MRU scan still requires external post-processing using relatively complex software. This has proved to be a limiting factor in widespread routine implementation of MRU functional analysis and use of MRU functional parameters similar to nuclear medicine. We present software, developed in a pediatric radiology department, that not only enables comprehensive automated functional analysis, but is also very user-friendly, fast, easily operated by the average radiologist or MR technician and freely downloadable at www.chop-fmru.com . A copy of IDL Virtual Machine is required for the installation, which is obtained at no charge at www.ittvis.com . The analysis software, known as "CHOP-fMRU," has the potential to help overcome the obstacles to widespread use of functional MRU in children.

[Functional MR urography in children]

MR Urography (MRU) provides both morphologic and functional information without radiation exposure. It enables the assessment of split renal function, excretion, and quantification of obstruction. MRU is thus complementary to ultrasonography in the assessment of pre- and post-natal obstructive uropathies in children. If available, MRU should be definitely preferred to intravenous urography.

Time-resolved dynamic contrast-enhanced MR urography for the evaluation of ureteral peristalsis: initial experience

PURPOSE

To determine the feasibility of time-resolved dynamic contrast-enhanced magnetic resonance urography (MRU) for the evaluation of ureteral peristalsis using a data-sharing 3D gradient echo sequence with spiral k-space filling.

MATERIALS AND METHODS

Eight patients (M=3, F=5, mean 48.1 years) were referred for MRU for the evaluation for renal mass (n=3), hematuria (n=2), urinary tract tuberculosis (n=1), postoperative bladder cancer (n=1), and postoperative ureteric reimplantation (n=1). Dynamic MRU was performed for 120 seconds at 1.5T after intravenous furosemide and gadolinium administration using an oblique sagittal, time-resolved T1 3D gradient echo sequence with 1 second effective temporal resolution. Study quality was assessed based on artifacts and extent of ureteric visualization. Frequency of peristalsis from the renal pelvis to urinary bladder was evaluated for each subject.

RESULTS

A total of 16 ureters were examined. Image quality was good in four ureters, satisfactory in 11 ureters, and poor in one ureter. Mean peristaltic frequency was 3.5 waves per minute (range, 2.5-6.5 waves/minute) in normal ureters (n=11). Five ureters were considered abnormal (one urinary tract tuberculosis and four postsurgical ureters), and all had decreased or no peristalsis (0-1.5 waves per minute).

CONCLUSION

MRU using a time-resolved, data-sharing 3D contrast-enhanced technique is able to demonstrate ureteral peristalsis and permits quantification of ureteral peristaltic frequency.

MR urography: technique and results for the evaluation of urinary obstruction in the pediatric population

MR urography has the potential to revolutionize imaging of the urinary tract in both adults and children, because of its ability to provide an unprecedented level of anatomic information and quantitative functional evaluation of each kidney. MR urography can now provide useful assessment of obstructive uropathy and may provide predictive information about which children will benefit from surgery. It has the potential to identify parameters that indicate a significant obstruction as opposed to self-limited hydronephrosis. Further technical developments in the field will produce greater insights into the pathophysiology of not only urologic disorders but also disorders of the kidney itself.

Potential of MR-imaging in the paediatric abdomen

OBJECTIVE

To describe the potential and relevant applications of MR-imaging (MRI) in typical paediatric abdominal conditions and diseases.

METHOD

The commonly used indications, applications, and sequences as well as typical imaging findings of paediatric abdominal MRI are presented and discussed, with emphasis on specific paediatric needs and queries. Only applications as used in routine clinical work are listed, other more sophisticated and advanced techniques will only briefly be mentioned. Furthermore, some aspects of paediatric MR Urography are presented and discussed.

CONCLUSION

Though conventional imaging methods (ultrasound and plain film) are valuable and - particularly in the paediatric abdomen - form the mainstay of routine imaging in paediatric abdominal radiology, some conditions require sectional imaging. MRI is increasingly applied to these queries in neonates, infants and children as an alternative method to CT without any radiation burden, and - when performed adequately and skilfully - can answer most treatment relevant questions. MR will increasingly be applied with new applications and broader availability also with functional information deriving from new equipment and research offering an ideal one stop imaging approach to many conditions also in children.

Magnetic resonance urography in children

Magnetic resonance (MR) urography is a powerful 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 of MR urography and common clinical applications, such as the evaluation of hydronephrosis, reflux nephropathy, and renal dysplasia.