Dynamic gadolinium-enhanced magnetic resonance urography for assessing drainage in dilated pelvicalyceal systems with moderate renal function: preliminary results and comparison with diuresis renography

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.

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

OBJECTIVE

The aim of this study was to evaluate combined two-dimensional (2D) and three-dimensional (3D) dynamic MR urography with respiratory compensation in children with anomalies of the genitourinary tract, allowing for computation of split renal function and assessment of urinary tract obstruction.

METHODS

Dynamic MR urography was performed in 53 children (3 months-16 years of age) with anomalies of the urinary tract. A protocol for dynamic MR urography and nephrography was implemented at 1.5 T using a navigator-triggered 2D TurboFLASH sequence. Split renal function and contrast-medium excretion were assessed after the bolus injection of 0.05 mmol kg(-1) body weight of gadolinium dimeglumine. In the excretory phase, a 3D gradient-echo data set with high spatial resolution was acquired. In all patients, mercaptoacetyltriglycine (MAG3) scintigraphy was obtained as a reference standard.

RESULTS

In all children, dynamic MR nephrography and urography could be performed with excellent compensation of breathing artefacts providing region of interest analysis in nearly identical kidney positions. The assessment of contrast-medium excretion into the ureter allowed for discrimination of functional from non-functional stenosis. Split renal function assessed by MRI showed an excellent agreement with the MAG3 reference standard with a correlation coefficient r = 0.95. Additionally recorded 3D data sets offered good depiction of anatomical anomalies in all patients.

CONCLUSION

The proposed protocol provides a robust technique for assessment of ureteral obstruction and split renal function with compensation of breathing artefacts, short post-processing time and excellent 3D spatial resolution.

ADVANCES IN KNOWLEDGE

The combined protocol of 2D and 3D MR urography is an efficient technique for assessment of renal morphology and function.

[Magnetic resonance urography in pediatric urology]

Magnetic resonance urography (MRU) provides high resolution imaging of the urogenital system and the use of paramagnetic contrast agents enables a functional depiction. This review summarizes existing data concerning this diagnostic procedure in pediatric urology. A systematic search and assessment of the literature was performed.A total of 12 studies were reviewed in detail. In mostly small study populations a great heterogeneity concerning methodology, use of comparative examinations and standards of reference was noted. Besides the quality of anatomical imaging, the functional study of renal excretory function and differential renal function was also assessed. Only a few studies performed statistical analyses.The authors' rating of MRU was mostly positive. Due to methodical weaknesses, lack of independent standards of reference and statistical analyses the overall level of evidence was low. Further high quality studies will be necessary to assess the value of MRU for the diagnostic workup in pediatric urology.

Application of magnetic resonance urography in diagnosis of congenital urogenital anomalies in children

Magnetic resonance urography (MRU) has become a useful adjuvant in evaluating urogenital anomalies. In present study, we evaluated the ability of MRU in diagnosis of different congenital urogenital anomalies when the results of conventional imaging modalities were inconclusive. A total of 90 children were included in this series. The children were evaluated with T2-weighted and contrast-enhanced T1-weighted MRU sequences. The results were compared with findings obtained with ultrasonography, intravenous urography, renal nuclide scan, and voiding cystourethrography. MRU was requested in these children because conventional imaging modalities were equivocal or a co-existing urogenital anomaly was suspected. Only those cases that underwent surgery were included in this study and the surgical findings were set as the reference standard in statistical evaluation. The records of 61 boys with mean (range) age of 2.3 years (2 months-12 years) and 29 girls with mean (range) age of 3.3 years (3 months-12 years) were reviewed. The final diagnosis was ureteropelvic junction obstruction (n = 25), vesicoureteral junction obstruction (n = 16), ureterocele (n = 19), ectopic kidney (n = 11), posterior urethral valve (n = 17), and polycystic kidney (n = 2). The overall sensitivity of MRU, intravenous urography, renal nuclide scan, ultrasonography, and voiding cystourethrography in diagnosis of the aforementioned anomalies were 86, 63, 50, 44, and 41%, respectively. MRU was much more sensitive than other imaging modalities in diagnosis of end-ureteral dilation (100%) and ureterocele (89%). MRU provides a reliable noninvasive technique for imaging of the congenital anomalies in the urinary tract of children with T2-weighted MRU sequences providing unenhanced static-water images of the urinary tract as well as depicting adjacent soft-tissue lesions, and T1-weighted MRU technique imitating conventional intravenous urography. Both MRU sequences can be combined for a comprehensive examination of the urinary tract.

Upper urinary tract dilatation: prenatal diagnosis, management and outcome

Upper urinary tract dilatation is one of the most common abnormalities detected on prenatal ultrasound scanning. It is commonly due to transient urine flow impairment (UFI) at the level of the pelvi-ureteric and vesico-ureteric junctions, which improves with time in most cases. It is usually in the neonatal period that the diagnosis is confirmed and during the first 18 months of life that the prognosis of the dilatation is defined.

Nuclear imaging in the genitourinary tract: recent advances and future directions

For almost three decades, noninvasive radionuclide procedures for the evaluation of renal disease have been important components of nuclear medicine practice. With the introduction of new imaging agents and procedures, these techniques can provide valuable data on perfusion and function of individual kidneys. In general, these procedures are easy to perform and carry a low radiation burden and sedation is not required. Moreover, radionuclide imaging of the genitourinary tract has become an invaluable asset to clinicians in the evaluation of renal parenchyma and urologic abnormalities.

MR urography: techniques and clinical applications

Magnetic resonance (MR) urography comprises an evolving group of techniques with the potential for allowing optimal noninvasive evaluation of many abnormalities of the urinary tract. MR urography is clinically useful in the evaluation of suspected urinary tract obstruction, hematuria, and congenital anomalies, as well as surgically altered anatomy, and can be particularly beneficial in pediatric or pregnant patients or when ionizing radiation is to be avoided. The most common MR urographic techniques for displaying the urinary tract can be divided into two categories: static-fluid MR urography and excretory MR urography. Static-fluid MR urography makes use of heavily T2-weighted sequences to image the urinary tract as a static collection of fluid, can be repeated sequentially (cine MR urography) to better demonstrate the ureters in their entirety and to confirm the presence of fixed stenoses, and is most successful in patients with dilated or obstructed collecting systems. Excretory MR urography is performed during the excretory phase of enhancement after the intravenous administration of gadolinium-based contrast material; thus, the patient must have sufficient renal function to allow the excretion and even distribution of the contrast material. Diuretic administration is an important adjunct to excretory MR urography, which can better demonstrate nondilated systems. Static-fluid and excretory MR urography can be combined with conventional MR imaging for comprehensive evaluation of the urinary tract. The successful interpretation of MR urographic examinations requires familiarity with the many pitfalls and artifacts that can be encountered with these techniques.

Magnetic resonance urography in pediatric urology

PURPOSE OF REVIEW

Magnetic resonance urography (MRU) has emerged as a powerful diagnostic tool in the evaluation of the pediatric genitourinary tract. The purpose of this review is to familiarize the reader with the basic techniques, strengths and limitations, as well as the current and potential future applications of MRU in pediatric urology.

RECENT FINDINGS

MRU can provide detailed anatomical information and assess renal function and drainage in a single study. MRU does not employ ionizing radiation and may be utilized in patients with iodine-based contrast allergy or impaired renal function. MRU has been most often applied to the evaluation of hydronephrosis and provides valuable insight into a wide range of obstructive uropathies. MRU was shown to be superior to renal scintigraphy for the diagnosis of pyelonephritis and renal scarring. The use of MRU for the assessment of urolithiasis and vesicoureteral reflux is limited and technical refinements are required. Potential future applications include fetal MRU, virtual endoscopy, and MRU-guided procedures. The development of new contrast agents and new image-processing software will further enhance the diagnostic potential of MRU in pediatric urology.

SUMMARY

MRU is currently thought of as a problem-solving tool to define anatomy and function when conventional methods fall short. This technique is likely to emerge as the imaging modality of choice for children with complex genitourinary pathology.

Renal dysplasia and MRI: a clinician's perspective

Renal dysplasia is a common abnormality in children. The role of MRI in evaluating children with renal dysplasia is evolving. More information is clearly necessary before MRI replaces conventional imaging modalities. In order to appropriately use MRI, the radiologist must have an understanding of the clinical questions that are important in the management of children with renal dysplasia. This review provides background information on renal dysplasia for the pediatric radiologist. The focus is on unilateral disease, especially multicystic dysplastic kidneys, and bilateral dysplasia, which is the most common cause of kidney failure in children. The emphasis is on the important clinical issues, and the potential of MRI as a methodology for providing clinically useful information not otherwise available from other imaging modalities.

The role of magnetic resonance imaging in pediatric urology

PURPOSE OF REVIEW

Magnetic resonance imaging has emerged as a powerful diagnostic tool for the imaging of the pediatric genitourinary tract. The aim of this review is to familiarize the reader with the current applications and basic techniques utilizing magnetic resonance imaging in pediatric uroradiology.

RECENT FINDINGS

Magnetic resonance imaging can provide both a detailed anatomic and functional assessment of the pediatric genitourinary tract in a single study without the use of ionizing radiation. Magnetic resonance urography combines static and dynamic evaluation of the urinary tract following contrast administration and has been most often applied to the evaluation of hydronephrosis. In addition to unparalleled anatomic assessment, it allows for the evaluation of glomerular filtration rate, renal transit time, and differential renal function. It also provides unique insights into a wide range of obstructive uropathies and has been demonstrated to be useful in the evaluation of complex genitourinary anomalies. Magnetic resonance voiding cystourethrography has been used to rule out vesicoureteral reflux. Magnetic resonance imaging has also been demonstrated to be superior to nuclear scintigraphy for the diagnosis of pyelonephritis and renal scarring.

SUMMARY

Magnetic resonance imaging has emerged as a powerful tool for the diagnosis of pediatric genitourinary anomalies. It provides functional and anatomic assessment with a single procedure that in most cases is superior to conventional procedures. Magnetic resonance imaging will probably become the modality of choice for the imaging of pediatric genitourinary tract anomalies.

Magnetic resonance urography in the evaluation of prenatally diagnosed hydronephrosis and renal dysgenesis

PURPOSE

We present our experience with dynamic contrast enhanced magnetic resonance urography for evaluation and treatment in infants born with prenatally recognized hydronephrosis. We determined the characteristics of renal dysgenesis in this population.

MATERIALS AND METHODS

We reviewed magnetic resonance urography images done within the first 6 months of life in 67 infants born with prenatally recognized hydronephrosis. High resolution imaging was used to establish a morphological diagnosis. Functional evaluation was used to assess obstruction and individual renal function. Voiding cystourethrography was performed in 62 patients.

RESULTS

Our study included 67 infants (87 renal units). There were 54 boys and 13 girls with a mean age of 2.8 months (range 0.9 to 4.6). Of these 87 renal units 30 (35%) had ureteropelvic junction obstruction, 18 (21%) had primary megaureters, 10 (11%) had nondilating vesicoureteral reflux, 10 (11%) had fetal folds, 8 (9%) had posterior urethral valves, 6 (7%) had ectopic ureters, 4 (5%) had multicystic dysplastic kidneys and 1 (1%) had a normal study. Magnetic resonance urography revealed renal dysgenesis in 24 renal units (28%), consisting of loss of corticomedullary differentiation, renal cystic changes distinct from multicystic dysplastic kidneys, solid renal dysplasia, hypoplasia and dysmorphic calyces.

CONCLUSIONS

Magnetic resonance urography is an excellent addition to our armamentarium for evaluating neonatal hydronephrosis and renal dysgenesis. Due to its comprehensiveness magnetic resonance urography has the potential to become the study of choice for evaluating infants with significant prenatally recognized hydronephrosis. However, further prospective, comparative studies in larger patient populations are needed to justify the cost and the need for sedation in infants.

Magnetic resonance urography for evaluating outcomes after pediatric pyeloplasty

PURPOSE

We report the role of magnetic resonance urography in children with ureteropelvic junction obstruction. Differential renal function, the single kidney glomerular filtration rate index, renal transit time, renal length and renal pelvis anteroposterior diameter were compared before and after pyeloplasty.

MATERIALS AND METHODS

Magnetic resonance urography was performed before and after pyeloplasty in 24 patients with a mean age of 1.9 years (range 3 months to 10 years). Renal length, renal transit time and renal pelvis anteroposterior diameter were determined by the radiologist. The volume of functioning renal tissue and descending aorta were segmented and the ratio of the volumes of functioning kidney tissue was used to calculate differential renal function. Rutland-Patlak plots were used to calculate single kidney glomerular filtration rate index, that is the Patlak score.

RESULTS

Mean renal pelvis renal pelvis anteroposterior diameter was 3.3 cm preoperatively and 2.5 cm postoperatively (p = 0.0003). There was no difference in average renal length (p = 0.22). Of the 24 cases 22 (92%) showed stable or improved differential renal function. Improvement in renal transit time was seen in 20 of 23 cases (87%). Of 15 patients with complete Patlak scores 14 (93%) showed postoperative improvement. Mean preoperative and postoperative differential renal function, renal transit time and Patlak score were 36% and 41% (p = 0.003), 16.2 and 8.6 minutes (p = 0.0005), and 6.6 and 11.9 ml per minute (p = 0.01), respectively.

CONCLUSIONS

Magnetic resonance urography provides superior anatomical and unprecedented functional information to fully define the preoperatively and postoperative status of corrected ureteropelvic junction obstruction. Magnetic resonance urography has the potential to become the imaging study of choice for evaluating pediatric hydronephrosis and obstructive uropathy.

Functional renal imaging: nonvascular renal disease

Functional renal imaging-a fast-growing field of MR-imaging-applies different sequence types to gather information about the kidneys other than morphology and angiography. This update article presents the current status of different functional imaging approaches and presents current and potential clinical applications. Apart from conventional in-phase and opposed-phase imaging, which already yields information about the tissue composition, BOLD (blood-oxygenation level dependent) sequences, DWI (diffusion-weighted imaging) sequences, perfusion measurements, and dedicated contrast agents are used.