NORA: a simple and reliable parameter for estimating renal output with or without frusemide challenge

Nuclear medicine and pediatric nephro-urology: a long-lasting successful partnership

Congenital anomalies of the kidney and urinary tract, as well as urinary infections, are very frequent in children. After the clinical and laboratory evaluation, the first imaging procedure to be done is a renal and bladder ultrasound, but afterwards, a main contribution comes from nuclear medicine. Through minimally invasive and sedation-free procedures, nuclear medicine allows the evaluation of the functional anatomy of the urinary tract, and the quantification of renal function and drainage. If pediatric dosage cards provided by scientific societies are used, radiation exposure can also be low. In the pediatric conditions previously mentioned, nuclear medicine is used both for initial diagnosis and follow-up, mostly in cases of suspicion of ureteropelvic or ureterovesical junction syndromes, as well as vesicoureteral reflux or renal scars of febrile infectious episodes. Pediatric nephro-urology constitutes a significant workload of pediatric nuclear medicine departments. The following paragraphs are a revision of the renal radiopharmaceuticals, as well as the nuclear nephro-urology procedures - dynamic and static renal scintigraphy, and direct and indirect radionuclide cystography. A summary of the techniques, main indications, interpretation criteria and pitfalls will be provided. Some future directions for the field are also pointed out, among which the most relevant is the need for nuclear medicine professionals to use standardized protocols and integrate multidisciplinary teams with other pediatric and adult health professionals that manage these life-long pediatric pathologies, which are recognized as an important cause of adult chronic kidney disease.

Deep learning of renal scans in children with antenatal hydronephrosis

INTRODUCTION

Antenatal hydronephrosis (ANH) is one of the most common anomalies identified on prenatal ultrasound, found in up to 4.5% of all pregnancies. Children with ANH are surveilled with repeated renal ultrasound and when there is high suspicion for a ureteropelvic junction obstruction on renal ultrasound, a mercaptuacetyltriglycerine (MAG3) Lasix renal scan is performed to evaluate for obstruction. However, the challenging interpretation of MAG3 renal scans places patients at risk of misdiagnosis.

OBJECTIVE

Our objective was to analyze MAG3 renal scans using machine learning to predict renal complications. We hypothesized that our deep learning model would extract features from MAG3 renal scans that can predict renal complications in children with ANH.

STUDY DESIGN

We performed a case-control study of MAG3 studies drawn from a population of children with ANH concerning for ureteropelvic junction obstruction evaluated at our institution from January 2009 until June of 2021. The outcome was renal complications that occur ≥6 months after an equivocal MAG-3 renal scan. We created two machine learning models: a deep learning model using the radiotracer concentration versus time data from the kidney of interest and a random forest model created using clinical data. The performance of the models was assessed using measures of diagnostic accuracy.

RESULTS

We identified 152 eligible patients with available images of which 62 were cases and 90 were controls. The deep learning model predicted future renal complications with an overall accuracy of 73% (95% confidence inteveral [CI] 68-76%) and an AUC of 0.78 (95% CI 0.7, 0.84). The random forest model had an accuracy of 62% (95% CI 60-66%) and an AUC of 0.67 (95% CI. 0 64, 0.72) DISCUSSION: Our deep learning model predicted patients at high risk of developing renal complications following an equivocal renal scan and discriminate those at low risk with moderately high accuracy (73%). The deep learning model outperformed the clinical model built from clinical features classically used by urologists for surgical decision making.

CONCLUSION

Our models have the potential to influence clinical decision making by providing supplemental analytical data from MAG3 scans that would not otherwise be available to urologists. Future multi-institutional retrospective and prospective trials are needed to validate our model.

Diuretic Renal Scintigraphy Protocol Considerations

Diuretic renal scintigraphy plays a critical diagnostic role by providing a physiologic means for differentiating between obstructive and nonobstructive hydronephrosis as well as assessing the function of the affected kidney. The exam accuracy is highly dependent upon and benefits from close attention to the protocol. This article reviews kidney anatomy and physiology, patient preparation, available radiopharmaceuticals, diuretic administration, acquisition, processing, quantification, and interpretation criteria.

Pediatric Nephro-Urology: Overview and Updates in Diuretic Renal Scans and Renal Cortical Scintigraphy

Nuclear medicine offers several diagnostic scans for the evaluation of congenital and acquired conditions of the kidneys and urinary track in children. Tc-99m-MAG 3 diuretic renal scans are most commonly used in the evaluation and follow up of urinary track dilatations. They provide functional information on the differential renal function and on drainage quality which is allows distinction between obstructed and non-obstructed kidneys and the need for surgical correction vs conservative management in kidneys with impaired drainage. Standardized imaging and processing protocols are essential for correct interpretation and for meaningful comparisons between follow up scans. Different approaches and conceptions led to some contradicting recommendations between SNMMI and EANM guidelines on diuretic renography in children which caused confusion and to the emergence of self-made institutional protocols. In Late 2018 the two societies published joint procedural guidelines on diuretic renography in infants and children which hopefully will end the confusion. Tc-99m DMSA scans provide important information about the function of the renal cortex allowing detection of acute pyelonephritis, renal scars dysplasia and ectopy as well as accurate determination of the differential renal function. They are commonly used in the evaluation of children with urinary tract infections and affect clinical management. A standardized imaging and processing protocol improves the diagnostic accuracy of these studies. SPECT or pinhole images should be a routine part of the imaging protocol. This is one of the recommendations in the new EANM and SNMMI procedural guidelines for renal cortical scintigraphy in children available online on the SNMMI website and is under publication. This article provides an overview on the clinical role of diuretic renography and cortical scintigraphy in children and describes the imaging protocols focusing on the new recommendations in the procedural guidelines.

A gravity-assisted approach to the management of urinary diversion: 99mTc-MAG3 diuresis renography with F + 10(sp) method

OBJECTIVE

Radical cystectomy with permanent urinary diversion is the gold standard treatment for invasive muscle bladder cancer. Hydronephrosis is common in these patients, but Ultrasound (US) or Computed Tomography Urography (CTU) scan are unable to discriminate obstructive from non-obstructive hydronephrosis. We used Diuresis Renography (DR) with F + 10 in seated position (sp) method in the identification of patients with a Uretero-ileal Anastomosis Stricture (UAS) who would benefit from surgical therapy.

METHODS

We studied 39 asymptomatic patients, who underwent radical cystectomy and urinary diversion. Based on radiological findings (US, CTU) 44 kidneys were hydronephrotic. All patients underwent a ^99mTc-MAG3 DR with F + 10(sp) method. We acquired a DR for 20 min with the patient in a seated position. Patient drank 400-500 mL of water at 5 min after tracer injection and received a 20 mg bolus of Furosemide at 10 min during dynamic acquisition. The indices Time to peak, diuretic half time, and 20 min/peak ratio have been evaluated. Retrograde pyelography confirmed UAS in all patients with DR obstructive findings. We repeated DR as follow-up in two subgroups of patients.

RESULTS

DR with F + 10(sp) method showed obstructive findings in 36 out of 44 hydronephrotic kidneys. 6 patients showed non-obstructive findings. 32 patients showed obstructive findings (20 out of 32 developed UAS within 12 months after surgery). Fifteen pts underwent a surgical treatment of UAS. In 1 patient with equivocal findings, we observed an ileo-ureteral reflux.

CONCLUSIONS

The DR with F + 10(sp) method in the seated position has a lower uncertain diagnostic rate, compared to the radiological findings of US or CTU, in management of bladder cancer patients with urinary diversion. The semiquantitative indices diuretic half time and 20 min/peak ratio evaluated in a condition of favorable gravity reduce uncertain responses improving interobserver concordance.

Advantages of gravity-assisted diuretic renogram: F + 10 (seated position) method

INTRODUCTION

In 1978, O'Reilly introduced the diuretic renogram using the F + 20 method. Initially, the patient was examined in the seated position. A dose of 40 mg furosemide was injected intravenously 20 min following tracer injection and dynamic acquisition was prolonged for 15-20 min. In 1992, the guidelines suggested to study patients in the supine position to avoid risk of diuretic-induced hypotension and reduce patient movement. Unfortunately, equivocal findings were reported in 15-30% of cases. Side effects such as bladder fullness and disruption because of voiding were reported. Several methods had been proposed in the supine position, such as the well-tempered diuretic renogram F + 20, F - 15, F0 and F + 2, with different time in minute of diuretic administration in relation to tracer injection. However, as confirmed by many studies, there was no clear evidence suggesting superiority among these methods. We suggest using the diuretic renogram with the F ± 10(sp) method for the diagnosis of obstruction in adult patients with hydronephrosis and for the follow-up in patients who underwent a surgical treatment of the urinary tract.

METHODS

We searched all international guidelines and articles of most influential authors published from 1978 to October 2020 on diuretic renogram.

RESULTS

We selected 60 articles.

DISCUSSION

F + 10(sp) method improves patient compliance avoiding bladder fullness-related problems, without need of catheterization. It allows for a more reliable quantification of the renal output, thanks to outflow indices that are favored by gravity effects.

Nuclear Medicine in Pediatric Nephro-Urology: An Overview

In the context of ante-natally diagnosed hydronephrosis, the vast majority of children with a dilated renal pelvis do not need any surgical treatment, as the dilatation resolves spontaneously with time. Slow drainage demonstrated at Tc-99m-mercaptoacetyltriglycine (MAG3) renography does not necessarily mean obstruction. Obstruction is defined as resistance to urinary outflow with urinary stasis at the level of the pelvic-ureteric junction (PUJ) which, if left untreated, will damage the kidney. Unfortunately this definition is retrospective and not clinically helpful. Therefore, the identification of the kidney at risk of losing function in an asymptomatic patient is a major research goal. In the context of renovascular hypertension a DMSA scan can be useful before and after revascularisation procedures (angioplasty or surgery) to assess for gain in kidney function. Renal calculi are increasingly frequent in children. Whilst the vast majority of patients with renal stones do not need functional imaging, DMSA scans with SPECT and a low dose limited CT can be very helpful in the case of complex renal calculi. Congenital renal anomalies such as duplex kidneys, horseshoe kidneys, crossed-fused kidneys and multi-cystic dysplastic kidneys greatly benefit from functional imaging to identify regional parenchymal function, thus directing further management. Positron emission tomography (PET) is being actively tested in genito-urinary malignancies. Encouraging initial reports suggest that F-18-fluorodeoxyglucose (FDG) PET is more sensitive than CT in the assessment of lymph nodal metastases in patients with genito-urinary sarcomas; an increased sensitivity in comparison to isotope bone scans for skeletal metastatic disease has also been reported. Further evaluation is necessary, especially with the promising advent of PET/MRI scanners. Nuclear Medicine in paediatric nephro-urology has stood the test of time and is opening up to new exciting developments.

Comparison of the EANM and SNM guidelines on diuretic renography in children

OBJECTIVE

When taking into account the Society of Nuclear Medicine (SNM) and European Association of Nuclear Medicine (EANM) guidelines on diuretic renography in children, we see important divergences in the preparation, acquisition, processing, and interpretation of the results. In this study, we estimated the quality of renal drainage according to these two guidelines.

PATIENTS AND METHODS

Ninety kidneys with hydronephrosis or severe vesicorenal reflux were processed and analyzed according to the SNM (estimation of the T1/2 of the washout curve and conclusions about the possible existence of obstruction) and EANM guidelines (estimation of normalized residual activity or NORA, and output efficiency or OE on the late postmicturition images, without any conclusion about the possible existence of obstruction). Among the 90 kidneys, 39, 20, and 31 were considered to have normal, equivocal, or poor drainage (obstruction), respectively, when the SNM guidelines were used.

RESULTS

All 39 kidneys with good drainage according to SNM were also considered as normal using the EANM guidelines. Among the 20 equivocal cases based on T1/2, concordance between the two guidelines was obtained in only 35 and 0% when using NORA and OE (OE was considered normal in all 20 cases), respectively. Among the 31 cases defined as obstructed by SNM, only five were classified as 'poor drainage' using NORA and no single case was classified thus using OE.

CONCLUSION

This limited study demonstrates that the use of different guidelines can lead to different interpretations of the results. This is unacceptable, and an agreement between both pediatric task groups of the SNM and EANM is urgently required.

Validation of IAEA software package for the analysis of scintigraphic renal dynamic studies: parameters of renal transit in children with renal pelvic dilatation

PURPOSE

The objectives of the study were to use the International Atomic Energy Agency (IAEA) software package for the analysis of scintigraphic renal dynamic studies to obtain values of curve parameters and excretory parameters in children with hydronephrosis and to validate the reliability of these numerical outputs by comparing with values established by consensus reports.

PATIENTS AND METHODS

Fifty children with hydronephrosis (median age, 16 months; 30 boys, 20 girls; 99 kidneys) underwent Tc-MAG3 diuresis renography. Studies were analyzed by 2 observers, and according to the assessment of images, renograms, and differential function, kidneys were classified as normal (42, kidneys contralateral to hydronephrotic kidney), hypotonic unobstructed (49), and obstructed (8). The IAEA software was applied to each renogram. The parameters analyzed were as follows: normalized residual activity at 20 minutes (NORA 20) and on postmicturition (PM) acquisition, output efficiency at 20 minute (OE 20), PM to maximum renal count ratio (PM/max), and mean transit time (MTT).

RESULTS

Mean values for normal, hypotonic unobstructed, and obstructed kidneys were as follows: NORA 20: 0.25, 0.57, and 2.16; OE 20 (%): 94.5, 87, and 57; normalized residual activity on PM acquisition: 0.02, 0.03, and 0.27; PM/max: 0.01, 0.02, and 0.13; and MTT (minutes): 1.9, 3.5, and 8.9, respectively. Difference between obstruction/dilatation and normal/dilatation was significant (P < 0.0001), as well as the correlation between NORA 20/OE 20 (R = -0.982). Cutoff values to predict obstruction were as follows: NORA 20, 1.6; OE 20, 73%; NORA PM, 0.11; PM/max, 0.06; and MTT, 8.23 minutes.

CONCLUSIONS

The IAEA software package gives reliable values of numerical parameters of renal excretion. The use of the software improves diagnostic accuracy of diuresis renography in children.

Radionuclides in nephrourology, Part 2: pitfalls and diagnostic applications

Radionuclide renal scintigraphy provides important functional data to assist in the diagnosis and management of patients with a variety of suspected genitourinary tract problems, but the procedures are underutilized. Maximizing the utility of the available studies (as well as the perception of utility by referring physicians) requires a clear understanding of the clinical question, attention to quality control, acquisition of the essential elements necessary to produce an informed interpretation, and production of a report that presents a coherent impression based on data contained in the report and that specifically addresses the clinical question. To help achieve these goals, part 1 of this review addressed the available radiopharmaceuticals, quality control, and quantitative indices, including the measurement of absolute and relative renal function. Part 2 assumes familiarity with part 1 and focuses on the common clinical indications of suspected obstruction and renovascular hypertension; part 2 also summarizes the status of radionuclide renal imaging in the evaluation of the transplanted kidney and the detection of infection, discusses potential pitfalls, and concludes with suggestions for future research. The series of SAM questions accompanying parts 1 and 2 has been designed to reinforce and extend points made in the review. Although the primary focus is the adult patient, aspects of the review also apply to the pediatric population.

Computer-assisted diagnosis in renal nuclear medicine: rationale, methodology, and interpretative criteria for diuretic renography

The goal of artificial intelligence, expert systems, decision support systems, and computer-assisted diagnosis (CAD) in imaging is the development and implementation of software to assist in the detection and evaluation of abnormalities, to alert physicians to cognitive biases, to reduce intraobserver and interobserver variability, and to facilitate the interpretation of studies at a faster rate and with a higher level of accuracy. These developments are needed to meet the challenges resulting from a rapid increase in the volume of diagnostic imaging studies coupled with a concurrent increase in the number and complexity of images in each patient data. The convergence of an expanding knowledge base and escalating time constraints increases the likelihood of physician errors. Errors are even more likely when physicians interpret low-volume studies such as technetium-99m-mercaptoacetyltriglycine diuretic scans where imagers may have had limited training or experience. Decision support systems include neural networks, case-based reasoning, expert systems, and statistical systems. iRENEX (renal expert) is an expert system for diuretic renography that uses a set of rules obtained from human experts to analyze a knowledge base of both clinical parameters and quantitative parameters derived from the renogram. Initial studies have shown that the interpretations provided by iRENEX are comparable to the interpretations of a panel of experts. iRENEX provides immediate patient-specific feedback at the time of scan interpretation, can be queried to provide the reasons for its conclusions, and can be used as an educational tool to teach trainees to better interpret renal scans. It also has the capacity to populate a structured reporting module and generate a clear and concise impression based on the elements contained in the report; adherence to the procedural and data entry components of the structured reporting module ensures and documents procedural competency. Finally, although the focus is CAD applied to diuretic renography, this review offers a window into the rationale, methodology, and broader applications of computer-assisted diagnosis in medical imaging.

Radionuclides in nephrourology, part 1: Radiopharmaceuticals, quality control, and quantitative indices

Radionuclide renal scintigraphy provides important functional data to assist in the diagnosis and management of patients with a variety of suspected genitourinary tract problems, but the procedures are underutilized. Maximizing the utility of the available studies (as well as the perception of utility by referring physicians) requires a clear understanding of the clinical question, attention to quality control, acquisition of the essential elements necessary to produce an informed interpretation, and production of a report that presents a coherent impression that specifically addresses the clinical question and is supported by data contained in the report. To help achieve these goals, part 1 of this review covers information that should be provided to the patient before the scan, describes the advantages and limitations of the available radiopharmaceuticals, discusses quality control elements needed to optimize the study, summarizes approaches to the measurements of renal function, and focuses on recommended quantitative indices and their diagnostic applications. Although the primary focus is the adult patient, aspects of the review also apply to the pediatric population.

Inter- and intra-observer reproducibility of quantitative renographic parameters of differential function and renal drainage in children

PURPOSE

To evaluate inter- and intra-observer reproducibility of renographic quantitative parameters of input and output in children.

METHODS

100 children with unilateral or bilateral uropathy were selected, aiming to cover the entire range of ages, overall glomerular filtration rate (GFR), differential renal function (DRF) and quality of drainage. Renograms were acquired and processed according to the EANM guidelines, using a non-commercial software. Following parameters were tested: DRF using integral and Patlak methods, normalized residual activity (NORA) and output efficiency (OE) at 20 min and on the late post-erect post-micturition acquisition. Three observers from the same department and one from Santiago (Chile) processed independently the 100 renograms using the same renal software. Two observers reprocessed the 100 renograms again two months later in order to evaluate the intra-observer reproducibility.

RESULTS AND CONCLUSION

No significant difference was observed between the four observers, whatever the considered parameter of input function or output. For left DRF (Integral and Patlak methods), 95% of the individual differences were between -5% and +5 %. They were between -0.5 and +0.5 units for both NORA 20 and NORA PM, and between -10% and +10% for OE 20 and OE PM. Inter-and intra- observer reproducibility were comparable. Outliers tended to be more frequent for Patlak than for Integral. Very low GFR (< 20 mL/min/1.73 m(2)), very young age (first days of life), huge megaureters, NORA values higher than 2.0, OE values below 60% and bladder in the renal background area (ectopic kidney) were the main characteristics of extreme differences.

The antenatally detected pelvi-ureteric junction stenosis: advances in renography and strategy of management

This review includes an analysis of new developments in the field of renography, the predictive factors suggesting the need for pyeloplasty in cases of pelvi-utereric stenosis detected antenatally and integration of the pelvi-ureteric junction stenosis within the framework of antenatally detected hydronephrosis.

Guidance document for structured reporting of diuresis renography

This Guidance Document for structured reporting of diuresis renography in adults was developed by the International Scientific Committee of Radionuclides in Nephro-urology (ISCORN; http://www.iscorn.org). ISCORN chose diuresis renography for its first structured report Guidance Document because suspected obstruction is the most common reason for referral, most radionuclide renal studies are conducted at institutions that perform fewer than 3 studies per week, and a large percentage of studies are interpreted by physicians with limited training in nuclear medicine. Ten panelists were asked to categorize specific reporting elements as essential, recommended, optional (without sufficient data to support a higher ranking), and unnecessary (does not contribute to scan interpretation or quality assurance). The final document was developed through an iterative series of comments and questionnaires with a majority vote required to place an element in a specific category. The Guidance Document recommends a reporting structure organized into indications, clinical history, study procedure, findings and impression and specifies the elements considered essential or recommended in each category. The Guidance Document is not intended to be restrictive but, rather, to provide a basic structure and rationale so that the diuresis renography report will: (1) communicate the results to the referring physician in a clear and concise manner designed to optimize patient care; (2) contain the essential elements required to evaluate and interpret the study; (3) clearly document the technical components of the study necessary for accountability, quality assurance and reimbursement; and (4) encourage clinical research by facilitating better comparison and extrapolation of results between institutions.

Key variables for interpreting 99mTc-mercaptoacetyltriglycine diuretic scans: development and validation of a predictive model

OBJECTIVE

The purpose of this study was to facilitate interpretation of (99m)Tc-mercaptoacetyltriglycine (MAG3) diuretic scans by identifying key interpretative variables and developing a predictive model for computer-assisted diagnosis.

MATERIALS AND METHODS

Ninety-seven studies were randomly selected from an archived database of MAG3 baseline and furosemide acquisitions and scan interpretations (obstruction, equivocal finding, or no obstruction) derived from a consensus of three experts. Sixty-one studies (120 kidneys) were randomly chosen to build a predictive model for diagnosing or excluding obstruction. The other 36 studies (71 kidneys) composed the validation group. The probability of normal drainage (no obstruction) at the baseline acquisition and the probability of no obstruction, equivocal finding, or obstruction after furosemide administration were determined by logistic regression analysis and proportional odds modeling of MAG3 renographic data.

RESULTS

The single most important baseline variable for excluding obstruction was the ratio of postvoid counts to maximum counts. Renal counts in the last minute of furosemide acquisition divided by the maximum baseline acquisition renal counts and time to half-maximum counts after furosemide administration in a pelvic region of interest were the critical variables for determining obstruction. The area under the receiver operating characteristic curve (AUC) for predicting normal drainage in the validation sample was 0.93 (standard error, 0.02); sensitivity, 85%; specificity, 93%. The AUC for the diagnosis of obstruction after furosemide administration was 0.84 (standard error, 0.06); sensitivity, 82%; specificity, 83%.

CONCLUSION

A predictive system has been developed that provides a promising computer-assisted diagnosis approach to the interpretation of MAG3 diuretic renal scans; this system has also identified the key variables required for scan interpretation.

Guidelines for standard and diuretic renogram in children

Special consideration needs to be given to children who undergo dynamic renography. The Paediatric Committee of the European Association of Nuclear Medicine has updated the previous guidelines. Details are provided on how to manage the child, the equipment, and the acquisition and processing protocols. The pitfalls, difficulties and controversies that are encountered are also discussed, as well as the interpretation of the results.

The International Atomic Energy Agency software package for the analysis of scintigraphic renal dynamic studies: a tool for the clinician, teacher, and researcher

Under the auspices of the International Atomic Energy Agency, a new-generation, platform-independent, and x86-compatible software package was developed for the analysis of scintigraphic renal dynamic imaging studies. It provides nuclear medicine professionals cost-free access to the most recent developments in the field. The software package is a step forward towards harmonization and standardization. Embedded functionalities render it a suitable tool for education, research, and for receiving distant expert's opinions. Another objective of this effort is to allow introducing clinically useful parameters of drainage, including normalized residual activity and outflow efficiency. Furthermore, it provides an effective teaching tool for young professionals who are being introduced to dynamic kidney studies by selected teaching case studies. The software facilitates a better understanding through practically approaching different variables and settings and their effect on the numerical results. An effort was made to introduce instruments of quality assurance at the various levels of the program's execution, including visual inspection and automatic detection and correction of patient's motion, automatic placement of regions of interest around the kidneys, cortical regions, and placement of reproducible background region on both primary dynamic and on postmicturition studies. The user can calculate the differential renal function through 2 independent methods, the integral or the Rutland-Patlak approaches. Standardized digital reports, storage and retrieval of regions of interest, and built-in database operations allow the generation and tracing of full image reports and of numerical outputs. The software package is undergoing quality assurance procedures to verify the accuracy and the interuser reproducibility with the final aim of launching the program for use by professionals and teaching institutions worldwide.

[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.

Normalized residual activity and output efficiency in case of early furosemide injection in children

OBJECTIVE

Values for output efficiency (OE) and normalized residual activity (NORA) in paediatric patients have been published previously. However, it is now a usual practice to inject furosemide at the beginning of a renogram acquisition (F0 procedure). The aim was to evaluate OE and NORA obtained on F0 renograms, in normal and abnormal paediatric kidneys.

METHODS

Three groups of kidneys were selected: group 1, normal kidneys (n=155); group 2, dilated but unobstructed kidneys (n=20); and group 3, hydronephrotic kidneys (n=84). A 20-min Tc-mercaptoacetyltriglycine renogram was obtained under early furosemide injection (F0) and was completed by late postmicturition (PM) images. OE and NORA were calculated at the end of the renogram and on the PM images.

RESULTS

Group 1: NORA and OE calculated at the end of the F0 renogram revealed better drainage than without F0 stimulation. The PM parameters were comparable with those previously obtained after late furosemide injection (F+20). Group 2: the drainage, despite the early injection of furosemide, was often unsatisfactory at the end of the F0 renogram, but improved dramatically upon the PM acquisition. Group 3: almost normal values up to very abnormal ones were observed. In 35% of kidneys, the values of drainage were out of the range of group 2.

CONCLUSION

Under early furosemide injection, renal drainage in the normal kidneys was better than in basic conditions. In dilated unobstructed kidneys, NORA and OE obtained on late images after micturition were, respectively, below 1.5 and above 80%.

[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.

Normal differential renal function does not indicate a normal kidney after partial ureteropelvic obstruction and subsequent relief in 2-week-old piglets

PURPOSE

We investigated the functional consequences of relieving ureteric obstruction in young pigs with experimental hydronephrosis (HN) induced by partial unilateral ureteropelvic obstruction.

MATERIALS AND METHODS

Three groups of animals were followed from the age of 2 weeks to the age of 14 weeks: Eight animals had severe or grades 3-4 HN throughout the study. Six animals had relief of the obstruction after 4 weeks. Six animals received sham operations at both ages. Morphological and functional examinations were performed at age 6 weeks and again at age 14 weeks and consisted of magnetic resonance imaging (MRI), technetium-diethylenetriaminepentaaceticacid ((99m)Tc-DTPA) renography, renal technetium-dimercaptosuccinicacid ((99m)Tc-DMSA) scintigraphy, and glomerular filtration rate (GFR) measurement.

RESULTS

After relief of the partial obstruction, there was reduction of the pelvic diameter and improvement of urinary drainage. Global and relative kidney function was not significantly affected by either obstruction or its relief. Renal (99m)Tc-DMSA scintigraphy showed a change in both the appearance of the kidney and a change in the distribution within kidneys even after relief of obstruction.

CONCLUSION

This study shows that partial ureteric obstruction in young pigs may be associated with little effect on global and differential kidney function. However, even after relief of HN, the distribution of (99m)Tc-DMSA in the kidney remains abnormal suggesting that a normal differential renal function may not represent a normal kidney.

Decision support systems in diuresis renography

The volume of diagnostic imaging studies performed in the United States is rapidly increasing resulting from an increase in the number of patients as well as an increase in the volume of studies per patient. Concurrently, the number and complexity of images in each patient data set are also increasing. Nuclear medicine physicians and radiologists are required to master an ever-expanding knowledge base whereas the hours available to master this knowledge base and apply it to specific tasks are steadily shrinking. The convergence of an expanding knowledge base and escalating time constraints increases the likelihood of physician errors. The problem is particularly acute for low-volume studies such as MAG3 diuresis renography where many imagers may have had limited training or experience. To address this problem, renal decision support systems (DSS) are being developed to assist physicians evaluate suspected obstruction in patients referred for diuresis renography. Categories of DSS include neural networks, case-based reasoning, expert systems and statistical systems; RENEX and CART are examples of renal DSS currently in development. RENEX (renal expert) uses a set of rules obtained from human experts to analyze a knowledge base of expanded quantitative parameters obtained from diuresis MAG3 scintigraphy whereas CART (classification and regression tree analysis) is a statistical method that grows and prunes a decision tree based on an analysis of these quantitative parameters in a training data set. RENEX can be queried to provide the reasons for its conclusions. Initial data show that the interpretations provided by RENEX and CART are comparable to the interpretations of a panel of experts blinded to clinical information. This project should serve as a benchmark for the scientific comparison and collaboration of these 2 fields of medical decision-making. Moreover, we anticipate that these DSS will better define the essential interpretative criteria, foster standardized interpretation, teach trainees to better interpret renal scans, enhance diagnostic accuracy and provide a methodology applicable to other diagnostic problems in radiology and medicine.

International Scientific Committee of Radionuclides in Nephrourology (ISCORN) consensus on renal transit time measurements

This report is the conclusion of the international consensus committee on renal transit time (subcommittee of the International Scientific Committee of Radionuclides in Nephrourology) and provides recommendations on measurement, normal values, and analysis of clinical utility. Transit time is the time that a tracer remains within the kidney or within a part of the kidney (eg, parenchymal transit time). It can be obtained from a dynamic renogram and a vascular input acquired in standardized conditions by a deconvolution process. Alternatively to transit time measurement, simpler indices were proposed, such as time of maximum, normalized residual activity or renal output efficiency. Transit time has been mainly used in urinary obstruction, renal artery stenosis, or renovascular hypertension and renal transplant. Despite a large amount of published data on obstruction, only the value of normal transit is established. The value of delayed transit remains controversial, probably due to lack of a gold standard for obstruction. Transit time measurements are useful to diagnose renovascular hypertension, as are some of the simpler indices. The committee recommends further collaborative trials.

Antenatally detected hydronephrosis

The strategy of management of children with hydronephrosis has considerably changed as a result of the development of ultrasound techniques, allowing a prenatal detection. Hydronephrosis is defined as a dilation of the renal collecting system, and several entirely different clinical entities can be considered this general heading, whereas early detection may have a different impact depending on the entity considered. The present work aims to describe a certain number of these clinical entities, to discuss the strategic options of management that are proposed, and to evaluate the role of medical imaging, in particular the radionuclide approach. Congenital ureteropelvic junction anomaly, vesicoureteral reflux, posterior urethral valves, and duplex kidney will be successively considered. Multicystic dysplastic kidney disease, although not classified as hydronephrosis, will be mentioned because it may be mistaken for hydronephrosis.

99mTc-MAG3 renography: normal values for MAG3 clearance and curve parameters, excretory parameters, and residual urine volume

OBJECTIVE

Specific quantitative measurements have been recommended to assist in the interpretation of technetium-99m mercaptoacetyltriglycine (MAG3) renal studies. Our objective was to define the sex- and age-specific normal ranges for these recommended parameters.

MATERIALS AND METHODS

Data were obtained from a retrospective analysis of 106 subjects who were evaluated for kidney donation. The MAG3 clearance was calculated using a common camera-based method. The relative uptake, prevoid/postvoid and postvoid/maximum count ratios were determined using whole-kidney regions of interest (ROIs). Time to peak, time to half-peak, 20 min/maximum and 20 min/2-3 min count ratios were determined for cortical and whole-kidney ROIs. Residual urine volume was calculated on the basis of the pre- and postvoid bladder counts and voided urine volume.

RESULTS

The mean camera-based MAG3 clearance was 321 +/- 69 mL/min/1.73 m2, essentially the same as the mean plasma sample MAG3 clearance in comparable populations. The percentages of relative uptake in the right and left kidneys were 49% and 51% +/- 4%, respectively; no difference was seen between men and women. Cortical values were lower than the whole-kidney values (p < 0.001); the mean cortical 20 min/maximum count ratio was 0.19 (SD, 0.07 and 0.04 for right and left kidneys, respectively). The mean postvoid/maximum whole-kidney count ratio was < 0.1, and the mean postvoid residual bladder volume was < 30 mL.

CONCLUSION

Normal limits adjusted for age and sex have been established. Applying normal ranges to quantitative MAG3 parameters may assist in the interpretation of MAG3 scintigraphy and facilitate appropriate patient management.

Pediatric applications of renal nuclear medicine

This review should be regarded as an opinion based on personal experience, clinical and experimental studies, and many discussions with colleagues. It covers the main radionuclide procedures for nephro-urological diseases in children. Glomerular filtration rate can be accurately determined using simplified 2- or 1-blood sample plasma clearance methods. Minor controversies related to the technical aspects of these methods concern principally some correction factors, the quality control, and the normal values in children. However, the main problem is the reluctance of the clinician to apply these methods, despite the accuracy and precision that are higher than with the traditional chemical methods. Interesting indications are early detection of renal impairment, hyperfiltration status, and monitoring of nephrotoxic drugs. Cortical scintigraphy is accepted as a highly sensitive technique for the detection of regional lesions. It accurately reflects the histological changes, and the interobserver reproducibility in reporting is high. Potential technical pitfalls should be recognized, such as the normal variants and the difficulty in differentiating acute lesions from permanent ones or acquired lesions from congenital ones. Although dimercaptosuccinic acid scintigraphy seems to play a minor role in the traditional approach to urinary tract infection, recent studies suggest that this examination might influence the treatment of the acute phase, the indication for chemoprophylaxis and micturating cystography, and the duration of follow-up. New technical developments have been applied recently to the renogram: tracers more appropriate to the young child, early injection of furosemide, late postmicturition and gravity-assisted images and, finally, more objective parameters of renal drainage. Pitfalls mainly are related to the interpretation of drainage on images and curves. Dilated uropathies represent the main indication of the renogram, but the impact of this technique on the management of the child is, in a great number of cases, still a matter of intense controversy. Direct and indirect radionuclide cystography are interesting alternatives to the radiograph technique and should be integrated into the process of diagnosis and follow-up of vesicoureteral reflux.

Renal pelvis volume during diuresis in children with hydronephrosis: implications for diagnosing obstruction with diuretic renography

PURPOSE

We measured the volume of the renal pelvis during diuretic renography (DR) in children with normal and hydronephrotic kidneys to determine if changes in pelvic volume could affect the accuracy of DR in diagnosing obstruction.

MATERIALS AND METHODS

We studied 18 patients 1 month to 10 years old with unilateral hydronephrosis ultimately proved to be either obstructive or nonobstructive. Simultaneous DR and ultrasound were performed with patients supine using the gamma camera. Ultrasound measurements of the renal pelvis in 3 dimensions, obtained before and at intervals after diuretic injection, were used to calculate renal pelvic volume. The contralateral normal kidneys were used as controls.

RESULTS

Between 15 and 60 minutes after diuretic injection the renal pelvis enlarged to a maximum volume in all hydronephrotic and normal kidneys and then gradually decreased in size. Mean average increase in volume for hydronephrotic kidneys ranged from 46% in obstructed kidneys to 88% in nonobstructed kidneys. Volume expansion caused dilution of isotope within the renal pelvis, which resulted in prolongation of elimination half-time (T1/2) in 42% of nonobstructed hydronephrotic kidneys sufficient to register an obstructed washout pattern. However, there were no differences in the initial pelvic volume or the rate or extent of increases or decreases in pelvic volume that would permit nonobstructed hydronephrotic kidneys to be distinguished from obstructed ones.

CONCLUSIONS

The renal pelvis enlarges during diuresis in children with hydronephrosis. This enlargement causes dilution of isotope within the renal pelvis during DR, which prolonged the isotope washout rate or T1/2 sufficiently to produce an obstructed washout pattern in more than 40% of hydronephrotic kidneys that were ultimately proved to be nonobstructed. This misdiagnosis of obstruction is particularly likely to occur in children younger than 2 years because pelvic volume expansion is so exaggerated. Consequently, T1/2 appears to be particularly vulnerable to inaccuracy in diagnosing obstruction in this age group, and, therefore, it should not be relied on as an operative determinant.

The estimation of renal transit using renography--our opinion

Renal transit estimation using renography has been employed for decades. A variety of methods have been developed, ranging from simple quantitative to more sophisticated techniques. In this review, the methods are discussed in perspective of their advantages and drawbacks. Finally, the most robust methods for estimation of renal transit are proposed.

Interpretation of the renogram: problems and pitfalls in hydronephrosis in children

OBJECTIVE

To discuss the main steps of renographic technique and underline some pitfalls related to the acquisition, processing and interpretation of diuretic renography, an important method for guiding the management of asymptomatic congenital hydronephrosis.

METHODS

Despite guidelines and consensus protocols, renographic procedures differ among centres, causing difficulties in comparison and controversy in the interpretation of results. Thus we comprehensively assessed published papers on the subject of diuretic renography.

RESULTS

Differential renal function (DRF) is a robust measure provided there is adequate background subtraction. Pitfalls are related to the drawing of regions of interest, particularly in infants, to estimating the interval during which DRF is calculated, and to an adequate signal-to-noise ratio. There is no definition of a 'significant' reduction in DRF. The classical variables of the diuretic renogram may not allow an estimate of the best drainage. Poor pelvic emptying may be apparent because the bladder is full and because the effect of gravity on drainage is incomplete. Estimating the drainage as residual activity rather than any parameter on the slope might be more adequate, especially if the time of frusemide administration is changed. Renal function and pelvic volume can influence the quality of drainage. Drainage may be better estimated using new tools.

CONCLUSION

Provided the investigation is standardized and potential pitfalls accounted for, the diuretic renogram provides valuable and reproducible quantitative information on DRF and drainage.

The influence of renal function on normalized residual activity

OBJECTIVE

To quantify the influence of overall renal function on normalized residual activity (NORA) and to evaluate the modifying factors.

METHODS

A computer simulation model generated renograms by convolution of plasma disappearance curves with artificially created retention functions. From a database, 1099mTc-MAG3 plasma curves were selected, corresponding to renal clearances ranging from 33 to 405 ml x min(-1). The retention functions had three properties: (1) until the minimal transit time (MinTT), no output and a linear increase in transit time after MinTT; (2) a ratio of MinTT to mean transit time (MTT) equal to 0.3 or 0.8; and (3) a MTT between 3 and 60 min, increasing in steps of 1 min. The model generated 1160 renograms and for each of them the NORA was calculated at 20, 40 and 60 min. For each value of MTT, the coefficient of variation (CV) of the NORA was calculated at 20, 40 and 60 min.

RESULTS

For the same retention function, different clearances resulted in different values of NORA. The degree of variability of NORA depended on several factors, including the time of measurement, the MTT and the MinTT to MTT ratio. For clearances between 100 and 400 ml x min(-1), the CV of the NORA ranged from 15% to 30%, whilst for clearances below 100 ml x min(-1), the CV of the NORA ranged from 22% to 67%. Little influence of the MinTT to MTT ratio was observed.

CONCLUSION

NORA is influenced by overall renal function. The influence is limited for 99mTc mercaptoacetyltriglycine (99mTc-MAG3) renal clearances over 100 ml x min(-1), whilst for clearances less than 100 ml x min(-1), the NORA is influenced much more.

99mTc-MAG3 diuretic renography in children: a comparison between F0 and F+20

The aim of this work was to compare the quality of renal drainage obtained with two well-described procedures of diuretic renography (F+20 and F0 tests). We selected 36 clinically stable children, aged 10 days to 17 years, with unilateral (25) or bilateral (11) hydronephrosis, in whom both F+20 and F0 tests were successively performed. In all cases, a late image (PM) was acquired after micturition and after changing the position of the patient. The following parameters were calculated: the time to the maximum of the basic renogram (Tmax); and the normalized residual activity (NORA) and output efficiency (OE) at the end of the 20 min renogram, at the end of the furosemide test (35 min) and on the PM image. In F+20, the renal drainage was better on the PM image than at the end of the diuretic renogram, whereas, in F0, the renal drainage was better on the PM image than at the end of the 20 min diuretic renogram. When comparing F0 and F+20, both OE and NORA parameters revealed slightly better drainage at the end of the 20 min F0 renogram than at the end of the 35 min F+20 diuretic renogram. The drainage obtained on the late post-voiding image was comparable for both F0 and F+20 tests. In conclusion, the quality of drainage obtained during the F+20 and F0 procedures can easily be compared using both OE and NORA. A very similar quality of drainage was reached for both procedures when considering only the PM image. This PM view remains mandatory irrespective of the timing of the furosemide injection and despite the use of tracers with a high extraction rate.

When could the administration of furosemide be avoided?

PURPOSE

The purpose of this study was to evaluate whether some parameters of the basic renogram allow one to omit the administration of furosemide in cases of hydronephrosis.

MATERIALS AND METHODS

One hundred thirty-seven children (274 kidneys) referred for uni- or bilateral hydronephrosis were evaluated retrospectively. In all children additional furosemide challenges followed by postmicturition views were acquired because of unsatisfactory renal emptying. The patients were categorized into 2 groups according to the residual renal activity on the postmicturition view: those with good emptying (R-) of both kidneys, for which the administration of furosemide was considered of no influence, and those with partial or no emptying of at least 1 kidney (R+). The renogram parameters chosen for predicting R+ and R- were time to maximum (Tmax), output efficiency at 20 minutes (OE20), and normalized residual activity at 20 minutes (NORA20). For each parameter, the number of children was then calculated, for whom the administration of furosemide could have been omitted.

RESULTS

A total of 112 children were categorized as R- and 25 as R+. The cutoff values for 100% negative predictive value of Tmax, OE20, and NORA20 were 4.5 minutes, 66%, and 1.45 respectively. Application of these cutoff values for the parameters yields, in retrospect, 6 (4%), 29 (21%), and 22 (16%) children respectively for whom administration of furosemide could have been omitted.

CONCLUSION

On the basis of OE20 and NORA20, the administration of furosemide could have been omitted in a substantial number of patients, despite unsatisfactory renal emptying on the basic renogram.

Analysis of compartmental models of type 4 nuclear renograms with calculation of flow rate parameters and instantaneous drainage rates

OBJECTIVE

To estimate the dynamic rates of arterial delivery and renal drainage in renograms with the Homsy sign, using optimized computed compartmental modelling.

METHODS

Eleven F-15 renograms and one F+15 renogram (using 99mTc-mercaptoacetyltriglycine) with the Homsy sign were studied, with 26 controls. Compartmental models were constructed for each renogram using components (blood, renal, bladder) linked by variables (arterial rate, drainage rate). Each model was optimized using the Marquadt least-squares method to numerical data from the time-activity curves (TACs). The model renal component at sample points along the TAC was minimized and the corresponding drainage rates calculated.

RESULTS

The models were optimized, with a mean (range) r2 of 0.811 (0.68-0.88). There were continuous low drainage rates for all type 4 renograms, with no quadrupling of the flow rate, as predicted by the standard model.

CONCLUSION

The standard model is unlikely to be correct and the Homsy sign is probably an artefact seen in patients with impeded urinary drainage. Computer modelling of individual renograms is feasible and can provide useful insights into the pathophysiology of renal uptake and drainage.

Impaired drainage on diuretic renography using half-time or pelvic excretion efficiency is not a sign of obstruction in children with a prenatal diagnosis of unilateral renal pelvic dilatation

PURPOSE

Delayed drainage on diuretic renography is an accepted sign of obstruction in adults and symptomatic children. We investigated how to analyze the diuretic challenge as well as assess the significance of impaired drainage.

MATERIALS AND METHODS

We followed 24 children with a unilateral prenatal diagnosis of pelvic dilatation up to a minimum of 2 years. A total of 91 diuretic renograms were performed. All children had stable differential renal function and renal pelvic diameter did not change by greater than 9 mm. on sequential ultrasound. Kidneys with stable differential function and no increase in dilatation were considered not obstructed. Analysis of the diuretic challenge included half-time, a post-void image with a change in posture, that is the child erect for 5 to 7 minutes, and drainage considering renal function using the pelvic excretion efficiency. Prolonged drainage was defined as a half-time of greater than 20 minutes or a post-void pelvic excretion efficiency of less than 71%.

RESULTS

Median patient age at presentation was 0.32 years and median followup was 3.07 years. The affected nonobstructed hydronephrotic kidney showed impaired drainage in 68% of the children using the half-time parameter, and in 80% and 44% using pelvic excretion efficiency before and after voiding, respectively. Variability in drainage was documented on sequential diuretic renography.

CONCLUSIONS

Using the guidelines for data acquisition and processing of diuretic renograms we nevertheless noted impaired drainage in 44% of this young group with nonobstructed kidneys. The half-time parameter was an inappropriate parameter. The diagnosis of obstruction cannot be simply based on delayed drainage in this group of asymptomatic children with a prenatal diagnosis of unilateral renal pelvic dilatation.

Radionuclide studies in paediatric nephro-urology

The main tool of radionuclide techniques applied to paediatric uro-nephrology is the quantitation of function, which is an information not easily obtained by other diagnostic modalities. The radiation burden is low. Drug sedation is only rarely needed, whatever the age of the patient. Accurate determination of glomerular filtration rate can be obtained by means of an intravenous injection of Cr-51 EDTA and one or two blood samples. Tc-99m DMSA scintigraphy is an accurate method for evaluation of regional cortical impairment during acute pyelonephritis and later on, for detection of permanent scarring. Tc-99m MAG3 renography is nowadays a well-standardized method for accurate estimation of the split renal function and of renal drainage with or without furosemide challenge. This technique is particularly indicated in uni- or bilateral uropathies with or without renal and/or ureteral dilatation. Direct and indirect radionuclide cystography are two alternative modalities for X-ray MCUG. Their relative place in the strategy of management of vesicoureteral reflux is discussed.

Diuretic renography in infants with prenatal unilateral hydronephrosis: an explanation for the controversy about poor drainage

OBJECTIVE

To present an explanation for impaired drainage on diuretic renography in infants with a prenatal diagnosis of unilateral renal pelvic dilatation (RPD) who are stable both in terms of renal function and dilatation on follow-up investigations, despite undergoing no surgical intervention, and who undergo diuretic renography postnatally; this should provide some insight into whether impaired drainage is a sign of obstruction in these asymptomatic infants.

MATERIALS AND METHODS

Using a combination of published studies on the technique of diuretic renography and an analysis of such studies, a theoretical model of the infant kidney was developed to assess the possibility of prolonged drainage.

RESULTS

The results from the model showed prolonged drainage in many different situations, thus offering an explanation of expected impaired drainage even if there was no obstruction.

CONCLUSION

Understanding the pathophysiology of prenatally diagnosed RPD allows different interpretations of the diuretic renogram and may affect the treatment of these children.

Factors influencing the accuracy of renal output efficiency

Output efficiency (OE) has been proposed as an objective tool for the estimation of renal emptying. The aim of this paper was to evaluate some factors that may affect the value of this parameter obtained by a 99Tcm MAG3 renogram. In 22 patients, the effect of different types of renal background correction was calculated. In 10 patients, simultaneous gamma camera renography and multiple blood sampling allowed the error of using a heart curve instead of a plasma curve to be evaluated. Finally, an evaluation was carried out on the effect of neglecting the change of plasma activity between the end of the furosemide acquisition and the post-micturition view obtained after repositioning of the patient on the gamma camera: 142 patients who had had multiple blood sampling were retrospectively selected for that purpose. It has been shown that all these factors may significantly affect the value of OE, particularly in cases with poor renal drainage. Unless standardization of the procedure is introduced for some of these factors, the cut-off levels for good, fair and poor drainage may vary between centres.