Estimation Of Differential Renal Function Research Articles

Estimation of differential renal function on routine abdominal imaging employing compressed-sensed contrast-enhanced MR: a feasibility study referenced against dynamic renal scintigraphy in patients with deteriorating renal retention parameters

PurposeTo assess whether high temporal/spatial resolution GRASP MRI acquired during routine clinical imaging can identify several degrees of renal function impairment referenced against renal dynamic scintigraphy.MethodsThis retrospective study consists of method development and method verification parts. During method development, patients subject to renal imaging using gadoterate meglumine and GRASP post-contrast MRI technique (TR/TE 3.3/1.6 ms; FoV320 × 320 mm; FA12°; Voxel1.1 × 1.1x2.5 mm) were matched into four equally-sized renal function groups (no-mild-moderate-severe impairment) according to their laboratory-determined estimated glomerular filtration rates (eGFR); 60|120 patients|kidneys were included. Regions-of-interest (ROIs) were placed on cortices, medullary pyramids and collecting systems of bilateral kidneys. Cortical perfusion, tubular concentration and collecting system excretion were determined as TimeCortex=Pyramid(sec), SlopeTubuli (sec−1), and TimeCollecting System (sec), respectively, and were measured by a combination of extraction of time intensity curves and respective quantitative parameters. For method verification, patients subject to GRASP MRI and renal dynamic scintigraphy (99mTc-MAG3, 100 MBq/patient) were matched into three renal function groups (no-mild/moderate-severe impairment). Split renal function parameters post 1.5–2.5 min as well as MAG3 TER were correlated with time intensity parameters retrieved using GRASP technique; 15|30 patients|kidneys were included.ResultsMethod development showed differing values for TimeCortex=Pyramid(71|75|93|122 s), SlopeTubuli(2.6|2.1|1.3|0.5 s−1) and TimeCollecting System(90|111|129|139 s) for the four renal function groups with partial significant tendencies (several p-values < 0.001). In method verification, 29/30 kidneys (96.7%) were assigned to the correct renal function group.ConclusionHigh temporal and spatial resolution GRASP MR imaging allows to identify several degrees of renal function impairment using routine clinical imaging with a high degree of accuracy.

Correction of differential renal function for asymmetric renal area ratio in unilateral hydronephrosis.

Children with unilateral hydronephrosis are followed up with anteroposterior pelvic diameter (APD), hydronephrosis grade, mercaptoacetyltriglycine (MAG-3) drainage pattern and differential renal function (DRF). Indeterminate drainage preserved DRF in higher grades of hydronephrosis, in some situations, complicating the decision-making process. Due to an asymmetric renal area ratio, falsely negative DRF estimations can result in missed optimal surgery times. This study was designed to assess whether correcting the DRF estimation according to kidney area could reflect the clinical situation of a hydronephrotic kidney better than a classical DRF calculation, concurrently with the hydronephrosis grade, APD and MAG-3 drainage pattern. We reviewed the MAG-3, dimercaptosuccinic acid (DMSA) scans and ultrasonography (US) of 23 children (6 girls, 17 boys, mean age: 29 ± 50 months) with unilateral hydronephrosis. MAG-3 and DMSA scans were performed within 3 months (mean 25.4 ± 30.7 days). The closest US findings (mean 41.5 ± 28.2 days) were used. DMSA DRF estimations were obtained using the geometric mean method. Secondary calculations were performed to correct the counts (the total counts divided by the number of pixels in ROI) according to kidney area. The renogram patterns of patients were evaluated and separated into subgroups. The visual assessment of DMSA scans was noted and the hydronephrotic kidney was classified in comparison to the normal contralateral kidney's uptake. The correlations of the DRF values of classical and area-corrected methods with MAG-3 renogram patterns, the visual classification of DMSA scan, the hydronephrosis grade and the APD were assessed. DRF estimations of two methods were statistically different (p: 0.001). The categories of 12 hydronephrotic kidneys were changed. There were no correlations between classical DRF estimations and the hydronephrosis grade, APD, visual classification of the DMSA scan and uptake evaluation. The DRF distributions according to MAG-3 drainage patterns were not different. Area-corrected DRF estimations correlated with all: with an increasing hydronephrosis grade and APD, DRF estimations decreased and MAG-3 drainage patterns worsened. A decrease in DRF (< 45 %) was determined when APD was ≥ 10 mm. When APD was ≥ 26 mm, a reduction of DRF below 40 % was determined. Our results suggest that correcting DRF estimation for asymmetric renal area ratio in unilateral hydronephrosis can be more robust than the classical method, especially for higher grades of hydronephrotic kidneys, under equivocal circumstances.

Pediatric MR Urography: Indications, Techniques, and Approach to Review

Magnetic resonance (MR) urography is a valuable imaging modality for assessing disorders of the pediatric urinary tract. It allows comprehensive evaluation of the kidneys and urinary tract in children by providing both morphologic and functional information without exposing the child to ionizing radiation. Pediatric MR urography can be used to thoroughly evaluate renal and urinary tract abnormalities that are difficult to identify or fully characterize with other imaging techniques, and it has the potential to allow earlier diagnosis while decreasing the number of imaging studies performed. Common indications for pediatric MR urography include evaluation of complex renal and urinary tract anatomy, suspected urinary tract obstruction, operative planning, and postoperative assessment. MR hydrography (T2-weighted imaging of urine) excellently depicts dilated or obstructed urinary systems, whereas postcontrast imaging (gadolinium-enhanced T1-weighted imaging of the kidneys and urinary system) excellently depicts nondilated or nonobstructed urinary systems. Postcontrast MR urography also allows a functional evaluation of the kidneys and urinary tract that includes estimation of differential renal function. The authors review common indications for pediatric MR urography, detail MR urography techniques, compare the strengths and weaknesses of MR urography with those of alternative imaging strategies for children, and describe numerous common and uncommon abnormalities of the pediatric kidneys and urinary tract.

Classical vs. unit area method in the evaluation of differential renal function in unilateral hydronephrosis.

There are some problematic results in determination of differential renal function (DRF) by means of Tc-99m DMSA renal scintigraphy in hydronephrotic kidneys. In this study the classical method (CM) and unit area methods (UAM) in the estimation of DRF in unilateral hydronephrosis before and after intervention were compared. Twenty patients (12 M, 8 F; mean: 42.6±18.5 years old) who were candidates for surgery or intervention because of unilateral hydronephrosis were the subjects of this study. All the patients were evaluated by Tc-99m DMSA scintigraphy before and 3-6 months after the intervention. In order to estimate DRF both CM and UAM (obtained by division of the counts including the kidney ROI to pixel of the same ROI) were performed. Bland-Altman analyses were performed in order to compare the DRF values obtained from both methods. The agreement between CM and UAM was poor in the preoperative estimation, however, the agreement was good after the operation or intervention. In this study it seems that DRF estimation with CM in unilateral hydronephrosis might be problematic in the determination of surgery thus UAM might be introduced as the method of choice in the determination of DRF in unilateral hyronephrosis.

Model-based extraction of input and organ functions in dynamic scintigraphic imaging

Image-based definition of input function (IF) and organ function is a prerequisite for kinetic analysis of dynamic scintigraphy or positron emission tomography. This task is typically done manually by a human operator and suffers from low accuracy and reproducibility. We propose a probabilistic model based on physiological assumption that time–activity curves (TACs) arise as a convolution of an IF and tissue-specific kernels. The model is solved via the Variational Bayes estimation procedure and provides estimates of the IF, tissue-specific TACs and their related spatial distributions (images) as its results. The algorithm was tested with data of dynamic renal scintigraphy. The method was applied to the problem of differential renal function estimation and the IF estimation and the results are compared with competing techniques on data-sets with 99 and 19 patients. The MATLAB implementation of the algorithm is available for download.

Comparison of Creatinine Based and Kidney Volume Based Methods of Estimating Glomerular Filtration Rates in Potential Living Kidney Donors

Accurate assessment of kidney function is critical to evaluate living kidney donors. Direct glomerular filtration rate measurement using isotopes is currently the gold standard but it is complex and costly. We evaluated the performance of surrogate markers of the glomerular filtration rate in living kidney donors by comparing direct measurement of the rate to the creatinine based equation estimated rate, the kidney volume based estimated rate using a newly developed equation and creatinine clearance. We first statistically compared direct glomerular filtration rate measurement to the results of the Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) creatinine based equations, and to creatinine clearance in 54 potential renal donors from 2006 to 2010. In 32 donors with cross-sectional computerized tomography available we used measured functional renal volume with age, gender, weight and serum creatinine to estimate the rate based on kidney volume according to a previously reported model. Kidney volume based measurement was compared to direct glomerular filtration rate measurement and assessed against the results of the best performing creatinine based equation. In the first group of 54 donors the correlation index of the estimated glomerular filtration rate according to MDRD and CKD-EPI creatinine based equations, and to creatinine clearance was low compared to direct measurement. In the subset of 32 potential donors the kidney volume based estimated rate correlated better with direct measurement than MDRD equation results with higher accuracy (estimated 87.5% and 75.0% within 30% and 10% of direct rate measurement, respectively). To estimate the glomerular filtration rate in healthy individuals a volume based model correlated better than the MDRD equation, which is the best performing creatinine based equation used to estimate the rate. By providing a more robust estimation of the glomerular filtration rate in healthy potential kidney donors, the volume based model adds value to routine preoperative computerized tomography above that of anatomical evaluation.

Correlation between differential renal function estimation using CT-based functional renal parenchymal volume and 99m Tc - DTPA renal scan

Introduction and Objective:Nuclear renal scan is currently the gold standard imaging study to determine differential renal function. We propose helical CT as single modality for both the anatomical and functional evaluation of kidney with impaired function. In the present study renal parenchymal volume is measured and percent total renal volume is used as a surrogate marker for differential renal function. The objective of this study is to correlate between differential renal function estimation using CT-based renal parenchymal volume measurement with differential renal function estimation using 99mTC - DTPA renal scan.Materials and Methods:Twenty-one patients with unilateral obstructive uropathy were enrolled in this prospective comparative study. They were subjected to 99mTc - DTPA renal scan and 64 slice helical CT scan which estimates the renal volume depending on the reconstruction of arterial phase images followed by volume rendering and percent renal volume was calculated. Percent renal volume was correlated with percent renal function, as determined by nuclear renal scan using Pearson coefficient.Results and Observation:A strong correlation is observed between percent renal volume and percent renal function in obstructed units (r = 0.828, P < 0.001) as well as in nonobstructed units (r = 0.827, P < 0.001).Conclusion:There is a strong correlation between percent renal volume determined by CT scan and percent renal function determined by 99mTC - DTPA renal scan both in obstructed and in normal units. CT-based percent renal volume can be used as a single radiological tests for both functional and anatomical assessment of impaired renal units.

Comparison of 99mTc- Ethylene Dicysteine and 99mTc-Dimercaptosuccinic Acid Scintigraphy for the Evaluation of Cortical Scarring and Differential Renal Function in Children with Recurrent Urinary Tract Infection

ABSTRACT Introduction Urinary tract infection (UTI) is the most common and severe bacterial infection in children. Renal scarring and associated deterioration in the differential renal function is a frequent finding. Scarring may occur even in asymptomatic patients without vesicoureteric reflux. Materials and methods Fifty-three children (43 M:10 F, mean age:5.3 years; range 2-10 years) with evidence of recurrent UTI were enrolled in the study. Patients with duplex or crossed fused ectopic kidneys and with acute or chronic renal failure were excluded from the study protocol. Each patient underwent 99mTc-DMSA and 99mTc-EC renal scintigraphy within a period of 2 weeks. Results Analysis of results was performed by comparing the diagnostic accuracy of the summed 99mTc-EC and 99mTc-DMSA images for the detection of renal cortical scars and correlation (linear regression analysis) between the two renal scintigraphic procedures for the estimation of differential renal function. 99mTc-DMSA imaging demonstrated scarring in 41 kidneys whereas 99mTc-EC scintigraphy revealed scarring in 29/41 kidneys only. The percentage function of both kidneys with 99mTc-EC and 99mTc-DMSA showed good correlation. The r2 for left kidney was 0.95 and for right kidney was 0.94. Conclusion 99mTc-EC scintigraphy has low sensitivity (70%) for the detection of cortical scarring as compared to 99mTc-DMSA (100%) renal imaging. On the hand, 99mTc-DMSA static imaging gives good estimate for the DRF and the values are in good agreement with the corresponding values derived from dynamic 99mTc-EC scanning. How to cite this article Raja S, Pareek V, Singh B, Sharma S, Rao KLN, Mittal BR. Comparison of 99mTc-Ethylene Dicysteine and 99mTc-Dimercaptosuccinic Acid Scintigraphy for the Evaluation of Cortical Scarring and Differential Renal Function in Children with Recurrent Urinary Tract Infection. J Postgrad Med Edu Res 2012;46(4):183-186.

Image Guided Percutaneous Probe Ablation for Renal Tumors in 65 Solitary Kidneys: Functional and Oncological Outcomes

We evaluated the oncological and functional outcomes of computerized tomography guided percutaneous cryotherapy or radio frequency ablation of kidney tumors in patients with a solitary kidney. We reviewed the medical charts of patients with a solitary kidney who underwent percutaneous probe ablation for renal masses at our institution from April 2002 through March 2010. Followup consisted of computerized tomography or magnetic resonance imaging 1 day postoperatively, at 3, 6 and 12 months, and annually thereafter. Serum creatinine and estimated glomerular filtration rate were used to measure renal function. The cryotherapy and radio frequency ablation groups were compared for demographics, the 2-year actuarial survival rate and renal function. Overall 65 patients were included in this retrospective analysis, of whom 29 (44.6%) underwent cryotherapy and 36 (55.4%) underwent radio frequency ablation. Median followup was 15.1 (IQR 4.4 to 32.9) and 38.8 months (13.8 to 50.7), respectively. The 2 groups were comparable in median age, body mass index, American Society of Anesthesiologists score, tumor size and preoperative estimated glomerular filtration rate. The 3 primary treatment failures, including 1 after cryotherapy and 2 after radio frequency ablation, were successfully re-treated with thermal ablation. There were 14 recurrences after radio frequency ablation and 3 after cryotherapy. Two-year actuarial overall, cancer specific, recurrence-free and metastasis-free survival rates for cryotherapy vs radio frequency ablation were 89% vs 93%, 100% vs 96%, 69% vs 58% and 86% vs 91%, respectively. For each group no significant decrease in renal functional parameters was found at the latest followup visit. Computerized tomography guided percutaneous probe ablation represents a safe treatment option in surgical patients at high risk with a solitary kidney. It provides low morbidity, acceptable short-term cancer control and minimal clinical impact on postoperative renal function.

Clinical Evaluation of Ultra-Low Dose Contrast-Enhanced CT in Patients Presenting with Acute Ureteric Colic

Objective: To determine the diagnostic accuracy of ultra-low dose contrast-enhanced CT (ULDCECT) and its ability to measure differential renal function (DRF) in patients presenting clinically with acute ureteric colic by comparison to IVU (using an equivalent radiation exposure) and DMSA, respectively. Patients and methods: Fifty-three patients presenting clinically with acute ureteric colic underwent IVU, ULDCECT and DMSA on the same day of their hospital admission. Diagnostic accuracy of ULDCECT and IVU was compared to interventional findings and clinical outcome. Estimation of DRF by ULDCECT was derived through measurement of enhancing renal volumes and DMSA. Results: ULDCECT had superior sensitivity (97%) and specificity (100%) in the identification of renal tract stone disease compared to IVU (84 and 95% respectively), with comparable radiation exposure (1.7 mSv versus 1.4 mSv). Furthermore, ULDCECT revealed non-urological pathology in eight patients (15%), including perforated abdominal viscus and acute appendicitis. There was a very good correlation of ULDCECT and DMSA-derived DRF (regression of near unity, Pearson's correlation coefficient of 0.72 ( p &lt; 0.0001)). Conclusion: ULDCECT provides diagnostically accurate imaging in patients presenting with acute ureteric colic and significantly outperforms IVU for a comparable radiation burden. Use of ULDCECT instead of conventional CT-KUB may significantly reduce lifetime radiation exposure of ureteric colic patients without loss of diagnostic accuracy.

Differential renal function estimation by dynamic renal scintigraphy: influence of background definition and radiopharmaceutical

Differential renal function (DRF) calculation with 99mTc-diethylenetriamine-pentaacetic acid (DTPA) or mercaptoacetyltriglycine (MAG3) is gaining clinical importance in the evaluation of patients with ureteropelvic junction obstruction with hydronephrosis (HN). Although many decisions regarding surgery are based on the functional changes detected by serial diuretic renography, the reliability of DRF estimation has been questioned. Factors such as the correction of nonrenal activity included in the renal region of interest (background subtraction) and immature function resulting in poor renal extraction may cause unusual elevation in the differential function. The aim of this study is to evaluate the impact of the radiopharmaceutical and positioning of the background on the DRF. A prospective study was undertaken in 83 patients (48 male, 35 female, median age 5 years) with unilateral or bilateral ureteropelvic junction obstruction with or without HN. Forty-five and 38 renograms were performed with 99mTc-DTPA and 99mTc-MAG3, respectively. DRF was calculated using two different regions of interest (subrenal and perirenal) for background subtraction. Of the 83 patients, 37 also had dimercaptosuccinic acid scans. The difference between DRF based on background selection, age, radiopharmaceutical, and correlation with dimercaptosuccinic acid uptake was analyzed. The difference in DRF between two background (BG) drawings (sebrenal and perirenal) and 95% confidence intervals were calculated. For 83 renograms, the mean difference was 4.82 (range -7 to +25, SD 5.26). The 95% confidence intervals were -3.67 to 5.97. Analysis of the data revealed that greater spread of DRF between the techniques was seen in patients with right HN (mean 7.96, P<0.001). In patients with right HN, when lower pole background activity was used, the right renal function was overestimated by an average of 4.67%. When MAG3 was used, all patients had statistically significant DRF for the different BG subtraction techniques, whereas the DRF values were only statistically different in those with right HN when DTPA was used. The current study supports the existence of BG-related variation in the DRF calculations. We found that the average counts in the perirenal BG more precisely represent nonrenal activity and recommend the use of semilunar-perirenal background region of interest to reduce the overlapping hepatic activity.

Reproducibility of 99mTc-mercaptoacetyltriglycine renography: population comparison

To evaluate reproducibility of diuretic renography, performed according to current guidelines in adult and pediatric patient populations. Fifty adult and 50 pediatric renograms were processed twice by each of three observers. For differential renal function (DRF) assessment, intraclass correlation coefficient (ICC), standard deviation of DRF calculation and the repeatability parameter were calculated. For drainage assessment, ICC was calculated. Intraobserver and interobserver analysis was performed for both parameters. Patient groups and subgroups (age, DRF asymmetry, drainage) were compared by analysis of variance. Interobserver analysis, adult patient group: DRF-repeatability 4.20%, ICC 0.99. Drainage-ICC 0.92/1.00 (left/right kidney). Pediatric patient group: DRF-repeatability 7.80%, ICC 0.97. Drainage-ICC 0.93/0.85 (left/right kidney). Intraobserver analysis, adult patient group: DRF-repeatability 2.61%, ICC 0.99. Drainage-ICC 0.92/1.00 (left/right kidney). Pediatric patient group: DRF-repeatability 4.76%, ICC 0.98. Drainage-ICC 0.92/0.88 (left/right kidney). Highest repeatability and thus highest DRF dispersion was found in the subgroup of patients with poor/impaired kidney drainage and reduced DRF (repeatability 11.3%, analysis of variance, P<0.001). Reproducibility of DRF estimation was excellent in adults in both intraobserver and interobserver analysis. In pediatric patients, intraobserver DRF reproducibility was very good, whereas variation in interobserver analysis was rather high with a potential influence on patient management, but occurred mainly in a subgroup of patients with impaired drainage and ipsilaterally reduced DRF. Drainage assessment was highly reproducible in both patient groups; factors confounding drainage interpretation in discordant patient cases remained unidentified.

Diagnostic Accuracy of Urinary Creatinine Concentration in the Estimation of Differential Renal Function in Patients with Obstructive Uropathy

Objectives: To determine the diagnostic accuracy of spot urine creatinine concentration (UCC) as a new test for the evaluation of differential renal function in obstructed kidneys (DRF_ok) drained by percutaneous nephrostomy tube (PCNT). Methods: In patients with obstructed kidneys drained by PCNT, DRF_ok was derived from UCC by comparing the value of UCC in the obstructed kidney to the value in the contralateral kidney, and was derived from dimercaptosuccinic acid (DMSA) renal scans and creatinine clearance (CCr) using standard methods. Subsequently, the results of UCC were compared to the results of DMSA and CCr. Results: 61 patients were enrolled. Bland-Altman plots to compare DMSA and UCC showed that the upper limit of agreement was 14.8% (95% CI 10.7–18.5) and the lower limit was –19.9% (95% CI –23.8 to –16.1). The sensitivity and specificity of detecting DMSA DRF_ok ≤35% using UCC was 85.2 and 91.2%, respectively. When UCC was compared to CCr, Bland-Altman tests gave an upper limit of agreement of 10.4% (95% CI 7.9–12.8) and a lower limit of agreement of –11.3% (95% CI –13.8 to –8.9). Conclusions: UCC is accurate in the estimation of DRF_ok drained by PCNT.

Robustness of estimation of differential renal function in infants and children with unilateral prenatal diagnosis of a hydronephrotic kidney on dynamic renography: How real is the supranormal kidney?

The two methods recommended for estimation of differential renal function (DRF) in the renography guidelines published by the European Association of Nuclear Medicine are the area under the background-subtracted time-activity curves (AUCs) (often called the integral method) and the regression slope of the background-subtracted Rutland/Patlak plot analysis. The current study investigated the agreement/disagreement of DRF estimations obtained using these two techniques. This report also focusses on the occurrence of supranormal function of the affected kidney (defined as DRF >55%) and reviews the related technical and physiological factors. A total of 394 renographic studies in 101 children with a prenatal diagnosis of unilateral renal pelvic dilatation confirmed on postnatal studies were retrieved from optical disc and reprocessed by one author. DRF was calculated using the Rutland/Patlak plot and the AUC over the time period 40-120 s following an injection of( 99m)Tc-mercaptoacetyltriglycine. The difference in DRF between the methods (Rutland/Patlak minus AUC) and 95% limits of agreement were calculated. The age distribution of the difference between the methods was also analysed. For all 394 measurements the mean difference was -0.8% (range -21.0% to 16.9%, SD 3.9%). The 95% limits of agreement were -7.0% to 8.6%. Analysis of the data revealed that greater spread of DRF between the techniques was seen in studies performed at a younger age: a discrepancy of >5% DRF was significantly more common in those <1 year of age than in those >1 year old (25.3% vs 9.9%; chi-square, p<0.0005). Supranormal function was found less frequently using the Rutland/Patlak method than with the AUC method (8.4% vs 11.2%; chi-square, p<0.0005). The frequency of this diagnosis was reduced to 4.6% when both methods were required to be in agreement. The current study supports the existence of age-related variation in the disparity of DRF estimations using the AUC and Rutland/Patlak methods in children with unilateral pelvic dilatation. The close agreement between the AUC and Rutland/Patlak techniques in estimation of DRF in older children supports their use. However, careful quality control of the renogram analysis is essential in young babies. Supranormal renal function (>55% DRF) may in fact be much less common in this group of children than is currently reported.

RENAL PELVIS VOLUME DURING DIURESIS IN CHILDREN WITH HYDRONEPHROSIS: IMPLICATIONS FOR DIAGNOSING OBSTRUCTION WITH DIURETIC RENOGRAPHY

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. 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. 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. 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.

A14 The use of contrast enhanced multi-detector computed tomography in the estimation of differential renal function

A14 The use of contrast enhanced multi-detector computed tomography in the estimation of differential renal function

Effect of the size of regions of interest on the estimation of differential renal function in children with congenital hydronephrosis

The estimation of differential renal function from dynamic renography affects clinical decisions. The estimation requires the kidneys to be delineated with regions of interest. However, in the presence of unilateral hydronephrosis it is not unusual for the affected kidney to be enlarged so that the regions of interest required to delineate the normal and abnormal kidneys are themselves dissimilar in size. The question, which then arises is, will this difference in the sizes of the regions of interest affect the resultant estimation of differential renal function? Eighteen children aged 1 month to 7 years, with prenatal ultrasound diagnosis of unilateral hydronephrosis where the affected kidney was larger than the normal kidney, underwent a total of 57 diuretic renograms using 99mTc-mercaptoacetyltriglycine. The renographic data were retrieved from optical disc and re-analysed. Regions of interest were generated which enclosed each kidney plus a region of interest of equal size to the abnormal large kidney was placed over the normal kidney. The consensus report from the Scientific Committee of Radionuclides in Nephrology described the Rutland-Patlak plot and integral methods for the estimation of differential renal function from dynamic renography. These two methods were used to analyse renal curves with and without background subtraction. Evaluation of the results suggest that technical factors, including the size of the region of interest, may affect differential renal function, and may, in part, explain the reports of the super-normal kidney in the literature.

Optimizing background correction when calculating differential renal function in the presence of hydroureteronephrosis using 99Tc(m)-DTPA.

We performed a prospective study to establish the optimal background correction algorithm for the determination of differential renal function (DRF), using 99Tc(m)-diethylenetriamine pentaacetate (99Tc(m)-DTPA) in the presence of unilateral hydronephrosis, with 24 h 99Tc(m)-dimercaptosuccinic acid (99Tc(m)-DMSA) uptake as the 'gold standard'. From September 1996 to June 1997, 12 males and 4 females (mean age 10 years, range 1 month to 72 years), presenting with unilateral hydronephrosis, were studied. All patients underwent both DTPA renography and quantitative DMSA scintigraphy within 24 h. In all patients, using a surface method, the DRF of the obstructed kidney was determined using infrarenal, suprarenal and perirenal background correction, time intervals of 60-180 s (t1), 120-180 s (t2) and 80-140 s (t3), and the application or non-application of a Rutland-Patlak correction (RPC). In the absence of RPC, for all three types of background correction, no difference in DTPA DRF for any of the three time intervals was noted; higher DTPA DRF values were found (mean +/- S.D.: overestimates of 7.8+/-24.4%, 6.5+/-9.5% and 3.3+/-14.9% for suprarenal, infrarenal and perirenal background correction, respectively). Application of RPC resulted in an overall decrease in both the mean and standard deviation values, which was most pronounced with infrarenal background correction: -0.38+/-6.5% for t1, 0.31+/-6.3% for t2 and -1.3 +/-6.9% for t3 (t1 vs t2, P = 0.06; t3 vs t1 or t2, P = 0.04). Our results suggest that infrarenal background correction using t1 or t2 and RPC is the best algorithm for DRF estimation using 99Tc(m)-DTPA renography.

Estimation of Differential Renal Function in Children With a Prenatal Diagnosis of Unilateral Pelvic Dilatation

Estimation of Differential Renal Function in Children With a Prenatal Diagnosis of Unilateral Pelvic Dilatation