Prognostic Value of Effective Renal Plasma Flow for First-year Renal Outcome in Kidney Allograft Recipients.

INTRODUCTION: Many studies have suggested that post-transplantation renal allograft function is associated with long-term allograft outcomes. However, accurate examination through non-invasive methods remains rare. The aim of the present study is to assess the association between 99mTc mercaptoacetyltriglycine (MAG3) effective renal plasma flow (ERPF) and first-year post-transplantation renal allograft function. METHODS: We conducted a retrospective cohort study at our center between January 2011 and December 2016. Kidney transplant recipients without an ERPF examination within 14 days post-transplantation, or those with less than 1 year of follow-up were excluded. Eligible cases were divided into 3 groups according to first-year eGFR <45, 45 < eGFR <60, eGFR >60. The Kruskal-Wallis test and χ2 were used for comparisons between continuous and categorical variables. RESULTS: A total of 123 patients were analyzed. Each group received 41 patients. The baseline characteristics were comparable in the 3 groups, except for repeated transplantation and delayed graft function. The results of the ERPF median (interquartile range) for the 3 groups were 193 (140.0-244.5) in the eGFR < 45 group, 236 (182.5-301.0) in the 45 < eGFR < 60 group, and 294 (202.5-384.5) in the eGFR > 60 group (P < .001). The receiver operating characteristic analysis showed that a cutoff ERPF value of >276 exhibited the best sensitivity (65.85%) and specificity (75.61%) for predicting first-year eGFR > 60 mL/min/1.73 m2, with an area under the receiver operating characteristic curve of .712, P < .0001. CONCLUSION: Our findings suggest that an ERPF value of more than 276 is likely to be associated with a favorable first-year renal graft outcome after transplantation. The 99mTc MAG3 ERPF may be a non-invasive alternative to sequential protocol biopsies.

Correlation of the ERPF with the extraction fraction values of technetium-99m mercaptoacetyltriglycine.

OBJECTIVE: The objective of this study was to determine if a correlation exists between the effective renal plasma flow (ERPF) and the extraction fraction (EF) using 99mTc MAG3 in children. This EF has been previously described with 9mTc DTPA. However, the renal imaging agent of choice has become 9mTc MAG3. MATERIAL AND METHOD: The study was approved by The Children's Hospital of Philadelphia's institutional review board. Informed consent was also obtained A retrospective study of 29 children (16 males, 13 females) of ages 1 month to 19.5 years who underwent 99mTc MAG3 renal scintigraphy from September 2001 to December 2001 was analysed. EF values were calculated with and without attenuation correction in each kidney by determining the counts in a region of interest, correcting for background and comparing the counts with the injected dose. The EF was compared to the ERPF calculated using the Schlegel's method. The correlation between the EF and the ERPF corrected and non-corrected for soft tissue attenuation, were determined and were identified by using linear regression analysis. RESULTS: There was significant correlation between the ERPF and the EF with (r = 0.62, p < 0.05 on the left, r = 0.51, p = 0.005 on the right) than without attenuation correction (r = 0.54, p = 0.003 on the left, r = 0.42, p = 0.022 on the right). CONCLUSION: These results indicate a correlation of the ERPF calculated using the Schlegel's method with EF obtained from a 99mTc MAG3 renal scintigraphy. The EF may be the good alternative parameter for calculation of renal function, potentially more practical in pediatric patient and the ERPF for 99mTc MAG3 using the established software program based on Schlegel's formula.

A Bayesian 3-compartment model for 99mTc-MAG3 clearance.

UNLABELLED: Because recent reports have questioned the traditional 2-compartment model for calculating tracer clearance after a single intravenous injection, a 3-compartment model was evaluated in this study. METHODS: Bayesian statistics were used, which facilitated curve fitting by treating all subjects simultaneously. (99m)Tc-Mercaptoacetyltriglycine clearance data from 154 adults and 109 children were measured at several centers, typically 6-9 plasma samples spanning 5-90 min, and fitted by 2- and 3-compartment Bayesian models. RESULTS: Clearance estimates were found to be systematically lower for the 3-compartment model than for the 2-compartment model. A single-sample procedure based on the 3-compartment model was found to eliminate most of the known discrepancy between formulas based on single-injection and continuous-infusion reference methods. CONCLUSION: A 3-compartment model led to lower and probably more accurate clearance estimates than the conventional 2-compartment model. A new single-sample method is presented, based on the 3-compartment model as reference standard.

Effect of arteriovenous difference in measuring renal function by single-injection plasma clearance: role of bolus.

Error estimates for arteriovenous difference were calculated by two models, a lag time model and a compartmental model, using Tc99m-diethylenetriaminepentaacetic acid (DTPA) plasma clearance curves from 40 subjects and Tc99m-MAG3 (mercaptoacetyltriglycine) curves from 18 subjects. It was found that correcting for the effect of the initial bolus largely cancelled the conventional arteriovenous difference, so that the net error was negligible.

Radiopharmacokinetics, renal clearance and dosimetry of 99mTc-MAG3.

BACKGROUND: Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) is a radiopharmaceutical for tubular function and can be prepared with 99m-technetium and the ligand Bz-MAG3 (Instituto Nacional de Investigaciones Nucleares, Mexico City). No radiopharmacokinetic parameters have been found for the healthy adult Mexican population with 99mTc-MAG3, prepared with the nationally produced or imported Bz-MAG3 kit. METHODS: The radiopharmacokinetic parameters and the clearance of 99mTc-MAG3 in seven healthy Mexican volunteers were determined by the single- and multi-sample methods. Computer programs were used for the calculations. RESULTS: Using several plasma samples from 0-43 min and the BIEXP program, it was shown that 99mTc-MAG3 follows a two-compartment model of distribution, with an apparent volume in the central compartment Vdcc = 3.8 + 0.7 l, a volume of distribution at steady state Vdss = 6.7 + 1.0 l, T1/2 alpha = 0.07 + 0.02 h-1, T1/2 beta = 0.49 + 0.15 h-1, mean residence time MRT = 0.60 + 0.17 h and clearance = 208 + 57 (ml/min)/1.73 m2. In comparison, the clearance value with a single sample drawn 43 min post-injection and calculated with Tauxe's formula was 193 +/- 59 (ml/min)/m2. CONCLUSIONS: The 15 ml difference between the two methods is neither statistically different (p = 0.11) nor important for routine clinical studies. The single-sample method is recommended because it is reliable and can be done at the same time that the dynamic renal scan is acquired. Estimated absorbed radiation dose was calculated for several organs.

Improving the accuracy of 99Tcm-mercaptoacetyltriglycine clearance by using two blood samples instead of one? Paediatric Task Group of the EANM.

From a database of 133 patients (98 children and 35 adults) who underwent multiple blood sampling for 99Tcm-mercaptoacetyltriglycine (MAG3) clearance, we determined simplified algorithms allowing the estimation of clearance. A one-compartment model with two blood samples was applied. The best choices for the adult population were the 12 and 90 min blood samples, giving a standard error of the estimate (S.E.E.) of less than 10 ml min-1 1.73 m-2; for the children, the 10 and 80 min blood samples gave a S.E.E. of 20 ml min-1 1.73 m-2; for both the adults and the children, the 10 and 70 min blood samples gave the best results with, however, a S.E.E. of 19 ml min-1 1.73 m-2. The use of such a combined algorithm will therefore result in a degradation of the results in adults, suggesting that a separate algorithm for each group is preferable. We compared the accuracy of the two blood sample method to the one blood sample method based on previously published algorithms for children and adults, respectively. The S.E.E. was significantly lower, in adults as well as in children, using the empirical two blood sample method. This two blood sample method seems potentially useful for routine practice in adult patients. The advantages of using such a method in children is balanced by the practical problems inherent in the need to take a second blood sample during the first 10 min, at a time when the plasma activity is rapidly decreasing.

Plasma clearance of 99Tcm-MAG3: accuracy of five single-sample methods.

The aim of this study was to compare the accuracy of five single-injection, single-sample methods for the assessment of plasma clearance of 99Tcm-MAG3 in adults. In 51 patients, a reference plasma clearance was determined on the basis of 16 blood samples. It ranged from 13 to 313 ml.min-1. In patients with a plasma clearance less than 75 ml.min-1, there was a large difference between the clearance obtained by a single-sample method and the reference method. Thus single-sample methods should not be used with these patients. In patients with a plasma clearance higher than 75 ml.min-1, the relative difference was (mean +/- s): 6.07 +/- 9.96% (Russell et al., 1989), 14.22 +/- 8.08% (Müller-Suur et al., 1991), 7.29 +/- 6.21% (Bubeck et al., 1992), 6.64 +/- 7.71% (Russell et al., 1996) and 17.39 +/- 7.39% (Piera et al., 1997). Reference clearance was overestimated by all five single-sample methods, especially by the methods of Müller-Suur et al. and Piera et al. The smallest standard deviation was obtained using the method of Bubeck et al. This method is recommended for use in patients with a plasma clearance greater than 75 ml.min-1.

Estimation of 99Tcm-MAG3 clearance using a single blood sample obtained over a continuous time interval.

Simplified methods based on a single blood sample have been proposed to estimate the clearance of 131I-hippuran (HIP) and 99Tcm-mercaptoacetyltriglycine (MAG). The blood sample is usually drawn at that time which yields a minimum error between the estimated clearance and that obtained by the standard nine-sample method. In this paper, we establish the regression equations to obtain the HIP and MAG clearances using one sample withdrawn during a fixed time interval. As HIP has long been the agent of choice, we have also established regression equations to estimate the clearance of HIP using one sample after MAG administration. Our results suggest that it is possible to obtain plasma samples 30-50 min post-injection which result in an error of the estimate only slightly higher than the minimum.

Reproducibility of a single-sample method for 99Tcm-MAG3 clearance under clinical conditions.

The aim of this study was to assess the intra-individual reproducibility of 99Tcm-mercaptoacetyltriglycine (99Tcm-MAG3) clearance in routine clinical practice in various circumstances using a single-sample method. Three groups of 30 patients each were enrolled in the study. Investigations were repeated on the same day with two different levels of activity (group A), within 1 week (group B), or after 1 year (group C). Blood samples were taken after 20 and 25 min and clearance values were averaged to minimize incidental errors after calculation according to the formula proposed by Bubeck et al. For clearance estimation on the same day, time-dependent background correction for residual activity was carried out. The mean difference was -2.0%, +6.0% and -1.5% (S.D. = 6.3%, 15.7% and 11.7%) for groups A, B and C respectively, taking into account values > 100 ml min-1 only. We demonstrated that 99Tcm-MAG3 clearance is highly reproducible under the same conditions. However, a repeat clearance measurement on a separate day revealed large differences. Therefore, in follow-up studies for evaluation of changing kidney function (e.g. surgery or chemotherapy), differences should exceed 30% (i.e. 2 S.D. of group B) to be statistically significant.

Calculation of renal retention function without deconvolution.

The aim of this study was to evaluate Rutland's method for the recovery of renal retention function without deconvolution. Renograms (n=5800) were generated by convolving 10 real input functions with 580 artificially created retention functions. Their ratios of minimal to mean transit time ranged from 0.1 to 1.0, and for mean transit time ranged from 3 to 60 min. The retention function was recovered from each renogram and its associated input function by calculating the first derivative of the residence time of the tracer in the kidney. Minimal, mean, and maximal transit time of the recovered retention function were calculated and compared with the original values. Qualitatively, the recovered retention function differed little from the original one. Quantitatively, values for recovered minimal transit time equalled original minimal transit time in all cases, whilst recovered mean transit time and maximal transit time equalled, respectively, the original mean transit time and maximal transit time if the original minimal to mean transit time ratio equalled 1. If this ratio was less than 1, recovered mean transit time was higher than original mean transit time and recovered maximal transit time was lower than original maximal transit time. For values of mean and maximal transit time, the differences from the original value increased with increasing original mean and maximal transit time, respectively, and with increasing renal clearance and decreasing minimal to mean transit time ratio. It is confirmed that Rutland's method is a particularly interesting alternative to deconvolution analysis. The errors that occur when recovering the retention function are relatively small.

Estimation of 99mTc-MAG3 clearance by single-sample methods and camera-based methods.

We compared single-sample methods, proposed by Russell et al. and Bubeck et al., and camera-based methods in calculating 99mTc-MAG3 clearance, and determined camera-based methods that provide estimates comparable to those measured by the Russell method. Twenty-one patients underwent 99mTc-MAG3 renal scintigraphy, and clearance was measured by the Russell method and Bubeck method. Various renogram parameters were determined based on the slope of the renogram and area under the renogram, and correlated with the clearance measured by the Russell method. Camera-based clearance was calculated with the obtained regression equations and with equations determined previously using the Bubeck method as a standard. The Bubeck method provided lower measures than the Russell method in high renal function. Clearance measured by the Russell method was well correlated with renogram parameters, and clearance calculated with the obtained regression equation was comparable to that measured by the Russell method. When camera-based clearance was predicted with the previous equation, it was lower than the result obtained by the Russell method in high function. In conclusion, there are systematic differences in 99mTc-MAG3 clearance calculated by different methods. The camera-based methods obtained in this study appear to facilitate comparison of results obtained by the Russell method and camera-based method.

Evaluation of the single-injection plasma disappearance of technetium-99m mercaptoacetyltriglycine method for determination of effective renal plasma flow in dogs with normal or abnormal renal function.

Effective renal plasma flow (ERPF) was evaluated, using continuous-infusion p-aminohippurate clearance (CLPAH) and single-injection plasma clearance of technetium-99m mercaptoacetyltriglycine (99mTc-MAG3; CLMAG3) methods. Simultaneous clearance determinations were made in 6 dogs: 2 determinations for each dog before, and 1 determination after renal failure was induced by administration of amphotericin B. Linear regression analysis was used to derive an equation to estimate ERPF from CLMAG3 after the single IV injection. A Student's t-test was used to compare pharmacokinetics between the dogs when they were healthy and when they were in renal failure. An F-test was used to determine the appropriate Student's t-test. Results indicated that CLMAG3 correlated reasonably well (r = 0.83, P < 0.0001) with ERPF obtained from the CLPAH value. The volume of distribution and elimination of 99mTc-MAG3 decreased during renal failure. Although there was minimal binding of 99mTc-MAG3 to erythrocytes, it was significantly (P = 0.0008) lower during renal failure. Protein binding was not significantly different during renal failure. All dogs had signs of nausea and emesis at variable times after injection of 99mTc-MAG3. Determination of CLMAG3 after a single injection provides an adequate means to rapidly assess ERPF in dogs. The technique could easily be performed in dogs with renal disease, thus providing valuable information regarding progression of naturally acquired renal failure.

Off-site determinations of effective renal plasma flow using technetium-99m-MAG3 and single blood sampling.

UNLABELLED: This study evaluated the feasibility of determining effective renal plasma flow (ERPF) at an off-site central laboratory by transferring blood samples from the on-site laboratory. METHODS: Blood samples were obtained from 66 patients referred for renal imaging with 99mTc-MAG3. ERPF values were determined using the single blood sample method (BSM) at both on- and off-site laboratories. The ERPF values were classified clinically as normal or abnormal. Both the ERPF values and clinical classification were compared between on- and off-site laboratories. RESULTS: The off-site ERPF overestimated those on-site by 2.8% (paired Student's t-test p < 10(-5)). However, off-site ERPF values highly correlated with the values obtained on-site (r = 0.99; p < 10(-5)). In addition, the clinical classification for each patient determined at each site was identical. CONCLUSION: ERPF can be determined accurately off-site. This method should allow many nuclear medicine departments access to the ERPF determination by the BSM at a central off-site laboratory.

[Application of measuring 99mTc-MAG3 plasma clearance based on one-compartment model (MPC method) to pediatric patients].

Measurement of 99mTc-MAG3 plasma clearance based on 1-compartment model (MPC method) were applied to 12 pediatric patients and evaluated for the factors which might affect the calculated results. Depth correction is a critical factor for the measurement of renal uptake. Three different equations for estimating renal depth were compared with the real depth measured by ultrasonography. The equation proposed by K. Itoh was suitable though the equations by T. Ito and Raynaud were insufficient. Estimation of distribution volume, which is regarded as circulating plasma volume (CPV), is also critical for the calculation of MAG3 clearance by MPC method. Precisely, hematocrit measured by venous sampling and circulating blood volume (CBV) calculated as 7.5% of body weight are used for estimation of CPV. However, assumed CPV as 5% of body weight was acceptable if the hematocrit was not severely deviated from the normal value. Simplified MPC method utilizing two factors mentioned above gave a positive correlation with Russell's one point sampling method. In conclusion, MPC method is applicable for pediatric patients.

[Comparison of single sample methods for determination of plasma clearance using 99mTc-MAG3].

We compared relationship among three single blood sampling methods which have been proposed for determination of plasma clearance with 99mTc-MAG3. Russell's and Bubeck's algorithms were employed for 48 adults (average age: 53 years) and Bubeck's and Piepsz's algorithms were used in 9 children (average age: 5.8 years). Three methods showed very high correlation among them. However, Russell's and Piepsz's methods were about 1.4 times higher than Bubeck's method in calculating plasma clearance of 99mTc-MAG3. The present study indicates that three methods discussed here are useful for the determination of plasma clearance with 99mTc-MAG3. In addition, Bubeck's method may be preferable as a reference for single plasma sampling method because of common application to adults and children.

[Improved the accuracy of 99mTc-MAG3 plasma clearance method: the problem of the calculated plasma volume and its modification].

The 99mTc-MAG3 plasma clearance method (MPC method), reported by Oriuchi et al., is a simple and useful count-based gamma camera method for calculating the 99mTc-MAG3 plasma clearance (CLMAG). However, a discrepancy of CLMAG calculated by MPC method (MPC-CLMAG) from the tubular extraction rate (TER) calculated by Russell's single-sample clearance determination (Russell-TER) was noted. The calculated plasma volume is assumed to be the cause. Since the plasma volume is reported to have a linear correlation with body surface area, Dissmann's formula was applied to calculate the plasma volume. Then Dissmann's formula was replaced by Ogawa's formula in the MPC method, and the procedure was then called the modified MPC method. The CLMAG were obtained using MPC method, modified MPC method and the TER was obtained Russell's method in 95 patients with urological disorders. Then the MPC-CLMAG and modified MPC-CLMAG were compared with Russell-TER. Comparison of the MPC-CLMAG with the Russell-TER demonstrated a coefficient of correlation of 0.82, but dissociation of the slope of regression lines was found between males and females. The modified MPC-CLMAG improved the coefficient of correlation to 0.92, and diminished the dissociation of the slope of regression lines between males and females. We verified that the dissociation was due to the plasma volume calculated by Ogawa's formula. Ogawa's formula included hematocrit, body weight, body height and different coefficients for gender. The plasma volume calculated by Ogawa's formula were lower in males and higher in females than that calculated by Dissmann's formula. And marked discrepancy in the plasma volume in patients with a body surface area below 0.5 m2 was observed. So the MPC method might become more accurate by substituting Dissmann's formula for Ogawa's formula resolting in a method that is applicable to both males and females, children and adults in clinical use.

A comparison of single plasma sample methods to estimate renal clearance using 99mTc-ethylenedicysteine and 99mTc-mercaptoacetyltriglycine.

Several single sample methods for determination of (99m)Tc-mercaptoacetyltriglycine (MAG3) clearance are being used clinically. Kabasakal et al. proposed a similar formula for (99m)Tc-ethylenedicysteine (EC). This study was performed to compare his method with Bubeck et al. formula for (99m)Tc-MAG3 already in use. Twenty-eight subjects divided in two groups were registered which included 22 patients with various renal diseases (group-I) and six normal volunteers (group II). All subjects were studied twice using both the radiopharmaceuticals. The images and renogram parameters, that is TMAX and T1/2 of both the agents, were similar in all the subjects. The clearance of the (99m)Tc-EC was however considerably higher than (99m)Tc-MAG3 in both the groups (mean ± SEM =279 ± 14 ml min(-1)/1.73 m(2) versus 177 ± 15 ml min(-1)/1.73 m(2) in group-I and 377 ± 11.90 ml min(-1)/1.73 m(2) versus 238 ± 8.23 ml min(-1)/1.73 m(2) in group II). This difference was more pronounced in cases with reduced renal functions. Among the Effective Renal Plasma Flow (ERPF) values determined from EC and MAG3 clearances in six normal volunteers, four cases only in MAG3 had ERPF below the lower limit. This study has demonstrated superiority of single sample method for (99 m)Tc-EC clearance over its analogous method for (99m)Tc-MAG3.

Quantitative analysis of the effect of probenecid on pharmacokinetics of 99mTc-mercaptoacetyltriglycine in dogs.

Effect of probenecid on pharmacokinetics of 99mTc-mercaptoacetylytriglycine (99mTc-MAG3) in dogs was investigated before (control), and after 15 min and 24 h of i.v. injection of probenecid (20 mg/kg). Plasma concentration-time profiles of 99mTc-MAG3 were described with a two-compartment open model. Plasma 99mTc-MAG3 clearances (Clp, ml/min/kg) were 7.9 +/- 0.5, 3.3 +/- 0.5 and 4.8 +/- 1.3 in control, 15 min and 24 h after probenecid administration respectively. Similarly, the biological half-lives at elimination phase (t(1/2), h) were 0.61 +/- 0.09, 0.79 +/- 0.11 and 0.74 +/- 0.12, and volumes of distribution at steady state (Vdss, L/kg) were 0.29 +/- 0.04, 0.20 +/- 0.05 and 0.25 +/- 0.06 respectively. The prolonged biological half-life and decreased Vdss decreased Clp significantly. Clp was a function of plasma probenecid concentration based on Michaelis-Menten kinetics. The maximum Clp inhibition (Imax) by probenecid and the plasma probenecid concentration that induced 50% of Imax (I50) were estimated to be 72 +/- 12% and 13 +/- 8 microg/ml respectively. This means that the rest (about 28%) of the Clp is not blocked by probenecid alone, suggesting the possibility of another route(s) of elimination or renal transporters which are independent from probenecid. Moreover, inter-species correlation between Clp of 99mTc-MAG3 and body weight are discussed.

99mTc-MAG3 kinetics in the normal pig. A comparison to 131I-OIH and 125I-iothalamate after single injection and during continuous infusion.

An invasive comparative study of some pharmacokinetic aspects of 99mTc-mercaptoacetyltriglycine (MAG3), 131I-orthoiodohippurate (OIH), and 125I-iothalamate (iothalamate) was performed in six pigs 0-150 min after a simultaneous single injection (SI) and during a subsequent 90 min of continuous infusion (CI). The total plasma clearance and the renal clearance of MAG3 were about 75% that of OIH. The renal clearance of MAG3 was about 2 1/2 times the glomerular filtration rate. The distribution volume of MAG3 was 71% that of iothalamate and only 47% that of OIH. There was a significant hepatic plasma clearance of MAG3 of 5.9 ml min-1 and 3.9% of the injected dose was excreted in the bile. HPLC analysis revealed that technetium was excreted in urine and bile mainly labelled to MAG3. The average red blood cell (RBC) binding after single injection/during continuous infusion was 1.0%/2.3% for MAG3, 13.5%/9.0% for OIH, and 3.1%/5.3% for iothalamate. The binding of OIH to RBC in arterial blood increased from 8% at 1 min post-injection to 21% at 150 min post-injection. The RBC binding was higher in the renal vein, indicating incomplete back diffusion from RBC to plasma. The protein binding was 90% for MAG3, 49% for OIH and 16% for iothalamate. The renal plasma extraction of MAG3 was constant but significantly smaller after SI (0.54) than during CI (0.62). Following SI, the renal plasma extraction of OIH decreased continuously from 0.85 to 0.52, 3-150 min post-injection. On the average there was no significant difference in renal plasma extraction after SI and during CI of either OIH (0.72 versus 0.77) or iothalamate (0.26 versus 0.27). It is concluded that MAG3 is preferential to OIH as a tracer for renal function studies using a single injection technique mainly due to the constant renal extraction of MAG3.

Tissular distributions and kinetics of two renal 99mTc-radiopharmaceuticals in rat.

A digital radioimager (RI), conventional radioautography (RA), and tracks microradioautography (MRA) were used to assess the biodistributions and kinetics of 99mTc-dimercaptosuccinic (99mTc-DMSA) and 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) in rat at both macroscopic and microscopic levels. Three groups of male Wistar rats were studied. Using gamma-counting, kidney, liver, spleen and blood kinetics of both tracers were assessed in the three groups. Using RA and RI, renal slices were analyzed in group 1 the animals being sacrified from 2 to 60 min after injection of 99mTc-MAG3, and in group 2 the animals being sacrificed from 0.5 to 24 hr after injection of 99mTc-DMSA. Using MRA, renal slices were analyzed for 99mTc-DMSA (group 3). RA films and RI images displayed the variation with time of the cortical and medullary uptakes of the tracers. No regional heterogeneity within the different structures could be seen neither with RA films nor with MRA. The remaining activity in the blood 24 hr after injection of 99mTc-DMSA was evaluated. The tissular distributions of both tracer being homogenous, mean values of cortical uptake seems to be acceptable for dosimetric studies. Our results incite to use of 99mTc-MAG3 instead of 99mTc-DMSA when both tracers may be indicated.