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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.

Mono-compartmental analysis based on 2- and 4-h blood samples (BS) of 51Cr-EDTA (EDTA, ethylenediaminetetraacetic acid) is commonly used for the calculation of the glomerular filtration rate (GFR). The purposes of this study were to estimate the magnitude of error in clearance induced by errors in the time of sampling and activity measurement; to estimate the impact of changing the interval between the BS; and to assess the influence of a higher number of BS in reducing the error. A model of mono-exponential curves based on a finite number of BS was created. Normally distributed random errors were introduced in the time of sampling and activity measurement. In a first step, three different time intervals were used; in a second step, seven different numbers of BS were used, all taken between 120 and 240 min. For each setting, the random errors were successively introduced 200 times and the coefficients of variation (CV) of the calculated clearances were determined. Variable errors in clearance were induced by errors in the time of sampling and activity measurement. In general, the observed errors were higher for high and low clearance, with lower errors for moderately reduced clearances. The errors in indicating the time of sampling played an important role for high clearance, whereas the errors in activity measurements led to important errors for low clearance. Prolonging the interval from 1 to 2 h resulted generally in an important decrease in error, except in the range 60-100 ml x min(-1). Prolonging the interval from 2 to 3 h resulted in only a small additional decrease in error, except for very low clearance. Errors in indicating the time of sampling and in activity measurements induce errors in clearance determination. These errors cannot be significantly reduced by simply increasing the number of BS or by prolonging the interval between the samples. It is probably better, in most cases, to keep using the 2-4-h method and to take extreme care when indicating the time of sampling and when measuring the activity, instead of increasing the number of samples or lengthening the procedure.

It has been suggested that the slope of the second exponential of the plasma disappearance curve may be used to monitor changes in renal function instead of plasma clearance calculated using the slope-intercept method. The purpose of this study was to evaluate the magnitude of error in the slope induced by errors in sampling time and in activity measurement, and to compare it with the error observed in clearance. A model of mono-exponential curves based on two blood samples, taken at 120 and 240 min, was created. Normally distributed random errors were introduced into the sampling times and activity measurements. For each setting, the random errors were successively introduced 200 times and the coefficients of variation of the calculated slopes and clearances were determined. Variable errors in slope and clearance were induced by errors in sampling time and activity measurement. In general, the observed errors in the slope were high in the case of low slope values, decreasing progressively for increasing slope values. The errors in clearance followed a different pattern: highest errors were observed in the case of very low clearance, decreasing progressively for higher clearance values and attaining the minimal value at a lambda around 0.006 min-1, which corresponds to clearance of about 90 ml.min-1. The magnitude of the errors then started to increase again for higher clearance. For a large range of clearance values, the errors in the slope were higher than the errors in clearance. The only exceptions were cases with very high clearance rates. In conclusion, clearance calculation using the slope-intercept method should be preferred to that using the slope alone for monitoring changes in renal function.

Unlabelled: The overall and single-kidney clearance in children with acute urinary tract infection was investigated retrospectively using the combination of the relative 99mTc-dimercaptosuccinic acid (DMSA) uptake and the 51Cr-ethylenediaminetetraacetic acid clearance., Methods: There were 180 patients with both normal kidneys, 56 with clear unilateral abnormalities on DMSA scintigraphy and 11 with two abnormal kidneys. Half of the patients were younger than 2 y, and because of the progressive maturation of the renal function, they were not considered in the analysis of the absolute overall and single-kidney clearance; nevertheless, they were included in the analysis of the relative DMSA percentage uptake., Results: When only one kidney was affected on DMSA scintigraphy, the clearance of the affected kidney was lower than on the normal side and often abnormally low. In these unilaterally affected kidneys, contralateral compensation mechanisms tended to occur, resulting in preservation of overall clearance. This compensation was probably not present only on the contralateral side. On the abnormal side, the clearance was normal in about half of the cases, probably because of intrarenal compensation occurring in regions not damaged by the infection. In addition to these compensation mechanisms, hyperfiltration was probably present in many cases of acute urinary tract infection with intact or unilaterally damaged kidneys.

The aim of this study was to test the reproducibility of the second exponential of the plasma disappearance curve of 51Cr-EDTA and to compare it with the single slope-intercept method. The test was performed twice among 24 young healthy volunteers at an interval of 8 days and under similar physiological conditions. After the intravenous injection of 3.7 MBq of 51Cr-EDTA, four blood samples were taken between 1.5 and 4 h and combinations of two, three or all four of these were used to calculate the slope of the plasma clearance curve. The clearances rates were calculated using these slopes and the corresponding intercepts of the slopes with the y-axis. The standard deviation of the differences between the first and the second measurements was between 8 and 10% for the different clearance estimates, and between 11 and 17% for the different slope estimates, reflecting the wider variability of the slope estimate. Using the first series of measurements, the change of timing for blood sampling introduced a wider variability for the slope estimate than for the clearance estimate.

The aim of this study was to evaluate the variability of the Patlak-Rutland slope as applied to the renal clearance method. We analysed the 99Tcm-mercaptoacetyltriglycine renograms of 17 non-selected patients (both children and adults, number of kidneys = 34) with a single kidney glomerular filtration rate of 6-73 ml min-1 1.73 m-2. the acquisition time for the renograms was 20 min with a frame duration of 20 s. First, correction for background activity was introduced using the perirenal area and the size ratio between the kidney and the perirenal area. The Patlak plot was then applied. The first two points were systematically rejected and a series of linear fits calculated from the experimental points, starting from the third point (i.e. 1 min). The final point of the fit never exceeded the time of the peak of the renogram minus one minute (Tmax - 1) and was always less than 5 min. Although simple visual inspection of the slopes would suggest that the experimental points were distributed accurately along a straight line, it appeared that the slope was strongly dependent on the number of points used for the determination of the fit. As a second step, we restricted the number of points for fitting to the time interval between 1 min and 2 min 40 s. This procedure appeared to show that the Patlak methodology is reliable, giving rise to only small variations in slope, depending on the number of points chosen. However, even in this narrow time interval, significant errors can be made, either because of the very early escape of the radionuclide or because of statistical noise (e.g. in renal failure the signal-to-noise ratio is unfavourable). Therefore, it is advisable, when using this methodology, to restrict the fitting procedure to the second minute of the study and to check visually that this fixed time interval gives rise to a slope that is well adapted to the Patlak plot.

It has been suggested that a prolonged course of hyperfiltration could lead to progressive deterioration of renal function. In order to test this hypothesis, the following protocol was applied to 60 male Wistar rats. At 12 weeks of life, the rats were submitted to a surgical procedure: sham operation (25 rats), unilateral nephrectomy (25 rats) or 3/4 nephrectomy (10 rats). The three groups were again divided into two subgroups: one with high-protein intake (36%) and one with a low-protein intake (12%). In order to avoid any additional traumatic procedure which could shorten the animal's life, the glomerular filtration rate (GFR) was measured without blood sampling, using a previously validated technique based on an image recorded by a gamma camera between the 9th and the 10th min after intravenous injection of 99m technetium diethylenetriaminepentaacetate (DPTA). The sum of both kidneys and bladder activity was expressed as a percentage of the injected dose. The test was performed before surgery and every month thereafter. Six weeks after surgery, the highest filtration rate was found in the rats with "two kidneys/high-protein diet", followed by the "two kidneys/low-protein diet", the "one kidney/high-protein diet", the "one kidney/low-protein diet" and the "1/2 kidney". The overall GFR in the one kidney/high-protein diet rat and in the 1/2 kidney rat was respectively 80% and 55% of the pre-operative values. Until 109 weeks of age, the survival rate was comparable in the five groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The importance of renal clearance in uronephrology has motivated the continuous reassessment of well-established methods and the relentless search for better techniques. Concerning radionuclide methods, data in the current literature confirm the validity of the simplified one-compartment model or the empirical single-sample method for renal clearance measurement, and new algorithms have been described to broaden the application of the techniques to the pediatric population. Based on the same principles, accurate measurement of renal clearance can also be obtained using contrast agents. Using the technique for determination of the glomerular filtration rate during radiographic contrast examination is recommendable. However, potential adverse effects of the contrast substances should be compared with those of other methods before using this technique for measuring renal clearance without scheduled contrast roentgenographic examination. Controversy remains concerning the validity of predicting glomerular filtration rate from plasma creatinine. Although the predicted clearance is correlated with reference clearance, analysis of individual results reveals that important differences of up to 50 mL/min frequently occur.

A prospective therapeutic strategy based on separate glomerular filtration rate (SGFR) was evaluated in 14 prenatally detected asymptomatic neonates, suspected of having pelviureteric junction obstruction. The patients with low SGFR were referred for pyeloplasty with the hope to improve the renal function. A marked improvement occurred in only one patient, although the drainage function (furosemide test) did improve in all cases. A conservative attitude was adopted for those children with normal SGFR. In 6 of them, a progressive increase of SGFR was noted, related to the normal maturation of the function, followed by a stabilization in the normal range. In 1 patient, a sudden decrease of SGFR was observed around 1 year and the patient was shifted into the surgical group. In this patient, an initial partial response of the kidney to a furosemide injection changed into a persistent non-response, whereas in the other non-operated patients, partial or good response was always recorded, although the responses were essentially variable on successive tests. On the basis of these data, the protocol was slightly modified, the patients with persistent non-response to furosemide after 6 months of life being shifted to the surgical group.

Partial obstruction of the left ureter was created in 19 rats and a relative 99Tcm-DMSA uptake was obtained 5 and 24 h after intravenous injection of the tracer. A systematic and variable overestimation of the left to right uptake ratio was found at 5 h, with a mean error of 15.8% (S.D. = 12.2).

Repetitive quantitative renal extraction studies of 99Tcm-MAG 3, performed in nine rats, demonstrated excellent reproducibility of successive measurements. These results are better than with 99Tcm-DTPA, due to the higher renal extraction of the 99Tcm-MAG 3. The % of renal uptake 10 min after the injection was not influenced by the elapsed time between the end of the 99Tcm-MAG 3 preparation and its i.v. administration.

Although several authors have claimed that the function of an obstructed kidney could be overestimated on Tc-99m DMSA imaging, the clinical importance of such an overestimation has not been well documented. Partial obstruction of one ureter was created in a rat, and a relative Tc-99m DMSA uptake was obtained 4 hours after intravenous injection. By puncture of the isolated obstructed kidney, it was shown that the function of that kidney was overestimated by at least 17%.