99mTc-DTPA gamma-camera renography: normal values and rapid determination of single-kidney glomerular filtration rate

A method for 99mTc-diethylenetriaminepentaacetate (DTPA) gamma-camera renography is presented. From each renogram, an uptake index (UI) proportional to the single-kidney glomerular filtration rate (SKGFR) is defined. If the proportionality factor between UI and SKGFR is the same in all patients, UI can be used as an accurate measure of SKGFR. In order to test this, 99mTc-DTPA renography was performed in 101 patients with glomerular filtration rates (GFR) varying between 4 and 172 ml/min. The sum of the right- and left-kidney UIs correlated well with the total GFR calculated from the simultaneously measured plasma clearance of 99mTc-DTPA after a single injection. The correlation coefficient was 0.97. The method was tested in a prospective study of 57 patients. The total GFR estimated from the renograms was not significantly different from the GFR calculated from the plasma clearance of 99mTc-DTPA. The coefficient of variation--a combination of inaccuracy and imprecision in the estimates as well as in the reference values-was 11.8% at a GFR of 100 ml/min. It is concluded that, in adults, the SKGFR can be calculated as part of the clinical routine from 99mTc-DTPA gamma-camera renography without determining the injected dose or collecting urine or blood samples. Normal values for some parameters of the renogram obtained in 25 normal subjects are given.     

Glomerular filtration rate in relation to extracellular fluid volume: Similarity between99mTc-DTPA and inulin

The rate constant ( ₂) of the terminal exponential of the technetium-99m diethylene triamine pentaacetic acid (DTPA) plasma clearance curve is close to the ratio of glomerular filtration rate (GFR) to extracellular fluid volume (ECV) and is therefore a convenient, already normalised, measure of filtration function. Since ₂ depends on the distribution volume of the tracer, our aim was to compare ₂ from inulin and^99mTc-DTPA and also to compare the equilibration kinetics of the two filtration markers. Fifty millititres of^99mTc-DTPA (250 MBq) and inulin (10%), mixed in the same syringe, were given by intravenous injection in 15 patients undergoing routine^99mTc-DTPA renography for a variety of clinical indications. Frequent antecubital venous blood samples were taken up to about 4 h after injection to construct plasma clearance curves from which GFR, ECV and GFR/ECV (i.e. the reciprocal of mean transit time through the distribution volume) were calculated.^99mTc-DTPA/inulin concentration ratio curves were also constructed after normalisation to the ratio in the syringe. GFR given by the two markers correlated closely (DTPA=0.98·inulin—0.4ml/min;r=0.98).^99mTc-DTPA had the same distribution volume as inulin, had a similar transit time through it and gave the same value of ₂ (r=0.98). GFR/ECV from^99mTc-DTPA accordingly correlated closely with GFR/ECV from inulin (DTPA=0.75·inulin+0.99 ml/min;r=0.95). Even though the distribution volumes and the times to equilibration (i.e. to reach the terminal exponential) were similar, the distribution volume of^99mTc-DTPA at about 10 min after injection was, after subtraction of the plasma volume, about twice that of inulin.We confirm the validity of^99mTc-DTPA for measuring GFR. ₂ is a convenient measure of GFR, can be based on the terminal exponential of inulin of^99mTc-DTPA curves and can be converted to GFR/ECV with an appropriate scaling factor. The kinetics or the two clearance curves with respect to anatomical correlates of the exponentials and the rates of diffusion throughout the respective distribution volumes requires further study.     

Determination of glomerular filtration rate (GFR) by analysis of capillary blood after single shot injection of 99mTc-DTPA

^99mTc-DTPA was prepared from a kit produced by the Institute of Atomic Energy, Oslo, Norway. Radiochemical purity as determined with gel chromatography ranged from 98.5–99.7% (n=7). The radiopharmaceutical showed no red cell uptake and not more than 0.2% protein binding in in vitro biokinetic studies.The clearance of ^99mTc-DTPA was compared to the clearance of ¹²⁵I-Iothalamate simultaneously using single shot intravenous injection and biexponential analysis of plasma activity disappearance rate according to Sapirstein et al. (1955). ¹²⁵I-Iothalamate was found to have a higher second volume of distribution than ^99mTc-DTPA, but there was no statistically significant difference in clearance.GFR calculated from capillary serum ^99mTc-DTPA count rates was in all subjects investigated virtually identical with GFR calculated from simultaneously collected venous plasma samples.Estimation of GFR on the basis of plasma activity curves obtained from sampling in two hours gave higher values than estimation from four hours sampling irrespective of kidney function and whether ^99mTc-DTPA or ¹²⁵I-Iothalamate was used.It is concluded that ^99mTc is almost entirely bound to DTPA after intravenous injection of the ^99mTc-DTPA complex, and that the complex is a suitable agent for determination of glomerular filtration rate, using both venous and capillary blood sampling.     

Extravascular chest wall technetium 99m diethylene triamine penta-acetic acid: implications for the measurement of renal function during renography

Measurement of individual kidney glomerular filtration rate (IKGFR) from the gamma-camera technetium 99m diethylene triamine penta-acetic acid (^99mTc-DTPA) renogram requires a continuous measurement of arterial activity. This is usually based on a region of interest (ROI) placed over the cardiac blood pool on the posterior view, with the assumption of negligible contamination from activity in the extravascular space of the chest wall. By injecting a small dose of technetium 99m human serum albumin (HSA) before the^99mTc-DTPA in 12 patients undergoing routine renography, the contribution of extravascular activity to the total signal recorded over the cardiac blood pool was calculated to be 11.0% (SE 2.1%) 1.5 min after DTPA injection, rising to 35.1% (SE 2.5%) at 15 min. Subtraction of the time-activity curve recorded from a ROI of the same size over the right lung generated a pure blood signal as shown by almost identical HSA/DTPA signal ratios recorded in blood samples taken 5 min after HSA and 15 min after DTPA and from the gamma-camera at the corresponding times. The effect of using a cardiac blood pool time-activity curve uncorrected for extravascular activity was to overestimate IKGFR by an average factor of 1.17 (SE 0.03). Offprint requests to: A.M. Peters     

Measurement of glomerular filtration rate with 99mTc-DTPA: A comparison of gamma camera methods

A comparison has been made between three gamma camera methods for estimation of glomerular filtration rate (GFR) using ^99mTc-DTPA in a group of 27 patients with widely different renal function. Plasma clearance of ^99mTc-DTPA by multiple blood sampling was used as the reference. Percentage uptake of chelate in the bladder and kidneys at 20 min after injection gave the lowest standard error of 8.0 ml/min. Techniques using early uptake of isotope in the kidneys at 2 min after injection gave less accurate estimates. Correction for the vascular activity in the renal region of interest improved the results for the 2 min uptake technique. Gamma camera techniques provide rapid estimates of GFR which are less accurate than those obtained by plasma clearance of labelled chelate.     

Differences between99mTc-DTPA and99mTc-MAG3 captopril renographies in renovascular hypertension

Captopril renography (CRS) with^99mTc-DTPA and^99mTc-MAG3 was performed on a 21-year-old woman with renovascular hypertension due to right renal artery stenosis caused by fibromuscular dysplasia. In the affected kidney, the renogram pattern was substantially changed with^99mTc-DTPA and^99mTc-MAG3 following the administration of captopril, and the quantitated renal uptake indicating individual renal function was significantly decreased in^99mTc-DTPA and slightly decreased in^99mTc-MAG3. In the contralateral normal kidney, the renogram showed some minor changes with both radioagents, while the quantitated renal uptake was significantly decreased with^99mTc-DTPA and substantially increased with^99mTc-MAG3. The combined use of physiologically different renal agents^99mTc-DTPA and^99mTc-MAG3 is helpful in investigating hemodynamic and functional changes in the stenosed kidney as well as the normal kidney in RVH.     

Comparison of methods for determination of glomerular filtration rate: Tc-99m-DTPA renography, predicted creatinine clearance method and plasma sample method

Background: The gamma camera uptake method with Tc-99m-DTPA is simple and less time consuming for the determination of the glomerular filtration rate (GFR). However, its diagnostic accuracy is debated. Gates’ method and predicted creatinine clearance method were compared with plasma clearance method with Tc-99m-DTPA for the measurement of GFR.Materials and Methods: Tc-99m-DTPA renography was performed on 133 patients (69 males and 64 females; age range being 24 to 84 years) with a wide range of renal function. The GFR was determined simultaneously by 3 methods; (1) gamma camera uptake method (modified Gates, Gates); (2) predicted creatinine clearance method (Cockcroft-Gault, CG); (3) single- or two-plasma clearance method (plasma sample clearance method, PSC). The PSC was chosen as a reference.Results: The regression equation of the Gates and the CG against the PSC wasY=11.89 + 1.041X (r=0.790, p<0.001, RMSE=23.55 ml/min/1.73 m²) andY=8.845+0.7899X (r=0.8270, p<0.001, RMSE =16.27 ml/min/1.73 m²), respectively. In comparison with the GFR by PSC, the Gates tended to everestimate the GFR, and contrarily the CG tended to underestimate the GFR.Conclusion: The Gates correlates well with the PSC. However, the Gates is even less precise than the CG. The Gates’ method in Tc-99m-DTPA renography is not suitable for the estimation of GFR in routine practice.     

The effect of radiopharmaceutical choice on the assessment of the relative renal function in upper urinary tract obstruction

The relative function of the obstructed kidney (RFOK) was assessed in 43 adult patients with upper urinary tract obstruction (UUTO) using ^99mTc-DTPA and ¹³¹I-ortho-iodohippurate (OIH) dynamic studies and ^99mTc-DMSA dynamic and static studies. The patients were divided into five groups according to the duration and degree of obstruction. Findings were as follows: a) in patients with the first occurrence of acute severe obstruction (group 1), the relative glomerular filtration rate (GFR) was significantly less than the relative effective renal plasma flow (ERPF); b) in patients with chronic severe obstruction and long term uroinfection, the relative ERPF decreased significantly compared with the relative GFR; c) the RFOK calculated from the DMSA dynamic study was the same as both the relative GFR or ERPF in any group; d) the RFOK calculated from the DMSA static study seemed to parallel the relative ERPF more closely than the relative GFR, but in group one it was significantly higher than any of three other estimates. It is concluded that ^99mTc-DTPA is the radiopharmaceutical of choice in obstructive uronephropathy, but when interpreting the RFOK, the time course and severity of obstruction, the presence or absence of uroinfection should also be considered.     

Accurate assessment of long-term nephrotoxicity after peptide receptor radionuclide therapy with 177Lu-octreotate

Purpose

Renal radiation during peptide receptor radionuclide therapy (PRRT) may result in glomerular damage, a potential reduction of glomerular filtration rate (GFR) and ultimately lead to renal failure. While reported PRRT nephrotoxicity is limited to data derived from serum creatinine—allowing only approximate estimates of GFR—the aim of this study is to accurately determine PRRT-induced long-term changes of renal function and associated risk factors according to state-of-the-art GFR measurement.

Methods

Nephrotoxicity was analysed using ^99mTc-diethylenetriaminepentaacetic acid (DTPA) clearance data of 74 consecutive patients with gastroenteropancreatic neuroendocrine tumours (GEP NET) undergoing PRRT with ¹⁷⁷Lu-octreotate. The mean follow-up period was 21 months (range 12–50) with a median of five GFR measurements per patient. The change of GFR was analysed by linear curve fit. Potential risk factors including diabetes mellitus, arterial hypertension, previous chemotherapy, renal impairment at baseline and cumulative administered activity were analysed regarding potential impact on renal function loss. In addition, Common Terminology Criteria for Adverse Events (CTCAE) v3.0 were used to compare nephrotoxicity determined by ^99mTc-DTPA clearance versus serum creatinine.

Results

The alteration in GFR differed widely among the patients (mean ?2.1?±?13.1 ml/min/m² per year, relative yearly reduction ?1.8?±?18.9 %). Fifteen patients (21 %) experienced a mild (2–10 ml/min/m² per year) and 16 patients (22 %) a significant (>10 ml/min/m² per year) decline of GFR following PRRT. However, 11 patients (15 %) showed an increase of >10 ml/min/m² per year. Relevant nephrotoxicity according to CTCAE (grade ≥3) was observed in one patient (1.3 %) with arterial hypertension and history of chemotherapy. Nephrotoxicity according to serum creatinine was discordant to that defined by GFR in 15 % of the assessments and led to underestimation in 12 % of patients. None of the investigated factors including cumulative administered activity contributed to the decline of renal function.

Conclusion

Serious nephrotoxicity after PRRT with ¹⁷⁷Lu-octreotate is rare (1.3 %). However, slight renal impairment (GFR loss >2 ml/min/m² per year) can frequently (43 %) be detected by ^99mTc-DTPA clearance assessments. Cumulative administered activity of ¹⁷⁷Lu-octreotate is not a major determinant of renal impairment in our study.     

Measurement of the ratio of glomerular filtration rate to plasma volume from the technetium-99m diethylene triamine pentaacetic acid renogram: comparison with glomerular filtration rate in relation to extracellular fluid volume

Individual kidney glomerular filtration rate (IKGFR) can be measured from the renogram from the rate of uptake of technetium-99m diethylene triamine penta-acetic acid (^99mTc-DTPA). A blood sample is required to derive IKGFR in millilitres per minute, which is then usually normalised to body surface area. We describe a technique which does not require a blood sample, is already normalised for plasma volume and uses the robust Patlak plot for measuring renal uptake. The rate of kidney uptake, dR(t)ldt, at time = 0, as a fraction of the injected dose, is equal to the fraction of the plasma volume (PV) filtered per minute, i.e. IKGFR/PV. The gradient dR(0)/dt cannot be accurately measured directly but is equal to [ · LV(0)], where is the renal uptake constant (proportional to IKGFR) and LV is the count rate over a left ventricular ROI. LV(0) was obtained by extrapolation of LV(t), while a is the slope of the Patlak plot up to 3 min. GFR/PV (i.e. right plus left kidneys) in patients with normal renal function was about 0.04 min^–1, as would be expected from normal values of GFR (120 ml/min) and plasma volume (3 l). GFR/PV correlated significantly with the ratio of GFR to extracellular fluid volume (ECV), measured from the terminal exponential of the plasma clearance curve (GFR/PV = 3.2.GFR/ECV + 5.3 ml/min/1 [r = 0.82,n = 82]). GFR/PV (r = 0.74) and GFR/ECV (r = 0.82) both correlated inversely and non-linearly with plasma creatinine in 43 studies where the measurement was made within 1 week of the^99mTcDTPA study. They also correlated significantly with the plasma cyclosporin trough level in 14 patients with dermatomyositis on the 30 occasions when this measurement was made within 1 week of the renogram (r = –0.38,P < 0.05 for GFR/PV andr = –0.77,P < 0.001 for GFR/ECV). The ratio of GFR/PV to GFR/ECV is the ratio of extracellular fluid volume to plasma volume, and this was 4.0 (SD 0.99). We conclude that both GFR/PV and GFR/ECV can be easily measured with^99mTc-DTPA and are physiologically valid expressions of GFR. Although GFR/PV and GFR/ECV correlate with each other, the question is raised as to which of the two fluid volumes is the most appropriate for normalising GFR. Correspondence to: A.M. Peters     

Comparative assessment of techniques for estimation of glomerular filtration rate with 99mTc-DTPA

The relative accuracy of five simplified methods of measuring glomerular filtration rate was prospectively assessed using ^99mTc-DTPA. The slope of the biological clearance curve, the 3-h volume of dilution and three renal tracer uptake methods (Piepsz, Gates and Nielsen) were concurrently compared with a multiple blood sampling reference method. The volume of dilution method from a single blood sample was markedly superior to the other four simplified methods which all had a similar degree of accuracy.     

Comparison of glomerular filtration rate by Gates method with Cockroft Gault equation in unilateral small kidney

Objective

To compare the glomerular filtration rate (GFR) by ^99mTc DTPA scan and the Cockroft Gault method in unilateral small kidney.

Materials and methods

The present study was conducted in the Department of Nuclear Medicine at the Sher-i-Kashmir Institute of Medical Sciences (SKIMS), India from July 2007 to April 2011. The present study included 47 patients with a diagnosis of unilateral small kidney on ultrasound. Out of 47 patients, 21 (44.7%) were males and 26 (55.3%) were females. Image processing was done using camera based methods. The GFR was automatically calculated by a software in a commercially available computer according to the Gates algorithm. The predicted creatinine clearance was calculated according to the Cockroft and Gault equation.

Results

Mean total GFR by DTPA Gates method was 73.6 ± 18.6 ml/min and by the Cockroft Gault (CG) method was 79.8 ± 32.2 ml/min. The difference was statistically insignificant indicating an agreement between both the methods in measuring GFR.

Conclusions

To discuss the advantages of isotopic renography, CG cannot give individual kidney GFR and so is not of much use in the unilateral small kidney wherein the main aim is to know the function of the individual kidneys. Furthermore because of low cost and less radiation burden, this test might be preferred for routine practice in nuclear medicine.     

Estimation of glomerular filtration rate and technetium-99m diethylene triamine penta-acetic acid using chromium-51 ethylene diamine tetra-acetic acid

Simultaneous measurements of the clearance rate of chromium-51 ethylene diamine tetra-acetic acid (⁵¹Cr-EDTA) and technetium-99m diethylene triamine penta-acetic acid (^99mTc-DTPA) were performed in 54 patients with a range of function between 9 and 176 ml/min. Using multiple blood samples the two clearance values correlated well (r = 0.97, SEE 8.6 ml/min) and DTPA clearance was higher by 2.9%. For each radiopharmaceutical the plasma clearance rates obtained using multiple blood samples were compared with those obtained with simplified methods, i.e., the 60–180 min two-sample method of Russell and the mono-exponential method with the Brochner-Mortensen correction. For both radiopharmaceuticals the clearance values correlated well with the Russell method (r = 0.99, SEE = 4.1 ml/min for EDTA;r = 0.99, SEE 4.9 ml/min for DTPA) and the mono-exponential method (r = 0.99, SEE 3.6 ml/min for EDTA;r = 0.99, SEE 3.9 ml/min for DTPA). The mean plasma clearance obtained using multiple blood samples did not differ significantly from that obtained with the Russell method, either in patients with a glomerular filtration rate (GFR)<30 ml/min or in patients with GFR30 ml/min. The mean plasma clearance obtained using multiple blood samples differed significantly from that obtained with the mono-exponential method because of the great difference observed in patients with GFR30 ml/min. It is concluded that the Russell two-sample method after injection of^99mTc-DTPA is accurate enough for routine clinical use.     

Transplant renography: 99m-Tc-DTPA versus 99m-Tc-MAG3. a preliminary note

^99mTc-MAG3 has been proposed as a replacement for both ¹³¹I-hippuran and ^99mTc-DTPA on clinical grounds. We undertook a prospective preliminary study to ascertain whether ^99mTc-MAG3 works better than ^99mTc-DTPA in the follow up of renal transplant recipients. Seventeen patients (21 renograms each MAG3 and DTPA) were studied, together, with a reference group of 10 patients in whom MAG3 and Hippuran clearance rates were determined simultaneously. As expected, ^99mTc-MAG3 analog images were excellent and ^99mTcMAG3 clearance correlated very well with ¹³¹I-hippuran clearance (r=0.978). MAG3 values were 60% of hippuran values. However, when the corresponding renographic and perfusion findings were faced with different diagnostic challenges, such as post transplant renal failure and rejection, ^99mTc MAG3 did not differ from ^99mTc-DTPA in a significant way. ^99mTc-DTPA was superior to ^99mtc-MAG3 in one case of rejection.     

99mTc-MAG3: Dynamic studies in patients with renal disease

Animal studies have suggested that ^99mTc-mercapto-acetylglycyl-glycyl-glycine (^99mTc-MAG3) might be suitable for the determination of the renal plasma flow (RPF) because of its high renal clearance. In this study ¹³¹I-orthoiodohippurate (¹³¹I-OIH) and ^99mTc-MAG3 (labeling always >95%) were administered simultaneously in 11 patients (creatinine clearance ranging from 14 to 130 ml/min per 1.73 m²) to measure effective RPF(ERPF) using the standard technique (UV/P). Glomerular filtration rate (GFR; clearance of ¹²⁵I-thalamate, ¹²⁵I-OT) was also measured. The mean ratio of ^99mTc-MAG3 clearance to ¹³¹I-IOH clearance was 0.55±0.02 (SEM), P<0.01, n=16, and was independant of GFR and ERPF. To study this difference in renal handling ofthe radiopharmaceuticals, renal extractions by the right kidney were determined in another six patients after a single shot of the agents. Renal extraction of ^99mTc-MAG3 was 0.60±0.03 after 5 min, and 0.41±0.08 after 30 min. Renal extraction of ¹³¹I-OIH amounted to 0.86±0.04 and 0.77±0.03, respectively. Using renal extractions of 0.41 and 0.77, respectively, it appeared that calculated renal plasma flows measured simultaneously with ^99mTc-MAG3 and ¹³¹I-OIH were similar. Protein binding 30 min after the priming dose was 66% for ^99mTc-MAG3 and 47% for ¹²³I-OIH. We conclude that in spite of a high renal clearance (ratio to ¹²⁵I-OT clearance 2.69±0.27), ^99mTc-MAG3 seems unsuitable for an accurate determination of the RPF. This conclusion is strongly supported bythe observation that the ratio of ^99mTc-MAG3 to ¹³¹I-IOH clearance markedly decreased from 0.66 to 0.32 in a patient with an increase in urinary protein loss.     

Comparison of radionuclide estimation of glomerular filtration rate using technetium 99m diethylenetriaminepentaacetic acid and chromium 51 ethylenediaminetetraacetic acid

Simultaneous measurements of the clearance rates of technetium 99m diethylenetriaminepentaacetic acid (^99mTc-DTPA) and chronium 51 ethylenediaminetetraacetic acid (⁵¹Cr-EDTA) were performed in 30 patients with a range of renal function (glomerular filtration rates between 9 and 120 ml/min). Using multiple blood samples, the two clearance values correlated well (r=0.991, standard error 3.9 ml/min), but DTPA clearance was systematically higher by 7.6%. For each radiopharmaceutical, an equation was derived to correct clearance values obtained using only plasma samples taken at 2 and 4 h for the systematic error inherent in this technique compared with analysis of the complete plasma concentration-time curve. The root mean square error remaining after application of these equations was 1.9 ml/min for both the EDTA and DTPA data. The corresponding errors obtained using the equation derived by Brochner-Mortensen for EDTA plasma clearance were 2.2 ml/min and 1.9 ml/min, respectively, these values were not significantly different from those obtained using the equations derived in this study.     

Bone marrow transplantation: effects of conditioning and cyclosporin prophylaxis on microvascular permeability to a small solute (technetium 99m diethylene triamine penta-acetic acid)

Microvascular permeability to small diffusible solutes has rarely been measured at a clinical level. We have developed a simple non-invasive technique for measuring the permeability surface area (PS) product, which is suitable for clinical use. We illustrate its potential value in six subjects who underwent bone marrow transplantation for chronic myeloid leukaemia. These patients received high-dose cyclosporin A (CyA) for prevention of graft versus host disease (GVHD) and sustained an easily measurable increase in microvascular permeability to technetium 99m diethyltriamine penta-acetic acid (^99mTc-DTPA). This was measured as the PS product, which increased from 1.1 (SD 0.3) to 2.2 (0.4) ml/min per 100 ml tissue between baseline and treatment with CyA for prevention of GVHD (P<0.01). The increase broadly correlated with nephrotoxicity which was measured, from the plasma DTPA clearance, as global glomerular filtration rate (GFR). This decreased from 106 (11.1) to 49 (6.7) ml/min (P<0.001). These abnormalities, both in PS product and GFR, were sustained for several months, after which they tended to return towards baseline levels. We conclude firstly that this technique has a potential clinical role and secondly that endothelial abnormalities due to CyA deserve further study.     

Effects of extra-renal background subtraction and kidney depth correction in the measurement of GFR by gamma camera renography

99Tcm-DTPA gamma camera renography was performed in 83 patients with a wide range of renal function. An uptake index (UI) proportional to the single kidney glomerular filtration rate (GFR) was calculated from the renograms according to two different algorithms, one based on a blood background taken from a region of interest (ROI) over the heart (method I), and the other a modification of that procedure including an extra-renal background subtraction (method II). The extra-renal background was defined by a ROI closely surrounding the kidney, making the separation between the extra-renal background and intra-renal blood background possible. Method II was further evaluated by comparing the results without and with correction for kidney depth (method III), the skin-kidney distance being measured by sonography. Calculated UI from the renograms was compared with measured 51Cr-EDTA plasma clearance as the reference method. Method I overestimated GFR at low kidney function. Addition of the extra-renal background subtraction (method II) eliminated that error and correction for kidney depth improved the accuracy (the standard error of the estimate was reduced from 18.2 min-1 to 12.3 min-1). It is concluded that the measurement of GFR by gamma camera renography is improved by these additional operations.     

Comparison of methods for determination of glomerular filtration rate: Tc-99m-DTPA renography,predicted creatinine clearance method and plasma sample method

BACKGROUND: The gamma camera uptake method with Tc-99m-DTPA is simple and less time consuming for the determination of the glomerular filtration rate (GFR). However, its diagnostic accuracy is debated. Gates' method and predicted creatinine clearance method were compared with plasma clearance method with Tc-99m-DTPA for the measurement of GFR. MATERIALS AND METHODS: Tc-99m-DTPA renography was performed on 133 patients (69 males and 64 females; age range being 24 to 84 years) with a wide range of renal function. The GFR was determined simultaneously by 3 methods; (1) gamma camera uptake method (modified Gates, Gates); (2) predicted creatinine clearance method (Cockcroft-Gault, CG); (3) single- or two-plasma clearance method (plasma sample clearance method, PSC). The PSC was chosen as a reference. RESULTS: The regression equation of the Gates and the CG against the PSC was Y = 11.89 + 1.041X (r = 0.790, p < 0.001, RMSE = 23.55 ml/min/1.73 m2) and Y = 8.845 + 0.7899X (r = 0.8270, p < 0.001, RMSE = 16.27 ml/min/1.73 m2), respectively. In comparison with the GFR by PSC, the Gates tended to overestimate the GFR, and contrarily the CG tended to underestimate the GFR. CONCLUSION: The Gates correlates well with the PSC. However, the Gates is even less precise than the CG. The Gates' method in Tc-99m-DTPA renography is not suitable for the estimation of GFR in routine practice.     

Glomerular filtration rate and the kinetics of 123I-metaiodobenzylguanidine

We have recently reported evidence that the calcium antagonist nifedipine can improve the tumour retention of ¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) in patients with malignant phaeochromocytoma. During studies of the pharmacological modification of tumour MIBG kinetics, it is important to distinguish clearly between a direct effect on MIBG cellular retention by a pharmaceutical, and secondary effects due, for example, to a change in glomerular filtration rate (GFR). In order to provide the fundamental kinetic data required for the numerical modelling of the effect of nifedipine on tumour MIBG kinetics, we have investigated the influence of GFR on MIBG plasma and renal kinetics. The ¹²³I-MIBG plasma curve and MIBG renal plasma clearance rate were studied in ten patients, ranging from subjects without biochemical or scintigraphic evidence of phaeochromocytoma to individuals with widely disseminated metastatic disease. GFR was measured using the ^99mTc-DTPA plasma clearance method. In four cases, the studies were repeated with the patients taking oral nifedipine. Statistically significant correlations were found between GFR and the MIBG plasma concentration, MIBG renal plasma clearance rate and the early (0 to 5 min) renal excretion of MIBG. The data permit the evaluation of the plasma integral during the first few min following bolus injection, a quantity important in the numerical modelling of tumour kinetics. GFR was found to have a major influence on whole-body MIBG kinetics, but there was also evidence of the effect of the metastatic tumour burden.