Technetium 99m mercaptoacetyltriglycine gamma camera clearance calculations: methodological problems

Role of Technetium-99m N,N-Ethylenedicysteine Renal Scintigraphy in the Evaluation of Differential Renal Function and Cortical Defects

PURPOSE

This study was performed to evaluate the effectiveness of technetium-99m N,N-ethylenedicysteine (Tc-99m EC) in comparison to technetium-99m dimercaptosuccinic acid (Tc-99m DMSA) scintigraphy. Differential renal function (DRF) was calculated by both methods and the cortical-phase images of dynamic Tc-99m EC scintigraphy were evaluated for parenchymal defects.

MATERIALS AND METHODS

A total of 62 patients with various kidney disorders ranging in age from 1 to 44 years underwent both Tc-99m DMSA and Tc-99m EC scintigraphy. Tc-99m EC summed images of the cortical phase and Tc-99m DMSA images were evaluated visually and quantitatively. Visual analysis was used to define renal parenchymal abnormalities. Quantitative analysis was used in the calculation of DRF. The Tc-99m DMSA scan was taken as the gold standard, and the summed Tc-99m EC scan findings were compared against it.

RESULTS

The images obtained with Tc-99m DMSA and Tc-99m EC scintigraphy revealed 99 and 97 focal defects, respectively. The 2 renal parenchyma defects located in the ventral middle sections remained undetected with Tc-99m EC scintigraphy. DRF of the kidneys in each patient was compared using both radiopharmaceuticals. Highly positive correlation between the differential function of these 2 investigations was found (R = 0.91, P = 0.001). The values of mean DRF of the left kidney on Tc-99m EC and Tc-99m DMSA images were 45.8 +/- 19.1 and 45.0 +/- 20.4, respectively. There were no significant differences (P > 0.05).

CONCLUSION

This study suggests that although Tc-99m DMSA scintigraphy remains the gold standard method for evaluating parenchymal abnormalities, Tc-99m EC scintigraphy can be a reliable single-modality study to evaluate renal cortical defects, DRF, perfusion, drainage of the urinary system, and indirect evidence of vesicoureteric reflux with the added advantage of low radiation exposure to the patient.

The estimation of renal transit using renography--our opinion

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

Assessment of the optimal time interval and background region of interest in the measurement of differential renal function in Tc-99m-EC renography

BACKGROUND

Differential renal function (DRF) measurements are routinely corrected for background, which mainly affects the reproducibility and accuracy of the measurement. The present study was conducted to identify the most appropriate background ROI and optimal time interval in the calculation of DRF for EC renography.

MATERIALS AND METHODS

Nineteen patients were studied. For determination of DRF in EC renography, the selected time intervals were 0.5-1.5; 0.5-2; 1-2; 1.5-2.5; 2-3 min, and the background ROI types were inferolateral crescent, lateral crescent, and perirenal shaped. The reference DRF was obtained through DMSA study. For low functioning kidney of each patient, relative uptake differences between the DMSA and EC scans were calculated. Then, the mean differences and the standard deviations were found.

RESULTS

The highest correlation was between the DRF values obtained using inferolateral background ROI in 0.5-2 minutes of EC scintigraphy and the DRF values obtained through posterior DMSA images (r = 0.9889). However, there were no statistically significant differences between the mean DRF values obtained for each time interval with each ROI type (p > 0.05). For all the time intervals and background ROIs, the mean of the differences was <0.9%. In conclusion, in obtaining comparable DRF values from EC and DMSA studies, none of the background types proved superior. Also our research for optimal time interval showed that EC scintigraphy underestimates the DRF when compared to DRF obtained from DMSA study. The DRF has a tendency to decrease as the later time intervals are used. The time intervals less than 2.5 minutes show lower underestimation of DRF values.

Factors influencing the accuracy of renal output efficiency

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

Consensus report on quality control of quantitative measurements of renal function obtained from the renogram: International Consensus Committee from the Scientific Committee of Radionuclides in Nephrourology

Among all the physiological indices that can be quantified using renography, measurement of renal function is the most basic. These measurements are used to make critical clinical management decisions and, as such, their reliability needs to be quality assured. This article seeks to address each aspect of the renography procedure, with particular emphasis on the effect on measurement of relative renal function. Estimation of individual kidney function is mentioned, but only briefly. A consensus approach was adopted, overseen, and directed by a chairman appointed by the Scientific Committee of the International Radionuclides in Nephro-Urology Group. The chairman selected the panel of experts from eight different countries based on their practical experience in the field. Where evidence exists to support the various recommendations it is given. Otherwise, the stated guidance represents the considered opinion of a body of experts, based on long experience and unpublished data. Some necessary compromises were made to account for the fact that renography is seldom performed solely with the purpose of measuring relative renal function. The technicalities of renography have always been a source of debate in nuclear medicine, which is reflected by the fact that a consensus could simply not be reached on a small number of issues. The structure of the report ensures that these are clearly indicated. This should serve to highlight gaps in our current knowledge, thus helping to direct future research. It is envisaged that the recommendations will be revised on a 2-year cycle to ensure that they remain up to date. An "open" process will be used to encourage participation and ownership. It is hoped that promotion of these guidelines, suitably complemented by audit processes, will raise standards in the practice of gamma camera renography.

Recent advances in pediatric nuclear medicine

This review is devoted to some controversial topics in the field of pediatric nuclear medicine. In most cases, drug sedation can be avoided and the nuclear medicine procedure can be successfully achieved simply by taking the emotional life of the child into account. Factors such as past negative experiences (painful procedures, hospitalizations), unfamiliar environment (frightening examination room), physical aggressions related to the nuclear medicine procedure (intravenous injections, cystography), and the feeling of loss of parents' protection all contribute to the child's anxiety. People in charge of pediatric procedures should be adequately trained to be aware of these factors and to create the best environmental conditions to avoid unnecessarily frightening the child. Methods for measuring renal clearance in children are numerous. It is my aim to review the different methods proposed in the literature, including the nonradioisotopic methods, the reference radioisotopic methods, the various simplified algorithms using blood samples, and the gamma-camera methods. Gastroesophageal reflux scintigraphy is a well-established procedure for the detection of gastro-esophageal reflux in children. However, despite the numerous advantages of this technique, it has not gained wide acceptance in the field of pediatric gastroenterology. This review focuses mainly on the comparison between scintigraphy and pH metry. Finally, the applications of 99m technetium-hexamethylpropylenamine brain single photon emission computer tomography in the field of pediatric neurology are still under development; this part of the review is an attempt to summarize the real contribution of this technique.

Determination of the technetium-99m mercaptoacetyltriglycine plasma clearance in children by means of a single blood sample: a multicentre study. The Paediatric Task Group of the EANM

A multicentre European study was undertaken in order to determine a reasonable algorithm allowing the determination of overall technetium-99m mercaptoacetyltriglycine clearance using a single blood sample. Employing multiple blood sample clearance as a reference method, it was shown that an acceptable estimation of the MAG3 renal clearance could be obtained using a blood sample taken at any time between 30 and 40 min after tracer injection. After correction for body surface area, comparison of clearance determined using (a) the single blood sample and (b) the multiple blood samples provided a coefficient of correlation of 0.949 and an SEE of 27 ml/min. This algorithm is valid for clearance values higher than 100 ml/min/1.73 m2 and for children older than 1 year of age.

Clearance and distribution parameters of 99mTc-EHIDA, -DTPA and -MAG-3 by dynamic liver/kidney scintigraphy

The radiopharmaceuticals (RF) EHIDA, DTPA and MAG-3 (labeled by 99mTc), commonly used in dynamic liver/kidney scintigraphy, are distributed in intravascular (i.v.) and extravascular (e.v.) spaces, as they are simultaneously cleared from the blood passing through their target organ (liver/kidney). The drop in concentration of these RF in blood is therefore determined by distribution as well as by clearance up to the time of equilibrium. From that time only the rate of decrease of RF in blood expresses the "true" (liver/kidney) clearance and this clearance parameter is a clinically reliable index of the function of the target organ. (A) The method of analysis of the clearance curve obtained from the heart region has been reported; the method is based on a physiological approach with respect to the distribution processes of the RF in the organism. Apart from the main important parameter, T (clear) (half-time of the "pure" clearance of the resp. RF from its distribution space), two further parameters are obtained: T (distr.) (half-time of the e.v. distribution of the RF) and END (distr.) (end of this distribution). (B) The results of 218 patients examined using 99mTc-EHIDA, 192 using DTPA and 65 using MAG-3 have been statistically processed. The mutual correlation of all parameters [T (distr.), END (distr.), T (clear)] within each group of patients as well as the differences of corresponding parameters between the groups of patients are studied. The main purpose of the work was to obtain the reliable clearance parameters of the RF with extravascular distribution for routine clinical practice.(ABSTRACT TRUNCATED AT 250 WORDS)

Technetium-99m (99mTc) mercaptoacetyltriglycine: update on the new 99mTc renal tubular function agent

Technetium-99m (99mTc) mercaptoacetyltriglycine (MAG3) is a new renal radiopharmaceutical that was recently introduced as a 99mTc-labeled replacement for iodine-131 (131I) o-iodohippurate (OIH). Since its introduction, a wide variety of in vitro and in vivo studies have been performed to characterize the high-performance liquid chromatography (HPLC)-purified complex and kit formulations. [99mTc]MAG3 has a slower plasma clearance, a higher plasma protein binding, less red blood cell (RBC) penetration, a lower extraction ratio, and a smaller volume of distribution than OIH. Because of the slower plasma clearance, [99mTc] MAG3 cannot be used as a direct measurement of effective renal plasma flow. Simplified methods have been developed to calculate [99mTc]MAG3 clearances, as well as regression equations to convert these clearances to an equivalent OIH value. The image quality of [99mTc]MAG3 is superior to [131I]OIH; the renogram curves and the fraction of the dose of the two agents that appears in the urine are almost identical, even though the plasma clearance of [99mTc]MAG3 is only 50% to 65% that of OIH. [99mTc]MAG3 compares favorably with OIH in patients with a wide range of clinical problems. The radiation dose to a patient with normal renal function using standard imaging doses is higher for [99mTc]MAG3 than for [131I]OIH, but in patients with impaired renal function, the radiation dose from [131I]OIH is much higher than [99mTc]MAG3. [99mTc]MAG3 also provides superior image quality compared with [99mTc]diethylenetriaminepentaacetic acid (DTPA) in patients with impaired renal function, but it is important to note that [99mTc]MAG3 cannot be used to measure the glomerular filtration rate (GFR). [99mTc]MAG3 is the most promising 99mTc tubular function agent to date, and it has replaced OIH and [99mTc]DPTA in a number of institutions. However, there are physiologic differences between these three agents and, therefore, they should not be expected to behave identically in all clinical conditions.

Quantification of renal haemodynamics with radionuclides

Non-invasive quantification of renal function with radionuclides is an important role of nuclear medicine. With modern commercial preparations of technetium-99m diethylene triamine penta-acetic acid (DTPA), glomerular filtration rate (GFR) can be measured accurately either from the rate of disappearance of the tracer from plasma or from its rate of uptake into the kidneys. Determination of the latter with the gamma camera allows measurement of individual kidney GFR. Renal blood flow (RBF) can be measured from plasma clearance of hippurate or from first-pass kinetics of intravenously injected tracer using the gamma camera. The filtration fraction can be obtained from separate measurement of GFR and RBF, either globally from plasma clearance studies or of each kidney from gamma camera studies. Because they are central to the understanding of plasma clearance studies, the effective distribution volumes of the various tracers used for renal function studies are also discussed in detail.