Feasibility of gamma camera-based GFR measurement using renal depth evaluated by lateral scan of 99mTc-DTPA renography.

OBJECTIVE: Gamma camera-based measurement of glomerular filtration rate (GFR) with 99mTc-diethylenetriaminepentaacetic acid (DTPA) is an established non-invasive measurement of split renal function; however, it is not as accurate as the plasma sample method. Therefore, study into improving the accuracy of such method is clinically relevant. The aim of this study was to elucidate the feasibility of gamma camera-based GFR measurement using renal depth evaluated by lateral scan of 99mTc-DTPA renography and comparing the results with those of GFR using renal depth measured by CT, and three representative formulas. METHODS: The study population comprised 38 patients (median, 69 years; male 28, female 10; median estimated GFR, 67.4 ml/min) with renourinary disorders. Scintigraphy was performed after intravenous injection of 370 MBq 99mTc-DTPA by dynamic data acquisition for 20 min, followed by a bilateral static scan of the abdomen for 3 min. All patients underwent computed tomography (CT) within 2 months from renography. GFR was calculated by renography using renal depth determined in five ways; lateral scan of 99mTc-DTPA, CT, and three formulas previously created with using weight, height and age. GFRs were compared with estimated GFR (eGFR). The depth of both kidneys measured as described above was compared and evaluated the laterality of the renal depth. RESULTS: The median values of GFR calculated with renal depth determined by 99mTc-DTPA renography, CT, and the three formulas were 87.3, 83.9, 67.8, 68.3, and 71.5 ml/min, respectively. All of them correlated significantly with eGFR (r = 0.734, r = 0.687, r = 0.728, r = 0.726, and r = 0.686, respectively), however, no significant difference was observed among five correlation coefficients. Bland-Altman plot revealed that eGFR had error and fixed bias when compared with GFRs calculated using renal depth determined by renography, CT, and Taylor's formula. The depth of both kidneys measured by 99mTc-DTPA renography was equivalent to that measured by CT, however, those measured by the three formulas were significantly smaller than that measured by 99mTc-DTPA renography. The depth of the right kidney was larger than that of the left kidney using all three formulas in all patients. However, CT detected only 66% of patients to have a deeper right kidney than left kidney. CONCLUSION: Lateral scanning is a feasible procedure to measure renal depth for accurate and reasonable split GFR measurements using 99mTc-DTPA renography.

Effect of Verapamil on Kidney Function Using Radionuclide Imaging.

BACKGROUND AND OBJECTIVE: Calcium channel blockers (CCBs) are among the most widely used prescribed drugs for the treatment of cardiovascular diseases. The present study investigates the effect of verapamil, which is most commonly used as a CCB, on kidney function using radionuclide imaging. METHODS: Ten New Zealand white rabbits were used in vitro (4) and in vivo (6) studies. Isometric tensions were recorded for isolated renal artery ring segments, while renographic studies were performed using Technetium-99m mercaptoacetyltriglycine and Gamma camera. Time to peak activity (Tmax) and time from peak to 50% activity (T1/2), were calculated from the renograms for control and treated rabbits with verapamil. RESULTS: In vitro, verapamil shifted the curve of phenylephrine concentration-dependent contraction on renal artery to the right, and decrease the highest contraction by 30 ± 3%. In vivo, the average values of Tmax for control and treated rabbits were 2.8 ± 0.1 and 2.2 ± 0.2 min respectively. The T1/2 for control and treated rabbits were 4.7 ± 0.05 and 4.2 ± 0.08 min respectively. The differences were statistically significant: p < 0.05. There is 30 ± 4% decrease in the 2 values. This indicates that there is a rapid renal uptake of the tracer and clearance of the radioactivity after verapamil. CONCLUSION: Verapamil dilates the renal artery and accelerates both the Tmax and T1/2 in the renogram. It increases renal blood perfusion and protects kidney function and therefore improves its work. However, verapamil should not be used while performing renograms to avoid misleading results.

REPEATABILITY AND RELIABILITY OF GLOMERULAR FILTRATION RATE DETERMINATION VIA GAMMA CAMERA UPTAKE OF TC-99M-DTPA IN CATS WITH CHRONIC KIDNEY DISEASE.

Measurement of glomerular filtration rate (GFR) via gamma camera uptake of 99mTc-diethylenetriaminepentaacetic acid is a standard method for quantifying renal function. Aims of this retrospective, observer agreement study were to determine intra- and interobserver variation in GFR values for cats with chronic kidney disease and to determine whether renal insufficiency classification changed between observers. Guideline cut-points were established for the difference in repeated GFRs to differentiate changes caused by therapeutic effect vs. inherent variation. Included cats had a diagnosis of chronic kidney disease and had undergone GFR examinations between the years of 2010 and 2013. Twenty-nine GFR studies were sampled. Each study was read twice, 6 months apart, by two veterinary radiologists and one radiology resident. Modified Bland-Altman plots were used to investigate differences between readings 1 and 2 by observer and between pairs of observers by reading. Reliability of clinical classification was assessed through comparisons between readings and observers. Measurements were not systematically different between readings for the experienced observers but were higher in reading 1 than reading 2 for the inexperienced observer. Measurements were not systematically different between the experienced observers in reading 1 or between any two observers in reading 2. Reliability for GFR measurements was high among experienced observers; variations in GFR measurements rarely led to differences in clinical classification. Results suggested that, for experienced observers, changes in GFR values following treatment in cats with chronic kidney disease between -0.4 and 0.4 mL/min/kg may be due to inherent variability rather than treatment effect.

A new quantitative method for estimating glomerular filtration rate and its clinical value.

BACKGROUND AND AIM: The estimation of the glomerular filtration rate (GFR) is essential for the renal function. However, all estimation methods for GFR have advantages and disadvantages. The aim of this study was to develop a new quantitative method for estimating GFR and evaluate its clinical value. METHODS: The new GFR was estimated by quantifying the accumulation of Tc-99m DTPA in the dual kidneys and bladder during a gamma camera renogram study in 116 patients with chronic kidney disease. GFR was determined by this new method (nGFR), Gates' gamma camera technique (gGFR), a two-plasma sampling method (tGFR) and creatinine-based clearance as estimated by Cockcroft-Gault (cGFR) and abbreviated MDRD (aGFR) formulae. The correlation analysis, Bland-Altman analysis and receiver-operating characteristic (ROC) plots were carried out among above methods. RESULTS: The nGFR value has significant correlation with tGRF (r = 0·827, P<0·01). The nGFR had the best overall performances with a lowest bias deviation (3·1 ml min(-1) /1·73 m(2) ), better precision (53·0 ml min(-1) /1·73 m(2) ), narrowest interquartile range (13·5 ml min(-1) /1·73 m(2) ) and best accuracy (68·1%) within 30% of the tGFR, compared with those of gGFR, cGFR and aGFR. The new method had the similar maximum accuracy with the Gates' method and creatinine clearance as estimated by Cockcroft-Gault and abbreviated modification of diet in renal disease (MDRD) method. The new method had better repeatability characteristic compared with the Gates' method. CONCLUSIONS: The new method for estimating GFR had the better performances compared with the Gates' method and creatinine clearance as estimated by Cockcroft-Gault and MDRD method.

The accuracy of quantitative parameters in (99m) Tc-MAG3 dynamic renography: a national audit based on virtual image data.

Assessment of image analysis methods and computer software used in (99m) Tc-MAG3 dynamic renography is important to ensure reliable study results and ultimately the best possible care for patients. In this work, we present a national multicentre study of the quantification accuracy in (99m) Tc-MAG3 renography, utilizing virtual dynamic scintigraphic data obtained by Monte Carlo-simulated scintillation camera imaging of digital phantoms with time-varying activity distributions. Three digital phantom studies were distributed to the participating departments, and quantitative evaluation was performed with standard clinical software according to local routines. The differential renal function (DRF) and time to maximum renal activity (Tmax ) were reported by 21 of the 28 Swedish departments performing (99m) Tc-MAG3 studies as of 2012. The reported DRF estimates showed a significantly lower precision for the phantom with impaired renal uptake than for the phantom with normal uptake. The Tmax estimates showed a similar trend, but the difference was only significant for the right kidney. There was a significant bias in the measured DRF for all phantoms caused by different positions of the left and right kidney in the anterior-posterior direction. In conclusion, this study shows that virtual scintigraphic studies are applicable for quality assurance and that there is a considerable uncertainty associated with standard quantitative parameters in dynamic (99m) Tc-MAG3 renography, especially for patients with impaired renal function.

Multicenter evaluation of renography with an automated physical phantom.

PURPOSE: The diversity of the dynamic radionuclide renal imaging (renography) study protocols sets challenges for the overall study quality, therefore raising a need for national quality control. The aim of this study was to encourage the standardization of renography in Finland and to evaluate the development after a previous study performed in 1997. METHODS: The new Heikkinen phantom was imaged in each of the 20 participating nuclear medicine laboratories. The results were interpreted in the manner of a regular patient study, and reconstructions and printouts were made according to the clinical routines of each laboratory. Four quantitative parameters were calculated and compared between laboratories. The reports were also assessed in a blind test. RESULTS: The average error in T(max) values ranged from -5 to 7% (-29 to +18% in 1997), in T(1/2) from 0 to 35% (-43 to +66%), in RCA20 from -20 to +28% (-50 to +82%) and in relative uptake from -3 to 5%. The difference from average in relative uptake ranged from -4 to 5% (-21 to +36%). CONCLUSION: The results showed that the errors in T(max) and relative uptake were generally within quite acceptable margins, and the variation in quantitative parameters between laboratories was shown to be smaller than 14 years earlier. The reason might be the use of new software packages as well as increased efforts to improve the quality of the studies.

UK audit of analysis of quantitative parameters from renography data generated using a physical phantom.

BACKGROUND: In this second UK audit of quantitative parameters obtained from renography, phantom simulations were used in cases in which the 'true' values could be estimated, allowing the accuracy of the parameters measured to be assessed. MATERIALS AND METHODS: A renal physical phantom was used to generate a set of three phantom simulations (six kidney functions) acquired on three different gamma camera systems. A total of nine phantom simulations and three real patient studies were distributed to UK hospitals participating in the audit. Centres were asked to provide results for the following parameters: relative function and time-to-peak (whole kidney and cortical region). As with previous audits, a questionnaire collated information on methodology. Errors were assessed as the root mean square deviation from the true value. RESULTS: Sixty-one centres responded to the audit, with some hospitals providing multiple sets of results. Twenty-one centres provided a complete set of parameter measurements. Relative function and time-to-peak showed a reasonable degree of accuracy and precision in most UK centres. The overall average root mean squared deviation of the results for (i) the time-to-peak measurement for the whole kidney and (ii) the relative function measurement from the true value was 7.7 and 4.5%, respectively. These results showed a measure of consistency in the relative function and time-to-peak that was similar to the results reported in a previous renogram audit by our group. CONCLUSION: Analysis of audit data suggests a reasonable degree of accuracy in the quantification of renography function using relative function and time-to-peak measurements. However, it is reasonable to conclude that the objectives of the audit could not be fully realized because of the limitations of the mechanical phantom in providing true values for renal parameters.

Dynamic (99m)Tc-MAG3 renography: images for quality control obtained by combining pharmacokinetic modelling, an anthropomorphic computer phantom and Monte Carlo simulated scintillation camera imaging.

In dynamic renal scintigraphy, the main interest is the radiopharmaceutical redistribution as a function of time. Quality control (QC) of renal procedures often relies on phantom experiments to compare image-based results with the measurement setup. A phantom with a realistic anatomy and time-varying activity distribution is therefore desirable. This work describes a pharmacokinetic (PK) compartment model for (99m)Tc-MAG3, used for defining a dynamic whole-body activity distribution within a digital phantom (XCAT) for accurate Monte Carlo (MC)-based images for QC. Each phantom structure is assigned a time-activity curve provided by the PK model, employing parameter values consistent with MAG3 pharmacokinetics. This approach ensures that the total amount of tracer in the phantom is preserved between time points, and it allows for modifications of the pharmacokinetics in a controlled fashion. By adjusting parameter values in the PK model, different clinically realistic scenarios can be mimicked, regarding, e.g., the relative renal uptake and renal transit time. Using the MC code SIMIND, a complete set of renography images including effects of photon attenuation, scattering, limited spatial resolution and noise, are simulated. The obtained image data can be used to evaluate quantitative techniques and computer software in clinical renography.

Determination of kidney function with 99mTc-DTPA renography using a dual-head camera.

OBJECTIVE: Single-head gamma camera renography has been used for decades to estimate kidney function. An estimate of the glomerular filtration rate (GFR) can be obtained using Tc-diethylenetriaminepentaacetic acid (Tc-DTPA). However, because of differing attenuation, an error is introduced when the kidney depth or kidney size is unequal. This error can be reduced using geometric mean data obtained from dual-head renography. The aim of this study was to compare single-head versus dual-head assessment of single kidney function. METHODS: Thirty-four patients were examined with (a) single-head renography, acquiring counts from the left ventricle and kidneys from a posterior projection, and simultaneously with (b) dual-head renography, acquiring counts from the left ventricle from an anterior projection and kidneys from both anterior and posterior projections using geometric mean values. Single kidney GFR from both models was estimated (GFRcam1 and GFRcam2, respectively) and compared with GFR determined with plasma samples of Tc-DTPA (GFRps). RESULTS: The prediction intervals of GFRcam1 and GFRcam2 compared with GFRps did not differ significantly (SD of GFRcam1-GFRps=17.6 ml/min and SD of GFR2-GFRps=15.5 ml/min; P=0.48). The corresponding coefficients of variation were 16.5 and 14.7%, respectively. CONCLUSION: There is no difference in variance between GFR estimated from single-head renography and that estimated using dual-head renography. Hence, dual-head camera renography might be useful in daily practice with the potential to provide a better estimate of absolute function in each kidney and the relative kidney function in patients with differing kidney depths and/or malformed kidneys.

Estimation of Tc-99m MAG3 clearance using camera-based methods without blood sampling.

PURPOSE: To establish camera-based methods for estimating Tc-99m mercaptoacetyltriglycine (MAG3) clearance without blood sampling. MATERIALS AND METHODS: The results of renal scintigraphy with Tc-99m MAG3 obtained from 160 patients were analyzed retrospectively. Eight renogram parameters were calculated for each patient based on the area under the renogram (area method) and slope of the renogram (slope method) using different periods for analysis (1-2 and 1-2.5 minutes for the area method; 0.5-1.5 and 0.5-2 minutes for the slope method) and different backgrounds for subtraction (perirenal and subrenal backgrounds). The 8 parameters were then correlated with MAG3 clearance measured by the single-sample methods proposed by Russell et al and Bubeck et al to determine the equation for the conversion of renogram parameters to clearance. RESULTS: All 8 renogram parameters were highly correlated with clearance measured by the single-sample methods, and the obtained equations enabled the estimation of clearance from image data. Selection between the area and slope methods, between different periods for analysis, or between perirenal and subrenal backgrounds did not cause large differences in the estimation. CONCLUSION: The camera-based methods determined in the present study allow the estimation of MAG3 clearance with acceptable accuracy.

Guidelines for standard and diuretic renogram in children.

Special consideration needs to be given to children who undergo dynamic renography. The Paediatric Committee of the European Association of Nuclear Medicine has updated the previous guidelines. Details are provided on how to manage the child, the equipment, and the acquisition and processing protocols. The pitfalls, difficulties and controversies that are encountered are also discussed, as well as the interpretation of the results.

Determination of split renal function by 3D reconstruction of CT angiograms: a comparison with gamma camera renography.

OBJECTIVE: The objective of our study was to examine the correlation between CT-based and radionuclide renography-based measures of split renal function in a healthy population of live potential kidney donors using 3D models generated from CT angiography. MATERIALS AND METHODS: The records of 173 renal donor candidates who had undergone CT and radionuclide renography between March 1, 2005, and February 28, 2006, were retrospectively evaluated; of those 173 patients, 152 met study inclusion criteria. A blinded investigator using 3D models that were created semiautomatically from the unenhanced, arterial, and excretory phase data made measurements of CT renal volumes and attenuations. The mean renal attenuation and volume were used to calculate the net accumulation of contrast material and split renal function for comparison with radionuclide renography. Split function from CT was calculated in the arterial and excretory phases as well as based on split renal volume and the Patlak method. RESULTS: All four CT-based methods for the calculation of split renal function showed correlation with no significant difference from radionuclide renography (p > 0.05, Student's t test). Pearson's correlation coefficients varied from 0.36 to 0.63 (p < 0.001 for each). Difference scores revealed that the excretory and renal volume splits had the narrowest range and showed a linear, nonzero relationship to the renography splits. Bland-Altman analysis confirmed that the majority of difference scores between each CT method and the radionuclide renography were within the 95% CI of the differences. CONCLUSION: Split renal function based on 3D CT models can provide a "one-stop" evaluation of both the anatomic and the functional characteristics of the kidneys of living potential kidney donors. The excretory phase data and the split renal volume data show the best correlation and the smallest difference scores compared with radionuclide renography data.

Radionuclide investigations of the urinary tract in the era of multimodality imaging.

This article presents the role of nuclear medicine procedures in investigating renal and parenchymal disease, as well as upper urinary tract abnormalities. More specifically, the use of scintigraphy is described in the exploration of urinary tract dilatation and UTIs, vesicoureteric reflux, renovascular hypertension, and renal transplants. With a low radiation burden and the absence of sedation, these nuclear medicine procedures are easy to perform and can provide clinicians with valuable data on renal perfusion and the function of individual kidneys, as well as on urinary tract dynamics. However, knowledge of limitations and technical pitfalls is essential in understanding the role of scintigraphy among contemporary imaging methods and the unique information it supplies in nephrourology.

In vivo radionuclide uptake quantification using a multi-pinhole SPECT system to predict renal function in small animals.

PURPOSE: In vivo quantification of radiopharmaceuticals has great potential as a tool in developing new drugs. We investigated the accuracy of in vivo quantification with multi-pinhole single-photon emission computed tomography (SPECT) in rats. METHODS: Fifteen male Lewis rats with different stages of renal dysfunction were injected with 50 MBq 99mTc-dimercaptosuccinic acid. Four to six hours after injection, SPECT of the kidneys was acquired with a new four-headed multi-pinhole collimator camera. Immediately after imaging the rats were sacrificed and the kidneys were counted in a gamma-counter to determine the absorbed activity. SPECT data were reconstructed iteratively and regions of interest (ROIs) were drawn manually. The absolute activity in the ROIs was determined. RESULTS: Uptake values ranging from 0.71% to 21.87% of the injected activity were measured. A very strong linear correlation was found between the determined activity in vivo and ex vivo (r2=0.946; slope m=1.059). CONCLUSION: Quantification in vivo using this multi-pinhole SPECT system is highly accurate.

A dynamic renal phantom for nuclear medicine studies.

Dynamic radionuclide renal study (renography) provides functional and structural information of the kidney and urinary tract noninvasively. Our purpose in this study is to describe the construction and test results of a dynamic renal phantom with different clinical features of radionuclide renography. The phantom consisted of five pieces of different shaped Plexiglas boxes: Two kidneys, one liver, two square shaped boxes (one heart and one bladder). The bladder was internally divided into two compartments in order to collect each kidney output separately. The dynamic circulation of the phantom was maintained under a hydrostatic pressure approximately equal to 13.3 kPa (average human blood pressure). The standard dose distribution among different organs and different renographic parameters were calculated from series of normal patients study (91 with 99mTc-DTPA, 68 with 99mTc-EC). All the studies were performed with same camera (Siemens Orbiter Digitrac 7500) equipped with LEAP (low energy all purpose) collimator using ADAC Pegasys II analytic package program under the same clinical procedure. Different regions of interest (ROIs) were drawn for concerning organs and counts per second (CPS) were collected for each ROI. The series of renogram curves were generated by phantom-studies with different flow rates for left kidney (LK) and right kidney (RK). The renal index (RI) for an individual study was calculated as the product of two indexes: "Relative Renal Function" (RRF) (water-volume of LK/RK) and "Relative Renal Time" (RRT) (Tmax of LK/RK). The most significant correlation was found in total CPS for LK and RK between the EC group and phantom studies (p < 0.001). The calculated RI values were used to simulate the patients' study with different clinical features. The dynamics were found reproducible. The phantom is suitable for using in calibration and quality control protocols of the renogram procedure used in Nuclear Medicine.

The gamma camera as an absolute measurement device: determination of glomerular filtration rate in 99mTc-DTPA renography using a dual head gamma camera.

AIM: The aim of this study was to design a general nuclear medicine method for fast, accurate and direct determination of the clearance of a radioactive indicator provided that all uptake compartments of the radioactive indicator could be included in the field of view of the gamma camera. METHODS: The data material for clearance calculation in the gamma camera method (GCM) comprises: (1) a transmission map of a part of the body using a water filled flood field phantom with a uniform distribution of the radioisotope, (2) the background corrected activity curves in the anterior and posterior views over all uptake compartments following the injection of the radioactive indicator, and (3) the activity of the radioactive indicator in at least two blood samples drawn during the examination. With a view to determining glomerular filtration rate (GFR) in 99mTc-DTPA renography the gamma camera method was tested in a group of 26 adult subjects in whom GFR was determined simultaneously using the simplified multiple samples method (MSM) with plasma samples drawn 3-5 h following the injection of 51Cr-EDTA. RESULTS: For values of GFR above 30 ml.min(-1) the regression line of GFR in the MSM versus GFR in the GCM was not significantly different from the line of identity. The reliability of the GCM alone was about 14%, 11% and 6% for GFR values of 30, 60 and 120 ml.min(-1) and, therefore, the reliability of the GCM and the simplified MSM for prediction of GFR was almost the same. CONCLUSION: Since the recording of the renal count rates in the anterior and posterior views permits an accurate determination of the split renal function, the GCM yields reliable estimates also of the single kidney GFR.

New automated physical phantom for renography.

UNLABELLED: Physical phantoms have been used to test the diagnostic proficiency of nuclear medicine professionals and the accuracy of their equipment in external quality assurance surveys. No dynamic renal phantoms are commercially available. A new renal phantom, presented in this paper, was constructed and patented in the United States. METHODS: The organs to be simulated by the phantom were in the form of containers filled with radioactive solution, and the device further comprised movable steel and lead plates between the containers and the gamma-camera. The detectable radiation was regulated in accordance with automated computer-controlled step motors to move the attenuators to simulate a given patient situation. The reproducibility of the phantom measurements was defined as a coefficient of variation. Four different kidney-function simulations were repeated 3 times, and 6 parameters were compared. RESULTS: The average root mean square deviation of the coefficient of variation was 6.7% for the perfusion integral, 1.3% for time to reach the maximum activity, 19.7% for mean transit time, 3.3% for function (Patlak [%]), 1.0% for outflow index (%), and 6.5% for time to reach the half-activity from maximum. CONCLUSION: With this phantom, the true values of most parameters measured are well known; it closely approaches true extraction, washout, and attenuation properties and curves, and the images produced are similar to those of patient studies. Compared with the first manual version, this new automated phantom is easy to use. Any desired clinical situation can be programmed. It is a promising tool for quality assurance and calibration of renography.