Renal function measurements from MR renography and a simplified multicompartmental model.
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The purpose of this study was to determine the accuracy and sources of error in estimating single-kidney glomerular filtration rate (GFR) derived from low-dose gadolinium-enhanced T1-weighted MR renography. To analyze imaging data, MR signal intensity curves were converted to concentration vs. time curves, and a three-compartment, six-parameter model of the vascular-nephron system was used to analyze measured aortic, cortical, and medullary enhancement curves. Reliability of the parameter estimates was evaluated by sensitivity analysis and by Monte Carlo analyses of model solutions to which random noise had been added. The dominant sensitivity of the medullary enhancement curve to GFR 1-4 min after tracer injection was supported by a low coefficient of variation in model-fit GFR values (4%) when measured data were subjected to 5% noise. These analyses also showed the minimal effects of bolus dispersion in the aorta on parameter reliability. Single-kidney GFR from MR renography analyzed by the three-compartment model (4.0-71.4 ml/min) agreed well with reference measurements from (99m)Tc-DTPA clearance and scintigraphy (r = 0.84, P < 0.001). Bland-Altman analysis showed an average difference of 11.9 ml/min (95% confidence interval = 5.8-17.9 ml/min) between model and reference values. We conclude that a nephron-based multicompartmental model can be used to derive clinically useful estimates of single-kidney GFR from low-dose MR renography. (+info)
DMSA findings in the evaluation of pediatric renal allograft.
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Owing to their minimally invasive nature, efficiency and availability, radionuclide renal diagnostic studies play an important role in assessing renal transplant function. Various quantitative parameters have been derived from the radionuclide renograms in the follow-up to assess changes in perfusion and function of the transplant kidneys. The aim of this study was to evaluate the changes in renal transplants with technetium-99m dimercaptosuccinic acid scintigraphy. Serial cortical renal scans of 66 patients were reviewed retrospectively. The studies were analyzed regarding the quality of the images and morphology of the kidneys. Cortical renal scintigraphy was unable to provide decisive information for the etiological diagnosis of renal graft dysfunction, thus not allowing a distinction to be made between different clinical situations. Despite being non-specific, it gives information that is not apparent on conventional imaging as well as the extent of pathology, which makes it a sensitive test in the follow-up of transplant pediatric patients. An early scan within the first weeks provides a baseline, which may help in the assessment of future complications. (+info)
Use of classification and regression trees in diuresis renography.
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RATIONALE AND OBJECTIVES: Decision support systems have the capacity to improve diagnostic performance and reduce physician errors. The purpose of this study was to evaluate the use of classification and regression trees (CART) with bootstrap aggregation as a decision support system in the baseline plus furosemide (F + 20) diuresis renography protocol to determine when obstruction can be excluded without the furosemide acquisition and to identify the key parameters for making this determination. MATERIALS AND METHODS: Patients with suspected ureteral obstruction were randomly assigned to a training set (80 patients, 157 kidneys) and a validation set (64 patients, 124 kidneys). Forty quantitative parameters (curve parameters, MAG3 clearance and voiding indices) were generated from each baseline Tc-99m mercaptoacetyltriglycine (MAG3) scan. Three expert readers independently evaluated each kidney regarding the need for furosemide and resolved differences by majority vote. CART with bootstrap aggregation was applied to the training set to generate prediction algorithms which were tested in the validation set. RESULTS: The algorithm agreed with the expert decision on the necessity of furosemide in 90% (111 of 124 kidneys), with misclassification rates of 10.0% and 10.9% for the left and right kidneys, respectively. The most important discriminators were the postvoid-to-maximum count ratio, the cortical 20-minute-to-maximum count ratio, and the postvoid-to-1-to-2-minute count ratio. CONCLUSION: CART can identify the key parameters for discriminating between nonobstruction and possible obstruction, has the potential to serve as a decision support tool to avoid unnecessary furosemide imaging, and can be applied to more complex imaging problems. (+info)
Influence of ureteral status on kidney washout during technetium-99m-DTPA diuresis renography in children.
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To assess the influence of the ureter on renal washout during 99mTc-DTPA diuresis renography, ureteral images were reviewed in 42 children (median age: 5 mo) referred for hydronephrosis. Sixty-minute acquisitions were obtained in hydrated patients under bladder drainage. Furosemide was injected at 30 min. An abnormal ureter was defined as an intense and continuous image of greater than 10 min. A washout index was determined on renal (KT1/2) and ureteral (UT1/2) curves. Curve patterns corresponding to normal (type I), obstructive (II) and nonobstructive (III) cases were described. Compared with the x-ray data, diuresis renography was highly sensitive (91%) and specific (98%) for detecting any abnormality. Despite an obstructive KT1/2 (greater than 20 min), no patient with an abnormal ureter underwent therapy at the ureteropelvic junction. After surgery at the lower level, hydronephrosis regressed. Our data indicate that abnormal ureter findings at diuresis renography have to be recognized before planning therapy for children with hydronephrosis. (+info)
A software engine to justify the conclusions of an expert system for detecting renal obstruction on 99mTc-MAG3 scans.
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The purposes of this study were to describe and evaluate a software engine to justify the conclusions reached by a renal expert system (RENEX) for assessing patients with suspected renal obstruction and to obtain from this evaluation new knowledge that can be incorporated into RENEX to attempt to improve diagnostic performance. METHODS: RENEX consists of 60 heuristic rules extracted from the rules used by a domain expert to generate the knowledge base and a forward-chaining inference engine to determine obstruction. The justification engine keeps track of the sequence of the rules that are instantiated to reach a conclusion. The interpreter can then request justification by clicking on the specific conclusion. The justification process then reports the English translation of all concatenated rules instantiated to reach that conclusion. The justification engine was evaluated with a prospective group of 60 patients (117 kidneys). After reviewing the standard renal mercaptoacetyltriglycine (MAG3) scans obtained before and after the administration of furosemide, a masked expert determined whether each kidney was obstructed, whether the results were equivocal, or whether the kidney was not obstructed and identified and ranked the main variables associated with each interpretation. Two parameters were then tabulated: the frequency with which the main variables associated with obstruction by the expert were also justified by RENEX and the frequency with which the justification rules provided by RENEX were deemed to be correct by the expert. Only when RENEX and the domain expert agreed on the diagnosis (87 kidneys) were the results used to test the justification. RESULTS: RENEX agreed with 91% (184/203) of the rules supplied by the expert for justifying the diagnosis. RENEX provided 103 additional rules justifying the diagnosis; the expert agreed that 102 (99%) were correct, although the rules were considered to be of secondary importance. CONCLUSION: We have described and evaluated a software engine to justify the conclusions of RENEX for detecting renal obstruction with MAG3 renal scans obtained before and after the administration of furosemide. This tool is expected to increase physician confidence in the interpretations provided by RENEX and to assist physicians and trainees in gaining a higher level of expertise. (+info)
Development and prospective evaluation of an automated software system for quality control of quantitative 99mTc-MAG3 renal studies.
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Quantitative nuclear renography has numerous potential sources of error. We previously reported the initial development of a computer software module for comprehensively addressing the issue of quality control (QC) in the analysis of radionuclide renal images. The objective of this study was to prospectively test the QC software. METHODS: The QC software works in conjunction with standard quantitative renal image analysis using a renal quantification program. The software saves a text file that summarizes QC findings as possible errors in user-entered values, calculated values that may be unreliable because of the patient's clinical condition, and problems relating to acquisition or processing. To test the QC software, a technologist not involved in software development processed 83 consecutive nontransplant clinical studies. The QC findings of the software were then tabulated. QC events were defined as technical (study descriptors that were out of range or were entered and then changed, unusually sized or positioned regions of interest, or missing frames in the dynamic image set) or clinical (calculated functional values judged to be erroneous or unreliable). RESULTS: Technical QC events were identified in 36 (43%) of 83 studies. Clinical QC events were identified in 37 (45%) of 83 studies. Specific QC events included starting the camera after the bolus had reached the kidney, dose infiltration, oversubtraction of background activity, and missing frames in the dynamic image set. CONCLUSION: QC software has been developed to automatically verify user input, monitor calculation of renal functional parameters, summarize QC findings, and flag potentially unreliable values for the nuclear medicine physician. Incorporation of automated QC features into commercial or local renal software can reduce errors and improve technologist performance and should improve the efficiency and accuracy of image interpretation. (+info)
Evaluation of two diuresis renography decision support systems to determine the need for furosemide in patients with suspected obstruction.
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OBJECTIVE: The purpose of this study was to compare the decisions regarding the need for furosemide made by two independent renal decision support systems, RENEX and CAR-TAN, with the need for furosemide determined in clinical practice and by expert reviewers using the baseline plus furosemide protocol. SUBJECTS AND METHODS: RENEX and CARTAN are independent decision support systems that reach their conclusions without operator input. RENEX is a knowledge-based system and CARTAN is a statistical decision support system. Both were trained using the same pilot group of 31 adult patients (61 kidneys) referred for suspected obstruction. Subsequently, both systems were prospectively applied to 102 patients (200 kidneys) of whom 70 received furosemide; decisions regarding the need for furosemide were compared with the clinical decisions and the decisions of three experts who independently scored each kidney on the need for furosemide. Differences were resolved by consensus. RESULTS: RENEX agreed with the clinical and experts' decisions to give furosemide in 97% (68/70) and 98% (65/66) of patients, respectively, whereas CARTAN agreed in 90% (63/70) and 89% (59/66), respectively, p < 0.03. In contrast, CARTAN agreed with the experts' decision to withhold furosemide in 78% of kidneys (87/111), whereas RENEX agreed in only 69% of kidneys (77/111), p = 0.008. CONCLUSION: Use of RENEX or CARTAN as decision support tools in the baseline plus furosemide protocol has the potential to help the radiologist avoid unnecessary imaging and reduce the technologist, computer, camera, and physician time required to perform the procedure. (+info)
Diuresis renography for differentiation of upper urinary tract dilatation from obstruction: F+20 and F-15 methods.
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INTRODUCTION: The aim of this study was to evaluate diuresis renography with an intravenous injection of furosemide 20 minutes after administering the radiopharmaceutical (F+20 protocol) or 15 minutes before (F-15 protocol) in patients with upper urinary tract dilatation. MATERIALS AND METHODS: Twenty-one patients with pyelocaliceal system dilatation, but not ureteral dilatation, on ultrasonography were evaluated. The patients underwent diuresis renography using the F+20 and F-15 protocols. Renal scan findings and kidney split function were recorded. Then, the patients underwent surgical or conservative treatment according to their clinical conditions and imaging results. Follow-up was done 3 and 6 months postoperatively by physical examination, intravenous urography, and diuresis renography. RESULTS: Eleven patients (52.4%) had complete obstruction in both protocols of renography, and 5 (23.8%) had an equivocal result in the F+20 and an obstructive pattern in the F-15. These patients underwent surgical operation. In 3 patients (14.3%), both protocols demonstrated a normal urinary tract. In 2 patients (9.5%), a nonobstructive response in the F+20 and an equivocal result in the F-15 were seen. One of them underwent surgical operation because of impaired kidney function during the follow-up and 1 was treated conservatively. Overall, obstruction was found in 16 out of 21 patients (76.2%) by the F-15 protocol, while it was found in 11 (52.4%) by the F+20 protocol (P=.01). The mean kidney split function was 55.15% +/- 7.82% and 54.81% +/- 6.87% in F+20 and F-15 protocols, respectively (P=.45). CONCLUSION: Using the F-15 protocol may reduce the equivocal results of the F+20 for diuresis renography. (+info)