iRENEX: a clinically informed decision support system for the interpretation of 99mTc-MAG3 scans to detect renal obstruction

Purpose

Decision support systems for imaging analysis and interpretation are rapidly being developed and will have an increasing impact on the practice of medicine. RENEX is a renal expert system to assist physicians evaluate suspected obstruction in patients undergoing mercaptoacetyltriglycine (MAG3) renography. RENEX uses quantitative parameters extracted from the dynamic renal scan data using QuantEM?II and heuristic rules in the form of a knowledge base gleaned from experts to determine if a kidney is obstructed; however, RENEX does not have access to and could not consider the clinical information available to diagnosticians interpreting these studies. We designed and implemented a methodology to incorporate clinical information into RENEX, implemented motion detection and evaluated this new comprehensive system (iRENEX) in a pilot group of 51 renal patients.

Methods

To reach a conclusion as to whether a kidney is obstructed, 56 new clinical rules were added to the previously reported 60 rules used to interpret quantitative MAG3 parameters. All the clinical rules were implemented after iRENEX reached a conclusion on obstruction based on the quantitative MAG3 parameters, and the evidence of obstruction was then modified by the new clinical rules. iRENEX consisted of a library to translate parameter values to certainty factors, a knowledge base with 116 heuristic interpretation rules, a forward chaining inference engine to determine obstruction and a justification engine. A clinical database was developed containing patient histories and imaging report data obtained from the hospital information system associated with the pertinent MAG3 studies. The system was fine-tuned and tested using a pilot group of 51 patients (21 men, mean age 58.2?±?17.1?years, 100 kidneys) deemed by an expert panel to have 61 unobstructed and 39 obstructed kidneys.

Results

iRENEX, using only quantitative MAG3 data agreed with the expert panel in 87?% (34/39) of obstructed and 90?% (55/61) of unobstructed kidneys. iRENEX, using both quantitative and clinical data agreed with the expert panel in 95?% (37/39) of obstructed and 92?% (56/61) of unobstructed kidneys. The clinical information significantly (p?Conclusion Our renal expert system for detecting renal obstruction has been substantially expanded to incorporate the clinical information available to physicians as well as advanced quality control features and was shown to interpret renal studies in a pilot group at a standardized expert level. These encouraging results warrant a prospective study in a large population of patients with and without renal obstruction to establish the diagnostic performance of iRENEX.     

RENEX: an expert system for the interpretation of 99mTc-MAG3 scans to detect renal obstruction.

A renal expert system (RENEX) has been developed to assist physicians detect renal obstruction in patients undergoing pre- and postfurosemide 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) scans. RENEX uses quantitative parameters extracted from the dynamic renal scan data and heuristic rules in the form of a knowledge base (KB) obtained from expert interpreters to conclude whether a kidney is obstructed. METHODS: Normal limits were established for 47 quantitative parameters extracted from the 99mTc-MAG3 scans of 100 potential renal donors. From these data the domain expert estimated 5 boundary conditions for each parameter: (i) definitely abnormal, (ii) probably abnormal, (iii) equivocal, (iv) probably normal, and (v) definitely normal. A sigmoid-type curve was then generated from these 5 boundary conditions, creating a parameter knowledge library used for converting the value of a prospective patient's individual quantitative parameters to a certainty factor (CF). Sixty heuristic rules were extracted from the domain expert to generate the KB for detecting obstruction. A forward-chaining inference engine was developed using the MYCIN combinatories (an approximation of Bayes theorem) to determine obstruction. A justification engine was implemented, which recorded the sequence of each rule that was fired and the current CF value of all input and output parameters at the time of instantiation to track and justify the logic of the conclusions. The entire system was fine tuned and tested using a pilot group of 32 patients (11 males, 21 females; mean age, 56.8 +/- 17.2 y; 63 kidneys) deemed by an expert panel to have 41 unobstructed kidneys, 13 obstructed kidneys,and 9 equivocal findings. RESULTS: RENEX agreed with the expert panel in 92% (12/13) of the obstructed kidneys, 93% (38/41) of the unobstructed kidneys, and 78% (7/9) of the kidneys interpreted as equivocal for obstructions. Processing time per patient was practically instantaneous using a 3.0-GHz personal computer programmed using interactive data language. CONCLUSION: We have developed a renal expert system for detecting renal obstruction using pre- and postfurosemide 99mTc-MAG3 renal scans, at a standardized expert level. These encouraging preliminary results warrant a prospective study in a large population of patients with and without renal obstruction to establish the diagnostic performance of this system.     

Decision support systems in diuresis renography

The volume of diagnostic imaging studies performed in the United States is rapidly increasing resulting from an increase in the number of patients as well as an increase in the volume of studies per patient. Concurrently, the number and complexity of images in each patient data set are also increasing. Nuclear medicine physicians and radiologists are required to master an ever-expanding knowledge base whereas the hours available to master this knowledge base and apply it to specific tasks are steadily shrinking. The convergence of an expanding knowledge base and escalating time constraints increases the likelihood of physician errors. The problem is particularly acute for low-volume studies such as MAG3 diuresis renography where many imagers may have had limited training or experience. To address this problem, renal decision support systems (DSS) are being developed to assist physicians evaluate suspected obstruction in patients referred for diuresis renography. Categories of DSS include neural networks, case-based reasoning, expert systems and statistical systems; RENEX and CART are examples of renal DSS currently in development. RENEX (renal expert) uses a set of rules obtained from human experts to analyze a knowledge base of expanded quantitative parameters obtained from diuresis MAG3 scintigraphy whereas CART (classification and regression tree analysis) is a statistical method that grows and prunes a decision tree based on an analysis of these quantitative parameters in a training data set. RENEX can be queried to provide the reasons for its conclusions. Initial data show that the interpretations provided by RENEX and CART are comparable to the interpretations of a panel of experts blinded to clinical information. This project should serve as a benchmark for the scientific comparison and collaboration of these 2 fields of medical decision-making. Moreover, we anticipate that these DSS will better define the essential interpretative criteria, foster standardized interpretation, teach trainees to better interpret renal scans, enhance diagnostic accuracy and provide a methodology applicable to other diagnostic problems in radiology and medicine.     

Diagnostic performance of an expert system for interpretation of 99mTc MAG3 scans in suspected renal obstruction.

The purpose of the study was to compare diuresis renography scan interpretation generated by a renal expert system with the consensus interpretation of 3 expert readers. METHODS: The expert system was evaluated in 95 randomly selected furosemide-augmented patient studies (185 kidneys) obtained for suspected obstruction; there were 55 males and 40 females with a mean age +/- SD of 58.6 +/- 16.5 y. Each subject had a baseline (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG3) scan followed by furosemide administration and a separate 20-min acquisition. Quantitative parameters were automatically extracted from baseline and furosemide acquisitions and forwarded to the expert system for analysis. Three experts, unaware of clinical information, independently graded each kidney as obstructed/probably obstructed, equivocal, and probably nonobstructed/nonobstructed; experts resolved differences by a consensus reading. These 3 expert categories were compared with the obstructed, equivocal, and nonobstructed interpretations provided by the expert system. Agreement was assessed using weighted kappa, and the predictive accuracy of the expert system compared with expert readers was assessed by the area under receiver-operating-characteristic (ROC curve) curves. RESULTS: The expert system agreed with the consensus reading in 84% (101/120) of nonobstructed kidneys, in 92% (33/36) of obstructed kidneys, and in 45% (13/29) of equivocal kidneys. The weighted kappa between the expert system and the consensus reading was 0.72 and was comparable with the weighted kappa between experts. There was no significant difference in the areas under the ROC curves when the expert system was compared with each expert using the other 2 experts as the gold standard. CONCLUSION: The renal expert system showed good agreement with the expert interpretation and could be a useful educational and decision support tool to assist physicians in the diagnosis of renal obstruction. To better mirror the clinical setting, algorithms to incorporate clinical data must be designed, implemented, and tested.     

Volume expanded diuretic renography in the postnatal assessment of suspected uretero-pelvic junction obstruction.

Controversy surrounds the role of 99mTc-diethylenetriamine pentaacetic acid renography in suspected uretero-pelvic junction obstruction in early life. Accordingly, we retrospectively reviewed 18 patients (28 hydronephrotic kidneys) with a mean age of 2 mo (range: 1 wk-6 mo) who underwent a total of 36 scans using intravenous volume expansion (10 ml/kg) and furosemide diuresis (1 mg/kg). Initial scans were classified as obstructed, not obstructed or indeterminate using differential renal function, furosemide washout T 1/2 and visual assessment of tracer clearance. Those initially classified as obstructed (n = 8) have been surgically confirmed. In the indeterminate (n = 6) and nonobstructed (n = 14) groups, three and two kidneys, respectively, developed obstruction on progress scans. Mean follow-up in the nonsurgical patients was approximately 9 mo (range: 4-17 mo). A total of 13 kidneys had developed obstruction by renographic criteria, and to date 12 have surgical confirmation. Our data indicate that: (1) scans classified as obstructed correlate well with surgery; (2) an initial classification of indeterminate or nonobstructed does not exclude later development of obstruction; and (3) serial scans correctly stratify children with possible uretero-pelvic junction obstruction.     

Increasing the dose of furosemide in patients with azotemia and suspected obstruction

Diuresis renography is widely used to distinguish obstructed from nonobstructed kidneys; however, the delivery of furosemide to its site of action in the loop of Henle is impaired in patients with azotemia. Consequently, the standard adult dose of 40 mg furosemide could be insufficient to generate an adequate diuretic response. This problem is illustrated by a patient with azotemia with bilateral nephrostomies who underwent Tc-99m MAG3 (mercaptoacetyltriglycine) diuresis renography with 40 mg furosemide to determine if his bilateral ureteral obstruction had resolved. The study showed findings typical for obstruction despite the fact that the patient could not have been obstructed because the nephrostomy tubes had not been clamped. When the study was repeated 6 days later with 80 mg furosemide and clamped nephrostomy tubes, there was good drainage bilaterally excluding obstruction. The nephrostomy tubes were removed and the patient's creatinine has subsequently remained stable for 3 years. In summary, this report illustrates the rationale for increasing the dose of furosemide in patients with azotemia referred for diuresis renography and shows how increasing the dose of furosemide could improve the diuretic response and minimize false-positive or indeterminate results.     

F+0 diuresis renography in infants and children.

The purpose of this study was to evaluate the feasibility of modifying diuresis renography by the simultaneous administration of 99mTc-mercaptoacetyltriglycine (MAG3) and furosemide in the investigation of hydronephrosis and hydroureteronephrosis in infants and children. Two parameters were assessed: the diuretic response in normal kidneys and the ability of the F+0 study to differentiate between renal obstruction and nonobstruction and to identify the level of obstruction in cases of renal obstruction. METHODS: Seventy-two patients (48 males, 24 females; age 2 d to 7 y; median age 6 wk) with sonographic diagnoses of hydronephrosis or hydroureteronephrosis were reviewed prospectively over a 3-y period. All patients had prior sonographic studies and micturating cystourethrography. Bladder catheterization was not routinely performed and was undertaken only if the child had suspected vesicoureteric junction (VUJ) obstruction or grade II or more vesicoureteric reflux. A weight-adjusted dose of 99mTc-MAG3 (maximum 200 MBq, minimum 20 MBq) and 1 mg/kg of furosemide (maximum 40 mg) were administered intravenously at the same time. Posterior imaging of the kidneys and bladder was performed for 20 min and followed by gravity-assisted drainage or imaging after voiding. All patients were followed-up for 6-12 mo, and the final diagnoses were based on either surgery or conservative management with repeated sonography or follow-up 99mTc-MAG3 studies (or both). The results of the F+0 diuresis renography were then compared with the final diagnoses. RESULTS: A renal unit was defined as a kidney and its ureter. There were 151 renal units with 1 patient having bilateral duplex kidneys, 6 patients having unilateral duplex kidneys and 1 patient having a solitary kidney. Fifty-five normal renal units and 96 abnormal renal units on the basis of sonographic findings were assessed. The furosemide clearance half-time for the 55 normal renal units was 1.3-6.3 min (mean 3.8 min). Of the 96 abnormal renal units, 53 were classified as nonobstructed and 43 were classified as obstructed. Of the 53 renal units classified as nonobstructed, there were 48 true-negative studies and 5 false-negative studies; of the 43 renal units classified as obstructed, there were 40 true-positive studies and 3 false-positive studies. The sensitivity was 88.9%, specificity was 94.1% and accuracy was 91.7%. The level of obstruction, either pelviureteric junction or VUJ, was also correctly identified. CONCLUSION: F+0 diuresis renography shows excellent diuretic responses in normal kidneys and is a valid method for the investigation of hydronephrosis and hydroureteronephrosis in infants and children.     

MAG3-F0 scintigraphy in decision making for emergency intervention in renal colic after helical CT positive for a urolith.

Patients with renal colic are evaluated with clinical, laboratory, and imaging methods for stratification for emergency decompression, medical treatment, or discharge and follow up. The current standard practice is heavily based on unenhanced helical CT for detecting uroliths. However, the presence of a urolith does not necessarily mean that the kidney is obstructed and requires emergency decompression. In this study, technetium-mercaptoacetyltriglycine (MAG3) diuretic scintirenography was used to detect obstruction in patients with renal colic. The contribution of this test to patient management after positive findings from helical CT was also studied. METHODS: Diagnostic criteria were established on the basis of previous experience with 60 patients who had renal colic and had undergone radiography of the kidneys, ureters, and urinary bladder (KUB) and diuretic Tc-MAG3 scintirenography and were followed up to correlate scintigraphic findings with clinical outcome. Subsequently, 80 patients with renal colic underwent scintigraphy within 12 h of presentation in the emergency room, after abdominal helical CT showed findings positive for calculus and suggestive of obstruction. After therapeutic oral or intravenous hydration and analgesics, diuretic dynamic renal scintigraphy (flow, function, delayed imaging) was performed after intravenous injections of 10 mCi (370 MBq) 99mTc-MAG3 and 40 mg furosemide (at zero time, or F0). Results were available soon after completion of the study and were considered in patient management. Four characteristic patterns of scintirenography, essential in patient stratification and treatment, had been standardized and were used for interpretation of the studies: the unobstructed kidney; the partially obstructed kidney, proximally or distally obstructed, with mild to severe obstruction and impairment of function; the totally obstructed kidney, with arrested renal function; and the unobstructed but dysfunctioning kidney after decompression, or stunned kidney. RESULTS: Among the 80 patients with positive helical CT findings, 56.5% were found to have obstruction by scintigraphy (32.5% partially, 24% completely); the remaining 43.5% did not have obstruction (21% without an indication of recent obstruction and 22.5% with stunned kidneys after spontaneous decompression). Occasionally, findings of preexistent urine extravasation or infection were present. Patients who, by scintigraphy, never had obstruction or had experienced spontaneous decompression did not require admission or emergency intervention; those with complete or severe obstruction required admission and decompression for relief of pain or restoration of function, whereas those with mild obstruction were treated variably with forced fluids, analgesics, or, less frequently, elective surgery. Outcome information from clinical examination, imaging, and interventional findings indicated that this stratification was successful. The test caused no side effects. CONCLUSION: For renal colic, clinical selection, KUB radiography, and even positive helical CT findings were all found to have a low positive predictive value for obstruction (in this study, 35%, 32%, and 56% respectively). Anatomic studies, including helical CT, should be followed by diuretic MAG3-F0 scintirenography to diagnose and quantify or exclude obstruction, detect spontaneous decompression, and appropriately stratify patients for emergency intervention, observation and medical therapy, or further work-up and discharge with referral to the clinic.     

The absent kidney in 99Tcm-MAG3 renogram: a dramatic reversible consequence of contrast nephrotoxicity superimposed on renal obstruction

99Tcm-mercaptoacetyltriglycine (MAG3) renogram is a robust imaging technique used to delineate upper urinary tract obstruction. The changes observed on the renogram are often reversible on relief of obstruction. We present two cases illustrating the extreme consequence of contrast nephrotoxicity on pre-existing obstructed kidneys. In one case, this led to severe impairment of perfusion and uptake observed on 99Tcm-MAG3 renogram and in the second case virtual non-visualization of the obstructed kidney. Subsequent treatment of obstruction, led to dramatic improvement in renal function. It is important for clinicians, nuclear medicine physicians and radiologists to be aware of the potential of contrast nephrotoxicity in obstructed kidneys.     

Renal vein Doppler sonography of obstructive uropathy

OBJECTIVE: Obstructive uropathy in the early stages can be difficult to diagnose using either standard sonography or the arterial resistive index. We tested the hypothesis that acute obstruction of the renal collecting system reduces the intraparenchymal renal compliance, which affects the intraparenchymal venous blood flow to a greater degree than the arterial flow. SUBJECTS AND METHODS: Twelve patients with clinical evidence of acute obstructive uropathy were referred for helical CT to confirm the diagnosis and to provide a gold standard by which we could evaluate the sonographic findings in the 12 test patients. Twelve patients without renal disease served as a control group. Doppler sonography of the interlobar arteries and veins of both kidneys then was performed, with the sonographer unaware of which kidney had an obstruction. Peak venous flow measurements and arterial resistive and venous impedance indexes were obtained. The impedance indexes of the obstructed and unobstructed kidney were compared for each patient. RESULTS: The mean arterial resistive indexes of the obstructed kidneys were larger than those of the unobstructed kidneys, 0.67 +/- 0.08 and 0.62 +/- 0.05, respectively (p = 0.05). The venous impedance indexes comparing obstructed and unobstructed sides were 0.38 +/- 0.25 and 0.80 +/- 0.25, respectively, a statistically significant result (p = 0.0002). On average, the peak venous flow signal in the obstructed kidney was 69% higher than that of the unobstructed kidney (p = 0.04) and 86% higher than that of the peak venous flow signal in the control group (p = 0.005). CONCLUSION: Renal obstruction alters the venous flow to a greater extent than the arterial flow, and a comparison between the venous flow in the obstructed and unobstructed kidneys may improve diagnostic accuracy.     

Quantitative SPECT of 99mTc-DMSA uptake in kidneys of infants with unilateral ureteropelvic junction obstruction: assessment of structural and functional abnormalities.

We evaluated individual renal function using quantitative SPECT of dimercaptosuccinic acid (DMSA) uptake by the kidneys (QDMSA) in infants with unilateral ureteropelvic junction (UPJ) obstruction and compared our findings with infants without obstruction. METHODS: QDMSA was performed on 13 infants (mean age of 2.8 +/- 2.8 mo) with unilateral UPJ obstruction and on 15 age-matched controls without obstruction. RESULTS: Control kidneys (n = 30) had a volume of 43.5 +/- 8.8 mL, a percentage injected dose (%ID)/mL 0.62 +/- 0.12 and uptake of 26.1% +/- 3.9%. Kidneys with UPJ obstruction (n = 13) had a volume of 61.2 +/- 19.3 mL, a %ID/mL of 0.42 +/- 0.11 and uptake of 25.4% +/- 8.2%. Contralateral kidneys (n = 13) had a volume of 44.0 +/- 11.9 mL, a %ID/mL of 0.57 +/- 0.16 and uptake of 24.2% +/- 4.6%. The uptake in obstructed kidneys was similar to that observed in contralateral and control kidneys (t = -0.77, P = 0.45; t = -0.37, P = 0.71; respectively). UPJ kidneys had a statistically significant increased volume and decreased %ID/mL, compared with contralateral kidneys (t = 3.35, P < 0.006 and t = 3.75, P < 0.003, respectively) and control kidneys (t = -4.2, P < 0.001 and t = 4.7, P < 0.001, respectively). There was no significant difference between contralateral kidneys and control kidneys regarding volume (t = -0.16, P = 0.87), %ID/mL (t = 0.98, P = 0.33) and uptake (t = -1.41, P = 0.16). Of 13 infants, 11 (85%) showed large kidneys with thinning of the renal cortex. In 1 infant, there was no difference between the obstructed and contralateral kidneys regarding volume, %ID/mL and uptake, and 1 infant showed significant decreased uptake in the UPJ kidney compared with the contralateral kidney. CONCLUSION: Although the overall renal function of the obstructed kidneys remained unchanged, there was a statistically significant decrease in the %ID/mL of renal tissue in UPJ kidneys, which may represent renal dysfunction. Increased functional volume with a thin cortex may represent a compensatory mechanism of the obstructed kidney. Such changes may contribute to the understanding of pathophysiologic mechanisms and may be an early sign of obstruction in infants with hydronephrosis. Further longitudinal studies with an extended number of infants and serial measurements of kidney volumes and %ID/mL are warranted to assess the significance of QDMSA in the management of infants with asymptomatic unilateral renal pelvic dilatation.     

Renal transplant pyelocaliectasis: role of duplex Doppler US in evaluation

To distinguish the obstructed from the nonobstructed dilated collecting system of transplanted kidneys without interventional diagnostic measures, the authors prospectively evaluated duplex Doppler analysis (determination of resistive index [RI]) in 35 renal transplant patients with pyelocaliectasis. Proof of the presence or absence of obstruction was obtained at interventional procedures in 18 patients and at clinical follow-up in 17. Thirteen kidneys were obstructed (mean RI, .81 +/- .06), while 22 had nonobstructive dilatation (mean RI, .66 +/- .07). The RI difference was statistically significant (P less than or equal to .01). Of 21 kidneys with a normal RI, only two had obstruction. In both of these, the obstruction was associated with a significant peritransplant collection of fluid due to a ureteral leak. In the seven obstructed transplanted kidneys with follow-up, the mean RI was .82 +/- .06 before nephrostomy and .67 +/- .05 after nephrostomy. Obstruction was a common cause of an elevated RI (greater than or equal to .75). Other causes of transplant dysfunction can be associated with an elevated RI and nonobstructed dilatation. More important, a normal RI should strongly argue against obstruction unless a ureteral leak is also present.     

Renal transit time with MR urography in children

PURPOSE: To prospectively evaluate use of dynamic contrast material-enhanced magnetic resonance (MR) urography for measurement of renal transit time (RTT) of a contrast agent through the kidney and collecting system so as to identify obstructive uropathy in children. MATERIALS AND METHODS: One hundred twenty-six children suspected of having hydronephrosis were hydrated prior to undergoing both conventional and dynamic contrast-enhanced MR urography of the kidneys and urinary tract. A three-dimensional sequence was used to track passage of contrast agent through the kidneys. Time between the appearance of contrast material in the kidney and its appearance in the ureter at or below the level of the lower pole of the kidney was defined as RTT. Bland-Altman plots were used to quantify intra- and interobserver performance. In 30 children, a nuclear medicine renogram was also obtained, and the half-life of renal signal decay after furosemide administration was derived and compared with the MR imaging RTT by using receiver operating characteristic curves. RESULTS: On the basis of RTT, kidneys were classified as normal (RTT RTT 490 seconds). Inter- and intraobserver agreement indicated that the technique is both robust and reproducible. Receiver operating characteristic analysis for comparison of results of MR imaging and diuretic renal scintigraphy showed good agreement between the modalities, with a mean area under the curve of 0.90. CONCLUSION: When used in conjunction with morphologic images obtained in the same examination, RTT generally allowed normal kidneys to be differentiated from obstructed and partially obstructed kidneys.     

Diuresis renography. A simultaneous comparison between 131I-hippuran and 99Tcm-MAG3

In 20 patients investigated for unilateral upper urinary tract obstruction diuresis renography was performed simultaneously with 131I-hippuran and 99Tcm-MAG3 using a gamma camera with dual isotope facilities. Furosemide was administered routinely 20 min after radionuclide injection. No significant differences were found in fractional share between the two kidneys, time to maximal activity, residual activity at 20 and 30 min, or rate of emptying after furosemide administration. The MAG3 curves showed, however, better counting statistics and on scintigrams with MAG3 more anatomic details (extent of dilation and site of obstruction) could be seen. It is concluded, that MAG3 is superior to hippuran in the evaluation of patients with possible unilateral upper urinary tract obstruction by diuresis renography.     

Renal Doppler ultrasound examination of ureteral obstruction in rabbits: effects of different sites and degrees of obstruction on renal resistive index

RATIONALE AND OBJECTIVES: We sought to investigate the usefulness of Doppler resistive index (RI) in the diagnosis and follow-up of obstructive uropathy of different degrees and different sites of obstruction. METHODS: Forty-six rabbits were classified as follows: group I, partial unilateral obstruction of the proximal ureter (n = 16); group II, complete unilateral obstruction of the proximal ureter (n = 17); group III, complete unilateral obstruction of the distal ureter (n = 13). The RI of the obstructed and contralateral kidneys was measured preoperatively and postoperatively 1 hour, 6 hours, 1 day, 3 days, 1 week, 2 weeks, and 4 weeks, respectively. In each group, the RI was analyzed for statistical differences in the preoperative versus postoperative kidneys, and the obstructed versus contralateral kidneys. We also analyzed the statistical differences in RIs of the obstructed kidneys, in interrenal RI differences (DeltaRI: RI of the obstructed kidney - RI of the contralateral kidney), and in RI ratio (RI of the obstructed kidney / RI of the contralateral kidney) between the 3 groups. RESULTS: The RIs in the obstructed versus contralateral kidneys were significantly increased (P < 0.05) postoperatively at 1 hour, 1 day, and 2 weeks in group I; 6 hours and 1 week in group II; and 1 hour, 6 hours, and 3 days in group III. In obstructed kidneys, the RIs in the postoperative versus preoperative kidneys were significantly increased (P < 0.05) from 1 hour to 2 weeks in group I and from 1 hour to 4 weeks in group II. There were no statistically significant differences in mean RI, DeltaRI, and RI ratio between the 3 groups during the preoperative and postoperative period. CONCLUSIONS: Doppler RI can be elevated in hydronephrotic kidney as a result of both partial and complete obstruction of the ureter. There are no RI differences among obstructed kidneys with different degree and different site of ureteral obstruction.     

Diuretic renography with the addition of quantitative gravity-assisted drainage in infants and children.

The aim of this study was to evaluate the use of quantitative gravity-assisted drainage (GAD) using >50% residual activity as an indicator to confirm obstruction in diuretic renography in the investigation of hydronephrosis and hydroureteronephrosis in infants and children. This was evaluated in 2 groups: furosemide clearance half-time (t 1/2) > 20 min (obstructed range) and t 1/2 = 10-20 min (indeterminate range). METHODS: Two hundred children (155 boys, 45 girls; age range, 2 d to 16 y; median age, 26 wk) were studied over a 2-y period. One hundred thirty-five F+20 (diuretic given 20 min after radiopharmaceutical) and 65 F+0 (simultaneous administration of diuretic and radiopharmaceutical) studies were performed with intravenous administration of 99mTc-mercaptoacetyltriglycine (MAG3) and furosemide. At the end of the 20-min diuretic phase, a 5-min post-GAD image was obtained, and the percentage of residual activity was calculated by comparison with the last 5 min of the diuretic phase. All patients were monitored for 6-12 mo, and the final diagnoses were based on either surgical findings or conservative management with follow-up sonography or 99mTc-MAG3 studies. Results of the diuretic renography using quantitative GAD were then compared with the final diagnoses. RESULTS: A renal unit was defined as a kidney and its ureter. In the 200 patients studied, 256 hydronephrotic renal units were analyzed: 10 units showed no function, 1 unit showed poor function, 131 units had t 1/2 < 10 min, 62 units had t 1/2 > 20 min, and 52 units had t 1/2 = 10-20 min. Of the 131 renal units with t 1/2 < 10 min, there was only 1 case of obstruction. Using GAD > 50% residual activity for the diagnosis of obstruction in 62 renal units with t 1/2 > 20 min, the sensitivity was 88.4%, the specificity was 73.7%, and the accuracy was 83.9%. Similarly, using GAD > 50% residual activity for the diagnosis of obstruction in 52 units with t 1/2 = 10-20 min, the sensitivity was 100%, the specificity was 79.5%, and the accuracy was 82.7%. CONCLUSION: The quantitation of GAD > 50% residual activity in diuretic renography can help to differentiate between obstruction and nonobstruction in renal units with t 1/2 > 20 min and t 1/2 = 10-20 min. The quantitation of GAD when t 1/2 < 10 min is not useful because obstruction has already been excluded.     

磁共振尿路成像技术的临床应用(附60例分析)

目的探讨磁共振尿路成像的检查技术及临床应用价值。方法采用快速自旋回波（ＦＳＥ）、重Ｔ２ＷＩ技术以及口服利尿剂、钆喷酸葡胺稀释液、腹部加压等方法对５５例病人和５例健康志愿者行磁共振尿路成像（ＭＲｕｒｏｇｒａｐｈｙ，ＭＲＵ）。结果检查６０例，ＭＲＵ＋ＭＲＩ阳性５６例，ＭＲＵ对尿路梗阻的显示，尤其对静脉尿路造影（ＩＶＵ）不能显影者效果良好，与常规ＭＲＩ结合在揭示病变和尿路梗阻之间的关系方面有独到之处。结论ＭＲＵ能显示尿路梗阻部位、程度，与ＭＲＩ结合能更清晰地诊断尿路梗阻的病因。ＭＲＵ将成为诊断泌尿系疾病的一种新型无创性影像学手段。     

Renal blood flow in pigs: changes depicted with contrast-enhanced harmonic US imaging during acute urinary obstruction.

PURPOSE: To evaluate contrast agent-enhanced harmonic ultrasonographic (US) imaging and Doppler hemodynamics during acute urinary obstruction. MATERIALS AND METHODS: In 12 piglets, the distal ureter was obstructed for 60 minutes, followed by intravenous injection of furosemide. In six piglets, ureteral pressure was further elevated to mean arterial pressure, and in six other piglets ureteral obstruction was released. Contrast-enhanced harmonic imaging was performed, and interlobar resistive index (RI) and renal blood flow were determined at baseline and during each experimental condition. A bolus injection curve was constructed by plotting mean pixel intensity versus time, and the area under this normalized curve was compared with renal blood flow values. RESULTS: Ureteral obstruction and high ureteral pressure reduced cortical renal blood flow to 88% and 66%, respectively, of baseline values. Administration of contrast agent resulted in marked homogeneous enhancement of the renal cortex. The area under the curve diminished during ureteral obstruction and correlated well with mean cortical blood flow. RI correlated well with renal perfusion pressure but poorly with changes in renal blood flow. CONCLUSION: Contrast-enhanced harmonic US imaging depicts changes in renal blood flow during acute obstruction. Interlobar RI is a good predictor of renal perfusion pressure but not of changes in renal blood flow.     

99Tcm-mercapto acetyl triglycine in paediatric renal tract disease.

The use of 99Tcm-mercapto acetyl triglycine (99Tcm-MAG3), a new hippuran substitute, has been reported widely in adults but not in children. Our experience of its use in 100 infants and children for renography and indirect micturating cystography (IMC) is reported. The average age was 5.6 years. 65 patients completed IMC studies and nine patients had 99Tcm-dimercaptosuccinic acid (99Tcm-DMSA) scans performed on the same day. The majority of patients were referred for the investigation of urinary tract infection. 32 kidneys were found to be scarred on 99Tcm-MAG3 scans, 17 kidneys and ureters refluxed on IMC and 14 kidneys were obstructed. The results of 99Tcm-MAG3 scans were compared with those of other urinary tract investigations including ultrasound, micturating cystography (MCUG), intravenous urography (IVU) and 99Tcm-DMSA scintigraphy. No kidney which was scarred had a normal 99Tcm-MAG3 scan. All significant degrees of dilatation or obstruction on IVU or ultrasound were also detected by 99Tcm-MAG3. 99Tcm-MAG3 gave more information than any other single imaging modality and we believe it represents an ideal initial screening test in the investigation of urinary tract infection in older toilet-trained children.     

Evaluation of dilated upper renal tracts by technetium-99m ethylenedicysteine f+0 diuresis renography in infants and children

AIM: To evaluate the feasibility of modifying diuresis renography by the simultaneous administration of Tc-99m ethylenedicysteine and furosemide in the investigation of hydronephrosis and hydroureteronephrosis in infants and children. Parameters assessed were the diuretic response in normal kidneys and the ability of the F+0 study to differentiate between renal obstruction and nonobstruction. METHODS: One hundred and thirty-three children (93 males, 40 females; mean age 35.2 months) with sonographic diagnoses of hydronephrosis or hydroureteronephrosis underwent F+0 diuresis renography. Tc-99m ethylenedicysteine (3.7 MBq/kg body weight) and furosemide at an appropriate dose were administered intravenously at the start of the study. Posterior imaging of the kidneys and bladder was performed for 20 min followed by imaging after voiding. All patients were followed-up for 12 months, and the results of the initial F+0 diuresis renography were compared with the final diagnoses. Final diagnosis was based on the pediatric urologist's decision of either surgery or conservative management. RESULTS: A renal unit was defined as a kidney and its ureter. There were 262 renal units with 4 patients having a solitary kidney. 90 normal and 172 abnormal renal units on sonography were assessed by F+0 diuresis renography. The furosemide clearance half time for the 90 normal renal units was 5.8 +/- 1.4 min. Of the 172 abnormal renal units, 100 were classified as nonobstructed and 72 as obstructed on diuresis renography. All 100 nonobstructed renal units were correctly classified with no false-negative studies; of the 72 renal units classified as obstructed, there were 43 true-positive studies and 29 false-positive studies. The sensitivity was 100%, specificity was 78% and accuracy was 83%. CONCLUSION: Tc-99m ethylenedicysteine F+0 diuresis renography is a valid method for the investigation of hydronephrosis and hydroureteronephrosis in infants and children.