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.     

A software engine to justify the conclusions of an expert system for detecting renal obstruction on 99mTc-MAG3 scans.

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.     

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.     

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.     

Unenhanced urinary CT: value of parenchymal attenuation measurements in differentiating acute vs. chronic renal obstruction

Objective

We aimed to search if the renal parenchymal attenuation measurements on unenhanced CT scans could be useful in differentiating acutely obstructed kidneys from chronic cases or unobstructed kidneys.

Material and methods

Unenhanced CT scans of 101 patients were retrospectively reviewed. Thirty-two patients with unilateral acute renal obstruction, 34 patients with unilateral chronic renal obstruction due to various reasons and 35 control subjects were included in the study. The parenchymal densities of both kidneys were measured, from the upper poles, middle portions, and lower poles of each kidney. The mean parenchymal densities of both kidneys were calculated in all three groups of subjects. Secondary signs of renal obstruction such as perinephric stranding, size of ureteral stone, degree of hydronephrosis were also noted for each kidney.

Results

The mean parenchymal attenuation value on the acutely obstructed side was lower than the unobstructed side, 24.21 ± 3.68 and 30.68 ± 4.75 respectively (p < 0.001). The mean parenchymal attenuation value on the acutely obstructed side (24.21 ± 3.68) was lower than both the chronically obstructed side (30.85 ± 4.53), and the control subjects (29.62 ± 3.03 on corresponding side). There was no statistically significant attenuation difference between right and left kidneys in the control group and chronic obstruction group.

Conclusion

Renal parenchymal attenuation measurements and attenuation differences of both kidney of same patient could be useful in differentiating acute unilateral obstruction from chronic cases.     

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.     

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.     

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.     

Quantitative elastography of renal transplants using supersonic shear imaging: a pilot study

Purpose

To evaluate the reliability of quantitative ultrasonic measurement of renal allograft elasticity using supersonic shear imaging (SSI) and its relationship with parenchymal pathological changes.

Materials and methods

Forty-three kidney transplant recipients (22 women, 21 men) (mean age, 51?years; age range, 18–70?years) underwent SSI elastography, followed by biopsy. The quantitative measurements of cortical elasticity were performed by two radiologists and expressed in terms of Young’s modulus (kPa). Intra- and inter-observer reproducibility was assessed (Kruskal-Wallis test and Bland-Altman analysis), as well as the correlation between elasticity values and clinical, biological and pathological data (semi-quantitative Banff scoring). Interstitial fibrosis was evaluated semi-quantitatively by the Banff score and measured by quantitative image analysis.

Results

Intra- and inter-observer variation coefficients of cortical elasticity were 20?% and 12?%, respectively. Renal cortical stiffness did not correlate with any clinical parameters, any single semi-quantitative Banff score or the level of interstitial fibrosis; however, a significant correlation was observed between cortical stiffness and the total Banff scores of chronic lesions and of all elementary lesions (R?=?0.34, P?=?0.05 and R?=?0.41, P?=?0.03,respectively).

Conclusion

Quantitative measurement of renal cortical stiffness using SSI is a promising non-invasive tool to evaluate global histological deterioration.

Key Points

? Supersonic shear imaging elastography can measure cortical stiffness in renal transplants ? The level of cortical stiffness is correlated with the global degree of tissue lesions ? The global histological deterioration of transplanted kidneys can be quantified using elastography     

Diffusion-weighted MR imaging findings of kidneys in patients with early phase of obstruction

Background

Diffusion-weighted (DW) magnetic resonance (MR) imaging is an MR technique used to show molecular diffusion. The apparent diffusion coefficient (ADC), as a quantitative parameter calculated from the DW MR images. The purpose of this study is to evaluate the ability of DW MR imaging in early phase of obstruction due to urolithiasis.

Materials and methods

Twenty-six patients with acute dilatation of the pelvicalyceal system detected by intravenous urography were included in this study. MR imaging was performed using a 1.5 T whole-body superconducting MR scanner. DW imaging can be performed using single-shot spin–echo, echo-planar imaging (EPI) sequences with the following diffusion gradient b values: 100, 600, 1000 s/mm². Circular region of interest (ROI) was placed in the renal parenchyma for the measurement of ADC values in the normal and obstructed kidney. For statistical analyses, Paired t test were used.

Results

In spite of obstructed kidneys had the lower ADC values compared to normal kidneys, these alterations were statistically insignificant.

Conclusion

We did not observe significantly different ADC values of early phase of obstructed kidneys compared to normal kidneys.     

Morphological measurements in computed tomography correlate with airflow obstruction in chronic obstructive pulmonary disease: systematic review and meta-analysis

Objectives

To determine the correlation between CT measurements of emphysema or peripheral airways and airflow obstruction in chronic obstructive pulmonary disease (COPD).

Methods

PubMed, Embase and Web of Knowledge were searched from 1976 to 2011. Two reviewers independently screened 1,763 citations to identify articles that correlated CT measurements to airflow obstruction parameters of the pulmonary function test in COPD patients, rated study quality and extracted information. Three CT measurements were accessed: lung attenuation area percentage?1 %pred) and FEV₁ divided by the forced volume vital capacity.

Results

Seventy-nine articles (9,559 participants) were included in the systematic review, demonstrating different methodologies, measurements and CT airflow obstruction correlations. There were 15 high-quality articles (2,095 participants) in the meta-analysis. The absolute pooled correlation coefficients ranged from 0.48 (95?% CI, 0.40 to 0.54) to 0.65 (0.58 to 0.71) for inspiratory CT and 0.64 (0.53 to 0.72) to 0.73 (0.63 to 0.80) for expiratory CT.

Conclusions

CT measurements of emphysema or peripheral airways are significantly related to airflow obstruction in COPD patients. CT provides a morphological method to investigate airway obstruction in COPD.

Key Points

? Computed tomography is widely performed in patients with chronic obstructive pulmonary disease (COPD) ? CT provides quantitative morphological methods to investigate airflow obstruction in COPD ? CT measurements correlate significantly with the degree of airflow obstruction in COPD ? Expiratory CT measurements correlate more strongly with airflow obstruction than inspiratory CT ? Low-dose CT decreases the radiation dose for diagnosis and quantitative emphysema evaluation     

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.     

Quantitative sodium MR imaging of native versus transplanted kidneys using a dual-tuned proton/sodium (1H/23Na) coil: initial experience

Objectives

To compare sodium (²³Na) characteristics between native and transplanted kidneys using dual-tuned proton (¹H)/sodium MRI.

Methods

Six healthy volunteers and six renal transplant patients (3 normal function, 3 acute allograft rejection) were included. Proton/sodium MRI was obtained at 3 T using a dual-tuned coil. Signal to noise ratio (SNR), sodium concentration ([²³Na]) and cortico-medullary sodium gradient (CMSG) were measured. Reproducibility of [²³Na] measurement was also tested. SNR, [²³Na] and CMSG of the native and transplanted kidneys were compared.

Results

Proton and sodium images of kidneys were successfully acquired. SNR and [²³Na] measurements of the native kidneys were reproducible at two different sessions. [²³Na] and CMSG of the transplanted kidneys was significantly lower than those of the native kidneys: 153.5?±?11.9 vs. 192.9?±?9.6 mM (P?=?0.002) and 8.9?±?1.5 vs. 10.5?±?0.9 mM/mm (P?=?0.041), respectively. [²³Na] and CMSG of the transplanted kidneys with normal function vs. acute rejection were not statistically different.

Conclusions

Sodium quantification of kidneys was reliably performed using proton/sodium MRI. [²³Na] and CMSG of the transplanted kidneys were lower than those of the native kidneys, but without a statistically significant difference between patients with or without renal allograft rejection.

Key Points

? Dual-tuned proton/sodium RF coil enables co-registered proton and sodium MRI. ? Structural and sodium biochemical property can be acquired by dual-tuned proton/sodium MRI. ? Sodium and sodium gradient of kidneys can be measured by dual-tuned MRI. ? Sodium concentration was lower in transplanted kidneys than in native kidneys. ? Sodium gradient of transplanted kidneys was lower than for native kidneys.     

Renal obstruction in patients with ileal loops: US evaluation

Ultrasound (US) is often employed as a screening test for hydronephrosis in the nondiverted kidney and has been used recently to evaluate the diverted kidney, specifically ileal loops, for obstruction. The utility of US in evaluating obstruction in patients with ileal loops has apparently not been previously explored. During a 2-year period, 87 kidneys drained by an ileal loop diversion were examined with US because of clinical indications of possible renal obstruction. In 33 kidneys, no hydronephrosis was seen on sonograms, and no obstruction was later proved; in 51 kidneys, shown by US to be hydronephrotic, only 19 (37%) were obstructed. Three left kidneys were not visualized with US. The percentage of hydronephrotic kidneys subsequently shown to be obstructed increased rapidly as the US appearance progressed from grade 1 (20%) to grade 3 (80%). In this series, US had a 100% sensitivity and a 50% specificity in evaluating patients with ileal loops for renal obstruction. Thus, for the adult patient, a direct contrast evaluation of the collecting system is suggested; for the pediatric patient, initial use of US is justified as a means to avoid radiation exposure.     

Diffusion tensor imaging and tractography of the kidneys: assessment of chronic parenchymal diseases

Objective

To assess renal dysfunction in chronic kidney diseases using diffusion tensor imaging (DTI).

Methods

Forty-seven patients with impaired renal function (study group) and 17 patients without renal diseases (control group) were examined using DTI sequences. Cortical and medullary regions of interest (ROIs) were located to obtain the corresponding values of the apparent diffusion coefficient (ADC) and the fractional anisotropy (FA). The mean values of the ADC and FA, for each ROI site, were obtained in each group and were compared. Furthermore, the correlations between the diffusion parameters and the estimated glomerular filtration rate (eGFR) were determined.

Results

In both the normal and affected kidneys, we obtained the cortico-medullary difference of the ADC and the FA values. The FA value in the medulla was significantly lower (P?=?0.0149) in patients with renal function impairment as compared to patients with normal renal function. A direct correlation between DTI parameters and the eGFR was not found. Tractography visualised disruption of the regular arrangement of the tracts in patient with renal function alteration.

Conclusion

DTI could be a useful tool in the evaluation of chronic kidney disease and, in particular, the medullary FA value seems to be the main parameter for assessing renal damage.

Key Points

? Magnetic resonance diffusion tensor imaging (MRDTI) provides new information about renal problems. ? DTI allows non-invasive repeatable evaluation of the renal parenchyma, without contrast media. ? DTI could become useful in the management of chronic parenchymal disease. ? DTI seems more appropriate for renal evaluation than diffusion-weighted imaging.     

Acoustic radiation force impulse (ARFI) in the evaluation of the renal parenchymal stiffness in paediatric patients with vesicoureteral reflux: preliminary results

Objectives

To prospectively evaluate acoustic radiation force impulse (ARFI) imaging of the kidneys in children with and without chronic renal disease.

Methods

Twenty-eight children (age range 9–16 years) with primary or secondary vesicoureteral reflux (≥ grade III) underwent scintigraphy and ultrasound with ARFI. Kidneys were divided—according to scintigraphy—into “affected” and “contralateral”; the results were compared with 16 age-matched healthy subjects. An ARFI value, expressed as speed (m/s) of wave propagation through the tissue, was calculated for each kidney through the mean of the values obtained at the upper, middle and lower third. The Wilcoxon test was used; P values <0.05 were considered statistically significant.

Results

The mean ARFI values obtained in the “affected” kidneys (5.70?±?1.71 m/s) were significantly higher than those measured in both “contralateral” (4.09?±?0.97, P?<?0.0001) and “healthy” kidneys (3.13?±?0.09, P?<?0.0001). The difference between values in the “contralateral” kidneys and “healthy” ones was significant (P?<?0.0001). The “affected” kidneys with secondary reflux had mean ARFI values (6.59?±?1.45) significantly higher than those with primary reflux (5.35?±?1.72).

Conclusions

ARFI values decrease from kidneys with secondary vesicoureteral reflux to kidneys with primary reflux to unaffected kidneys contralateral to reflux to normal kidneys.

Key points

? Acoustic radiation force impulse (ARFI) can quantify tissue elasticity during ultrasound examinations. ? Kidneys are highly heterogeneous and difficult to evaluate with ARFI. ? Kidneys damaged by vesicoureteral reflux are stiffer than normal. ? ARFI can identify initial damage in macroscopically normal kidneys.     

Relative and absolute 99Tcm-DMSA uptake measurements in normal and obstructed kidneys

Relative and absolute 99Tcm-DMSA uptake measurements were carried out on 25 adult patients among whom there were 23 normal and 25 malfunctioning kidneys. Data were collected at 3 and 6 h post intravenous tracer injection. Four methods of calculating absolute uptake were investigated and evaluated. These were based on: (1) posterior view and measured kidney depth; (2) posterior view and Raynauld's depth; (3) geometric mean assuming kidney thickness is small enough not to introduce self attenuation of counts in the kidney itself; (4) geometric mean taking kidney thickness into account. Whilst (1) and (2) were found to overestimate and underestimate renal uptake by up to 5 and 14%, respectively, (3) and (4) were found to be more accurate and comparable. The measurement of relative DMSA uptake (right to left) showed no change between the 1 and 6 h measurements for both obstructed and non-obstructed kidneys. Based on the results from method 4, the absolute renal DMSA uptake had a mean value of 25.4%, S.D. 8.9% and 30.0%, S.D. 9.2% at 3 and 6 h, respectively, for normal/non obstructed kidneys. For obstructed kidneys (responding to frusemide), the mean uptake was 23.0%, S.D. 7.2 and 25.6%, S.D. 6.7% at 3 and 6 h, respectively. For obstructed kidneys not responding to frusemide, the mean uptake was 16.8%, S.D. 3.9 and 20.6%, S.D. 4.8% at 3 and 6 h, respectively. No correlation was found between absolute DMSA uptake and degree of renal obstruction.     

Differences of renal parenchymal attenuation for acutely obstructed and unobstructed kidneys on unenhanced helical CT: a useful secondary sign?

OBJECTIVE: The purpose of this study was to ascertain whether the difference in attenuation frequently noted on unenhanced helical CT scans between a patient's acutely obstructed kidney and the unobstructed kidney is a reliable secondary sign of acute renal obstruction. CONCLUSION: In 95% of patients with acute renal obstruction, the affected kidney was less dense than the unobstructed kidney. When visually detected by radiologists using CT, this difference in density was at least two standard deviations above normal, making it a reliable secondary sign for acute obstruction.     

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.     

MRI in patients with chronic obstructive uropathy and compromised renal function: a sole method for morphological and functional assessment

The aim of this study was to assess the role of MRI as a single modality for anatomical and functional evaluation of obstructed kidneys in patients with compromised renal function. The study included 96 adults with unilateral or bilateral chronic obstructive hydronephrosis and compromised renal function (serum creatinine >or=1.8 mg dl(-1)). Patients were subjected to gadolinium-enhanced MRI (Gd-MRI), which determined the anatomy of both renoureteral units, as well as their function, through selective calculation of the glomerular filtration rate (GFR) of each kidney. All patients underwent a technetium-99m diethylenetriamine-pentaacetic acid renal scan. Moreover, a correlation was made between the GFR determined by Gd-MRI and the isotope GFR. The study comprised 59 males and 37 females. A comprehensive MRI study detected the cause of obstruction in all kidneys with non-calcular obstruction (sensitivity of 100%) and in 21 kidneys with calcular obstruction (sensitivity of 70%). The overall sensitivity of MRI combined with plain X-ray of the abdomen and ultrasound in the detection of various causes of obstruction was 97%. A comparison between the isotope GFR of the obstructed kidneys and the corresponding magnetic resonance urography (MRU) GFR showed perfect correlation. In conclusion, combined static and dynamic MRU is a promising technique that allows anatomical and functional evaluation of obstructed kidneys in patients with impaired renal function but, owing to the possible risk of nephrogenic systemic fibrosis in patients with a GFR <30 ml min(-1), the lowest possible dose of the most stable Gd-macrocyclic chelates should be used if a functional MRI study is required.