International Scientific Committee of Radionuclides in Nephrourology (ISCORN) consensus on renal transit time measurements

Nuclear medicine and pediatric nephro-urology: a long-lasting successful partnership

Congenital anomalies of the kidney and urinary tract, as well as urinary infections, are very frequent in children. After the clinical and laboratory evaluation, the first imaging procedure to be done is a renal and bladder ultrasound, but afterwards, a main contribution comes from nuclear medicine. Through minimally invasive and sedation-free procedures, nuclear medicine allows the evaluation of the functional anatomy of the urinary tract, and the quantification of renal function and drainage. If pediatric dosage cards provided by scientific societies are used, radiation exposure can also be low. In the pediatric conditions previously mentioned, nuclear medicine is used both for initial diagnosis and follow-up, mostly in cases of suspicion of ureteropelvic or ureterovesical junction syndromes, as well as vesicoureteral reflux or renal scars of febrile infectious episodes. Pediatric nephro-urology constitutes a significant workload of pediatric nuclear medicine departments. The following paragraphs are a revision of the renal radiopharmaceuticals, as well as the nuclear nephro-urology procedures - dynamic and static renal scintigraphy, and direct and indirect radionuclide cystography. A summary of the techniques, main indications, interpretation criteria and pitfalls will be provided. Some future directions for the field are also pointed out, among which the most relevant is the need for nuclear medicine professionals to use standardized protocols and integrate multidisciplinary teams with other pediatric and adult health professionals that manage these life-long pediatric pathologies, which are recognized as an important cause of adult chronic kidney disease.

Deep learning of renal scans in children with antenatal hydronephrosis

INTRODUCTION

Antenatal hydronephrosis (ANH) is one of the most common anomalies identified on prenatal ultrasound, found in up to 4.5% of all pregnancies. Children with ANH are surveilled with repeated renal ultrasound and when there is high suspicion for a ureteropelvic junction obstruction on renal ultrasound, a mercaptuacetyltriglycerine (MAG3) Lasix renal scan is performed to evaluate for obstruction. However, the challenging interpretation of MAG3 renal scans places patients at risk of misdiagnosis.

OBJECTIVE

Our objective was to analyze MAG3 renal scans using machine learning to predict renal complications. We hypothesized that our deep learning model would extract features from MAG3 renal scans that can predict renal complications in children with ANH.

STUDY DESIGN

We performed a case-control study of MAG3 studies drawn from a population of children with ANH concerning for ureteropelvic junction obstruction evaluated at our institution from January 2009 until June of 2021. The outcome was renal complications that occur ≥6 months after an equivocal MAG-3 renal scan. We created two machine learning models: a deep learning model using the radiotracer concentration versus time data from the kidney of interest and a random forest model created using clinical data. The performance of the models was assessed using measures of diagnostic accuracy.

RESULTS

We identified 152 eligible patients with available images of which 62 were cases and 90 were controls. The deep learning model predicted future renal complications with an overall accuracy of 73% (95% confidence inteveral [CI] 68-76%) and an AUC of 0.78 (95% CI 0.7, 0.84). The random forest model had an accuracy of 62% (95% CI 60-66%) and an AUC of 0.67 (95% CI. 0 64, 0.72) DISCUSSION: Our deep learning model predicted patients at high risk of developing renal complications following an equivocal renal scan and discriminate those at low risk with moderately high accuracy (73%). The deep learning model outperformed the clinical model built from clinical features classically used by urologists for surgical decision making.

CONCLUSION

Our models have the potential to influence clinical decision making by providing supplemental analytical data from MAG3 scans that would not otherwise be available to urologists. Future multi-institutional retrospective and prospective trials are needed to validate our model.

Diuretic Renal Scintigraphy Protocol Considerations

Diuretic renal scintigraphy plays a critical diagnostic role by providing a physiologic means for differentiating between obstructive and nonobstructive hydronephrosis as well as assessing the function of the affected kidney. The exam accuracy is highly dependent upon and benefits from close attention to the protocol. This article reviews kidney anatomy and physiology, patient preparation, available radiopharmaceuticals, diuretic administration, acquisition, processing, quantification, and interpretation criteria.

Deconvolution of Tc-99m-Mercaptoacetyltriglycine Renograms with the Concomitant Use of a Sparse Legendre Polynomial Representation and the Moore-Penrose Pseudo-inverse

Objectives:

This study aimed to introduce an improved deconvolution technique for Tc-99m-mercaptoacetyltriglycine renograms based on the combination of a sparse Legendre polynomial representation and the Moore-Penrose inversion matrix (LG). This method reduces the effect of noise on the measurement of renal retention function transit time (TT).

Methods:

The stability and accuracy of the proposed method were tested using a renal database containing Monte Carlo-simulated studies and real adult patient data. Two clinical parameters, namely, split function (SF) and mean TT (meanTT), obtained with LG were compared with values calculated with the established method that combines matrix deconvolution and a three-point linear smoothing (F121) as recommended by the 2008 International Scientific Committee of Radionuclides in Nephrourology consensus on renal TT measurements.

Results:

For simulated data, the root mean square error (RMSE) between the theoretical non-noisy renal retention curve (RRC) and the results of the deconvolution methods applied to the noisy RRC were up to two times lower with LG (p<0.001). The RMSE of the reconvoluted renogram and the theoretical one was also lower for LG (p<0.001) and showed better preservation of the original signal. The SF was neither improved nor degraded by the proposed method. For patient data, no statistically significant difference was found between the SF for the LG method compared with the database values, and the meanTT better agreed with the physician’s diagnosis than the matrix or clinical software (Hermes) outputs. A visual improvement of the RRC was also observed.

Conclusion:

By combining the sparse Legendre representation of the renogram curves and the Moore-Penrose matrix inverse techniques, we obtained improved noise reduction in the deconvoluted data, leading to better elimination of non-physiological signals -as negative values- and the avoidance of the smear effect of conventional smoothing on the vascular peak, which both influenced the meanTT measurement.

Diuretic Renal Scintigraphy: The State of Practice and a Potential Opportunity for Standardization

OBJECTIVE

The aim of this study was to assess variation in diuretic renal scintigraphy (DRS) practice patterns and quantify compliance with the national guidance in a large cohort of laboratories from different institutions and practice settings across the United States.

METHODS

By means of an institutional review board-approved protocol, we extracted 107 facility-specific, adult DRS protocols and associated 174 reports from the Intersocietal Accreditation Commission database, representing all laboratories applying for genitourinary scintigraphy certification during the 2016 to 2018 accreditation cycle. From these, we assessed 40 variables regarding facilities and staffing, patient preparation, examination technique and acquisition, image processing, and reporting.

RESULTS

Review of protocols and reports demonstrates a very high degree of variability in DRS practice across the United States and suboptimal compliance with societal guidelines and practice parameters. Some of the more variable or underreported parameters include the use of patient hydration, type and dosage of radiopharmaceutical, dosage and timing of diuretic administration, quantitative parameters assessed, and report content.

CONCLUSION

There is high variability in the performance and reporting of DRS among laboratories applying for accreditation, similar to that seen in studies of other nuclear medicine examinations. The wide degree of practice variance may have a significant impact on diagnostic accuracy and patient management, with inaccurate or incomplete results. This survey impresses the need for standardization and improved quality of this important nuclear medicine examination.

Advantages of gravity-assisted diuretic renogram: F + 10 (seated position) method

INTRODUCTION

In 1978, O'Reilly introduced the diuretic renogram using the F + 20 method. Initially, the patient was examined in the seated position. A dose of 40 mg furosemide was injected intravenously 20 min following tracer injection and dynamic acquisition was prolonged for 15-20 min. In 1992, the guidelines suggested to study patients in the supine position to avoid risk of diuretic-induced hypotension and reduce patient movement. Unfortunately, equivocal findings were reported in 15-30% of cases. Side effects such as bladder fullness and disruption because of voiding were reported. Several methods had been proposed in the supine position, such as the well-tempered diuretic renogram F + 20, F - 15, F0 and F + 2, with different time in minute of diuretic administration in relation to tracer injection. However, as confirmed by many studies, there was no clear evidence suggesting superiority among these methods. We suggest using the diuretic renogram with the F ± 10(sp) method for the diagnosis of obstruction in adult patients with hydronephrosis and for the follow-up in patients who underwent a surgical treatment of the urinary tract.

METHODS

We searched all international guidelines and articles of most influential authors published from 1978 to October 2020 on diuretic renogram.

RESULTS

We selected 60 articles.

DISCUSSION

F + 10(sp) method improves patient compliance avoiding bladder fullness-related problems, without need of catheterization. It allows for a more reliable quantification of the renal output, thanks to outflow indices that are favored by gravity effects.

Renal cortical transit time in the evaluation of prenatally detected presumed pelvi ureteric junction like obstruction: A systematic review

Introduction

Differentiating nonobstructive from obstructive dilatation of the kidney is a clinical dilemma in prenatally detected hydronephrosis. Many radionuclide renogram parameters have been used to differentiate obstructed from non-obstructed units, including cortical transit time (CTT). We evaluate the role of CTT in identifying obstruction through a systematic review.

Methods

A literature search of the MEDLINE, MEDLINE In-Process, and MEDLINE Epub Ahead of Print, EMBASE, Google scholar, Pub Med, and Cochrane Library was done using key words - radionuclide renogram, CTT, parenchymal transit time, cortical transit, renography to identify articles on the subject. The identified articles were assessed for appropriateness and reviewed.

Results

The initial search yielded a total of 1583 articles, after adding the articles from references and applying the inclusion and exclusion criteria a total of 28 articles were selected. CTT showed good inter observer agreement in identifying obstruction. The use of CTT as a single parameter for determining the need for surgery and to identify those kidneys which will have functional improvement after surgery has been evaluated and has been found to be useful. CTT is best used in conjunction with ultrasonography to make clinical decisions.

Conclusion

The commonly used visual method of estimating the CTT, is a promising parameter for the evaluation of prenatally detected pelviureteric junction obstruction. Further well-designed multicenter prospective studies are needed to establish it as the most specific parameter to differentiate obstructive from nonobstructive dilatation of the pelvicalyceal system.

Renal cortical transit time as a predictor for pyeloplasty in pediatric patients with unilateral hydronephrosis

Majority of patients with unilateral hydronephrosis (HN) detected on ultrasound do not require pyeloplasty. The measurement of the cortical transit time (CTT) has been demonstrated by several authors to predict the need for patients who may require pyeloplasty. The study aimed to assess if CTT would have predicted a drop in differential renal function (DRF) in patients with unilateral HN on the affected side and to assess whether CTT would differ on the first renogram between those patients who had a pyeloplasty and those who did not have a pyeloplasty. Sixty-eight patients with at least two renograms with unilateral HN with a normal contralateral kidney were observed retrospectively. The CTT was recorded for each kidney. Renograms were processed three times to measure the DRF. The mean of the three DRF measurements was used for analysis. The mean CTT of the left and right hydronephrotic kidneys was 6.0 min and 6.7 min, respectively. The relationship between CTT and DRF as well as CTT and anterior posterior diameter in the first renogram of those patients who did not have a pyeloplasty was statistically significant (P < 0.05). In the 20 patients who had a pyeloplasty, there was a drop of more than 10% in the DRF of three patients. No significant difference was found in CTT or DRF when comparing the group who had surgery against the group who did not have surgery. The current study was unable to demonstrate in our series of patients that CTT can predict a drop in DRF in those patients who would require pyeloplasty.

Cortical transit time: understanding utility and pitfalls in children with pelviureteric junction obstruction

INTRODUCTION

Delayed cortical transit time (CTT) has been recently studied and proposed as a parameter that can predict the need for surgery in children with pelviureteric junction obstruction (PUJO).

AIM

The aim of this study was to study the change in CTT, after surgery, in children with PUJO and to correlate CTT with intrapelvic pressure of the kidney.

MATERIAL AND METHODS

A prospective study was performed, and all children who underwent pyeloplasty from January 2016 to December 2017 were included. Pre-operative and postoperative renal ultrasonography and Technetium-99m mercaptoacetyltriglycerine Tc-MAG3 renal scintigraphy were performed. Cortical transit time was measured by a visual method by two different observers. The renal intrapelvic pressure of the kidney was also measured during surgery after giving a diuretic to replicate the diuresis induced during the renal scan. The correlation was studied between the pre-operative CTT and intrapelvic pressures and between the pre-operative CTT and the renal function of the affected kidney.

RESULTS

Thirty-one children were included in the study. The median age of children who underwent surgery was 50 months (2-168). In 71% of patients, the CTT was prolonged before surgery, whereas only 22.5% had delayed CTT after surgery. The mean CTT before surgery was 226.1 ± 74.8 s and decreased to 165.4 ± 55.9 s after surgery (p= <0.001). The mean intrapelvic pressure was 21 ± 7.5 cm H₂O. There was no correlation noted between the intrapelvic pressure and the CTT. A significant negative correlation was noted between the CTT and the different renal function of the kidney.

DISCUSSION

This is the first prospective study that studies the changes in CTT after surgery. Only retrospective studies had been conducted to date which concluded that CTT was delayed in most of the patients who had been operated. It has been proposed that the prolonged CTT is due to raised pressure in the kidney secondary to obstruction. This study did not find any correlation between the pressure and CTT. The significant negative correlation between CTT and renal function also emphasizes the need to take the renal function into consideration before interpreting and using the absolute value of CTT for guiding treatment.

CONCLUSION

Cortical transit time assessment by the visual method is a useful parameter in the management of children with PUJO. There is a significant improvement in CTT after surgery.

Dynamic 2-deoxy-2[18F] fluoro-D-glucose PET/MRI in human renal allotransplant patients undergoing acute kidney injury

Patients after solid organ kidney transplantation (KTX) often suffer from acute kidney injury (AKI). Parameters as serum creatinine indicate a loss of kidney function, although no distinction of the cause and prognosis can be made. Imaging tools measuring kidney function have not been widely in clinical use. In this observational study we evaluated 2-deoxy-2[18F] fluoro-D-glucose (FDG) PET/MRI in thirteen patients after KTX with AKI as a functional assessment of the graft. Twenty-four healthy volunteers served as control. General kidney performance (GKP), initial flow (IF) and renal response function (RF) were calculated by standardized uptake values (SUV) and time activity curves (TAC). The GKP measured for the total kidney and medulla was significantly higher in healthy patients compared to patients after KTX (p = 0.0002 and p = 0.0004, respectively), but no difference was found for the GKP of the cortex (p = 0.59). The IF in KTX patients correlated with renal recovery, defined as change in serum creatinine 10 days after PET/MRI (r = 0.80, p = 0.001). With regard to the RF, a negative correlation for tubular damage was found (r = -0.74, p = 0.004). In conclusion, parameters obtained from FDG PET/MRI showed a possible predictive feature for renal recovery in KTX patients undergoing AKI.

Response evaluation of SGLT2 inhibitor therapy in patients with type 2 diabetes mellitus using 18F-FDG PET/MRI

INTRODUCTION

Inhibitors of sodium-glucose linked transporter-2 (SGLT2i) are enhancing glucose excretion in the proximal renal tubules, and thus are increasingly used to lower blood glucose levels in patients with type 2 diabetes mellitus (T2DM). The glucose analog 2-deoxy-2-(¹⁸F) fluoro-D-glucose (FDG) can be used to quantify renal function in vivo, and due to an affinity for SGLT2 could also provide information about SGLT2 transporter function. Our objectives in this study were, therefore, to assess the impact of SGLT2i on renal function parameters in patients with T2DM and identify predictive parameters of long-term response to SGLT2i using dynamic FDG positron emission tomography (PET)/MRI.

METHODS

PET FDG renal function measures such as mean transit time (MTT) and general renal performance (GRP) together with glomerular filtration rate (GFR) were determined in 20 patients with T2DM before (T2DM_baseline) and 2 weeks after initiation of therapy with SGLT2i (T2DM_SGLT2i). Additionally, dynamic FDG PET data of 24 healthy subjects were used as controls.

RESULTS

MTT in T2DM_baseline was significantly higher than in healthy controls (5.7 min vs 4.3 min, p=0.012) and significantly decreased to 4.4 min in T2DM_SGLT2i (p=0.004). GRP of T2DM_SGLT2i was higher than of T2DM_baseline (5.2 vs 4.7, p=0.02) and higher but not significantly than of healthy individuals (5.2 vs 5.1, p=0.34). Expectedly, GFR of healthy participants was significantly higher than of T2DM_baseline and T2DM_SGLT2i (122 vs 92 and 86 mL/min/1.73 m², respectively; p<0.001). The higher the GRP value in kidneys of T2DM_SGLT2i, the lower was the glycated hemoglobin level 3 months after therapy initiation.

CONCLUSION

MTT and GRP values of patients with T2DM shifted significantly toward values of healthy control 2 weeks after therapy with SGLT2i begins. GRP in T2DM_SGLT2i was associated with better long-term glycemic response 3 months after initiation of therapy.

TRIAL REGISTRATION NUMBER

NCT03557138.

Determinants of the intercept and slope of glomerular filtration rate in recipients of a live donor kidney transplant

Background

Donor kidney function is considered a critical determinant of allograft survival after live donor (LD) kidney transplantation, but its independent impact on the evolution of graft function is less well defined. The objective of this study was to dissect the relative contribution of LD kidney function to baseline estimated glomerular filtration rate (eGFR) of recipients and its decline.

Methods

In this study 91 LD kidney transplantations performed between 2007 and 2015 were included. The eGFR of donated kidneys (eGFR-dk) was calculated from total LD eGFR (eGFR-dt) based on the results of isotope nephrography. Recipient eGFR (eGFR-r) determined 6‑monthly until 36 months posttransplantation served as dependent variable in mixed linear models estimating changes in baseline allograft function (intercept) and eGFR‑r slope. Models were adjusted either for eGFR-dk or eGFR-dt, in addition to other potential confounders.

Results

Overall, unadjusted mean eGFR‑r at baseline (6 months) and its annual decline in allograft function were 56.5 mL/min/1.73 m² and −0.2 mL/min/1.73 m², respectively. In multivariate analysis, eGFR-dk impacted on baseline eGFR‑r (0.6 mL/min/1.73 m² mean estimated increase per unit; P = 0.02) but not on its slope. In the eGFR-dt-adjusted model, a marginal effect was observed for LD age (P = 0.05). Both models identified antibody-mediated rejection (ABMR) as the strongest risk factor of accelerated loss of allograft function (eGFR‑r slope: approximately −6 mL/min/1.73 m² per year; P ≤ 0.02).

Conclusion

Donor-related characteristics, most prominently the function of donated kidneys and LD age, were predictive of eGFR at baseline. The ABMR was identified as the cardinal cause of progressive deterioration of allograft function.

Interobserver reproducibility of mercaptoacetyltriglicine renography in children and adults with suspected obstruction: parameters of drainage and function calculated by International Atomic Energy Agency software

OBJECTIVE

The aim of this study was to estimate interobserver reproducibility of Tc-99m mercaptoacetyltriglycine renography in children and adults by assessing the parameters of the International Atomic Energy Agency (IAEA) software for the analysis of dynamic renal studies.

METHODS

The renograms of 65 children and 65 adults covered a wide age range, different quality of drainage, overall function and differential renal function (DRF). Three observers were processing parameters of the IAEA software. Normalized residual activity at 20 min (NORA20), NORA on the postmicturition acquisition (NORApm), PM to maximum renal count ratio (PM/max), output efficiency at 20 min (OE20), OE 20 min after diuretic stimulation (OEF + 20), whole kidney mean transit time (MTT) and DRF by integral and Rutland-Patlak were calculated by observers.

RESULTS

The overall agreement between three observers was almost perfect [the average intraclass correlation coefficient (ICC) above 0.99] in children and adults, with no significant difference between the parameters of renal drainage, transit and DRF. ICCs for all parameters were higher than 0.980 in children under 12 months, even slightly greater for PM/max and OEF+20. In children with poor/incomplete drainage and DRF below 40%, ICCs were above 0.98. In the subgroup of adults with impaired overall tubular extraction rate, level of reproducibility was almost perfect. Slightly lower but still insignificant values of ICC were presented in adults with poor/incomplete drainage.

CONCLUSION

Our results indicate an excellent interobserver reproducibility for all quantitative parameters of IAEA software in both pediatric and adult patients.

Assessment of the kidney function parameters split function, mean transit time, and outflow efficiency using dynamic FDG-PET/MRI in healthy subjects

Background

Traditionally, isotope nephrography is considered as the method of choice to assess kidney function parameters in nuclear medicine. We propose a novel approach to determine the split function (SF), mean transit time (MTT), and outflow efficiency (OE) with 2-deoxy-2-[18F]fluoro-D-glucose (FDG) dynamic positron emission tomography (PET).

Materials and methods

Healthy adult subjects underwent dynamic simultaneous FDG-PET and magnetic resonance imaging (PET/MRI). Time-activity curves (TACs) of total kidneys, renal cortices, and the aorta were prospectively obtained from dynamic PET series. MRI images were used for anatomical correlation. The same individuals were subjected to dynamic renal Technetium-99 m-mercaptoacetyltriglycine (MAG3) scintigraphy and TACs of kidneys; the perirenal background and the left ventricle were determined. SF was calculated on the basis of integrals over the TACs, MTT was determined from renal retention functions after deconvolution analysis, and OE was determined from MTT. Values obtained from PET series were compared with scintigraphic parameters, which served as the reference.

Results

Twenty-four subjects underwent both examinations. Total kidney SF, MTT, and OE as estimated by dynamic PET/MRI correlated to their reference values by r = 0.75, r = 0.74 and r = 0.81, respectively, with significant difference (p < 0.0001) between the means of MTT and OE. No correlations were found for cortex FDG values.

Conclusions

The study proofs the concept that SF, MTT, and OE can be estimated with dynamic FDG PET/MRI scans in healthy kidneys. This has advantages for patients receiving a routine PET/MRI scan, as kidney parameters can be estimated simultaneously to functional and morphological imaging with high accuracy.

Interobserver agreement on cortical tracer transit in 99mTc-MAG3 renography applied to congenital hydronephrosis

OBJECTIVE

This study aims to evaluate interobserver agreement on visual analysis of technetium-99m mercaptoacetyltriglycine (Tc-MAG3) renal tissue transit used for the evaluation of antenatal hydronephrosis.

MATERIALS AND METHODS

Thirty-eight Tc-MAG3 diuretic renograms were retrospectively collected between 1 and 31 December 2015. The 1-min reframed images were presented to four nuclear medicine consultants and to two nuclear medicine residents, one in the first year of the training program and the others in their fourth and final year. These observers were asked to classify the radiotracer cortical transit (normal/delayed) based solely on visual assessment of the images. For the interobserver agreement, modified Fleiss' kappa (κ) analysis for multiple raters was carried out. For both groups, percentages of agreement were also calculated.

RESULTS

A total of 69 kidneys were evaluated. All four nuclear medicine consultants agreed on the classification of 88.4% of the kidneys. When the agreement of at least three of the four observers was considered, the percentage of agreement reached 98.6%. The two nuclear medicine residents agreed on the classification of 69.6% of the kidneys. The modified Fleiss' κ-value was 0.88 (95% confidence interval: 0.79-0.95) for the group of nuclear medicine consultants, indicating almost perfect agreement. For the residents, it was 0.39 (95% confidence interval: 0.16-0.59), suggesting fair agreement.

CONCLUSION

Our results seem to indicate that there is an almost perfect agreement in the qualitative identification of delayed cortical transit among physicians with experience at observing renographic images.

Nuclear Medicine in Pediatric Nephro-Urology: An Overview

In the context of ante-natally diagnosed hydronephrosis, the vast majority of children with a dilated renal pelvis do not need any surgical treatment, as the dilatation resolves spontaneously with time. Slow drainage demonstrated at Tc-99m-mercaptoacetyltriglycine (MAG3) renography does not necessarily mean obstruction. Obstruction is defined as resistance to urinary outflow with urinary stasis at the level of the pelvic-ureteric junction (PUJ) which, if left untreated, will damage the kidney. Unfortunately this definition is retrospective and not clinically helpful. Therefore, the identification of the kidney at risk of losing function in an asymptomatic patient is a major research goal. In the context of renovascular hypertension a DMSA scan can be useful before and after revascularisation procedures (angioplasty or surgery) to assess for gain in kidney function. Renal calculi are increasingly frequent in children. Whilst the vast majority of patients with renal stones do not need functional imaging, DMSA scans with SPECT and a low dose limited CT can be very helpful in the case of complex renal calculi. Congenital renal anomalies such as duplex kidneys, horseshoe kidneys, crossed-fused kidneys and multi-cystic dysplastic kidneys greatly benefit from functional imaging to identify regional parenchymal function, thus directing further management. Positron emission tomography (PET) is being actively tested in genito-urinary malignancies. Encouraging initial reports suggest that F-18-fluorodeoxyglucose (FDG) PET is more sensitive than CT in the assessment of lymph nodal metastases in patients with genito-urinary sarcomas; an increased sensitivity in comparison to isotope bone scans for skeletal metastatic disease has also been reported. Further evaluation is necessary, especially with the promising advent of PET/MRI scanners. Nuclear Medicine in paediatric nephro-urology has stood the test of time and is opening up to new exciting developments.

Delayed renal tissue tracer transit in Tc-99m-DTPA renography correlates with postoperative renal function improvement in UPJO patients

OBJECTIVE

The aim of the study was to explore the potential parameters for evaluating the improvement in relative renal function (RRF) in patients with unilateral ureteropelvic junction obstruction (UPJO) who underwent surgery. In this regard we observed the RRF expressed as the obstructed kidney's percentage contribution to overall renal function in technetium-99m diethylenetriaminepentaacetic acid (Tc-99m-DTPA) diuretic renography.

MATERIALS AND METHODS

Data on 47 patients, who underwent Anderson-Hynes pyeloplasty for diagnosed unilateral UPJO during the period of February 2003 to October 2014, were retrospectively collected. Tc-99m-DTPA diuretic renography was performed on all patients before and after surgery, and no morphological or functional abnormalities were detected on the contralateral kidney. Several parameters, especially renal tissue tracer transit (TTT), the response to furosemide stimulation, and RRF, were evaluated. All data were analyzed with the statistical software SPSS, 17.0, and a value of P less than 0.05 was considered statistically significant.

RESULTS

Data on 42 patients were eventually retained for further analysis; five patients were excluded because of indeterminate TTT. All patients showed obstructive response to furosemide stimulation with a preoperative RRF of 41±12%. Postoperative RRF of the obstructed kidneys was 47±11%, significantly higher than the preoperative RRF (P<0.05). Postoperative RRF improvement (absolute increment≥5%) was seen in 18/42 (43%) patients, and 24/42 (57%) of them manifested with postoperative drainage improvement. After surgery, both the RRF increment and the percentage of patients with postoperative RRF improvement in the preoperative delayed TTT group were significantly higher than those in the normal TTT group (12±7 vs. 2±4%, and 81 vs. 19%, respectively; P<0.05), but no significant difference in postoperative drainage improvement was detected between the two groups (56 vs. 54%, P>0.05). None of the other factors, including the preoperative RRF, obstructed kidney location, surgical method, sex, and age, had a significant influence on postoperative RRF improvement (P>0.05).

CONCLUSION

Preoperatively delayed TTT of Tc-99m-DTPA diuretic renography was an independent factor that correlated with RRF improvement of unilaterally hydronephrotic kidneys, and might provide valuable information for surgical decisions pertaining to UPJO patients.

Estimation of Response Functions Based on Variational Bayes Algorithm in Dynamic Images Sequences

We proposed a nonparametric Bayesian model based on variational Bayes algorithm to estimate the response functions in dynamic medical imaging. In dynamic renal scintigraphy, the impulse response or retention functions are rather complicated and finding a suitable parametric form is problematic. In this paper, we estimated the response functions using nonparametric Bayesian priors. These priors were designed to favor desirable properties of the functions, such as sparsity or smoothness. These assumptions were used within hierarchical priors of the variational Bayes algorithm. We performed our algorithm on the real online dataset of dynamic renal scintigraphy. The results demonstrated that this algorithm improved the estimation of response functions with nonparametric priors.

Bayesian blind separation and deconvolution of dynamic image sequences using sparsity priors

A common problem of imaging 3-D objects into image plane is superposition of the projected structures. In dynamic imaging, projection overlaps of organs and tissues complicate extraction of signals specific to individual structures with different dynamics. The problem manifests itself also in dynamic tomography as tissue mixtures are present in voxels. Separation of signals specific to dynamic structures belongs to the category of blind source separation. It is an underdetermined problem with many possible solutions. Existing separation methods select the solution that best matches their additional assumptions on the source model. We propose a novel blind source separation method based on probabilistic model of dynamic image sequences assuming each source dynamics as convolution of an input function and a source specific kernel (modeling organ impulse response or retention function). These assumptions are formalized as a Bayesian model with hierarchical prior and solved by the Variational Bayes method. The proposed prior distribution assigns higher probability to sparse source images and sparse convolution kernels. We show that the results of separation are relevant to selected tasks of dynamic renal scintigraphy. Accuracy of tissue separation with simulated and clinical data provided by the proposed method outperformed accuracy of previously developed methods measured by the mean square and mean absolute errors of estimation of simulated sources and the sources separated by an expert physician. MATLAB implementation of the algorithm is available for download.

Comparison of magnetic resonance imaging with radionuclide methods of evaluating the kidney

Nuclear medicine and MRI provide information about renal perfusion, function (glomerular filtration rate), and drainage. Some tracers that are used in nuclear medicine (technetium-diethylene triamine pentaacetic acid ([(99m)Tc-DTPA] and (51)chromium-EDTA) and some contrast media (CM) that are used for MRI (gadolinium-DTPA for instance) share the same pharmacokinetic properties, though, detection techniques are different (low-spatial resolution 2-dimensional projection with a good concentration-to-signal linearity for nuclear medicine and high-resolution 3-dimensional localization with nonlinear behavior for MRI). Thus, though based on the same principles, the methods are not the same and they provide somewhat different information. Many MRI perfusion studies have been conducted; some of them were compared with nuclear medicine with no good agreement. Phase contrast can reliably assess global renal blood flow but not perfusion at a tissular level. Arterial spin labeling has not proven to be a reliable tool to measure renal perfusion. Techniques using CM theoretically can assess perfusion at the tissular level, but they have not proven to be precise. To assess renal function, many models have been proposed. Some MRI techniques using CM, both semiquantitative (Patlak) and quantitative, have shown ability to roughly assess relative function. Some quantitative methods (Annet's and Lee's methods) have even showed that they could roughly estimate absolute renal function, with better results than estimated glomerular filtration rate. Quantification of drainage has not been much studied using MRI.

Validation of IAEA software package for the analysis of scintigraphic renal dynamic studies: parameters of renal transit in children with renal pelvic dilatation

PURPOSE

The objectives of the study were to use the International Atomic Energy Agency (IAEA) software package for the analysis of scintigraphic renal dynamic studies to obtain values of curve parameters and excretory parameters in children with hydronephrosis and to validate the reliability of these numerical outputs by comparing with values established by consensus reports.

PATIENTS AND METHODS

Fifty children with hydronephrosis (median age, 16 months; 30 boys, 20 girls; 99 kidneys) underwent Tc-MAG3 diuresis renography. Studies were analyzed by 2 observers, and according to the assessment of images, renograms, and differential function, kidneys were classified as normal (42, kidneys contralateral to hydronephrotic kidney), hypotonic unobstructed (49), and obstructed (8). The IAEA software was applied to each renogram. The parameters analyzed were as follows: normalized residual activity at 20 minutes (NORA 20) and on postmicturition (PM) acquisition, output efficiency at 20 minute (OE 20), PM to maximum renal count ratio (PM/max), and mean transit time (MTT).

RESULTS

Mean values for normal, hypotonic unobstructed, and obstructed kidneys were as follows: NORA 20: 0.25, 0.57, and 2.16; OE 20 (%): 94.5, 87, and 57; normalized residual activity on PM acquisition: 0.02, 0.03, and 0.27; PM/max: 0.01, 0.02, and 0.13; and MTT (minutes): 1.9, 3.5, and 8.9, respectively. Difference between obstruction/dilatation and normal/dilatation was significant (P < 0.0001), as well as the correlation between NORA 20/OE 20 (R = -0.982). Cutoff values to predict obstruction were as follows: NORA 20, 1.6; OE 20, 73%; NORA PM, 0.11; PM/max, 0.06; and MTT, 8.23 minutes.

CONCLUSIONS

The IAEA software package gives reliable values of numerical parameters of renal excretion. The use of the software improves diagnostic accuracy of diuresis renography in children.

Radionuclides in nephrourology, Part 2: pitfalls and diagnostic applications

Radionuclide renal scintigraphy provides important functional data to assist in the diagnosis and management of patients with a variety of suspected genitourinary tract problems, but the procedures are underutilized. Maximizing the utility of the available studies (as well as the perception of utility by referring physicians) requires a clear understanding of the clinical question, attention to quality control, acquisition of the essential elements necessary to produce an informed interpretation, and production of a report that presents a coherent impression based on data contained in the report and that specifically addresses the clinical question. To help achieve these goals, part 1 of this review addressed the available radiopharmaceuticals, quality control, and quantitative indices, including the measurement of absolute and relative renal function. Part 2 assumes familiarity with part 1 and focuses on the common clinical indications of suspected obstruction and renovascular hypertension; part 2 also summarizes the status of radionuclide renal imaging in the evaluation of the transplanted kidney and the detection of infection, discusses potential pitfalls, and concludes with suggestions for future research. The series of SAM questions accompanying parts 1 and 2 has been designed to reinforce and extend points made in the review. Although the primary focus is the adult patient, aspects of the review also apply to the pediatric population.

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.

Guidance document for structured reporting of diuresis renography

This Guidance Document for structured reporting of diuresis renography in adults was developed by the International Scientific Committee of Radionuclides in Nephro-urology (ISCORN; http://www.iscorn.org). ISCORN chose diuresis renography for its first structured report Guidance Document because suspected obstruction is the most common reason for referral, most radionuclide renal studies are conducted at institutions that perform fewer than 3 studies per week, and a large percentage of studies are interpreted by physicians with limited training in nuclear medicine. Ten panelists were asked to categorize specific reporting elements as essential, recommended, optional (without sufficient data to support a higher ranking), and unnecessary (does not contribute to scan interpretation or quality assurance). The final document was developed through an iterative series of comments and questionnaires with a majority vote required to place an element in a specific category. The Guidance Document recommends a reporting structure organized into indications, clinical history, study procedure, findings and impression and specifies the elements considered essential or recommended in each category. The Guidance Document is not intended to be restrictive but, rather, to provide a basic structure and rationale so that the diuresis renography report will: (1) communicate the results to the referring physician in a clear and concise manner designed to optimize patient care; (2) contain the essential elements required to evaluate and interpret the study; (3) clearly document the technical components of the study necessary for accountability, quality assurance and reimbursement; and (4) encourage clinical research by facilitating better comparison and extrapolation of results between institutions.

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.

Antenatal detection of pelviureteric junction stenosis: main controversies

Although renography has been used for half a century to evaluate the function of the infant kidney, there are still important disagreements among the specialists involved in this particular pathology. Each department of nuclear medicine has his own way to acquire and process a renogram; to interpret the obtained images, curves, and quantitative parameters; and to make recommendations for the referring physician. The urologist has his or her part of responsibilities because the decision for operating or not operating varies from one center to another and is generally determined by a series of unproven assumptions. The aim of the present work is to focus on the main controversies involving both the nuclear medicine physician and the urologist. Concerning the technique of renography. The bladder catheter, systematically recommended in different centers, can best be replaced in most of the cases by a much less-invasive procedure, namely the acquisition and processing of late postmicturition (PM) posterect images. The change of patient's position contributes strongly to the renal washout. Intravenous hydration is used to standardize the level of hydration. However, the patients, in most of the cases, are in good health, and adequate oral hydration is sufficient. Even if hydration was not ideal when the procedure began, the administration of furosemide and the late PM images will result in a very good drainage of a normal kidney. Any renal tracer with high extraction rate is adequate, but diethylene triamine pentaacetic acid ((99m)Tc-DTPA) does not allow a precise estimation of differential function in children younger than 6 months. The moment of furosemide injection (F0, F+20, F-15) does not influence the quality of the final renal washout, and the F0 procedure is recommended in cases of known hydronephrosis because it shortens the time of acquisition on the gamma camera and allows the simultaneous injection of both the tracer and the diuretic. Background correction remains controversial among nuclear medicine physicians. Including in the background area some liver and spleen activity, which are responsible for an important part of the extrarenal activity within the renal area, will improve the quality of the renogram curve, suppressing almost completely the initial vascular phase. The supporters of the Rutland-Patlak (R-P) fit for calculating differential function state that the vascular component is eliminated better than with use of the classical integral method. However, this method is based on a slope, with counting statistics being rather poor in infants with immature function. In most of the cases, the integral method will provide robust results. Determination of the same differential function by the use of both methods increases the level of confidence of the final results. It is generally admitted that the first renogram in children with antenatally detected hydronephrosis should be performed at approximately 1 month of age. However, there is a tendency to start earlier, and even in the first days of life, in case of huge hydronephrosis. The renogram should be repeated in case of significant hydronephrosis, significant increase of dilation, poor response to furosemide, or low initial differential function. Moderate dilation associated with normal differential function can probably be monitored by ultrasound alone. T(½) of the diuretic curve is an empiric parameter that does not take into account the bladder emptying and the change of patient's position. Output efficiency (OE) and normalized residual activity (NORA), measured on the late PM and posterect images, represent physiological parameters not dependent on the input function of the considered kidney and can be used whatever the moment of furosemide injection. There is presently no way to quantitatively measure cortical transit in antenatally detected pelviureteric junction syndrome; all methods are limited by the slight kidney motion related to respiratory movements and by the almost-complete superimposition between cortical area and collecting system. The best approach probably is a visual estimation. Concerning the position of the urologist. The main controversy is related to the definition of obstruction and the indication for surgery. Neither the degree of hydronephrosis nor the impairment of differential function and/or the quality of the response to furosemide can define which kidney is in danger of further deterioration. Alternatively, these parameters are unable to predict for which kidneys an improvement of differential function can be expected because of a pyeloplasty. It has not been excluded, according to recent published work, that cortical transit could be a better predictive factor of the risk of a conservative attitude or the benefits of a surgical procedure, but this procedure has still to be confirmed.

Functional renal imaging: new trends in radiology and nuclear medicine

The objective of this work is to compare the characteristics of various techniques for functional renal imaging, with a focus on nuclear medicine and magnetic resonance imaging. Even with low spatial resolution and rather poor signal-to-noise ratio, classical nuclear medicine has the advantage of linearity and good sensitivity. It remains the gold standard technique for renal relative functional assessment. Technetium-99m ((99m)Tc)-labeled diethylenetriamine penta-acetate remains the reference glomerular tracer. Tubular tracers have been improved: (123)I- or (131)I-hippuran, (99m)Tc-MAG3 and, recently, (99m)Tc-nitrilotriacetic acid. However, advancement in molecular imaging has not produced a groundbreaking tracer. Renal magnetic resonance imaging with classical gadolinated tracers probably has potential in this domain but has a lack of linearity and, therefore, its value still needs evaluation. Moreover, the advent of nephrogenic systemic fibrosis has delayed its expansion. Other developments, such as diffusion or blood oxygen level-dependent imaging, may have a role in the future. The other modalities have a limited role in clinical practice for functional renal imaging.

The International Atomic Energy Agency software package for the analysis of scintigraphic renal dynamic studies: a tool for the clinician, teacher, and researcher

Under the auspices of the International Atomic Energy Agency, a new-generation, platform-independent, and x86-compatible software package was developed for the analysis of scintigraphic renal dynamic imaging studies. It provides nuclear medicine professionals cost-free access to the most recent developments in the field. The software package is a step forward towards harmonization and standardization. Embedded functionalities render it a suitable tool for education, research, and for receiving distant expert's opinions. Another objective of this effort is to allow introducing clinically useful parameters of drainage, including normalized residual activity and outflow efficiency. Furthermore, it provides an effective teaching tool for young professionals who are being introduced to dynamic kidney studies by selected teaching case studies. The software facilitates a better understanding through practically approaching different variables and settings and their effect on the numerical results. An effort was made to introduce instruments of quality assurance at the various levels of the program's execution, including visual inspection and automatic detection and correction of patient's motion, automatic placement of regions of interest around the kidneys, cortical regions, and placement of reproducible background region on both primary dynamic and on postmicturition studies. The user can calculate the differential renal function through 2 independent methods, the integral or the Rutland-Patlak approaches. Standardized digital reports, storage and retrieval of regions of interest, and built-in database operations allow the generation and tracing of full image reports and of numerical outputs. The software package is undergoing quality assurance procedures to verify the accuracy and the interuser reproducibility with the final aim of launching the program for use by professionals and teaching institutions worldwide.

Normalized residual activity and output efficiency in case of early furosemide injection in children

OBJECTIVE

Values for output efficiency (OE) and normalized residual activity (NORA) in paediatric patients have been published previously. However, it is now a usual practice to inject furosemide at the beginning of a renogram acquisition (F0 procedure). The aim was to evaluate OE and NORA obtained on F0 renograms, in normal and abnormal paediatric kidneys.

METHODS

Three groups of kidneys were selected: group 1, normal kidneys (n=155); group 2, dilated but unobstructed kidneys (n=20); and group 3, hydronephrotic kidneys (n=84). A 20-min Tc-mercaptoacetyltriglycine renogram was obtained under early furosemide injection (F0) and was completed by late postmicturition (PM) images. OE and NORA were calculated at the end of the renogram and on the PM images.

RESULTS

Group 1: NORA and OE calculated at the end of the F0 renogram revealed better drainage than without F0 stimulation. The PM parameters were comparable with those previously obtained after late furosemide injection (F+20). Group 2: the drainage, despite the early injection of furosemide, was often unsatisfactory at the end of the F0 renogram, but improved dramatically upon the PM acquisition. Group 3: almost normal values up to very abnormal ones were observed. In 35% of kidneys, the values of drainage were out of the range of group 2.

CONCLUSION

Under early furosemide injection, renal drainage in the normal kidneys was better than in basic conditions. In dilated unobstructed kidneys, NORA and OE obtained on late images after micturition were, respectively, below 1.5 and above 80%.

Flow rate models in renal obstruction

BACKGROUND

In acute unilateral renal obstruction, calculated divided renal uptake following injection of tracer may be normal. Divided renal function as measured by uptake may be insensitive to fall in renal plasma flow (RPF) to the obstructed kidney. This study analyses afferent flow rate parameters of optimised models of renogram time activity curves (TAC). Afferent flow rate parameters may have differing sensitivity to altered RPF from divided renal tracer uptake and may be more sensitive to changes in cortical function in renal obstruction.

METHOD

Twenty-four background-corrected renogram TACs using 99mTc-labelled mercapto-acetyl-triglycine (MAG3) with a unilateral obstructive pattern and six normal control renograms TACs were studied. Optimised computed models of each curve were constructed using specialised software (ModelMaker, Cherwell Scientific) and using the Marquardt Least Squares method. Following optimisation to the TAC of each target renogram, the afferent flow rate parameters were calculated.

RESULTS

Following optimisation of models, afferent flow rate parameters, expressed as arbitrary units, (mean 0.15, SD 0.06) in acutely obstructed kidneys, were typically reduced in comparison with those of normal kidneys (mean 0.44, SD 0.04). (Paired t test; P<0.005). By contrast, this reduction in afferent flow rate parameter was greater than the reduction in differential tracer uptake for the obstructed kidney (divided renal function of the obstructed group; mean 0.3, SD 0.14 compared with the control group; mean 0.45, SD 0.05 (P<0.05).

CONCLUSION

Optimised modelling of TACs of obstructed renograms is feasible and may provide a more sensitive index of parenchymal dysfunction in early obstruction than comparing divided renal tracer uptake.

MR urography in children. Part 2: how to use ImageJ MR urography processing software

MR urography (MRU) is an emerging technique particularly useful in paediatric uroradiology. The most common indication is the investigation of hydronephrosis. Combined static and dynamic contrast-enhanced MRU (DCE-MRU) provides both morphological and functional information in a single examination. However, specific post-processing must be performed and to our knowledge, dedicated software is not available in conventional workstations. Investigators involved in MRU classically use homemade software that is not freely accessible. For these reasons, we have developed a software program that is freely downloadable on the National Institute of Health (NIH) website. We report and describe in this study the features of this software program.

Laparoscopic surgery on upper urinary tract in children younger than 1 year: technical aspects and functional outcome

PURPOSE

Minimally invasive procedures are increasingly important in pediatric urology. However, experience is still limited with minimally invasive operations on the upper urinary tract in infants. We analyzed 3 minimally invasive procedures (pyeloplasty, heminephroureterectomy and nephrectomy) in children younger than 1 year.

MATERIALS AND METHODS

We analyzed 67 children (mean +/- SD age 5.1 +/- 2.9 months) undergoing minimally invasive pyeloplasty in 26 patients (group 1), heminephroureterectomy in 18 (group 2) or nephrectomy in 23 (group 3) with regard to technical aspects, surgical outcome and complications. Preoperative and postoperative ultrasound and mercaptoacetyltriglycine renal scan were statistically evaluated in groups 1 and 2.

RESULTS

Mean +/- SD patient weight was 6.4 +/- 1.8 kg and mean +/- SD operative time was 113.2 +/- 41.6 minutes. Conversion to open surgery was necessary in 1 pyeloplasty. One complication (missed intraoperative bowel perforation) occurred. No blood transfusion was required in any child. After pyeloplasty there were improved tracer clearances (mercaptoacetyltriglycine scan) and improved morphologies of the pyelon (ultrasound) in all patients. In groups 1 and 2 there was no statistical difference between preoperative and postoperative partial function of the affected kidney. Mean +/- SD followup was 32.5 +/- 19.8 months.

CONCLUSIONS

Minimally invasive procedures on the upper urinary tract in children younger than 1 year are technically challenging, and require expertise of the surgeon and the entire team. Given these assumptions, such procedures can be safely performed with excellent functional outcomes.

Diuretic renography in hydronephrosis: renal tissue tracer transit predicts functional course and thereby need for surgery

PURPOSE

The recognition of those hydronephrotic kidneys which require therapy to preserve renal function remains difficult. We retrospectively compared the 'tissue tracer transit' (TTT) of (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG(3)) with 'response to furosemide stimulation' (RFS) and with 'single kidney function < 40%' (SKF < 40%) to predict functional course and thereby need for surgery.

METHODS

Fifty patients with suspected unilateral obstruction and normal contralateral kidney had 115 paired (baseline/follow-up) (99m)Tc-MAG(3) scintirenographies. Three predictions of the functional development were derived from each baseline examination: the first based on TTT (visually assessed), the second on RFS and the third on SKF < 40%. Each prediction also considered whether the patient had surgery. Possible predictions were 'better', 'worse' or 'stable' function. A comparison of SKF at baseline and follow-up verified the predictions.

RESULTS

The frequency of correct predictions for functional improvement following surgery was 8 of 10 kidneys with delayed TTT, 9 of 22 kidneys with obstructive RFS and 9 of 21 kidneys with SKF < 40%; for functional deterioration without surgery it was 2 of 3 kidneys with delayed TTT, 3 of 20 kidneys with obstructive RFS and 3 of 23 kidneys with SKF < 40%. Without surgery 67 of 70 kidneys with timely TTT maintained function. Without surgery 0 of 9 kidneys with timely TTT but obstructive RFS and only 1 of 16 kidneys with timely TTT but SKF < 40% lost function.

CONCLUSION

Delayed TTT appears to identify the need for therapy to preserve function of hydronephrotic kidneys, while timely TTT may exclude risk even in the presence of an obstructive RFS or SKF < 40%.

Probable range for whole kidney mean transit time values determined by reexamination of UK audit studies

OBJECTIVES

Inconsistency in the intercentre measurement of whole kidney mean transit time (MTT) has been reported in a previously published UK audit. The main objectives of this study were to identify a probable value of MTT for each kidney in the UK audit data and to find likely reasons for the reported variations.

METHODS

Datasets of MTT values were obtained by an independent review of the audit data by four experienced practitioners of deconvolution techniques. The deconvolution techniques used included the matrix method, a constrained least squares method as well as a residence time technique. The datasets were compared using t-test, linear regression, and mean difference analysis.

RESULTS

Twelve of a total of 13 datasets showed nonsignificant differences using a paired t-test (P>0.05). For each kidney (x), a collective mean and standard deviation, Mx and SDx, respectively, were calculated from these 12 datasets and a probable range was defined as Mx+/-3SDx. Average SDx/Mx was 3.6% (range 1.5-7.7%). For five kidneys, Mx exceeded the median of the audit results by 3.5-15.3 SDx (P<0.001).

CONCLUSION

Probable ranges for whole kidney MTT have been estimated with good precision. Underestimation of the area under the plateau of the renal retention function as well as overestimation of the plateau height might have contributed to an underestimation of MTT apparent in some audit results. Visual display of both the renal retention function and the reconvolution curve are suggested as simple quality control measures for analysis software.

Importance and limits of ischemia in renal partial surgery: experimental and clinical research

Introduction. The objective is to determine the clinical and experimental evidences of the renal responses to warm and cold ischemia, kidney tolerability, and available practical techniques of protecting the kidney during nephron-sparing surgery. Materials and methods. Review of the English and non-English literature using MEDLINE, MD Consult, and urology textbooks. Results and discussion. There are three main mechanisms of ischemic renal injury, including persistent vasoconstriction with an abnormal endothelial cell compensatory response, tubular obstruction with backflow of urine, and reperfusion injury. Controversy persists on the maximal kidney tolerability to warm ischemia (WI), which can be influenced by surgical technique, patient age, presence of collateral vascularization, indemnity of the arterial bed, and so forth. Conclusions. When WI time is expected to exceed from 20 to 30 minutes, especially in patients whose baseline medical characteristics put them at potentially higher, though unproven, risks of ischemic damage, local renal hypothermia should be used.