How reliable is renal ultrasound to measure renal length and volume in patients with chronic kidney disease compared with magnetic resonance imaging?

Deep Learning Algorithms To Predict DRF < 40% in Unilateral Hydronephrosis Based On Key Parameters of Urinary Tract Ultrasound

OBJECTIVES

For children with unilateral hydronephrosis, differential renal function (DRF) < 40% serves as a compelling indication for surgical intervention, and it can be assessed through diuretic renogram. However, a significant number of patients do not have convenient access to high-quality renograms. We conducted an analysis of the key parameters of urinary tract ultrasound in children with unilateral hydronephrosis, aiming to identify the correlation between ultrasound findings and the incidence of DRF < 40%.

METHODS

We retrospectively reviewed the dynamic renogram and urinary tract ultrasound data of 802 children with hydronephrosis presented to our department. Independent risk factors related to DRF < 40% were screened out. Several machine learning models were employed. The area under receiving operating curves (AUROC) was calculated for each model to compare their efficiency.

RESULTS

The renal pelvis anterior-posterior diameter (RPAPD), upper calyx dilation and renal length ratio were found to be independent risk factors for DRF < 40%. Among these factors, the renal length ratio had the highest AUROC of 0.820. These three factors, alone with the patients' age, were then introduced into three machine learning models: random forest, logistic regression and support vector machines (SVM), among which, the SVM exhibited the highest AUROC of 0.941, with a sensitivity of 90.32% and a specificity of 81.03%.

CONCLUSION

The length ratio exhibited the strongest correlation with DRF <40% among multiple ultrasound indexes. Moreover, the SVM model exhibited significant improvement compared to individual factors. Therefore, it can be employed to identify high-risk children with impaired renal function in the assessment of congenital hydronephrosis.

Ultrasonic renal length as an indicator of renal fibrosis severity in non-diabetic patients with chronic kidney disease

BACKGROUND

Debate continues regarding the potential of the ultrasonic renal length to serve as an indicator for evaluating the advancement of renal fibrosis in chronic kidney disease (CKD). This study investigates the independent association between renal length and renal fibrosis in non-diabetic CKD patients and assesses its diagnostic performance.

METHODS

From April 2019 to December 2021, 144 non-diabetic patients diagnosed with CKD who underwent a renal ultrasound examination and kidney biopsy were prospectively enrolled. Patients were categorized into the mild fibrosis group (n = 70) and the moderate-severe group (n = 74) based on the extent of fibrotic involvement. Ultrasonic renal length was measured from pole-to-pole in the coronal plane. A receiver operating characteristic (ROC) curve, multivariable logistic regression analysis, and a generalized additive model were performed.

RESULTS

A negative linear correlation was found between renal length and moderate-severe renal fibrosis risk. Each centimeter increase in renal length decreased the odds of moderate-severe fibrosis by 38% (OR: 0.62; 95% CI 0.41-0.93; P = 0.020). After adjusting for confounders, the relationship persisted (OR: 0.58; 95% CI 0.33-1.00; P = 0.048). However, renal length presented limited discrimination ability in distinguishing degrees of renal fibrosis while controlling the key confounding factors, yielding an area under the ROC curve of only 0.58 (95% CI 0.45-0.70).

CONCLUSION

While an inverse relationship exists between renal length and risk of having moderate-severe renal fibrosis in non-diabetic CKD patients, renal length alone is insufficient for diagnosing fibrosis severity, underscoring the need for additional diagnostic parameters in CKD assessment.

Ultrasound versus magnetic resonance imaging for calculating total kidney volume in patients with ADPKD: a real-world data analysis

BACKGROUND AND OBJECTIVES

This study aimed to compare Total kidney volume (TKV) measurements using US-ellipsoid (US-EL) and MRI-ellipsoid (MRI-EL) in patients with autosomal-dominant-polycystic-kidney-disease (ADPKD). It also evaluated whether the agreement between right (RKV) and left (LKV) kidney volume measurements differed.

METHODS

Retrospective analysis of a prospective data-base that included consecutive patients diagnosed with ADPKD. Total kidney volumes by 3D-US-EL were compared with those by MRI-EL. Bland-Altman-plots, Passing-Bablok-regression, and the concordance-correlation-coefficient (CCC) were used to compare right (RKV), left (LKV), and TKV measurements.

RESULTS

Thirty-two ADPKD patients, 14(43.7%) women, were included. Mean measured (mGFR) and estimated (eGFR) glomerular-filtration-rate (GFR) were 86.5 ± 23.9 mL/min and 78.9 ± 23.6 mL/min, respectively. Compared with MRI-EL, TKV (Mean difference: - 85.9 ± 825.6 mL; 95%CI - 498.5 to 326.7 mL; p = 0.6787), RKV (Mean difference: - 58.5 ± 507.7 mL; 95%CI - 312.2 to 195.2 mL; p = 0.6466), and LKV (Mean difference: - 27.4 ± 413.5 mL; 95%CI - 234.1 to 179.2 mL; p = 0.7918) were lower with US-EL than with MRI-EL, although without significant differences. According to Passing and Bablok-regression analysis, the Spearman correlation-coefficient was 0.96 (95%CI 0.92 to 0.98); 0.91 (95%CI 0.82 to 0.96), and 0.94 (95%CI 0.87 to 0.97) in the RKV, LKV, and TKV, respectively; p < 0.0001 each, respectively. CCC of RKV, LKV, and TKV measurements were 0.95, 0.89, and 0.94, respectively. The mGFR and eGFR showed statistically significant negative correlations with TKV measured by both MRI-EL (p = 0.0281 and p = 0.0054, respectively) and US-EL (p = p = 0.0332 and p = 0.0040, respectively).

CONCLUSIONS

This study found that ultrasound-based ellipsoid kidney volume measurements strongly correlated with MRI-based measurements, suggesting that ultrasound is a reliable, accessible alternative for assessing kidney volume, particularly when MRI is unavailable.

The added value of superb microvascular imaging for renal cortical thickness measurement in chronic kidney disease

PURPOSE

The aim of this study was to evaluate renal parenchymal thickness and renal cortical thickness measurements on brightness mode ultrasound (B-mode US) and B-mode US + Superb Microvascular Imaging (SMI) technique, comparing with computed tomography (CT) or magnetic resonance imaging (MRI) serving as a reference standard.

METHODS

Renal parenchymal thickness and renal cortical thickness measurements were obtained from B-mode US, B-mode US + SMI, and CT/MRI in a group of healthy subjects and a group of patients with chronic kidney disease (CKD). The mean differences and correlations of renal parenchymal thickness and renal cortical thickness were analyzed using dependent pair t-test and Pearson's correlation, respectively.

RESULTS

The mean difference in renal cortical thickness measurements between B-mode US + SMI and CT/MRI was lower than the mean difference between B-mode US alone and CT/MRI. Additionally, renal cortical thickness measured using B-mode US + SMI showed a stronger correlation with values obtained from CT/MRI than values measured using standard B-mode US alone.

CONCLUSION

The measurement of renal cortical thickness by B-mode US + SMI is more accurate than that by B-mode US alone.

Segmentation-based quantitative measurements in renal CT imaging using deep learning

BACKGROUND

Renal quantitative measurements are important descriptors for assessing kidney function. We developed a deep learning-based method for automated kidney measurements from computed tomography (CT) images.

METHODS

The study datasets comprised potential kidney donors (n = 88), both contrast-enhanced (Dataset 1 CE) and noncontrast (Dataset 1 NC) CT scans, and test sets of contrast-enhanced cases (Test set 2, n = 18), cases from a photon-counting (PC)CT scanner reconstructed at 60 and 190 keV (Test set 3 PCCT, n = 15), and low-dose cases (Test set 4, n = 8), which were retrospectively analyzed to train, validate, and test two networks for kidney segmentation and subsequent measurements. Segmentation performance was evaluated using the Dice similarity coefficient (DSC). The quantitative measurements' effectiveness was compared to manual annotations using the intraclass correlation coefficient (ICC).

RESULTS

The contrast-enhanced and noncontrast models demonstrated excellent reliability in renal segmentation with DSC of 0.95 (Test set 1 CE), 0.94 (Test set 2), 0.92 (Test set 3 PCCT) and 0.94 (Test set 1 NC), 0.92 (Test set 3 PCCT), and 0.93 (Test set 4). Volume estimation was accurate with mean volume errors of 4%, 3%, 6% mL (contrast test sets) and 4%, 5%, 7% mL (noncontrast test sets). Renal axes measurements (length, width, and thickness) had ICC values greater than 0.90 (p < 0.001) for all test sets, supported by narrow 95% confidence intervals.

CONCLUSION

Two deep learning networks were shown to derive quantitative measurements from contrast-enhanced and noncontrast renal CT imaging at the human performance level.

RELEVANCE STATEMENT

Deep learning-based networks can automatically obtain renal clinical descriptors from both noncontrast and contrast-enhanced CT images. When healthy subjects comprise the training cohort, careful consideration is required during model adaptation, especially in scenarios involving unhealthy kidneys. This creates an opportunity for improved clinical decision-making without labor-intensive manual effort.

KEY POINTS

Trained 3D UNet models quantify renal measurements from contrast and noncontrast CT. The models performed interchangeably to the manual annotator and to each other. The models can provide expert-level, quantitative, accurate, and rapid renal measurements.

Differential renal length index: useful measure in management of isolated unilateral hydronephrosis?

OBJECTIVE

To explore the usefulness of the 'differential renal length index' (iDRL) before and after pyeloplasty, as the anteroposterior diameter is commonly used to quantify hydronephrosis but inaccuracies arise due to interobserver variability, hydration status and pure intra-renal dilatation.

PATIENTS AND METHODS

Prospectively collected data, from two centres, of all children undergoing pyeloplasty for isolated unilateral pelvi-ureteric junction obstruction (PUJO) (2015-2021) were analysed. Subgroup analysis was undertaken: Group A - differential renal function (DRF) ≥40%, Group B - subnormal DRF (20-39%), and Group C - symptomatic. Children with structural anomalies of upper and lower urinary tract, bilateral involvement, and subnormal DRF (<20%) were excluded. All the children had a pre- and postoperative ultrasound scan and Tc99m mercapto-acetyltriglycine (MAG3) renograms. The iDRL was calculated as follows: iDRL = ([a - b]/b) × 100, where 'a' is the length of hydronephrotic kidney (cm) and 'b' is the length of contralateral normal kidney (cm). The mean difference and standard error of mean (SEM) between the pre- and postoperative iDRL was evaluated using the paired Student's t-test, with P < 0.05 considered statistically significant.

RESULTS

A total of 119 children with 1-year follow-up were included. For the entire cohort, the mean (SEM) preoperative iDRL was 27.7 (1.4) and postoperatively was 12.5 (1.1), with a mean (range) DRF improvement of 54% (44-66%) (P < 0.001). In Group A (n = 97), the mean (SEM) preoperative iDRL was 26.6 (1.5) and postoperatively was 13.1 (1.2), with a mean (range) DRF improvement of 50% (38-63%) (P < 0.001). In Group B (n = 22), the mean (SEM) preoperative iDRL was 32.6 (3.5) and postoperatively was 10.0 (2.8), with a mean (range) DRF improvement of 69% (49-89%) (P < 0.001). In Group C (n = 28), the mean (SEM) preoperative iDRL was 19.9 (2.3) and postoperatively was 7.7 (1.9), with a mean (range) DRF improvement of 61% (38-85%) (P < 0.001).

CONCLUSION

Our study identifies the iDRL as a useful measure of improvement following successful pyeloplasty. In the subgroup with DRF of >39% minimum improvement was >37%. Similar minimum DRF improvement was also noted (>37%) in hypo-functioning kidneys and symptomatic PUJO.

Increased prevalence of kidney cysts in individuals carrying heterozygous COL4A3 or COL4A4 pathogenic variants

BACKGROUND

Clinical variability among individuals with heterozygous pathogenic/likely pathogenic (P/LP) variants in the COL4A3/COL4A4 genes (also called autosomal dominant Alport syndrome or COL4A3/COL4A4-related disorder) is huge; many individuals are asymptomatic or show microhematuria, while others may develop proteinuria and chronic kidney disease (CKD). The prevalence of simple kidney cysts (KC) in the general population varies according to age, and patients with advanced CKD are prone to have them. A possible association between heterozygous COL4A3, COL4A4 and COL4A5 P/LP variants and KC has been described in small cohorts. The presence of KC in a multicenter cohort of individuals with heterozygous P/LP variants in the COL4A3/COL4A4 genes is assessed in this study.

METHODS

We evaluated the presence of KC by ultrasound in 157 individuals with P/LP variants in COL4A3 (40.7%) or COL4A4 (53.5%) without kidney replacement therapy. The association between presence of KC and age, proteinuria, estimated glomerular filtration rate (eGFR) and causative gene was analyzed. Prevalence of KC was compared with historical case series in the general population.

RESULTS

Half of the individuals with P/LP variants in COL4A3/COL4A4 showed KC, which is a significantly higher percentage than in the general population. Only 3.8% (6/157) had cystic nephromegaly. Age and eGFR showed an association with the presence of KC (P < .001). No association was found between KC and proteinuria, sex or causative gene.

CONCLUSIONS

Individuals with COL4A3/COL4A4 P/LP variants are prone to develop KC more frequently than the general population, and their presence is related to age and to eGFR. Neither proteinuria, sex nor the causative gene influences the presence of KC in these individuals.

Kidney volume normative values in Central European children aged 0-19 years: a multicenter study

BACKGROUND AND OBJECITVES

The currently available kidney volume normative values in children are restricted to small populations from single-centre studies not assessing kidney function and including none or only a small number of adolescents. This study aimed to obtain ultrasound-based kidney volume normative values derived from a large European White/Caucasian paediatric population with normal kidney function.

METHODS

After recruitment of 1427 children aged 0-19 years, 1396 individuals with no history of kidney disease and normal estimated glomerular filtration rate were selected for the sonographic evaluation of kidney volume. Kidney volume was correlated with age, height, weight, body surface area and body mass index. Kidney volume curves and tables related to anthropometric parameters were generated using the LMS method. Kidney volume predictors were evaluated using multivariate regression analysis with collinearity checks.

RESULTS

No clinically significant differences in kidney volume in relation to height were found between males and females, between supine and prone position and between left and right kidneys. Males had, however, larger age-related kidney volumes than females in most age categories. For the prediction of kidney volume, the highest coefficient correlation was observed for body surface area (r = 0.94), followed by weight (r = 0.92), height (r = 0.91), age (r = 0.91), and body mass index (r = 0.67; p < 0.001 for all).

CONCLUSIONS

This study presents LMS-percentile curves and tables for kidney volume which can be used as reference values for children aged 0-19 years.

Fully automated kidney image biomarker prediction in ultrasound scans using Fast-Unet+

Any kidney dimension and volume variation can be a remarkable indicator of kidney disorders. Precise kidney segmentation in standard planes plays an undeniable role in predicting kidney size and volume. On the other hand, ultrasound is the modality of choice in diagnostic procedures. This paper proposes a convolutional neural network with nested layers, namely Fast-Unet++, promoting the Fast and accurate Unet model. First, the model was trained and evaluated for segmenting sagittal and axial images of the kidney. Then, the predicted masks were used to estimate the kidney image biomarkers, including its volume and dimensions (length, width, thickness, and parenchymal thickness). Finally, the proposed model was tested on a publicly available dataset with various shapes and compared with the related networks. Moreover, the network was evaluated using a set of patients who had undergone ultrasound and computed tomography. The dice metric, Jaccard coefficient, and mean absolute distance were used to evaluate the segmentation step. 0.97, 0.94, and 3.23 mm for the sagittal frame, and 0.95, 0.9, and 3.87 mm for the axial frame were achieved. The kidney dimensions and volume were evaluated using accuracy, the area under the curve, sensitivity, specificity, precision, and F1.

Early Renal Ultrasound in Patients with Congenital Solitary Kidney Can Guide Follow-Up Strategy Reducing Costs While Keeping Long-Term Prognostic Information

We aimed to evaluate the prognostic value of renal length (RL) > 2 standard deviation scores (SDS) measured by renal ultrasound (RUS), across infancy, childhood and adolescence, in identifying which patients with congenital solitary functioning kidney (CSFK) are at lower risk of developing kidney injury (KI). We also estimated the cost saving of integrating the current follow-up protocols with an early RUS algorithm (ERUSA). Fifty-six CSFK adult patients who were 1–3 months old at first observation of undergoing RUS were enrolled. KI was defined by hypertension and/or proteinuria and/or declined renal function. ERUSA was assessed by early (at 1–3 months of life) RUS and was retrospectively tested in our patients. ERUSA establishes that patients with RL > 2SDS at early RUS do not undergo further follow-ups. The others undergo another RUS at 1 year of age along with follow-ups according with current protocols, with the exception of RUS which could be no longer performed. Direct and indirect costs were calculated for each analysed protocol and the cost saving of applying ERUSA was calculated. None of the patients with early RL > 2SDS presented KI in adulthood. A RL > 2SDS was predictive of absence of KI only at 1–3 months (OR = infinity) and 1 year of age (OR = 0.13; 95%CI: 0.03–0.66; p = 0.01). ERUSA provided a total cost-sparing ranging from 38.6% to 55.3% among the analysed follow-up protocols. With ERUSA, no patients developing KI in adulthood were missed. In conclusion, only a RL > 2SDS at 1–3 months and 1 year of age predicted good prognosis in young adulthood. ERUSA can guide a cost-sparing follow-up strategy in CSFK patients while maintaining important long-term information.

Compensatory Hypertrophy in Paediatric Patients with a Unilateral Ureteropelvic Junction Obstruction

Background

Compensatory hypertrophy is common in children with solitary functioning kidney, but it is unknown whether it also develops in children with unilateral partial reduction of kidney function.

Objective

The aim of this study was to assess whether children with a unilateral ureteropelvic junction obstruction (UPJO) show compensatory growth of the unaffected kidney. Furthermore, we investigated whether the length of the unaffected kidney was related to the degree of split kidney function lost and other possible risk factors. Lastly, we studied a possible relationship with signs of kidney injury.

Design, setting, and participants

We retrospectively analysed clinical information from 194 children with a unilateral UPJO who participated in the Aetiologic research into Genetic and Occupational/environmental Risk factors for Anomalies in children (AGORA) data- and biobank. Data on kidney length, split kidney function, and other factors possibly associated with kidney length were extracted from electronic patient records.

Outcome measurements and statistical analysis

Pearson’s correlation coefficients between the split kidney function and unaffected kidney length were calculated. Multivariable logistic regression analyses were performed to identify factors associated with kidney length and signs of kidney injury.

Results and limitations

Most children with a UPJO had an unaffected kidney length above the reference for age at the end of follow-up (median age 6.5 yr). A correlation with split kidney function was present only in children with a split kidney function of ≥60% in the unaffected kidney (r = 0.41). Aside from split kidney function, UPJO side was the only determinant of kidney length, while no associations between kidney length and kidney injury were identified.

Conclusions

Compensatory growth was visible in most children with a UPJO after sufficient follow-up time and was correlated with split kidney function in children with a severe UPJO. Contralateral kidney length provided no clear prognostic value for developing kidney injury. Studies with more patients and additional biomarkers of kidney injury are needed to further personalise care.

Patient summary

Children with obstruction of urine outflow in one kidney often had a larger contralateral kidney. However, the size of this kidney could not be used to predict which children would develop kidney injury.

Low agreement between kidney volume and kidney length z-scores

BACKGROUND

Pediatric nephrologists use kidney length and kidney volume z-scores to longitudinally assess normal nephron endowment. However, most radiologists only report kidney length. Agreement between kidney length and kidney volume z-scores in children has been understudied. This study aims to assess agreement between kidney length and kidney volume z-scores in children.

METHODS

This novel cross-sectional cohort study prospectively followed prematurely born babies from a large specialized prematurity follow-up center. A healthy control group matched the cases by age and sex and was recruited from schools. Children were assessed for kidney length and kidney volumes at age 5 by three independent ultrasonographers. All measurements were performed in triplicate. Detailed anthropometry, blood pressure, and kidney function were also obtained. Age-independent z-scores were calculated for all parameters according to Scholbach and Weitzel and compared using descriptive statistics.

RESULTS

We studied 89 premature patients (median 32 weeks gestational age) and 33 healthy controls (median 38 weeks gestational age). There were 732 determinations of kidney length, width, and thickness. The mean z-score of the right kidney length was 0.65 ± 0.08 (SEM) compared with 0.88 ± 0.08 of the left kidney length (p = 0.0003, two-sided paired t test). The squared correlation coefficient for kidney volume to kidney length was 0.32 (p < 0.0001). Bland and Altman analysis revealed considerable bias with - 1.36 ± 0.76 standard deviations and 95% limits of agreement from - 2.83 to - 0.16.

CONCLUSION

Reporting only kidney length results in significant overestimation of age-independent z-scores. Based on our findings, consideration to measuring all kidney dimensions may be more appropriate.

Hyaluronic acid coated bilirubin nanoparticles attenuate ischemia reperfusion-induced acute kidney injury

Acute kidney injury (AKI) is a common pathological process that is globally associated with a high morbidity and mortality rate. The underlying AKI mechanisms include over-produced reactive oxygen species (ROS), inflammatory cell infiltration, and high levels of inflammatory mediators. Bilirubin is an endogenous compound with antioxidant, anti-inflammatory and anti-apoptotic properties, and could, therefore, be a promising therapeutic candidate. Nanotechnology-mediated therapy has emerged as a novel drug delivery strategy for AKI treatment. In this study, we report a hyaluronic acid (HA) coated ε-polylysine-bilirubin conjugate (PLBR) nanoparticle (nHA/PLBR) that can selectively accumulate in injured kidneys and alleviate the oxidative/inflammatory-induced damage. The in vitro study revealed that nHA/PLBR has good stability, biocompatibility, and exhibited higher antioxidant as well as anti-apoptotic effects when compared to nPLBR or bilirubin. The in vivo study showed that nHA/PLBR could target and accumulate in the injured kidney, effectively relieve oxidative stress and inflammatory reactions, protect the structure and function of the mitochondria, and more importantly, inhibit the apoptosis of tubular cells in an ischemia/reperfusion-induced AKI rat model. Therefore, nHA/PLBR has the capacity to enhance specific biodistribution and delivery efficiency of bilirubin, thereby providing better treatment for AKI in the future.

A Comparability of Renal Length and Volume Measurements in MRI and Ultrasound in Children

Introduction: Despite the significant increase in use of magnetic resonance imaging (MRI) in children, there is still a lack of normal reference values of renal size in this method and reference values are being interpolated from the ultrasound (US) studies. The study provides comparative analysis of agreement in renal length and volume measurements between MRI and ultrasound. Materials and Methods: Ninety-three children with a mean age of 8.0 ± 6.0 years, who had undergone both renal US and MRI exams, were included in the study. Participants were divided into three subgroups; each kidney was considered separately. Group 1 included 106 kidneys without any anomalies. Group 2 comprised 48 kidneys with a dilated collecting system. Group 3 included 32 kidneys with a duplicated collecting system. Measurements were taken in three dimensions, and renal volume was calculated from the ellipsoid formula. Results: We found no significant difference between US and MRI measurements in Group 1 and Group 2. In Group 3, the difference between measurements in both imaging methods was significant. The mean difference varied from 0.05% in Group 1, 2.95% in Group 2, to 4.99% in Group 3. Conclusion: The US and MRI are comparable methods in renal size measurements. The interpolation of sonographic renal length and volume reference values to the MRI in the pediatric population is justified, as there is a strong agreement between both methods. Both methods can be used interchangeably for following up of the renal size changes in the pediatric population.