Split renal function measured by triphasic helical CT

Contrast-enhanced MRI for simultaneous evaluation of renal morphology and split renal function in living kidney donor candidates

PURPOSE

The evaluation process of potential living kidney donors focusses on renal anatomy and split renal function. This study aimed to evaluate a magnetic resonance imaging (MRI)-based approach for simultaneous evaluation of both and its impact on clinical decision making.

METHOD

Over a 3-year period, 65 potential living kidney donors were consecutively enrolled. The MRI protocol was extended by MR-nephrography to measure split renal function. Standard DTPA-scintigraphy was used for functional comparison.

RESULTS

Split renal function showed no systematic bias between the two methods (mean difference 0.3%, p = 0.08). Both methods would have yielded the same clinical decision for donor nephrectomy in 75% of the patients. In 25 % of the patients, one method indicated a relevant side difference while the other did not, and a different clinical decision could have been made based on split renal function alone.

CONCLUSIONS

MRI proved eligible for comprehensive living kidney donor evaluation and non-inferior to scintigraphy for determining split renal function. In clinical decision making, these two methods would have resulted in the same side for donor nephrectomy in a large proportion of potential donors. Whether MRN will be implemented in clinical practice depends on transplant centre infrastructure and policy.

A prospective study of novel mathematical analysis of the contrast-enhanced computed tomography vs renal scintigraphy in renal function evaluation

PURPOSE

whilst renal scintigraphy (RS) can be associated with interobserver variability, it remains the standard method of evaluating split renal function.

AIM

to compare the efficacy of the novel technique of kidney function assessment and renal scintigraphy.

METHOD

for this prospective single-arm study we recruited patients who were recommended dynamic renal scintigraphy with ⁹⁹mTc-DTPA (diethylenetriaminepentacetate). After scintigraphy, mathematical analysis of computed tomography (MACT) was done in all patients, by a single person (SK) blinded to RS results.

RESULTS

the study included a total of 97 patients with mean age of 50.9 (range, 23-78) years. From this sample, 65 were females and 32 males. All patients underwent both RS and contrast-enhanced computed tomography for further MACT in 2016-2018. CT results were found to be similar to renal scintigraphy results with Pearson correlation coefficient of 0.945 (р < 0.001). Substantial similarities in renal plasma flow for both kidneys were also observed (0.815, р < 0.001).

CONCLUSION

MACT proved feasible, effective and safe in estimating renal function. Its results are closely correlated with RS findings and could be easily integrated into surgical practice.

Correlation between computed tomography volumetry and nuclear medicine split renal function in live kidney donation: a single-centre experience

BACKGROUND

Potential live renal donors undergo both renal computed tomography angiogram (CTA) and nuclear imaging dimercaptosuccinic acid (DMSA) scans. Each kidney's renal function and vascular anatomy influences the choice of donor side. Although DMSA measures differential blood flow, it is a surrogate for renal function and nephron mass. Computed tomography techniques can provide volumetry information. The aim of this study was to determine the relationship between measured split renal volumes on computed tomography versus renal volumes derived from DMSA split function in live donors.

METHODS

Prospective data of live kidney donors assessed at a single Australian centre from 2014 to 2017 were reviewed. All patients had pre-operative CTA and DMSA imaging. Renal volume was determined via semi-automated software calculation from CTA three-dimensional image reconstructions by one investigator. Measured split renal volume was compared against calculated renal volume using measured DMSA split function (percentage split function multiplied by total renal volume).

RESULTS

Fifty-three patients were included in the study. Split renal volumes on three-dimensional CTA images correlate to calculated split volumes determined from DMSA (Pearson coefficient 0.95 for right renal volume, 0.95 for left). The decision of which kidney to remove can be achieved with CTA only. Omitting a DMSA scan would reduce the radiation load by 0.70 mSv (35 chest X-rays) and potential cost saving of AU$1062.00 per donor.

CONCLUSION

CTA technology allows accurate assessment of renal volumes that correlate well with DMSA split function. Avoiding a DMSA scan results in cost and radiation reduction in the assessment of a live kidney donor.

Can Split Renal Volume Assessment by Computed Tomography Replace Nuclear Split Renal Function in Living Kidney Donor Evaluations? A Systematic Review and Meta-Analysis

Background:

As part of their living kidney donor assessment, all living donor candidates complete a computed tomography (CT) angiogram, but some also receive a nuclear renogram for split renal function (SRF%).

Objective:

We considered whether split renal volume (SRV%) assessed by CT can predict SRF%.

Design:

Systematic review and meta-analysis.

Setting:

Living donor candidates undergoing evaluation as potential living kidney donors.

Patients:

Living donor candidates who received both a nuclear renogram for split function and CT for SRV as part of their living donor work-up.

Measurements:

Split renal volume from CT scans and SRF from nuclear renography.

Methods:

We performed a systematic review and meta-analysis of the literature, abstracting data and digitizing plots where possible. We searched Medline, EMBASE, and the Cochrane Library. We added data from donor candidates assessed in London, Ontario from 2013 to 2016. We used fixed and random-effects models to pool Fisher’s z-transformed Pearson’s correlation coefficient (r). We conducted random-effects meta-regression on digitized and aggregate data. Studies were restricted to living kidney donors or living donor candidates.

Results:

After pooling 19 studies (n = 1479), we obtained a pooled correlation of r = 0.74 (95% confidence interval [CI] = 0.61-0.82). By linear regression using individual-level data, we observed a 0.76% (95% CI = 0.71-0.81) increase in SRF% for every 1% increase in SRV%. Split renal volume had a specificity of 88% for discriminating SRF at a threshold that could influence the decision of which kidney is to be removed (between-kidney difference ≥10%). Predonation SRV and SRF both moderately predicted kidney function 6 to 12 months after donation: r = 0.75 for SRV and r = 0.73 for SRF; Δr = 0.05 (–0.02, 0.13).

Limitations:

Most studies were retrospective and measured SRV and SRF only on selected living donor candidates. Efficiency gains in removing the SRF from the evaluation will depend on the transplant program.

Conclusion:

Split renal volume has the potential to replace SRF for some candidates. However, it is uncertain whether it can do so reliably and routinely across different transplant centers. The impact on clinical decision-making needs to be assessed in well-designed prospective studies.

Trial registration:

The digitized data are registered with Mendeley Data (doi10.17632/dyn2bfgxxj.2).

Reliability of computed tomography-based renal cortex volume to determine split renal function in preoperative living kidney donors

Objective:

The purpose of this study was to assess the utility of CT-based renal cortex volume to estimate split renal function (SRF) in pre-transplant living kidney donors and to evaluate its reliability to predict graft function in the recipients.

Methods:

Our study recruited all adult potential donors who had both Tc-99m-diethylenetriamine pentacetate (DTPA) scintigraphy and CT angiography of the abdominal aorta done before donating their kidney. We compared the correlation between CT-based renal cortex volume combined with kidney function and DTPA scan as well as post-donation kidney function in the recipients.

Results:

The correlation between CT-based split cortex volume and DTPA-measured SRF before transplantation was strong (intraclass correlation coefficient = 0.954–0.968). The inter-rater reliability of two radiologists also showed substantial agreement (intraclass correlation coefficient = 0.97, p < 0.001). In contrast, the correlations between renal cortical volume of donated kidney adjusted to recipient body weight and recipient kidney function was poor at both 2 week and 2 year follow-up.

Conclusion:

CT-based renal cortex volume combined with pre-operative kidney function appears to be precise and reproducible to evaluate pre-transplant SRF. Nevertheless, the prediction of recipient graft function needs to be further investigated to ensure a good outcome.

Advances in knowledge:

This method is practicable for all potential donors who undergo kidney transplantation in terms of streamline donor workup without compromising information.

Renal Artery Diameter Is a Surrogate Marker for Kidney Volume in Living Kidney Donors

Donor kidney volume (KV) is an increasingly important parameter evaluated before living kidney donation; however, KV measurements on computed tomographic (CT) scanning requires a manually intensive process of manual or semiautomatic segmentation of kidneys with interobserver variation. Renal artery diameter (RAD) is an easier marker to measure, and this study aims to investigate the relationship between donor RAD and KV.

METHODS

A retrospective review of 77 patients who underwent living donor nephrectomy was conducted. Bilateral KVs were measured based on contrast-enhanced CT scan imaging, and renal artery maximum diameter was measured by direct visualization on the arterial phase of transverse CT sections.

RESULTS

On regression analysis, there was a significant association between the right and left RADs and their ipsilateral KVs with a regression coefficient of 7.9 (95% CI, 1.3-14.5; P = .02) and 9.8 (95% CI, 3.3-16.3; P = .004), respectively. Mean total RAD correlated with total KV with a regression coefficient of 9.3 (95% CI, 3.8-14.7; P = .001) and weakly correlated with estimated glomerular filtration rate with a Pearson coefficient of .10.

CONCLUSIONS

This study demonstrates that renal artery size is positively associated with KV and may be used as an easily measured surrogate marker for kidney size with its attended implications in living donor transplantation.

Automated Region of Interest Detection Method in Scintigraphic Glomerular Filtration Rate Estimation

The glomerular filtration rate (GFR) is a crucial index to measure renal function. In daily clinical practice, the GFR can be estimated using the Gates method, which requires the clinicians to define the region of interest (ROI) for the kidney and the corresponding background in dynamic renal scintigraphy. The manual placement of ROIs to estimate the GFR is subjective and labor-intensive, however, making it an undesirable and unreliable process. This work presents a fully automated ROI detection method to achieve accurate and robust GFR estimations. After image preprocessing, the ROI for each kidney was delineated using a shape prior constrained level set (spLS) algorithm and then the corresponding background ROIs were obtained according to the defined kidney ROIs. In computer simulations, the spLS method had the best performance in kidney ROI detection compared with the previous threshold method (threshold) and the Chan-Vese level set (cvLS) method. In further clinical applications, 223 sets of ^99mTc-diethylenetriaminepentaacetic acid renal scintigraphic images from patients with abnormal renal function were reviewed. Compared with the former ROI detection methods (threshold and cvLS), the GFR estimations based on the ROIs derived by the spLS method had the highest consistency and correlations (r = 0.98, p < 0.001) with the reference estimated by experienced physicians. The results indicate that the proposed automated ROI detection method has great potential in automated ROI detection for accurate and robust GFR estimation in dynamic renal scintigraphy.

Determination of Single-Kidney Glomerular Filtration Rate in Human Subjects by Using CT

PURPOSE

To test the hypothesis that computed tomography (CT)-derived measurements of single-kidney glomerular filtration rate (GFR) obtained in human subjects with 64-section CT agree with those obtained with iothalamate clearance, a rigorous reference standard.

MATERIALS AND METHODS

The institutional review board approved this HIPAA-compliant study, and written informed consent was obtained. Ninety-six patients (age range, 51-73 years; 46 men, 50 women) with essential (n = 56) or renovascular (n = 40) hypertension were prospectively studied in controlled conditions (involving sodium intake and renin-angiotensin blockade). Single-kidney perfusion, volume, and GFR were measured by using multidetector CT time-attenuation curves and were compared with GFR measured by using iothalamate clearance, as assigned to the right and left kidney according to relative volumes. The reproducibility of CT GFR over a 3-month period (n = 21) was assessed in patients with renal artery stenosis who were undergoing stable medical treatment. Statistical analysis included the t test, Wilcoxon signed rank test, linear regression, and Bland-Altman analysis.

RESULTS

CT GFR values were similar to those of iothalamate clearance (mean ± standard deviation, 38.2 mL/min ± 18 vs 41.6 mL/min ± 17; P = .062). Stenotic kidney CT GFR in patients with renal artery stenosis was lower than contralateral kidney GFR or essential hypertension single-kidney GFR (mean, 23.1 mL/min ± 13 vs 36.9 mL/min ± 17 [P = .0008] and 45.2 mL/min ± 16 [P = .019], respectively), as was iothalamate clearance (mean, 26.9 mL/min ± 14 vs 38.5 mL/min ± 15 [P = .0004] and 49.0 mL/min ± 14 [P = .001], respectively). CT GFR correlated well with iothalamate GFR (linear regression, CT GFR = 0.88*iothalamate GFR, r(2) = 0.89, P < .0001), and Bland-Altman analysis was used to confirm the agreement. CT GFR was also moderately reproducible in medically treated patients with renal artery stenosis (concordance coefficient correlation, 0.835) but was unaffected by revascularization (mean, 25.3 mL/min ± 15.2 vs 30.3 mL/min ± 18.5; P = .097).

CONCLUSION

CT assessments of single-kidney GFR are reproducible and agree well with a reference standard. CT can be useful to obtain minimally invasive estimates of bilateral single-kidney function in human subjects.

Correlation between CT-based measured renal volumes and nuclear-renography-based split renal function in living kidney donors. Clinical diagnostic utility and practice patterns

INTRODUCTION

Living donor evaluation involves imaging to determine the choice of kidney for nephrectomy. Our aim was to study the diagnostic accuracy and correlation between CT-based volume measurements and split renal function (SRF) as measured by nuclear renography in potential living donors and its impact on kidney selection decision.

METHODS

We analyzed 190 CT-based volume measurements in healthy donors, of which 65 donors had a radionuclide study performed to determine SRF.

RESULTS

There were no differences in demographics, anthropometric measurements, total volumes, eGFR, creatinine clearances between those who required a nuclear scan and those who did not. There was a significant correlation between CT-volume-measurement-based SRF and nuclear-scan-based SRF (Pearson coefficient r 0.59; p < 0.001). Furthermore, selective nuclear-based SRF allowed careful selection of donor nephrectomy, leaving the donor with the higher functioning kidney in most cases. There was also a significantly higher number of right-sided nephrectomies selected after nuclear-based SRF studies.

CONCLUSION

CT-based volume measurements in living donor imaging have sufficient correlation with nuclear-based SRF. Selective use of nuclear-scan-based SRF allows careful selection for donor nephrectomy.

Influence of early (F+0) intravenous furosemide injection on the split renal function using 99mTc-DTPA renography

In busy nuclear medicine departments, the F+0 protocol for diuretic renography is routinely used to shorten the acquisition time. The aim of this study was to evaluate the influence of the F+0 protocol on the split renal function (SRF) during a dynamic renal scan using technetium-99m diethylene triamine pentaacetic acid (Tc-DTPA) compared with that using the standard technetium-99m dimercaptosuccinic acid (Tc-DMSA). A total of 102 patients referred for a dynamic renal scan for varied etiologies were divided into two groups: the F+0 group, comprising 53 patients who were injected with furosemide just before Tc-DTPA injection, and the F+10 group, comprising 49 patients who were injected with the diuretic at the 10th minute after radiotracer injection. All patients were also subjected to a static cortical Tc-DMSA scan with geometric quantification of SRF. A highly significant statistical difference (P<0.001) was obtained on comparing the mean value of the difference in SRF calculated using DTPA and DMSA between the F+0 and F+10 groups, being 5.0±2.6 and 1.5±0.6%, respectively. All 49 patients in the F+10 group had a difference in split function of 5% or less, whereas 17/53 patients representing 32.1% of the F+0 group had a difference in SRF of greater than 5%. Early (F+0) furosemide injection before administration of Tc-DTPA has a significant influence on the estimation of SRF of the diseased kidney (either obstructed or functionally impaired) when compared with furosemide injection after standard Tc-DMSA administration. Care should be taken during interpretation of the scan findings when accurate split function is required.

Estimation of feline renal volume using computed tomography and ultrasound

Renal volume estimation is an important parameter for clinical evaluation of kidneys and research applications. A time efficient, repeatable, and accurate method for volume estimation is required. The purpose of this study was to describe the accuracy of ultrasound and computed tomography (CT) for estimating feline renal volume. Standardized ultrasound and CT scans were acquired for kidneys of 12 cadaver cats, in situ. Ultrasound and CT multiplanar reconstructions were used to record renal length measurements that were then used to calculate volume using the prolate ellipsoid formula for volume estimation. In addition, CT studies were reconstructed at 1 mm, 5 mm, and 1 cm, and transferred to a workstation where the renal volume was calculated using the voxel count method (hand drawn regions of interest). The reference standard kidney volume was then determined ex vivo using water displacement with the Archimedes' principle. Ultrasound measurement of renal length accounted for approximately 87% of the variability in renal volume for the study population. The prolate ellipsoid formula exhibited proportional bias and underestimated renal volume by a median of 18.9%. Computed tomography volume estimates using the voxel count method with hand-traced regions of interest provided the most accurate results, with increasing accuracy for smaller voxel sizes in grossly normal kidneys (-10.1 to 0.6%). Findings from this study supported the use of CT and the voxel count method for estimating feline renal volume in future clinical and research studies.

[Imaging evaluation of renal function: principles and limitations]

The kidney performs multiple functions. Glomerular filtration is the most studied of these functions. In clinical practice, the surgical indication for patients with unilateral uropathy is frequently based on the split renal function as demonstrated by scintigraphy. MRI is not yet validated as a technique but nonetheless offers an interesting non-radiating alternative to achieve both morphological and functional renal evaluation. Recent pulse sequences such as diffusion, arterial spin labeling, and blood oxygenation dependent imaging may also provide additional information. CT and US remain of limited value for the evaluation of renal function.

Renal parenchyma thickness: a rapid estimation of renal function on computed tomography

PURPOSE

To define the relationship between renal parenchyma thickness (RPT) on computed tomography and renal function on nuclear renography in chronically obstructed renal units (ORUs) and to define a minimal thickness ratio associated with adequate function.

MATERIALS AND METHODS

Twenty-eight consecutive patients undergoing both nuclear renography and CT during a six-month period between 2004 and 2006 were included. All patients that had a diagnosis of unilateral obstruction were included for analysis. RPT was measured in the following manner: The parenchyma thickness at three discrete levels of each kidney was measured using calipers on a CT workstation. The mean of these three measurements was defined as RPT. The renal parenchyma thickness ratio of the ORUs and non-obstructed renal unit (NORUs) was calculated and this was compared to the observed function on Mag-3 lasix Renogram.

RESULTS

A total of 28 patients were evaluated. Mean parenchyma thickness was 1.82 cm and 2.25 cm in the ORUs and NORUs, respectively. The mean relative renal function of ORUs was 39%. Linear regression analysis comparing renogram function to RPT ratio revealed a correlation coefficient of 0.48 (p < 0.001). The linear regression equation was computed as Renal Function = 0.48 + 0.80 * RPT ratio. A thickness ratio of 0.68 correlated with 20% renal function.

CONCLUSION

RPT on computed tomography appears to be a powerful predictor of relative renal function in ORUs. Assessment of RPT is a useful and readily available clinical tool for surgical decision making (renal salvage therapy versus nephrectomy) in patients with ORUs.

Determination of split renal function by 3D reconstruction of CT angiograms: a comparison with gamma camera renography

OBJECTIVE

The objective of our study was to examine the correlation between CT-based and radionuclide renography-based measures of split renal function in a healthy population of live potential kidney donors using 3D models generated from CT angiography.

MATERIALS AND METHODS

The records of 173 renal donor candidates who had undergone CT and radionuclide renography between March 1, 2005, and February 28, 2006, were retrospectively evaluated; of those 173 patients, 152 met study inclusion criteria. A blinded investigator using 3D models that were created semiautomatically from the unenhanced, arterial, and excretory phase data made measurements of CT renal volumes and attenuations. The mean renal attenuation and volume were used to calculate the net accumulation of contrast material and split renal function for comparison with radionuclide renography. Split function from CT was calculated in the arterial and excretory phases as well as based on split renal volume and the Patlak method.

RESULTS

All four CT-based methods for the calculation of split renal function showed correlation with no significant difference from radionuclide renography (p > 0.05, Student's t test). Pearson's correlation coefficients varied from 0.36 to 0.63 (p < 0.001 for each). Difference scores revealed that the excretory and renal volume splits had the narrowest range and showed a linear, nonzero relationship to the renography splits. Bland-Altman analysis confirmed that the majority of difference scores between each CT method and the radionuclide renography were within the 95% CI of the differences.

CONCLUSION

Split renal function based on 3D CT models can provide a "one-stop" evaluation of both the anatomic and the functional characteristics of the kidneys of living potential kidney donors. The excretory phase data and the split renal volume data show the best correlation and the smallest difference scores compared with radionuclide renography data.

Magnetic resonance nephrourography: current and developing techniques

MR nephrourography (MRNU) makes it possible to obtain structural and functional data within a single imaging examination without using ionizing radiation. The functional data available with MRNU allows renal physiology to be examined in ways that were not possible previously. Coupled with the exquisite soft-tissue contrast provided by standard MR images, MRNU can provide a comprehensive study that yields critical diagnostic information on structural diseases of the kidneys and collecting system, including congenital and acquired diseases, and also on the full range of the causes of dysfunction in the transplanted kidney.