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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 15  |  Issue : 3  |  Page : 211-214

Correlation of three-dimensional computerized tomographic renal parenchymal volumetry with DTPA split renal function in prospective donors - A retrospective study


1 Department of Radiology, SVIMS, Tirupati, Andhra Pradesh, India
2 Department of Nephrology, Chalmeda Anand Rao Institute of Medical Sciences, Karimnagar, Telangana, India
3 Department of Nephrology, SVIMS, Tirupati, Andhra Pradesh, India
4 Department of Nuclear Medicine, SVIMS, Tirupati, Andhra Pradesh, India

Date of Submission07-Jul-2020
Date of Decision12-Dec-2020
Date of Acceptance28-Apr-2021
Date of Web Publication30-Sep-2021

Correspondence Address:
Pavankumar G Kale
Departments of Radiology, SVIMS, Tirupati - 517 507, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijot.ijot_71_20

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  Abstract 

Introduction: Split renal function (SRF) in prospective renal donors is traditionally measured by means of scintigraphy. Recent studies have reported the utility of three-dimensional computerized tomographic renal volumetry as an alternative to scintigraphy in estimating SRF. As computed tomography (CT) angio is done routinely for donors use of the same CT for estimating renal functions can eliminate the radiation from scintigraphy. Methods: In our study, renal volume was estimated on computerized tomographic renal angiography images using Siemens volumetry software by drawing contours manually on images, wherein we found the mean total renal volume to be 212.7 ± 38 CC and mean split renal volume to be 49.76 CC ± 2.86 and 50.23CC ± 2.86 on the right and left side, respectively. Results: This split renal volume was corrected to body mass index and surface area wherein we found significant correlation between renal volume and function when both were corrected to body surface area (P < 0.0001). Conclusion: From our results, it appears that computerized tomographic renal angiography not only depicts anatomy but also can give information about renal function which needs further confirmation.

Keywords: Computerized tomography, renal volumetry, split renal function renal donors


How to cite this article:
Kale PG, Choudary GP, Sandeep P, Lakshmi AY, Kumar V S, Mantri R. Correlation of three-dimensional computerized tomographic renal parenchymal volumetry with DTPA split renal function in prospective donors - A retrospective study. Indian J Transplant 2021;15:211-4

How to cite this URL:
Kale PG, Choudary GP, Sandeep P, Lakshmi AY, Kumar V S, Mantri R. Correlation of three-dimensional computerized tomographic renal parenchymal volumetry with DTPA split renal function in prospective donors - A retrospective study. Indian J Transplant [serial online] 2021 [cited 2021 Dec 5];15:211-4. Available from: https://www.ijtonline.in/text.asp?2021/15/3/211/327396


  Introduction Top


The renal parenchymal volume (RPV) is considered as an indicator of functional residual capacity of the kidney.[1],[2],[3],[4] Renal volume, along with a number of clinical parameters, may become an important tool for the evaluation of renal diseases, renovascular diseases as well as kidney transplantation. Preoperative radiological evaluation of renal donors is done to select the kidney to be harvested in each patient. Recent studies suggest that spiral computed tomography (CT) angiography can replace renal angiography and excretory urography in the evaluation of potential kidney donors.[5],[6],[7],[8],[9],[10],[11],[12],[13],[14] The evaluation of predonation renal function is a key factor in living donor assessment to obtain detailed information to minimize the risk for the living donor.[15],[16],[17],[18],[19] Tc-99m-mercapto-acetyltriglycin scintigraphy is used for assessment of Split renal function (SRF). Contrast-enhanced CT is used for renal vasculature and anatomy. Recent studies in living kidney donors showed that SRF could be evaluated preoperatively by CT-based analyses of the kidney volume.[20] The available CT-based solutions are heterogeneous with respect to complexity, postprocedure processing requirements, and inter-observer reliability.[21],[22],[23],[24],[25],[26],[27] The availability of reproducible, simple, fast, and accurate methods of computation, including semi-automated techniques, would be beneficial. Semi-automated segmentation tools are now well-established for kidney volumetry in polycystic kidney disease.[28],[29],[30],[31],[32] The most promising techniques for CT-based calculation of SRF in the literature are the modified ellipsoid volume (MELV) and smart region of interest (ROI) volumetry. MELV is a simple and fast measurement method.[33] In our study, we aim to use a simpler method of RPV calculation and correlation with scintigraphy measured SRF wherein multiple phases of CT acquisition and dedicated softwares will not be needed and it can be done on the available angiography images with the widely available volume measurement software tools on CT machines. Hence in this study, our objective was to measure the renal volumes on CT angiography, correct the renal volume to body mass index (BMI), body surface area and correlate the corrected volume to renal scintigraphy derived SRF.


  Materials and Methods Top


Institutional review board approval was obtained for the study. Being a retrospective study no ethical issues were involved in our study. We retrospectively searched the hospital information system maintained by our hospital for all potential donors screened for live renal donor evaluation between 2011, and 2017. Informed consent was waived off for this study as it included only review of existing patient data. A total of 51 potential donors who underwent evaluation for living renal transplantation were sorted out and 23 donors (5 men and 18 women with a mean age of 45 years), who underwent both dynamic CT and renal scintigraphy with 99mTc-DTPA could be included for analysis. Remaining 28 patients were excluded in view of inadequate data. The median interval between CT and 99mTc-DTPA scintigraphy was 1 month, ranging from 0 to 6 months. Primary objective of our study was to measure renal volumes on the CT angiography data and to correlate the same with SRF.

Imaging

All the CT scans were performed on 128–slice Siemens Somatom Definition. Triphasic abdominal CT angiography images included unenhanced, arterial phase, and excretory phase data sets for examination of renal function by contrast clearance. Iohexol 350 mg Iodine/mL (Omnipaque, GE Healthcare) was the contrast agent injected at a rate of 3–5 ml/s through a peripherally placed IV cannula according to a standardized protocol. Standardized settings were used as a starting point and were adjusted by CT technicians as necessary to produce images for interpretation. The general settings were 120 kVp, pitch of 0.891, and rotation speed of 0.75 s. A routine maximum of 300 mAs was used for each series. Arterial phase scanning was triggered when a tracker ROI in the proximal abdominal aorta reached 100 Hounsfield unit (HU). The scan for the renal parenchymal phase was started about 90 s after starting the injection. Excretory phase scanning occurred 180 s after the same trigger. Images were constructed at the following slice thicknesses and increments, respectively: Unenhanced, 3 mm at 3 mm; arterial, 3 mm at 3 mm; and excretory, 3 mm at 3 mm. Patients with partial studies due to unsuccessful administration of contrast material because of extravasation were not included in the study. If the CT examination did not include the entire renal volumes or if there were any focal lesions in the renal parenchyma, the patient was excluded from the study. Postprocessing of the acquired data is done on Siemens syngo software. ROI was drawn slice by slice on 0.6 mm axial arterial phase images. The renal contour was drawn manually with cursor pointed on the renal parenchyma; volume was estimated by Siemens volumetry software. Threshold of HU value of voxels to be included in volume measurement was set between 10 and 500 voxels with above and below this HU range were excluded by the software from volume calculation. The data thus obtained were recorded and analyzed using Microsoft Excel sheet.

Volume correction and ratios

Calculated renal volumes of either kidney were added up and the percentage of individual renal volume was calculated as percentage renal volume (PRV). This PRV was corrected to body surface area by taking individual PRV and dividing it by body surface area. Likewise, the PRV was also separately individually corrected to BMI. This corrected PRV was separately correlated with SRF measured on scintigraphy.

Statistical analysis

Statistical analysis was performed using SPSS Statistics (Version 20; IBM Corp., Armonk, NY, USA) as our statistical tool. Descriptive statistics are given as mean and standard deviations (SD), for comparison between CT renal volume and DTPA-scintigraphy two-sample test, assuming unequal variances was used.

Patient consent

Informed consent was waived off for this study as it included only review of existing patient data.

Ethics statement

Institutional review board approval was obtained for the study. Being a retrospective study no ethical issues were involved in our study. SVIMS institutional ethics committee IRB number –ROC.NO.AS/11/IEC/SVIMS/2017. All protocols were followed as per the Declartion of Helsinki The procedure was carried out in accordance with the Declaration of Helsinki and International Council for Harmonization-Good Clinical Practice (ICH-GCP).


  Results Top


Of the 23 patients analyzed for the study, the mean age of the patients was 45.6 years, with a range of 30–56 years. The study group comprised 78.2% women. The mean (±SD) creatinine clearance was 124 ± 34 mL/min. The mean DTPA renography determined right split function for our population was 49.2% ± 4.3% and ranged from 29% to 63%. Mean BMI was 23.02, mean surface area was 1.5656 m2, mean GFR was 98.29 mL/min/1.73 m2 mean total renal volume was 212.75 cc and mean split renal volume calculated as a percentage of total volume was 49.76% on the right side and 50.234% on the left side, the ratio of PRV to body surface area was 38.97% on the right side and 39.30 on the left side.


  Discussion Top


During the evaluation of renal donors in the initial period, excretory urography and renal angiography were in use. With advancement in the technology, the procedures such as renal scintigraphy and preoperative CT angiography have been introduced in donor evaluation to study renal morphology and the anatomical aspects of the renal vasculature. In recent literature importance of CT volumetry as a modality in studying renal function is being considered as a possible one-stop solution for anatomy and function.[34] In our institute, renal scintigraphy is done for knowing the SRF and CT angiography for vascular anatomy and evaluation of the urinary tract.

In our study, we have compared the volume measurements deciphered from CT and from renal scintigraphy being performed on donors and found that there was no statistically significant difference between the estimated renal function suggesting the usefulness of CT angiography as an alternative modality for estimation of function using less technically challenging methods. In our study, the CT angiography for serial renal donors during study period was evaluated and none of the scans were found to be inadequate for volume measurements. Interobserver variability was not assessed in our study.

In previous similar studies the RPV measured on CT angiography was corrected to the fraction of arterial contrast enhancement, In another study by Kato et al.,[27] renal cortical volume is corrected to arterial enhancement, and these modified volumes have been compared to SRF, but these method involved difficult calculations and requires precise timing of acquisition. In our study rather than correcting RPV to arterial enhancement we tried to correct it to body surface area and BMI, we believe this method is technically simpler.

In our study, there was a significant correlation between BMI corrected split RPV, and scintigraphy determined SRF with P < 0.0001 [Table 1] and [Table 2]. Significant correlation was also seen between split RPV corrected to body surface area and scintigraphy determined SRF with P < 0.0001 [Table 3] and [Table 4].
Table 1: T-test showing significant correlation between body mass index corrected split percentage renal volume, and scintigraphy determined split renal function in the right kidney

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Table 2: T-test showing significant correlation between body mass index corrected split percentage renal volume, and scintigraphy determined split renal function in the left kidney

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Table 3: T-test showing significant correlation between split percentage renal volume corrected to body surface area and scintigraphy determined split renal function in the right kidney

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Table 4: T-test showing significant correlation between split percentage renal volume corrected to body surface area and scintigraphy determined split renal function in the left kidney

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Limitations of our study

The authors were not blinded to the scintigraphy SRF values. Time required for volume measurement was not estimated. Ours was a single center study with small sample size.


  Conclusion Top


From our results, it appears that CT angiography not only just depicts anatomy but also can give information about renal function, which needs further confirmation by larger studies.

Future scope

With further validation of our results, pre-operative CT angiography can become a one-stop solution for assessment of both function and anatomy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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  [Table 1], [Table 2], [Table 3], [Table 4]



 

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