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ORIGINAL ARTICLE
Year : 2018  |  Volume : 26  |  Issue : 2  |  Page : 81-84

Establishing normal values for shear-Wave elastography of the renal cortex in healthy adults


Department of Radiology, Weill Cornell Medical College, NY 10065, USA

Date of Submission11-May-2017
Date of Acceptance04-Jul-2017
Date of Web Publication12-Jun-2018

Correspondence Address:
Dr. Ranjit S Sandhu
Department of Radiology, Weill Cornell Medical College, 525 East 68th Street, Box 141, NY 10065
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JMU.JMU_9_17

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  Abstract 

Background: Shear-wave elastography of the kidney has emerged as a potential clinical application of this novel imaging tool. However, normal velocity values for shear-wave elastography involving the cortex of healthy kidneys have not been definitively established, and both inter- and intraobserver reliability has yet to be comprehensively evaluated. Methods: This prospective study involved ultrasound examination of 11 healthy adults. Shear-wave velocity values were obtained at the renal cortex in the longitudinal and transverse planes by both junior (fellow) and senior (attending) radiologists. Results: The mean shear-wave velocity values ranged between 2.82 and 2.9 m/s, which did not vary significantly between observers (junior vs. senior) or method of measurement (longitudinal vs. transverse planes), P = 0.533. However, there was a wide variation for these measurements (0.51–4.99 m/s). Separate analysis of the measurement depth demonstrated no statistically significant association with the shear-wave velocity values, P = 0.477. Conclusion: Our results agree with previous publications and help establish normal shear-wave velocity values and their range for the renal cortex in adults.

Keywords: Elasticity imaging techniques, kidney cortex, observer variation


How to cite this article:
Sandhu RS, Shin J, Wehrli NE, Gao J. Establishing normal values for shear-Wave elastography of the renal cortex in healthy adults. J Med Ultrasound 2018;26:81-4

How to cite this URL:
Sandhu RS, Shin J, Wehrli NE, Gao J. Establishing normal values for shear-Wave elastography of the renal cortex in healthy adults. J Med Ultrasound [serial online] 2018 [cited 2021 Feb 25];26:81-4. Available from: http://www.jmuonline.org/text.asp?2018/26/2/81/234315


  Introduction Top


Ultrasound elastography of the kidneys is a potential application of this novel imaging tool that may become a clinical biomarker for disease. For example, qualitative strain elastography of renal transplant cortex and the corticomedullary strain ratio have been shown to correlate with renal cortical fibrosis.[1],[2] Quantitative shear-wave elastography utilizing acoustic radiation force impulse (ARFI) has demonstrated clinical applications in many areas of imaging, particularly liver imaging.[4] However, there is limited published work concerning normal shear-wave velocity values for the adult kidney.[5],[6],[7] Therefore, we designed a prospective study to determine these values in healthy adults and evaluate both inter- and intraobserver reliability. In addition, we sought to determine the effect of measurement depth on shear-wave velocity values.


  Methods Top


This prospective study was performed at an academic radiology department at a large tertiary care center in New York, NY, USA. The study was conducted in accordance with the Declaration of Helsinki and was approved by the local ethics committee of the institute. Informed written consent was obtained from all patients prior to their enrollment in this study. Eleven healthy adults without any reported history of kidney disease were recruited for this study.

The Acuson S3000 HELX (Siemens Medical Solutions, Malvern, PA, USA) equipped with a 6C1 (1.5–6.0 MHz) curved linear array transducer was used for acquiring grayscale, spectral Doppler, and virtual touch tissue quantification on ARFI imaging in the healthy adults.

During each encounter, both kidneys were evaluated. The participant was placed in the left and right lateral decubitus positions for imaging the right and left kidney, respectively. Before scanning each participant, standardized machine acquisition settings were set, which included MI 1.4, image depth 12–15 cm, scanning frequency 3.5 MHz, single focus, dynamic range 65, harmonic imaging, Map E/Space-time 2, and total gain 0–1. The presence or absence of hydronephrosis, calculi, masses, and perinephric collections was also assessed; the presence of any of these findings served as exclusion criteria.

For each participant, the following values were obtained during suspended respiration: kidney size in the longitudinal plane; main renal artery peak systolic velocity (PSV), end diastolic velocity (EDV), and resistive index (RI); inferior interlobular artery PSV, EDV, and RI; mid-interlobular artery PSV, EDV, and RI; superior interlobular artery PSV, EDV, and RI; shear-wave velocity values at the renal cortex (five measurements in the longitudinal plane at the upper, upper-mid, mid, mid-lower, and lower poles and three measurements in the transverse plane at upper, mid, and lower poles) [Figure 1] and [Figure 2]. All measurements were repeated yielding two measurements per parameter per observer. Each patient was scanned by both junior (fellow) and senior (attending) radiologists separately during the same visit. Measurements were stored as static images. Statistical analysis of the results (including ANOVA and Pearson's correlation coefficient analysis) was performed in Microsoft Excel version 15.11.2 and JASP version 0.8.0.1 Available from: https:www.//jasp-stats.org.
Figure 1: Examples of shear-wave velocity measurement at the renal cortex in the longitudinal and transverse planes, respectively

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Figure 2: Examples of shear-wave velocity measurement at the renal cortex in the longitudinal and transverse planes, respectively

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  Results Top


The kidneys of 11 healthy adults with normal body mass index were scanned (5 men and 6 women). The left kidney of one male participant was excluded from the analysis due to hydronephrosis. Measurements were obtained from all patients with analysis of over 700 shear-wave velocity values [Table 1], [Figure 3] and [Figure 4]. The average shear-wave velocity value for the renal cortex was 2.87 m/s with a wide range of values (0.51–4.99 m/s). The average shear-wave velocity values for the renal cortex in the longitudinal and transverse planes were 2.85 and 2.9 m/s, respectively. The average shear-wave velocity values for the renal cortex obtained by junior and senior observers were 2.84 and 2.82 m/s, respectively. Statistical analysis using ANOVA demonstrated that there was no statistically significant difference between the shear-wave velocity values with respect to plane of acquisition or observer (P > 0.050) [Table 2] and [Figure 5]. Subsequent analysis showed no statistically significant difference between shear-wave velocity values and gender (P > 0.050). Pearson correlation coefficient analysis of shear-wave velocity versus depth found a small strength of association, which was not statistically significant (P = 0.477) [Figure 6].
Table 1: Descriptive statistics for shear-wave velocity (m/s) measured in the longitudinal and transverse planes by junior and senior observers

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Figure 3: Distribution plots for shear-wave velocity (m/s) measured in the longitudinal and transverse planes by junior and senior observers

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Figure 4: Box plots (including violin and jitter elements) for shear-wave velocity (m/s) measured in the longitudinal and transverse planes by junior and senior observers

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Table 2: Statistical analysis of the shear-wave velocity using ANOVA found no statistically significant difference between shear-wave velocity values measured in the longitudinal or transverse planes by junior or senior observers (P = 0.533)

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Figure 5: Statistical analysis using ANOVA found no statistically significant difference between the shear-wave velocity values obtained by each observer in the longitudinal or transverse planes (error bars represent the 95% confidence intervals)

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Figure 6: Pearson's correlation coefficient analysis with correlation plot for shear-wave velocity values versus depth demonstrated a small strength of association, which was not statistically significant (P = 0.477)

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  Discussion Top


Shear-wave elastography of the kidney utilizing ARFI is a potential clinical application of this novel imaging tool, which has demonstrated successful clinical applications in other organs.[4] In the kidney, this tool has shown promise in the evaluation of chronic kidney disease, renal transplant function, and renal vein thrombosis.[1],[2],[3],[4] Concerning the normal values for shear-wave velocity values, Gallotti et al. examined 35 healthy participants and found a mean shear-wave velocity value of 2.24 m/s.[6] Bob et al. examined shear-wave velocity values in a mixed population of 88 patients including both healthy patients and those with renal disease, yielding median values of 2.29–2.45 m/s with a range of 0.58–4.14 m/s. Their subanalysis of patients without renal disease demonstrated median shear-wave velocity values of 2.42 and 2.54 m/s.[5] Similarly, Guo et al. demonstrated a mean shear-wave velocity value of 2.15 m/s in 327 healthy participants.[7] Our investigation of the shear-wave velocity values at the renal cortex in 11 healthy adults agrees with prior publications and confirms the reproducibility of these measurements. We demonstrated that observer experience and plane of acquisition do not significantly affect shear-wave velocity measurements of the renal cortex. In addition, we confirmed that these shear-wave velocity measurements are not affected by depth (within the depth range recommended by the manufacturer since depths exceeding this range will not yield any result). Our limitations mirror those of Bob et al. and include limited sample size and lack of objective data to confirm that healthy participants truly did not have any renal disease.[5] An additional limitation of our study is that the adult participants did not disclose their age, so subanalysis of any effect of age could not be performed. Our results build upon previously published results to establish a groundwork for determining normal values and their range. As suggested by Guo et al., future work examining shear-wave velocity values in renal disease states should correlate their findings with these results to determine if significant differences exist that can be used as potential biomarkers for disease.[7]

Financial support and sponsorship

Jing Gao received the Acuson S3000 ultrasound machine from Siemens Medical Solutions in support of this study.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Gao J, Weitzel W, Rubin JM, Hamilton J, Lee J, Dadhania D,et al. Renal transplant elasticity ultrasound imaging: Correlation between normalized strain and renal cortical fibrosis. Ultrasound Med Biol 2013;39:1536-42.  Back to cited text no. 1
[PUBMED]    
2.
Gao J, Min R, Hamilton J, Weitzel W, Chen J, Juluru K,et al. Corticomedullary strain ratio: A quantitative marker for assessment of renal allograft cortical fibrosis. J Ultrasound Med 2013;32:1769-75.  Back to cited text no. 2
[PUBMED]    
3.
Gao J, He W, Cheng LG, Li XY, Zhang XR, Juluru K,et al. Ultrasound strain elastography in assessment of cortical mechanical behavior in acute renal vein occlusion:In vivo animal model. Clin Imaging 2015;39:613-8.  Back to cited text no. 3
[PUBMED]    
4.
Bruno C, Minniti S, Bucci A, Pozzi Mucelli R. ARFI: From basic principles to clinical applications in diffuse chronic disease-a review. Insights Imaging 2016;7:735-46.  Back to cited text no. 4
[PUBMED]    
5.
Bob F, Bota S, Sporea I, Sirli R, Petrica L, Schiller A,et al. Kidney shear wave speed values in subjects with and without renal pathology and inter-operator reproducibility of acoustic radiation force impulse elastography (ARFI) – Preliminary results. PLoS One 2014;9:e113761.  Back to cited text no. 5
    
6.
Gallotti A, D'Onofrio M, Pozzi Mucelli R. Acoustic radiation force impulse (ARFI) technique in ultrasound with virtual touch tissue quantification of the upper abdomen. Radiol Med 2010;115:889-97.  Back to cited text no. 6
    
7.
Guo LH, Xu HX, Fu HJ, Peng A, Zhang YF, Liu LN,et al. Acoustic radiation force impulse imaging for noninvasive evaluation of renal parenchyma elasticity: Preliminary findings. PLoS One 2013;8:e68925.  Back to cited text no. 7
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2]


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