Magnetic resonance elastography‐derived stiffness of the kidneys and its correlation with water perfusion

Abstract

Stiffness plays an important role in diagnosing renal fibrosis. However, kidney stiffness is altered by perfusion changes in many kidney diseases. Therefore, the aim of the current study is to determine the correlation of kidney stiffness with water intake. We hypothesize that kidney stiffness will increase with 1 L of water intake due to increased water perfusion to the kidneys. Additionally, stiffness of the kidneys will correlate with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values before and after water intake. A 3 T MRI scanner was used to perform magnetic resonance elastography and diffusion tensor imaging of the kidneys on 24 healthy subjects (age range: 22‐66 years) before and after water intake of 1 L. A 3D T1‐weighted bladder scan was also performed to measure bladder volume before and after water intake. A paired t‐test was performed to evaluate the effect of water intake on the stiffness of kidneys, in addition to bladder volume. A Spearman correlation test was performed to determine the association between stiffness, bladder volume, ADC and FA values of both kidneys before and after water intake. The results show a significant increase in stiffness in different regions of the kidney (ie, percentage increase ranged from 3.6% to 7.5%) and bladder volume after water intake (all P < 0.05). A moderate significant negative correlation was observed between change in kidney stiffness and bladder volume (concordance correlation coefficient = ‐0.468, P < 0.05). No significant correlation was observed between stiffness and ADC or FA values before and after water intake in both kidneys (P > 0.05). Water intake caused a significant increase in the stiffness of the kidneys. The negative correlation between the change in kidney stiffness and bladder volume, before and after water intake, indicates higher perfusion pressure in the kidneys, leading to increased stiffness.

Reduction of breathing artifacts in multifrequency magnetic resonance elastography of the abdomen

“…An earlier study of our group shows that multifrequency MRE of the kidneys is improved when omitting any breathing command compared with breath‐hold MRE 25 . However, this case‐specific finding from a single subject was never reproduced or compared with other abdominal organs, as done in the present study. All protocols provided values in the range of published values of abdominal MRE (converting SWS to shear modulus by µ = SWS 2 · 1000 kg/m 3 ) 37‐39 or directly agreed with reported SWS values in that region 25,40 . The visible blurring of the magnitude images in free‐breathing MRE (see Figures 3‐6) suggests that stiffness values are strongly affected by breathing motion, which, however, is not the case.…”

Cerebral Ultrasound Time-Harmonic Elastography Reveals Softening of the Human Brain Due to Dehydration

“…For instance, it has been shown that liver stiffness increases with water ingestion and hepatic blood flow ( Ipek-Ugay et al, 2016 ; Tzschatzsch et al, 2016b ). The opposite effect, i.e., softening, has been observed in the pancreas and spleen ( Dittmann et al, 2017 ) while kidney stiffness has been reported to change only slightly with increasing bladder filling ( Gandhi et al, 2020 ) and hydration ( Marticorena Garcia et al, 2018 ).…”

MR Elastography of the Abdomen: Basic Concepts

“…Water intake before a MRE scan can act also as a confounding factor to estimate the stiffness of kidneys. In a recent study, Gandhi et al observed a negative correlation between difference in stiffness values and changes in bladder volumes before and after water intake [67]. This suggests that at lower bladder volume the kidneys are still filtering the water where perfusion pressure is high leading to an increased stiffness in the kidneys.…”

“…l While performing renal MRE, renal perfusion status should be taken into account to ensure reproducible detection [73]. Confounding stiffness changes due to excess water intake have been reported [67].…”