Renal Adiposity Confounds Quantitative Assessment of Markers of Renal Diffusion With MRI

Abstract

Objectives Recent studies have indicated that excessive fat may confound assessment of diffusion in organs with high fat content, such as the liver and breast. However, the extent of this effect in the kidney, which is not considered a major fat deposition site, remains unclear. This study tested the hypothesis that renal fat may impact DWI parameters, and proposes a three-compartment model (TCM) to circumvent this effect. Methods Using computer simulations, we investigated the effect of fat on assessment of apparent diffusion coefficient (ADC), intravoxel incoherent-motion (IVIM) and TCM-derived pure-diffusivity. We also investigated the influence of MR repetition (TR) and echo time (TE) on DWI parameters as a result of variation in the relative contribution of the fat signal. ADC, IVIM and TCM DWI parameters were calculated in domestic pigs fed a high-cholesterol (Obese) or normal diet (Lean), and correlated to renal histology. IVIM-derived pure diffusivity was also compared among fifteen essential hypertension (EH) patients classified by BMI (high vs. normal). Finally, pure diffusivity was calculated and compared in eight patients with atherosclerotic renal artery stenosis (ARAS) and five healthy subjects using IVIM and TCM. Results Simulations showed that unaccounted fat results in the underestimation of IVIM-derived pure-diffusivity. The underestimation increases as the fat fraction increases, with higher pace at lower fat contents. The underestimation was larger for shorter TR and longer TE values due to the enhancement of the relative contribution of the fat signal. Moreover, TCM, which incorporates highly diffusion-weighted images (b>2500s/mm2), could correct for fat-dependent underestimation. Animal studies in Lean and Obese confirmed lower ADC and IVIM pure-diffusivity in Obese vs. Lean pigs with otherwise healthy kidneys, while pure-diffusivity calculated using TCM were not different between the two groups. Similarly, EH patients with high BMI had lower ADC (1.9 vs. 2.1×10−3 mm2/s) and pure-diffusivity (1.7 vs. 1.9×10−3mm2/s) than those with normal BMI. Pure-diffusivity calculated using IVIM was not different between the ARAS and healthy subjects, but TCM revealed significantly lower diffusivity in ARAS. Conclusions Excessive renal fat may cause underestimation of renal ADC and IVIM-derived pure-diffusivity, which may hinder detection of renal pathology. Models accounting for fat contribution may help reduce the variability of diffusivity calculated using DWI.

Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI

“…Other, more complex, extended IVIM models can be found in the literature that aim to incorporate more characteristics of functioning renal tissue into the signal description. Three compartment models include an additional component taking into account multiple sources of intravoxel incoherent motion, e.g., due to the glomerular flow [29,30], vascular vs. tubular flow, or residual fat signal [31]. Other extended models combine IVIM with diffusion anisotropy for a more comprehensive description of both structural and microcirculation features [32,33].…”

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

“…2c) is more than one order of magnitude larger than the true diffusivity D t , which is typically lower than the ADC. 27 Findings-Similar to ADC, IVIM imaging detected decreased diffusion as well as lower perfusion in native kidney diseases [48][49][50][51][52][53][54][55] and dysfunctional renal allografts. [56][57][58] However, by yielding a larger number of renal physiological parameters, IVIM imaging offers new insights into renal pathophysiology.…”

Renal Functional MRI and Its Application

“…However, the dependence of the ADC on collagen deposition is currently uncertain. Further studies should examine the impact of excessive fat in DWI measurement, as it may result in an underestimation of parameters describing pathological changes …”