Estimation of Multi-Component Flow in the Kidney with Multi-b-value Spectral Diffusion

TL;DR

This study explores spectral diffusion MRI to differentiate and quantify flow and diffusion components in kidney allografts, showing potential for clinical assessment of fibrosis and function through advanced multi-b-value DWI analysis.

Contribution

It introduces spectral diffusion MRI with multi-Gaussian fD as a novel method to separate and quantify flow and diffusion in kidney tissue, improving upon traditional models.

Findings

Spectral diffusion fD correlates strongly with simulated anisotropic and anomalous components.

Higher allograft fibrosis scores associate with increased fD_tissue.

Impaired kidney function correlates with reduced fD_tubule, and higher proteinuria correlates with lower fD_vascular.

Abstract

Purpose: Examine the theory and potential clinical application of estimated intravoxel flow of separated perfusion, tubular flow, and diffusion from multi-b-value DWI in kidney allografts. Methods: Multi-b-value DWI (9 b-values; 0-800 s/mm2) from a kidney cortex is simulated with anisotropic and non-Gaussian (i.e. anomalous) vascular, tubular, and tissue components and analyzed with a Bayesian biexponential, least-squares triexponential, and spectral diffusion MRI. Comparison and application of biexponential, triexponential, and spectral diffusion fD is demonstrated in a two-center study of 54 kidney allografts patients (21F/33M, 48.8 SD 10.5years) and compared to fibrosis (Banff 2017 interstitial fibrosis and tubular atrophy score 0-6 from clinical biopsies of the renal cortex), impaired kidney function (CKD-EPI 2021 eGFR<45ml/min/1.73m2), and proteinuria. Results: Spectral diffusion fD demonstrated strong correlation to input fD of the simulated anisotropic and anomalous components. It agreed with both three-component diffusion and two-component diffusion. fD showed similar or improved agreement and correlation to input compared to individual parameters, and similar or improved agreement to corresponding bi- and triexponential models. In kidney allografts, spectral diffusion fD showed higher allograft fibrosis score had higher fD_tissue, impaired allograft function showed reduced fD_tubule, and fD_vascular negatively correlated with proteinuria across diagnostic groups of function and fibrosis. Conclusions: Spectral diffusion MRI with multi-Gaussian fD as a flow proxy separated different anomalous and anisotropic diffusion components of perfusion, tubular flow, and tissue diffusion and may hold clinical value in diffusion MRI of kidney pathophysiology.