arXiv subjects

Mira M. Liu

Publications and source records attributed to Mira M. Liu.

4 recordsLinked to original sources

arXiv2025

Detecting Early Kidney Allograft Fibrosis with Multi-b-value Spectral Diffusion MRI

Kidney allograft fibrosis is a marker of chronic kidney disease (CKD) and predicts functional decline, and eventual allograft failure. This study evaluates if spectral diffusion MRI can help detect early development and mild/moderate fibrosis in kidney allografts. In a prospective two-center study of kidney allografts, interstitial fibrosis and tubular atrophy (IFTA) was scored and eGFR was calculated from serum creatinine. Multi-b-value DWI (bvalues=[0,10,30,50,80,120,200,400,800mm2/s]) was post-processed with spectral diffusion, intravoxel incoherent motion (IVIM), and apparent diffusion coefficient (ADC). Connection between imaging parameters and biological processes was measured by Mann-Whitney U-test and Spearman's rank; diagnostic ability was measured by five-fold cross-validation univariate and multi-variate logistic regression. Quality control analyses included volunteer MRI (n=4) and inter-observer analysis (n=19). 99 patients were included (50$\pm$13yo, 64M/35F, 39 IFTA=0, 22 IFTA=2, 20 IFTA=4, 18 IFTA=6, 46 eGFR<=45mL/min/1.73m2, mean eGFR=47.5$\pm$21.3mL/min/1.73m2). Spectral diffusion detected fibrosis (IFTA>0) in patients with normal/stable eGFR>45ml/min/1.73m2 [AUC(95$\%$CI)=0.72(0.56,0.87),p=0.007]. Spectral diffusion detected mild/moderate fibrosis (IFTA=2-4) [AUC(95$\%$CI)=0.65(0.52,0.71),p=0.023], as did ADC [AUC(95$\%$CI)=0.71(0.54,0.87),p=0.013)]. eGFR, time-from-transplant, and allograft size could not. Interobserver correlation was >0.50 in 24 out of 40 diffusion parameters. Spectral diffusion MRI showed detection of mild/moderate fibrosis and fibrosis before decline in function. It is a promising method to detect early development of fibrosis and CKD before progression.

physics.med-ph↗

arXiv2025

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

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.

physics.med-ph↗

arXiv2024

A Method for Imaging the Ischemic Penumbra with MRI using IVIM

This work examines the hypothesis that intravoxel incoherent motion MRI (IVIM) can quantify local cerebral blood flow (qCBF), infarct volume, and define the ischemic penumbra for determination of the perfusion-diffusion mismatch (PWI/DWI) volume in a setting of acute ischemic stroke. Eight experiments were conducted in a pre-clinical middle cerebral artery occlusion (MCAO) model. IVIM and dynamic susceptibility contrast (DSC) imaging were acquired 2.5hr post-MCAO. IVIM was post-processed using software written in-house to produce parametric images of local qCBF, Water Transport Time (WTT), diffusion, and subsequently, PWI/DWI mismatch. These IVIM image parameters were compared with delay-and-dispersion-corrected local-AIF DSC perfusion image parameters including Tmax, qCBF, mean transit time (MTT), and mean diffusivity for DSC PWI/DWI mismatch. Final infarct volume was measured 4hrs post-occlusion. Early (2.5hr post-occlusion) DSC qCBF and IVIM qCBF in the diffusion negative MCA territory correlated strongly (slope=1.00, p=0.01,R2=0.69,Lins CCC=0.71), and both DSC and IVIM qCBF values negatively correlated with final infarct volume (R2=0.78,R2=0.61 respectively). The volume of hypoperfusion measured at 2.5 hours from DSC qCBF and from IVIM qCBF both predicted final infarct volume with good sensitivity and correlation (slope=2.08, R2=0.67, slope=2.50,R2=0.68 respectively). IVIM PWI/DWI ratio was correlated with infarct growth (R2=0.70) and WTT correlated with MTT (slope=0.82,R2=0.60). IVIM qCBF correlated strongly with local-AIF DSC qCBF and IVIM PWI/DWI correlated strongly with infarct growth. Both DSC and IVIM quantitative perfusion image acquired early after occlusion were able to predict final infarct volume, and IVIM simultaneous PWI/DWI ratio predicted infarct growth.

physics.med-ph↗

arXiv2024

Quantification of Collateral Supply with Local-AIF Dynamic Susceptibility Contrast MRI Predicts Infarct Growth

In ischemic stroke, leptomeningeal collaterals can provide compensatory blood flow to tissue at risk despite an occlusion, and impact treatment response and infarct growth. The purpose of this work is to test the hypothesis that local perfusion with an appropriate Local Arterial Input Function (AIF) is needed to quantify the degree of collateral blood supply in tissue distal to an occlusion. Seven experiments were conducted in a pre-clinical middle cerebral artery occlusion model. Magnetic resonance dynamic susceptibility contrast (DSC) was imaged and post-processed as cerebral blood flow maps with both a traditionally chosen single arterial input function (AIF) applied globally to the whole brain (i.e. "Global-AIF") and a novel automatic delay and dispersion corrected AIF (i.e. "Local AIF") that is sensitive to retrograde flow. Pial collateral recruitment was assessed from x-ray angiograms and infarct growth via serially acquired diffusion weighted MRI scans both blinded to DSC. The degree of collateralization at x-ray correlated strongly with quantitative perfusion determined using the Local AIF in the ischemic penumbra (R2=0.81) compared to a traditionally chosen Global-AIF (R2=0.05). Quantitative perfusion calculated using a Local-AIF was negatively correlated (less infarct progression as local perfusion increased) with infarct growth (R2 = 0.79) compared to Global-AIF (R2=0.02). Local DSC perfusion with a Local-AIF is more accurate for assessing tissue status and degree of leptomeningeal collateralization than traditionally chosen AIFs. These findings support use of a Local-AIF in determining quantitative tissue perfusion with collateral supply in occlusive disease.

physics.med-ph↗