Chemical-Shift-Encoded Magnetic Resonance Imaging and Spectroscopy to Reveal Immediate and Long-Term Multi-Organs Composition Changes of a 14-Days Periodic Fasting Intervention: A Technological and Case Report

Objectives: The aim of this study was to investigate the feasibility of measuring the effects of a 14-day Periodic Fasting (PF) intervention (<200 cal) on multi-organs of primary interest (liver, visceral/subcutaneous/bone marrow fat, muscle) using non-invasive advanced magnetic resonance spectroscopic (MRS) and imaging (MRI) methods.Methods: One subject participated in a 14-day PF under daily supervision of nurses and specialized physicians, ingesting a highly reduced intake: 200 Kcal/day coupled with active walking and drinking at least 3 L of liquids/day. The fasting was preceded by a 7-day pre-fasting vegetarian period and followed by 14 days of stepwise reintroduction of food. The longitudinal study collected imaging and biological data before the fast, at peak fasting, and 7 days, 1 month, and 4 months after re-feeding. Body fat mass in the trunk, abdomen, and thigh, liver and muscle mass, were respectively computed using advanced MRI and MRS signal modeling. Fat fraction, MRI relativity index T2* and susceptibility (Chi), as well as Fatty acid composition, were calculated at all-time points.Results: A decrease in body weight (BW: −9.5%), quadriceps muscle volume (−3.2%), Subcutaneous and Visceral Adipose Tissue (SAT −34.4%; VAT −20.8%), liver fat fraction (PDFF = 1.4 vs. 2.6 % at baseline) but increase in Spine Bone Marrow adipose tissue (BMAT) associated with a 10% increase in global adiposity fraction (PDFF: 54.4 vs. 50.9%) was observed. Femoral BMAT showed minimal changes compared to spinal level, with a slight decrease (−3.1%). Interestingly, fatty acid (FA) pattern changes differed depending on the AT locations. In muscle, all lipids increased after fasting, with a greater increase of intramyocellular lipid (IMCL: from 2.7 to 6.3 mmol/kg) after fasting compared to extramyocellular lipid (EMCL: from 6.2 to 9.5 mmol/kg) as well as Carnosine (6.9 to 8.1 mmol/kg). Heterogenous and reverse changes were also observed after re-feeding depending on the organ.Conclusion: These results suggest that investigating the effects of a 14-day PF intervention using advanced MRI and MRS is feasible. Quantitative MR indexes are a crucial adjunct to further understanding the effective changes in multiple crucial organs especially liver, spin, and muscle, differences between adipose tissue composition and the interplay that occurs during periodic fasting

MRI Principles, Hardware Components and Quantification

International audienceThis chapter describes magnetic resonance imaging (MRI) principles and the main components of an MRI scanner, in particular those responsible for the generation of magnetic fields and signal acquisition. The static magnetic field is employed both for polarizing the sample and imposing the frequency of excitation and signal acquisition. These two aspects determine the specifications and constraints of the magnet. The chapter explains how the magnetization relaxation to equilibrium can be modulated to obtain information on spatial localization or tissue composition. It discusses the principles of encoding an nuclear magnetic resonance (NMR) image performed using gradients of magnetic fields in a rather succinct way. In order to perform the spatial encoding of information, additional magnetic fields have to be superposed to the main static magnetic field. The NMR signal measured by a magnetic flux detector is obtained after the steps of amplification, demodulation, sampling and digitization via analog or digital converters

Méthodes d'estimation et modèles de diffusion avancés pour l'évaluation de la fibrose hépatique dans les maladies chroniques du foie

Mettre en oeuvre des modèles de diffusionavancés pour l’aide au diagnostic de la fibrosehépatique, et déterminer la méthode d’estimationparamétrique la plus adaptée parmi la méthode desmoindres carrés non linéaires (NLS), la méthode NLSsegmentée et la méthode bayésienne initialisée parNLS

Estimation of intravoxel incoherent motion (IVIM)-Kurtosis diffusion-weighted imaging and its application in liver

International audienceTo evaluate the feasibility of using intravoxel incoherent motion (IVIM)-Kurtosis diffusion-weightedimaging for the noninvasive staging of liver fibrosis in patients with chronic liver disease., we have implementednon-linear least squares (LSQ) -based methods. To fit the numerous parameters of the proposed IVIM-Kurtosismodel, a one-step fitting approach vs a three-step approach (segmented LSQ) were compared, analyzed andvalidated on patient data, for which complementary hepatic biomarkers obtained from blood and biopsies wereavailable

Optimization of b-values sampling scheme for several diffusion-weighted MRI models in the liver

To determine an optimal b-values sampling scheme for different non-Gaussian diffusion models in the liver, including diffusion kurtosis imaging (DKI), stretched-exponential model (SEM), intravoxel incoherent motion (IVIM), we optimized diffusion-weighting b-values sets using simulations mimicking real data and a b-value selection based on a Monte Carlo-like approach. Estimation performances were evaluated in terms of mean square error on signal and mean absolute percentage error on parameters in simulated data. The parameter estimation, with optimized set of b-values was finally applied on real data. The results showed that comparable fitting parameters and reconstructing signal can be obtained with fractional b-values

Chronic liver disease: The role of multiple diffusion-weighted models using the Bayesian shrinkage method for liver fibrosis assessment

Liver fibrosis is one of the leading features in chronic liver disease (CLD) since it conditions the prognosis and guides the treatment strategy. In this work, estimated parameters from various diffusion-weighted MRI models fitted by the Bayesian method were analyzed for the relationship with liver fibrosis through spearman's correlation and t-test. Four parameters (D , σ, D _F, D) were selected for fibrosis classification and achieved the best result based on the decision tree. Our result suggested that the statistical model and a hybrid IVIM-DKI model are promising models and confirmed the confounding effect of fat for diffusivity to assess liver fibrosis

Time Undersampled Acquisition for Multidimensional Sparse Signals With Application to Magnetic Resonance Spectroscopic Imaging

International audienceThis paper deals with acceleration of multidimensional signal acquisition. The signal is assumed to have multiple discrete spatial dimensions where each point is time varying. The one-dimensional Fourier transform of the time evolution of each point is assumed to have an a priori known bounded support. The Fourier transform of the spatial domain is divided into several partitions, each of which can be sequentially acquired over time. We propose a method for undersampling the time dimension that enables interleaving of the samples hence speeding up signal acquisition. This method, applied to realistic simulated magnetic resonance spectroscopic imaging data (MRSI), leads to a reduction in the acquisition time by a factor of three

Correction de phase pour l'Imagerie Spectroscopique Rapide

International audienc

Validation d'un indicateur du contenu apparent en lipides intra et extra-myocellulaires par imagerie spectroscopique spiralé à 3T

International audienceThis work presents a fast and simple method based on spiral MRSI for mapping the IMCL and EMCL apparent content, which is a challenging task and it compares this indicator to classical quantification results in muscles of interest