arXiv subjects

Guillaume Madelin

Publications and source records attributed to Guillaume Madelin.

6 recordsLinked to original sources

arXiv2026

Multinuclear fingerprinting

We developed a new magnetic resonance imaging method called multinuclear fingerprinting (MNF) which leverages simultaneously-acquired proton (1H) and sodium (23Na) data to generate seven quantitative maps of the whole brain: proton density (PD), T1 and T2 relaxation times from water, and tissue sodium concentration (TSC), T1, T2short and T2long from Na+ ions. MNF consists of two parts: (1) simultaneous 1H/23Na magnetic resonance fingerprinting (MRF), and (2) a super-resolution (SR) algorithm to increase the 23Na resolution to match the 1H resolution. It was tested on the brain of seven healthy subjects at 7 T, with a final resolution of 1.5x1.5x5 mm3 for all maps acquired in 13 min. MNF could provide new fundamental insights into the inter-relationship between morphology (i.e. tissue structure from the 1H maps) and physiology (i.e. ion homeostasis from the 23Na maps) in vivo to help improve our understanding of the human brain in general, and to study neuropathologies and their treatments. Since all 1H/23Na MRF data is acquired simultaneously, all images are exactly co-registered with identical spatial and temporal resolutions. MNF could be useful in future longitudinal studies for assessing local time-dependent and conjoint 1H/23Na MR changes during tasks or interventions. MNF was initially developed for neuroimaging, but it can be adapted to any other parts of the body.

physics.med-ph↗

arXiv2025

Correlation-weighted 23Na magnetic resonance fingerprinting in the brain

We developed a new sodium magnetic resonance fingerprinting ($^\text{23}\text{Na}$ MRF) method for the simultaneous mapping of $\text{T}_\text{1}$, $\text{T}_\text{2,long}^{*}$, $\text{T}_\text{2,short}^{*}$ and sodium density with built-in $Δ\text{B}_{1}^{+}$ (radiofrequency transmission inhomogeneities) and $Δ\text{f}_\text{0}$ corrections (frequency offsets). We based our $^\text{23}\text{Na}$ MRF implementation on a 3D FLORET sequence with 23 radiofrequency pulses. To capture the complex spin ${\frac{\text{3}}{\text{2}}}$ dynamics of the $^\text{23}\text{Na}$ nucleus, the fingerprint dictionary was simulated using the irreducible spherical tensor operators formalism. The dictionary contained 831,512 entries covering a wide range of $\text{T}_\text{1}$, $\text{T}_\text{2,long}^{*}$, $\text{T}_\text{2,short}^{*}$, $Δ\text{B}_\text{1}^{+}$ factor and $Δ\text{f}_\text{0}$ parameters. Fingerprint matching was performed using the Pearson correlation and the resulting relaxation maps were weighted with a subset of the highest correlation coefficients corresponding to signal matches for each voxel. Our $^\text{23}\text{Na}$ MRF method was compared against reference methods in a 7-compartment phantom, and applied in brain in five healthy volunteers at 7 T. In phantoms, $^\text{23}\text{Na}$ MRF produced values comparable to those obtained with reference methods. Average sodium relaxation time values in cerebrospinal fluid, gray matter and white matter across five healthy volunteers were in good agreement with values previously reported in the literature.

physics.med-ph↗

arXiv2024

Analysis of blurring due to short T2 decay at different resolutions in 23Na MRI

The nuclear magnetic resonance signal from sodium (23Na) nuclei demonstrates a fast bi-exponential T2 decay in biological tissues (T2,short = 0.5-5 ms and T2,long = 10-30 ms). Hence, blurring observed in sodium images acquired with center-out sequences is generally assumed to be dominated by signal attenuation at higher k-space frequencies. Most of the studies in the field primarily focus on the impact of readout duration on blurring but neglect the impact of resolution. In this paper, we examine the blurring effect of short T2 on images at different resolutions. A series of simulations, as well as phantom and in vivo scans were performed at varying resolutions and readout durations in order to evaluate progressive changes in image quality. We demonstrate that, given a fixed readout duration, T2 decay produces distinct blurring effects at different resolutions. Therefore, in addition to voxel size-dependent partial volume effects, the choice of resolution adds additional T2-dependent blurring.

physics.med-ph↗

arXiv2022

Quadrupolar $^{23}$Na$^{+}$ NMR Relaxation as a Probe of Subpicosecond Collective Dynamics in Aqueous Electrolyte Solutions

Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and temperature ranges. We demonstrate that quadrupolar nuclear relaxation is sensitive to subpicosecond dynamics not captured by previous models based on water reorientation or cluster rotation. While ions affect the overall water retardation, experimental trends are mainly explained by dynamics in the first two solvation shells of sodium, which contain mostly water. This work thus paves the way to the quantitative understanding of quadrupolar relaxation in electrolyte and bioelectrolyte systems.

physics.chem-ph↗

arXiv2019

Multinuclear Absolute MR Thermometry

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures. The proton magnetic resonance (MR) frequency shift method can be used to map relative temperature changes in tissues; however, spatiotemporal variations in the main magnetic field and the lack of an internal frequency reference at each location challenge the determination of absolute temperature. Here, we introduce a novel multinuclear method for absolute MR thermometry, based on the fact that the proton and sodium nuclei exhibit a unique and distinct characteristic frequency dependence with temperature. A one-to-one mapping between the precession frequency difference of the two nuclei and absolute temperature is demonstrated. Proof-of-concept experiments were conducted in aqueous solutions with different NaCl concentrations, in agarose gel samples, and in freshly excised ex vivo mouse tissues. One-dimensional chemical shift imaging was also conducted at two steady-state temperatures, demonstrating excellent agreement with infrared measurements.

physics.med-ph↗

arXiv2012

Sodium Magnetic Resonance Imaging: Biomedical Applications

In this article, we present an up-to-date overview of the potential biomedical applications of sodium MRI in vivo. Sodium MRI is a subject of increasing interest in translational research as it can give some direct and quantitative biochemical information on the tissue viability, cell integrity and function, and therefore not only help the diagnosis but also the prognosis of diseases and treatment outcomes. It has already been applied in vivo in most of human tissues, such as brain for stroke or tumor detection and therapeutic response, in breast cancer, in articular cartilage, in muscle and in kidney, and it was shown in some studies that it could provide very useful new information not available through standard proton MRI. However, this technique is still very challenging due to the low detectable sodium signal in biological tissue with MRI and hardware/software limitations of the clinical scanners. The article is divided in three parts: (1) the role of sodium in biological tissues, (2) a short review on sodium magnetic resonance, and (3) a review of some studies on sodium MRI on different organs/diseases to date.

physics.med-ph↗