: Active Trans-Plasma Membrane Water Cycling in Yeast is Revealed by NMR

International audienceMethods and Materials Yeast suspensions with increasing [RR e ]: Yeast suspensions at 30% wet wt/vol in minimal medium were bubbled with 95% O 2 /5% CO 2 (n =2) or 95% N 2 /5% CO 2 (n=1) for 1.5 hours before the first 1 H 2 O T 1 IR measurement. In one suspension bubbled with 95% O 2 /5% CO 2 , 10 mole of the uncoupler of oxidative phosphorylation, 2,4-dinitrophenol, (DNP) was added after 1.5 hour of O 2 bubbling, just prior to the first addition of RR e. Serial addition of RR to the yeast suspensions resulted in the following [RR e ] (mM) values in the medium: 0, 0.3, 0.6, 0.9, 1.2, 1.8, 2.4, 2.9, 3.5, 4.7, 7.0, 9.3, 11.6, 16.1, and 20.5. The total volume increased by 18% by the end of the titration, which was accounted for in calculating [RR e ]. The IR data acquired at each [RR e ] were analyzed by 2SX fitting and relaxivity fitting as described below. MR Measurements and Data Analyses: The 64 t I delay increments between the 180 o (composite) pulse and 90 o RF pulses of the IR pulse sequence are as follows (s): 0. Relaxograms: A 1D Inverse Laplace Transform (ILT) written in Matlab (TwoDLaplaceInverse, Magritek Limited, Wellington New Zealand) of [(M Z (∞)-M Z (t I))/2M Z (∞)] produced the longitudinal relaxogram, the apparent relaxation time constant (T 1 ) distribution. A two peak relaxogram yielded H 2 O i T 1 ′ (T′ 1i) and H 2 O e T 1 ′ (T′ 1e) values, where the T 1 ′ was taken as the peak position. The apparent relative water mole fractions were taken as the relative peak area values. Peak positions and areas were determined using Matlab routines (MathWorks Inc, Natick, MA). Extracting exchange parameters: As noted in the main manuscript, two different approaches for extracting exchange parameters from relaxographic data were employed. The first method, "2SX fitting," substitutes Eqs. (4-6) into the right hand side of Eq. (7) [(M Z (∞)-M Z (t I))/2M Z (∞)] = a L exp(-t I R 1L) + a s exp(-t I R 1s) (7) (main manuscript) The values of τ i , p i , and r 1e with fixed values for R 1i and R 1e0 are adjusted to match the IR time-course, [(M Z (∞)-M Z (t I))/2M Z (∞)], observed at each [RR e ] value. The second method, "relaxivity fitting," adjusts Eq. (4) and/or (5) to match the [RR e ]-dependence of the R 1L and/or R 1S obtained from the relaxograms (1, 2). Matlab was used for the 2SX and relaxivity fittings

High-Resolution 1.5-Tesla Magnetic Resonance Imaging for Tissue-Engineered Constructs: A Noninvasive Tool to Assess Three-Dimensional Scaffold Architecture and Cell Seeding

International audienceTissue-engineered scaffolds are made of biocompatible polymers with various structures, allowing cell seeding, growth, and differentiation. Noninvasive imaging methods are needed to study tissue-engineered constructs before and after implantation. Here, we show that high-resolution magnetic resonance imaging (MRI) performed on a clinical 1.5-T device is a reliable technique to assess three-dimensional structures of porous scaffolds and to validate cell-seeding procedures. A high-temperature superconducting detection coil was used to achieve a resolution of 30Â30Â30 mm 3 when imaging the scaffolds. Three types of structures with tuneable architectures were prepared from naturally derived polysaccharides and evaluated as scaffolds for mesenchymal stem cell (MSC) culture. To monitor cell seeding, MSCs were magnetically labeled using simple incubation with anionic citrate-coated iron-oxide nanoparticles for 30 min. Iron uptake was quantified using single-cell magnetophoresis, and cell proliferation was checked for 7 days after labeling. Three-dimensional (3D) microstructures of scaffolds were assessed using MRI, revealing lamellar or globular porous organization according to the scaffold preparation process. MSCs with different iron load (5, 12 and 31 pg of iron per cell) were seeded on scaffolds at low density (132 cells=mm 3) and detected on 3D gradient-echo MR images according to phase distortions and areas of intensely low signal, whose size increased with cell iron load and echo time. Overall signal loss in the scaffold correlated with the number of seeded cells and their iron load. Different organizations of cells were observed depending on the scaffold architecture. After subcutaneous implantation in mice, scaffolds seeded with labeled cells could be distinguished in vivo from scaffold with nonlabeled cells by observation of signal and phase heterogeneities and by measuring the global signal loss. High-resolution 1.5-T MRI combined with efficient intracellular contrast agents shows promise for noninvasive 3D visualization of tissue-engineered constructs before and after in vivo implantation

Molecular Magnetic Resonance and Ultrasound Imaging of Tumor Angiogenesis

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Front Cardiovasc Med

IntroductionInterventional cardiac MRI in the context of the treatment of cardiac arrhythmia requires submillimeter image resolution to precisely characterize the cardiac substrate and guide the catheter-based ablation procedure in real-time. Conventional MRI receiver coils positioned on the thorax provide insufficient signal-to-noise ratio (SNR) and spatial selectivity to satisfy these constraints.MethodsA small circular MRI receiver coil was developed and evaluated under different experimental conditions, including high-resolution MRI anatomical and thermometric imaging at 1.5 T. From the perspective of developing a therapeutic MR-compatible catheter equipped with a receiver coil, we also propose alternative remote active detuning techniques of the receiver coil using one or two cables. Theoretical details are presented, as well as simulations and experimental validation.ResultsAnatomical images of the left ventricle at 170 µm in-plane resolution are provided on ex vivo beating heart from swine using a 2 cm circular receiver coil. Taking advantage of the increase of SNR at its vicinity (up to 35 fold compared to conventional receiver coils), real-time MR-temperature imaging can reach an uncertainty below 0.1°C at the submillimetric spatial resolution. Remote active detuning using two cables has similar decoupling efficiency to conventional on-site decoupling, at the cost of an acceptable decrease in the resulting SNR.DiscussionThis study shows the potential of small dimension surface coils for minimally invasive therapy of cardiac arrhythmia intraoperatively guided by MRI. The proposed remote decoupling approaches may simplify the construction process and reduce the cost of such single-use devices.Thermometrie cardiaque haute résolution sur une IRM clinique en utilisant des antennes intracardiaquesL'Institut de Rythmologie et modélisation CardiaqueFrance Life Imagin

Microscopie locale par résonance magnétique chez l'homme et le petit animal à l'aide d'antennes miniatures en cuivre ou en céramique supraconductrice

There is significant interest to combine local microscopy magnetic resonance imaging (MRI) with biomedical research on human body (skin, peripheral articulations) and on small animal models. But this imaging technique faces a critical lack of sensitivity. The improvement of radiofrequency detection, through the development of small surface coils and optimised electronics, is an efficient way to provide the sensitivity needed to increase the spatial resolution, while preserving a high signal to noise ratio (SNR). Small coils made of copper or high temperature superconductor (HTS), were designed following the transmission line principal and fabricated using microtechnologies. They were characterised electrically and by imaging in order to evaluate their performance. We investigated different biomedical applications that were opened by the gain in sensitivity with our HTS coils at the standard field in MRI of 1.5 T. This new approach allowed to access isotropic voxels down to (60 µm)3 on explored regions such as peripheral human areas or various mouse sites, with an SNR 4 to 15 times better than the one reached with an analogous room-temperature copper coil. The accessible resolutions are comparable to those usually obtained at much higher fields where the imaging environment is more complex and more expensive. For several biomedical issues, imaging at 1.5 T with HTS coils can offer a true alternative to high field.Faire appel à la micro imagerie par résonance magnétique (IRM), pour étudier des pathologies chez l'homme (peau et articulations périphériques) ou sur le petit animal, à un intérêt considérable en recherche biomédicale. Mais cette technique est confrontée à un réel manque de sensibilité. L'amélioration du détecteur radiofréquence (RF), en développant des petites antennes de surface, est un moyen efficace de faire reculer les limites de résolution spatiale en conservant un rapport signal sur bruit (RSB) élevé. Dans ce contexte, des antennes miniatures en cuivre micromoulé ou en céramique supraconductrice ont été conçues sur le principe des lignes de transmission et fabriquées par micro technologie. Nous les avons caractérisées électriquement et en imagerie afin d'évaluer leur performance. Nous avons poursuivi l'exploration de plusieurs applications biomédicales ouvertes par l'utilisation d'une antenne supraconductrice à 1,5T, qui est l'intensité de champ la plus courante en IRM. Cette approche a permis d'accéder à des résolutions spatiales de (60 µm)3 isotrope sur des régions explorées telles que les zone périphériques du corps humain ou sur différents sites de la souris, avec des RSB 4 à 15 fois supérieurs à ceux obtenus avec une structure analogue en cuivre à température ambiante. D'après la théorie de Hoult-Lauterbur, un gain en RSB comparable serait obtenu avec un détecteur RF conventionnel au prix d'une augmentation considérable de l'intensité du champ, entre 4 et 14 T. Les résolutions ainsi accessibles sont comparables à celles couramment obtenues avec des équipements d'IRM haut champ, plus coûteux et de mise en œuvre complexe. Dans certains domaines de la recherche biomédicale, l'utilisation des antennes supraconductrices pourrait être envisagée comme une alternative aux hauts champs

Microscopie locale par résonance magnétique chez l'homme et le petit animal à l'aide d'antennes miniatures en cuivre ou en céramique supraconductrice

Faire appel à la micro imagerie par résonance magnétique (IRM), pour étudier des pathologies chez l homme (peau et articulations périphériques) ou sur le petit animal, à un intérêt considérable en recherche biomédicale. Mais cette technique est confrontée à un réel manque de sensibilité. L amélioration du détecteur radiofréquence (RF), en développant des petites antennes de surface, est un moyen efficace de faire reculer les limites de résolution spatiale en conservant un rapport signal sur bruit (RSB) éleve .Dans ce contexte, des antennes miniatures en cuivre micromoulé ou en céramique supraconductrice ont été conçues sur le principe des lignes de transmission et fabriquées par micro technologie. Nous les avons caractérisées électriquement et en imagerie afin d évaluer leur performance.Nous avons poursuivi l exploration de plusieurs applications biomédicales ouvertes par l utilisation d une antenne supraconductrice à 1,5T, qui est l intensité de champ la plus courante en IRM. Cette approche a permis d accéder à des résolutions spatiales de (60 m)3 isotrope sur des régions explorées telles que les zone périphériques du corps humain ou sur différents sites de la souris, avec des RSB 4 à 15 fois supérieurs à ceux obtenus avec une structure analogue en cuivre à température ambiante. Les résolutions ainsi accessibles sont comparables à celles couramment obtenues avec des équipements d IRM haut champ, plus coûteux et de mise en œuvre complexe. Dans certains domaines de la recherche biomédicale, l utilisation des antennes supraconductrices pourrait être envisagée comme une alternative aux hauts champs.There is significant interest to combine local microscopy magnetic resonance imaging (MRI) with biomedical research on human body (skin, peripheral articulations) and on small animal models. But this imaging technique faces a critical lack of sensitivity. The improvement of radiofrequency detection, through the development of small surface coils and optimised electronics, is an efficient way to provide the sensitivity needed to increase the spatial resolution, while preserving a high signal to noise ratio (SNR).Small coils made of copper or high temperature superconductor (HTS), were designed following the transmission line principal and fabricated using microtechnologies. They were characterised electrically and by imaging in order to evaluate their performance.We investigated different biomedical applications that were opened by the gain in sensitivity with our HTS coils at the standard field in MRI of 1.5 T. This new approach allowed to access isotropic voxels down to (60 m)3 on explored regions such as peripheral human areas or various mouse sites, with an SNR 4 to 15 times better than the one reached with an analogous room-temperature copper coil.The accessible resolutions are comparable to those usually obtained at much higher fields where the imaging environment is more complex and more expensive. For several biomedical issues, imaging at 1.5 T with HTS coils can offer a true alternative to high field.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The minimum admissible detuning efficiency of MRI receive-only surface coils

International audienceBackground:The minimum admissible detuning efficiency of a receive coil is an essential parameter for coil designers. A receive coil with inefficient detuning leads to inhomogeneous B$_1$ during excitation. Previously proposed criteria for quantifying the detuning efficiency rely on indirect measurements and are difficult to implement.Purpose:To present an alternative method to quantify the detuning efficiency of receive-only surface coilsStudy type:Theoretical study supported by simulations and phantom experiments. Phantoms: Uniform spherical (100 mm diameter) and cylindrical (66 mm diameter) phantoms. Field strength/sequence: Dual repetition time B$_1$ mapping sequence at 1.5 T, and Bloch-Siegert shift B1 mapping sequence at 3.0 T. Assessment:One non-planar (80 mm × 43 mm$^2$) and 2 planar (40 mm and 57 mm diameter) surface coils were built. Theoretical analysis was performed to determine the minimum detuning efficiency required to avoid B$_1$ distortions. Experimental B$_1$ maps were acquired for the non-planar and planar surface coils at both 1.5 T and 3.0 T and visually compared with simulated B1 maps to assess the validity of the theoretical analysis.Statistical tests: None.Results: Based on the theoretical analysis, the proposed minimum admissible detuning efficiency, defined as DE$_{thr}$= 20 Log (Q) + 13 dB, depended only on the quality factor (Q) of the coil and was independent of coil area and field strength. Simulations and phantom experiments showed that when the detuning efficiency was higher than this minimum threshold level, the B$_1$ field generated by the transmission coil was not modified by the receive coil. Data conclusion: The proposed criterion for assessing the detuning efficiency is simple to measure, and does not depend on the area of the coil or on the magnetic field strength, up to 3T. Experimental and simulated B$_1$ maps confirmed that detuning efficiencies above the theoretically derived minimal admissible detuning efficiency resulted in a non-distorted B$_1$ field

High-temperature superconducting radiofrequency probe for magnetic resonance imaging applications operated below ambient pressure in a simple liquid-nitrogen cryostat

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MRI – recent advances and new horizons

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