[18F]-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) is applied to delineate cerebral glucose metabolic patterns in Alzheimer’s disease (AD). Sodium MR imaging ( 23 Na-MRI) can reveal alterations in tissue sodium concentration (TSC) in the brain, potentially reflecting mitochondrial dysfunction and impaired cellular energy state. This initial study aims at investigating disease-specific topographical associations between glucose metabolism assessed via FDG-PET and regional TSC from 23 Na-MRI, thus improving our understanding of neuroenergetics alteration in AD. 20 patients with a biological biomarker-based diagnosis of prodromal/mild AD (mean age 68±7.5; 8 females; CDR 0.75±0.57, MMSE 23.9±4.2) received an FDG-PET, 23 Na-MRI and 1 H-MRI at 3T magnetic field (Siemens Prisma). A variable flip angle method was used to obtain TSC maps (Coste et al., 2019). To control for inter-individual differences, FDG-PET and TSC images were intensity-normalized to the brainstem to create normalized glucose metabolism (nFDG) and normalized TSC maps (nTSC) (de Souza et al., 2011; Nugent et al., 2020), respectively. The Hammersmith and VolBrain Segmentation atlases were applied for region-of-interest analysis and to create correlation matrices between nFDG, nTSC and normalized local brain volume. Regional nTSC negatively correlated with nFDG in AD patients mainly in temporal lobe structures and superior frontal gyri, indicating that decreased glucose metabolism was associated with increased TSC and vice versa. As expected, regional volume was positively correlated with nFDG in regions of the temporal lobe. When performing partial correlation controlling for volume, negative correlation clusters between nTSC and nFDG remained significant for superior frontal gyri and the anterior temporal lobes (Figure 1). For the first time, the association between local glucose consumption rates and sodium concentrations were investigated in AD using combined FDG-PET and 23 Na-MRI at 3T. Consistently to our recent findings of increased TSC in AD patients (Haeger et al., 2021), the negative correlations between nTSC and nFDG values in temporal and frontal brain regions, are confirming the interplay between reduced energy metabolism and sodium increase in AD, the exact nature of which remains to be determined. References: Coste […]. Magnetic Resonance Imaging 2019. Haeger […]. Alzheimer’s & Dementia 2021. Nugent […]. Scientific Reports 2020. de Souza […]. Brain 2011.

L'imagerie RMN du sodium (23Na) a démontrée à travers plusieurs études sa pertinence en tant que biomarqueur de viabilité cellulaire en particulier dans les maladies d'Alzheimer[1] ou la sclérose en plaques[2]. Les études actuelles utilisent des séquences à temps d'écho ultra-court combinées à des trajectoires déterministes non-Cartésiennes à travers l'espace de Fourier. Néanmoins, les temps d'acquisition restent long, même à très haut champ magnétique, en raison de la sensibilité intrinsèque et des concentrations tissulaires modérées du sodium. Bien que plus efficaces que les trajectoires Cartésiennes, les trajectoires non-Cartésiennes déterministes telles que TPI[3] n'exploitent pas au mieux la parcimonie de l'espace de Fourier en raison de leurs motifs géométriques. Par conséquent, nous avons proposé d'implémenter et évaluer une approche stochastique dénommée SPARKLING[4] (Fig. 1) dans le contexte de l'IRM 23Na cérébrale sous-échantillonnée. Guidé par une étude théorique basée sur un outil de simulation dédié, nous avons identifié des régimes favorables (en terme de signal et de résolution) exploitant la parcimonie des données IRM et ainsi d'accélérer (facteur d'accélération - FA = 8,32,64 et 128) l'acquisition tout en préservant les détails anatomiques et l'exactitude des concentrations en sodium calibrée à l'aide de 4 références externes[1]. Nous avons validé in vivo l'approche SPARKLING dans un de ces scénarios chez le volontaire sain (n=5 ; 7T Terra, Siemens Healthineers ; antenne 23Na 32 canaux, Rapid Biomedical), observant en particulier une qualité d'image similaire avec SPARKLING (Fig. 2: FA=32 ; TA= 5 min 38 s) comparé à celle d'acquisitions TPI plus longues (FA=8 ; TA= 22 min 34 s) avec un impact négligeable sur la quantification du sodium cérébral. A l'aide de SPARKLING, nous pouvons acquérir dans des conditions favorables des cartes cérébrales en sodium en un temps compatible avec les contraintes de la recherche clinique.

Purpose: The SNR at the center of a spherical phantom of known electrical properties was measured in quasi-identical experimental conditions as a function of magnetic field strength between 3 T and 11.7T. Methods: The SNR was measured at the center of a spherical water saline phantom with a gradient recalled echo sequence. Measurements were performed at NeuroSpin at 3, 7, and 11.7 T. The phantom was then shipped to Maastricht University and then to the University of Minnesota for additional data points at 7, 9.4, and 10.5T. Experiments were carried out with the exact same type of birdcage volume coil (except at 3 T, where a similar coil was used) to attempt at isolating the evolution of SNR with field strength alone. Phantom electrical properties were characterized over the corresponding frequency range. Results: Electrical properties were found to barely vary over the frequency range. Removing the influence of the flip-angle excitation inhomogeneity was crucial, as expected. After such correction, measurements revealed a gain of SNR growing as B-0(1.94 +/- 0.16) compared with B-0(2.13) according to ultimate intrinsic SNR theory. Conclusions: By using quasi-identical experimental setups (RF volume coil, phantom, electrical properties, and protocol), this work reports experimental data between 3 T and 11.7T, enabling the comparison with SNR theories in which conductivity and permittivity can be assumed to be constant with respect to field strength. According to ultimate SNR theory, these results can be reasonably extrapolated to the performance of receive arrays with greater than about 32 elements for central SNR in the same spherical phantom.

INTRODUCTION:Application of MRI in clinical routine mainly addresses structural alterations. However, pathological changes at a cellular level are expected to precede the occurrence of brain atrophy clusters and of clinical symptoms. In this context, 23Na-MRI examines sodium changes in the brain as a potential metabolic parameter. Recently, we have shown that 23Na-MRI at ultra-high-field (7 T) was able to detect increased tissue sodium concentration (TSC) in Alzheimer's disease (AD). In this work, we aimed at assessing AD-pathology with 23Na-MRI in a larger cohort and on a clinical 3T MR scanner. METHODS:We used a multimodal MRI protocol on 52 prodromal to mild AD patients and 34 cognitively healthy control subjects on a clinical 3T MR scanner. We examined the TSC, brain volume, and cortical thickness in association with clinical parameters. We further compared TSC with intra-individual normalized TSC for the reduction of inter-individual TSC variability resulting from physiological as well as experimental conditions. Normalized TSC maps were created by normalizing each voxel to the mean TSC inside the brain stem. RESULTS:We found increased normalized TSC in the AD cohort compared to elderly control subjects both on global as well as on a region-of-interest-based level. We further confirmed a significant association of local brain volume as well as age with TSC. TSC increase in the left temporal lobe was further associated with the cognitive state, evaluated via the Montreal cognitive assessment (MoCA) screening test. An increase of normalized TSC depending on disease stage reflected by the Clinical Dementia Rating (CDR) was found in our AD patients in temporal lobe regions. In comparison to classical brain volume and cortical thickness assessments, normalized TSC had a higher discriminative power between controls and prodromal AD patients in several regions of the temporal lobe. DISCUSSION:We confirm the feasibility of 23Na-MRI at 3T and report an increase of TSC in AD in several regions of the brain, particularly in brain regions of the temporal lobe. Furthermore, to reduce inter-subject variability caused by physiological factors such as circadian rhythms and experimental conditions, we introduced normalized TSC maps. This showed a higher discriminative potential between different clinical groups in comparison to the classical TSC analysis. In conclusion, 23Na-MRI represents a potential translational imaging marker applicable e.g.for diagnostics and the assessment of intervention outcomes in AD even under clinically available field strengths such as 3T. Implication of 23Na-MRI in association with other metabolic imaging marker needs to be further elucidated.

The pathophysiological processes underlying the development and progression of Alzheimer's disease (AD) on the neuronal level are still unclear. Previous research has hinted at metabolic energy deficits and altered sodium homeostasis with impaired neuronal function as a potential metabolic marker relevant for neurotransmission in AD. Using sodium (23 Na) magnetic resonance (MR) imaging on an ultra-high-field 7 Tesla MR scanner, we found increased cerebral tissue sodium concentration (TSC) in 17 biomarker-defined AD patients compared to 22 age-matched control subjects in vivo. TSC was highly discriminative between controls and early AD stages and was predictive for cognitive state, and associated with regional tau load assessed with flortaucipir-positron emission tomography as a possible mediator of TSC-associated neurodegeneration. TSC could therefore serve as a non-invasive, stage-dependent, metabolic imaging marker. Setting a focus on cellular metabolism and potentially disturbed interneuronal communication due to energy-dependent altered cell homeostasis could hamper progressive cognitive decline by targeting these processes in future interventions.

BACKGROUND: Lithium (Li) is a first-line treatment for bipolar disorder (BD). To study its cerebral distribution and association with plasma concentrations, we used Li-7 magnetic resonance imaging at 7T in euthymic patients with BD treated with Li carbonate for at least 2 years. METHODS: Three-dimensional Li-7 magnetic resonance imaging scans (N = 21) were acquired with an ultra-short echo-time sequence using a non-Cartesian k-space sampling scheme. Lithium concentrations ([Li]) were estimated using a phantom replacement approach accounting for differential T-1 and T-2 relaxation effects. In addition to the determination of mean regional [Li] from 7 broad anatomical areas, voxel-and parcellation-based group analyses were conducted for the first time for Li-7 magnetic resonance imaging. RESULTS: Using unprecedented spatial sensitivity and specificity, we were able to confirm the heterogeneity of the brain Li distribution and its interindividual variability, as well as the strong correlation between plasma and average brain [Li] ([Li](B) approximate to 0.40 x [Li](P), R = .74). Remarkably, our statistical analysis led to the identification of a well-defined and significant cluster corresponding closely to the left hippocampus for which high Li content was displayed consistently across our cohort. CONCLUSIONS: This observation could be of interest considering 1) the major role of the hippocampus in emotion processing and regulation, 2) the consistent atrophy of the hippocampus in untreated patients with BD, and 3) the normalization effect of Li on gray matter volumes. This study paves the way for the elucidation of the relationship between Li cerebral distribution and its therapeutic response, notably in newly diagnosed patients with BD.

AbstractBackgroundIn Alzheimer’s disease (AD), energy deficit is suspected to occur before clinical symptoms arise. Therefore, neuroimaging methods sensitive to metabolic alterations are attractive to improve diagnostics, therapeutics and follow‐ups of AD patients. An indirect measure of deficient Na+/K+‐ATPase‐activity during neurodegeneration is provided by the tissue sodium concentration (TSC) measured by Sodium‐(23Na)‐MRI.Method16 patients (7 Male, 71.7±8 years) diagnosed with AD (MoCA 15.1±7) were recruited from Ste. Anne Hospital in Paris as well as 16 cognitively healthy age‐matched control subjects (7 Male, 69±3.1 years; MoCA 28.1±1.8). Each subject underwent 23Na and 1H MRI examinations at the 7T MRI scanner (Siemens) at Neurospin, CEA. A dual‐resonance 1H/23Na volume coil (Rapid Biomedical) was used for a 23Na MRI protocol acquiring ultra‐short echo‐time images (3mm isotropic resolution) at two flip‐angles (a1=25º/a2=55º) (Coste et al., 2019). Briefly, processing steps comprised image reconstruction, denoising, motion‐ and B1‐inhomogeneities‐corrections, and a calibration step using 4 external references. Individual TSC maps were co‐registered to their T1‐weighted anatomical reference (MP2RAGE, 750 µm isotropic resolution) and a partial‐volume‐effect correction (Thomas et al., 2016) was implemented to limit the influence of sodium from cerebrospinal fluid. Anatomical and TSC images were normalized to the OASIS template using ANTs. A parameter free permutation analysis was performed voxel‐wise on normalized TSC images and on the LogJacobian of the deformation fields. After, region‐of‐interest‐analyses on hippocampus from VolBrain‐Atlas followed.ResultThe voxel‐based analysis showed significant widespread increases in TSC of AD patients, particularly in parietal, temporal and frontal regions. Interestingly, the observed TSC changes were located in areas not directly associated to significant structural changes (Fig 1). Furthermore, TSC in the hippocampus was found significantly higher in AD than in controls (42.9±4.3mmol/l; 35.8±3.9mmol/l; Wilcoxon‐rank‐sum; p=0.00015, z=3.8) and was correlated, after controlling for age, with both the MoCA‐scores (r=‐0.62; p=0.0002) and hippocampal volumes (r=‐0.39; p=0.032).ConclusionHigh‐field quantitative 23Na MRI in AD shows increased TSC values across a wide range of brain regions. These results may provide a deeper insight into metabolic alterations occurring during neurodegeneration. 23Na MRI could therefore serve as a useful tool to characterize disease progression or the impact of therapeutic intervention.

PURPOSE:The state-of-the-art method to quantify sodium concentrations in vivo consists in a fully relaxed 3D spin-density (SD) weighted acquisition. Nevertheless, most sodium MRI clinical studies use short-TR SD acquisitions to reduce acquisition durations. We present a clinically viable implementation of the Variable Flip Angle (VFA) method for robust and clinically viable quantification of total sodium concentration (TSC) and longitudinal relaxation rates in vivo in human brain at 3 T.METHODS:Two non-Cartesian steady-state spoiled ultrashort echo time (UTE) scans, performed at optimized flip angles, repetition time and pulse length determined under specific absorption rate constraints, are used to simultaneously compute T1 and total sodium concentration (TSC) maps using the VFA method. Images are reconstructed using the non-uniform Fast Fourier Transform algorithm and TSC maps are corrected for possible inhomogeneity of coil transmission and reception profiles. Fractioned acquisitions are used to correct for potential patient motion. TSC quantifications obtained using the VFA method are validated at first in comparison with a fully-relaxed SD acquisition in a calibration phantom. The robustness of similar VFA acquisitions are compared to the short-TR SD approach in vivo on seven healthy volunteers.RESULTS:The VFA method resulted in consistent TSC and T1 estimates across our cohort of healthy subjects, with mean TSC of 38.1 ± 5.0 mmol/L and T1 of 39.2 ± 4.4 ms. These results are in agreement with previously reported values in literature TSC estimations and with the predictions of a 2-compartment model. However, the short-TR SD acquisition systematically underestimated the sodium concentration with a mean TSC of 31 ± 4.5 mmol/L.CONCLUSION:The VFA method can be applied successfully to image sodium at 3 T in about 20 min and provides robust and intrinsically T1-corrected TSC maps.

PURPOSE:Quantifying multiple NMR properties of sodium could be of benefit to assess changes in cellular viability in biological tissues. A proof of concept of Quantitative Imaging using Configuration States (QuICS) based on a SSFP sequence with multiple contrasts was implemented to extract simultaneously 3D maps of applied flip angle (FA), total sodium concentration, T1, T2, and Apparent Diffusion Coefficient (ADC).METHODS:A 3D Cartesian Gradient Recalled Echo (GRE) sequence was used to acquire 11 non-balanced SSFP contrasts at a 6 × 6 × 6 mm3 isotropic resolution with carefully-chosen gradient spoiling area, RF amplitude and phase cycling, with TR/TE = 20/3.2 ms and 25 averages, leading to a total acquisition time of 1 h 18 min. A least-squares fit between the measured and the analytical complex signals was performed to extract quantitative maps from a mono-exponential model. Multiple sodium phantoms with different compositions were studied to validate the ability of the method to measure sodium NMR properties in various conditions.RESULTS:Flip angle maps were retrieved. Relaxation times, ADC and sodium concentrations were estimated with controlled precision below 15%, and were in accordance with measurements from established methods and literature.CONCLUSION:The results illustrate the ability to retrieve sodium NMR properties maps, which is a first step toward the estimation of FA, T1, T2, concentration and ADC of 23Na for clinical research. With further optimization of the acquired QuICS contrasts, scan time could be reduced to be suitable with in vivo applications.

HYPR flow is a 3D dynamic contrast-enhanced MRA technique providing isotropic sub-millimetre resolution with half-second temporal resolution. We compared HYPR flow and time-resolved imaging of contrast kinetics (TRICKS) MRA for the characterization of cerebral arteriovenous malformations (cAVMs), using catheter DSA as reference.

BackgroundOptimization of multi b-values MR protocol for fast intra-voxel incoherent motion imaging of the liver at 3.0 Tesla.MethodsA comparison of four different acquisition protocols were carried out based on estimated IVIM (D-Slow, D-Fast, and f) and ADC-parameters in 25 healthy volunteers. The effects of respiratory gating compared with free breathing acquisition then diffusion gradient scheme (simultaneous or sequential) and finally use of weighted averaging for different b-values were assessed. An optimization study based on Cramer-Rao lower bound theory was then performed to minimize the number of b-values required for a suitable quantification. The duration-optimized protocol was evaluated on 12 patients with chronic liver diseasesResultsNo significant differences of IVIM parameters were observed between the assessed protocols. Only four b-values (0, 12, 82, and 1310 s.mm(-2)) were found mandatory to perform a suitable quantification of IVIM parameters. D-Slow and D-Fast significantly decreased between nonadvanced and advanced fibrosis (P<0.05 and P<0.01) whereas perfusion fraction and ADC variations were not found to be significant.ConclusionResults showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as D-Slow and D-Fast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis. J. Magn. Reson. Imaging 2014. (c) 2014 Wiley Periodicals, Inc. J. Magn. Reson. Imaging 2015;41:1209-1217. (c) 2014 Wiley Periodicals, Inc.

MRI has proven its usefulness in the prediction of surgical anterior anal repair that cannot be done with the reference endosonographic exam. Conventional endorectal coils are often based on a single loop coil design and do not possess satisfactory radial uniformity which could impede the correct assessment of the anal sphincter. In this study, several double loop endorectal coils were designed, built, and assessed in simulations, on phantoms and in vivo. The optimum was found for a 50°–70° double loop endorectal coil which presents a better radial uniformity especially at close distance from the coil where the SNR is the highest. First in vivo experiments proved enhanced readability of the MR exam for the radiologist. © 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 44B: 39–49, 2014

A susceptibility matched endorectal coil was tested and compared against a classical endorectal coil design. For different phantom angulations, it enabled a significant decrease (~30%) of the FWHM of spectra acquired on in vitro NMR tubes. These promising results and the restricted FWHM observed suggest the interest of this new coil for the acquisition of in vivo spectra especially for the characterization of the colorectal cancer.

We compared a multi-echo gradient-echo magnetic resonance sequence (susceptibility-weighted angiography [SWAN]) with the T2* sequence for the detection of an arterial thrombus in acute ischaemic stroke.

Susceptibility-weighted magnetic resonance imaging (MRI) sequences may demonstrate various signal intensities of draining veins in cases of high-flow vascular malformation (HFVM), including arteriovenous malformation (AVM) and dural arteriovenous fistula (dAVF). Our objective was to evaluate susceptibility-weighted angiography (SWAN) for the detection of HFVM.

Objective Fluid-attenuated inversion recovery (FLAIR) vascular hyperintensities (FVH), initially described on 2D FLAIR images, are a useful imaging marker in patients with acute ischaemic stroke. We aimed to compare the sensitivity of the 3D CUBE FLAIR sequence with 2D FLAIR for the detection of FVH. Methods Forty-seven consecutive patients admitted for a suspected stroke were explored by 2D and 3D CUBE FLAIR MR sequences at 1.5 and 3 T. Three blinded readers assessed FVH defined as hyperintensities within cerebral arteries. Location of FVH, acute brain infarct and arterial stenosis were also assessed. 2D images were compared with 3D images for the detection of FVH. Agreement between readers was assessed. Results Of the 47 patients, 21 FVHs were observed on 2D FLAIR images of 15 patients (11 with acute brain infarct and 11 with an arterial stenosis). No FVH was visualised on 3D CUBE FLAIR images for either proximal or distal locations. Agreement between readers was excellent. Conclusion FVHs are not visible using 3D CUBE FLAIR images. This study suggests that, in suspected acute ischaemic stroke, the assessment of FVH should only be performed on conventional 2D FLAIR images. Key Points • Fluid-attenuated inversion recovery (FLAIR) vascular hyperintensities (FVH) are of neuroradiological importance. • FVHs are useful imaging markers in patients with an acute ischaemic stroke. • FVHs are not visible using 3D CUBE FLAIR images. • Assessment of FVH should be performed on conventional 2D FLAIR images.

Purpose: To assess the feasibility of a selective flow-tracking cartographic procedure applied to four-dimensional (4D) flow imaging and to demonstrate its usefulness in the characterization of dural arteriovenous fistulas (DAVFs).Materials and Methods: Institutional review board approval was obtained, and all patients provided written informed consent. Eight patients (nine DAVFs) underwent 3.0-T magnetic resonance (MR) imaging and digital subtraction angiography (DSA). Imaging examinations were performed within 24 hours of each other. 4D flow MR imaging was performed by using a 4D radial phase-contrast vastly undersampled isotropic projection reconstruction pulse sequence with an isotropic spatial resolution of 0.86 mm (5 minutes 35 seconds). Two radiologists independently reviewed images from MR flow-tracking cartography and reported the location of arterial feeder vessels and the venous drainage type and classified DAVFs according to the risk of rupture (Cognard classification). These results were compared with those at DSA. Quadratic weighted kappa statistics with their 95% confidence intervals (CIs) were used to test intermodality agreement in the identification of arterial feeder vessels, draining veins, and Cognard classification.Results: Interreader agreement for shunt location on MR images was perfect (kappa = 1), with good-to-excellent interreader agreement for arterial feeder vessel identification (kappa = 0.97; 95% CI = 0.92, 1.0), and matched in all cases with shunt location defined at DSA. There was good-to-excellent agreement between MR cartography and DSA in the definition of the main feeding arteries (kappa = 0.92; 95% CI = 0.83, 1.0), presence of retrograde flow in dural sinuses (kappa = 1), presence of retrograde cortical venous drainage (kappa = 1), presence of venous ectasia (kappa = 1), and final Cognard classification of DAVFs (kappa = 1, standard error = 0.35).Conclusion: MR selective flow-tracking cartography enabled the noninvasive characterization of cranial DAVFs. (C) RSNA, 2013