Trajectory correction enables free-running chemical shift encoded imaging for accurate cardiac proton-density fat fraction quantification at 3T.

Background: Metabolic diseases can negatively alter epicardial fat accumulation and composition, which can be probed using quantitative cardiac chemical shift encoded (CSE) cardiovascular magnetic resonance (CMR) by mapping proton-density fat fraction (PDFF). To obtain motion-resolved high-resolution PDFF maps, we proposed a free-running cardiac CSE-CMR framework at 3T. To employ faster bipolar readout gradients, a correction for gradient imperfections was added using the gradient impulse response function (GIRF) and evaluated on intermediate images and PDFF quantification.

Mitigating slice cross-talk in multi-slice multi-echo spin echo T mapping.

Purpose: To investigate whether a T inter-slice variation could occur when a multi-slice multi-echo spin echo (MESE) sequence is used for image acquisition and to propose an enhanced method for reconstructing T maps that can effectively address and correct these variations.

Methods: Bloch simulations were performed accounting for the direct saturation effect to evaluate magnetization changes in multi-slice 2D MESE sequence. Experimental phantom scans were performed to validate these simulations.

Comparative review of algorithms and methods for chemical-shift-encoded quantitative fat-water imaging.

Purpose: To propose a standardized comparison between state-of-the-art open-source fat-water separation algorithms for proton density fat fraction (PDFF) and quantification using an open-source multi-language toolbox.

Methods: Eight recent open-source fat-water separation algorithms were compared in silico, in vitro, and in vivo. Multi-echo data were synthesized with varying fat-fractions, B off-resonance, SNR and TEs.

Evaluation of a nnU-Net type automated clinical volumetric tumor segmentation tool for diffuse low-grade glioma follow-up.

Background And Purpose: Diffuse low-grade gliomas (DLGG) are characterized by a slow and continuous growth and always evolve towards an aggressive grade. Accurate prediction of the malignant transformation is essential as it requires immediate therapeutic intervention. One of its most precise predictors is the velocity of diameter expansion (VDE).

Quantitative magnetization transfer MRI unbiased by on-resonance saturation and dipolar order contributions.

Purpose: To demonstrate the bias in quantitative MT (qMT) measures introduced by the presence of dipolar order and on-resonance saturation (ONRS) effects using magnetization transfer (MT) spoiled gradient-recalled (SPGR) acquisitions, and propose changes to the acquisition and analysis strategies to remove these biases.

Methods: The proposed framework consists of SPGR sequences prepared with simultaneous dual-offset frequency-saturation pulses to cancel out dipolar order and associated relaxation (T ) effects in Z-spectrum acquisitions, and a matched quantitative MT (qMT) mathematical model that includes ONRS effects of readout pulses. Variable flip angle and MT data were fitted jointly to simultaneously estimate qMT parameters (macromolecular proton fraction [MPF], T , T , R, and free pool T ).

Spinal cord and brain tissue impairments as long-term effects of rugby practice? An exploratory study based on T and ihMTsat measures.

Rugby players are subject to multiple impacts to their head and neck that could have adverse neurological effects and put them at increased risk of neurodegeneration. Previous studies demonstrated altered default mode network and diffusion metrics on brain, as well as more foraminal stenosis, disc protrusion and neck pain among players of contact sports as compared to healthy controls. However, the long-term effects of practice and repetitive impacts on brain and cervical spinal cord (cSC) of the rugby players have never been systematically investigated.

A strategy to reduce the sensitivity of inhomogeneous magnetization transfer (ihMT) imaging to radiofrequency transmit field variations at 3 T.

Purpose: To minimize the sensitivity of inhomogeneous magnetization transfer gradient-echo (ihMT-GRE) imaging to radiofrequency (RF) transmit field ( ) inhomogeneities at 3 T.

Methods: The ihMT-GRE sequence was optimized by varying the concentration of the RF saturation energy over time, obtained by increasing the saturation pulse power while extending the sequence repetition time (TR). Different protocols were tested using numerical simulations and human in vivo experiments in the brain white matter (WM) of healthy subjects at 3 T.

Cortical inflammation and brain signs of high-risk atherosclerosis in a non-human primate model.

Atherosclerosis is a chronic systemic inflammatory disease, inducing cardiovascular and cerebrovascular acute events. A role of neuroinflammation is suspected, but not yet investigated in the gyrencephalic brain and the related activity at blood-brain interfaces is unknown. A non-human primate model of advanced atherosclerosis was first established using longitudinal blood samples, multimodal imaging and gene analysis in aged animals.

PET-MRI nanoparticles imaging of blood-brain barrier damage and modulation after stroke reperfusion.

In an acute ischaemic stroke, understanding the dynamics of blood-brain barrier injury is of particular importance for the prevention of symptomatic haemorrhagic transformation. However, the available techniques assessing blood-brain barrier permeability are not quantitative and are little used in the context of acute reperfusion therapy. Nanoparticles cross the healthy or impaired blood-brain barrier through combined passive and active processes.

Comparison of 2D simultaneous multi-slice and 3D GRASE readout schemes for pseudo-continuous arterial spin labeling of cerebral perfusion at 3 T.

Objective: In this perfusion magnetic resonance imaging study, the performances of different pseudo-continuous arterial spin labeling (PCASL) sequences were compared: two-dimensional (2D) single-shot readout with simultaneous multislice (SMS), 2D single-shot echo-planar imaging (EPI) and multishot three-dimensional (3D) gradient and spin echo (GRASE) sequences combined with a background-suppression (BS) module.

Materials And Methods: Whole-brain PCASL images were acquired from seven healthy volunteers. The performance of each protocol was evaluated by extracting regional cerebral blood flow (rCBF) measures using an inline morphometric segmentation prototype.

T1-Based Synthetic Magnetic Resonance Contrasts Improve Multiple Sclerosis and Focal Epilepsy Imaging at 7 T.

Objectives: Ultra-high field magnetic resonance imaging (MRI) (≥7 T) is a unique opportunity to improve the clinical diagnosis of brain pathologies, such as multiple sclerosis or focal epilepsy. However, several shortcomings of 7 T MRI, such as radiofrequency field inhomogeneities, could degrade image quality and hinder radiological interpretation. To address these challenges, an original synthetic MRI method based on T1 mapping achieved with the magnetization-prepared 2 rapid acquisition gradient echo (MP2RAGE) sequence was developed.

A non-human primate model of stroke reproducing endovascular thrombectomy and allowing long-term imaging and neurological read-outs.

Stroke is a devastating disease. Endovascular mechanical thrombectomy is dramatically changing the management of acute ischemic stroke, raising new challenges regarding brain outcome and opening up new avenues for brain protection. In this context, relevant experiment models are required for testing new therapies and addressing important questions about infarct progression despite successful recanalization, reversibility of ischemic lesions, blood-brain barrier disruption and reperfusion damage.

Simultaneous multi-slice T1 mapping using MOLLI with blipped CAIPIRINHA bSSFP.

Background: This study evaluates the possibility for replacing conventional 3 slices, 3 breath-holds MOLLI cardiac T1 mapping with single breath-hold 3 simultaneous multi-slice (SMS3) T1 mapping using blipped-CAIPIRINHA SMS-bSSFP MOLLI sequence. As a major drawback, SMS-bSSFP presents unique artefacts arising from side-lobe slice excitations that are explained by imperfect RF modulation rendering and bSSFP low flip angle enhancement. Amplitude-only RF modulation (AM) is proposed to reduce these artefacts in SMS-MOLLI compared to conventional Wong multi-band RF modulation (WM).

Intravoxel Incoherent Motion at 7 Tesla to quantify human spinal cord perfusion: limitations and promises.

Purpose: To develop a noninvasive technique to map human spinal cord (SC) perfusion in vivo. More specifically, to implement an intravoxel incoherent motion (IVIM) protocol at ultrahigh field for the human SC and assess parameters estimation errors.

Methods: Monte-Carlo simulations were conducted to assess estimation errors of 2 standard IVIM fitting approaches (two-step versus one-step fit) over the range of IVIM values reported for the human brain and for typical SC diffusivities.

PET [C]acetate is also a perfusion tracer for kidney evaluation purposes.

Rationale: Renal positron emission tomography (PET) functional imaging allows non-invasive and dynamic measurements of functional and metabolic parameters. [O]HO is used as a perfusion tracer, and [C]acetate as an oxidative metabolism in this purpose, requiring two injections to assess those fundamental parameters. Yet, in cardiac physiology study, the high first-pass myocardial extraction fraction of [C]acetate allowed to use its influx rate as a blood flow marker too.

Simultaneous multi-slice cardiac cine with Fourier-encoded self-calibration at 7 Tesla.

Purpose: To accelerate cardiac cine at 7 tesla using simultaneous multi-slice (SMS) acquisition with self-calibration to resolve misalignment between calibration and imaging data due to breathing motion.

Methods: A spoiled-gradient echo cine sequence was modified with radiofrequency phase-cycled SMS excitations. A Fourier encoding strategy was applied along the cardiac phase dimension to allow for slice untangling and split-slice GRAPPA calibration.

High-resolution 3D diffusion tensor MRI of anesthetized rhesus macaque brain at 3T.

Diffusion Magnetic Resonance Imaging (dMRI) has been widely used to investigate human brain microstructure and connectivity and its abnormalities in a variety of brain deficits, whether acute, neurodevelopmental or neurodegenerative. However, the biological interpretation and validation of dMRI data modelling is still a crucial challenge in the field. In this respect, achieving high spatial resolution in-vivo dMRI in the non-human primate to compare these observations both with human dMRI on the one hand and 'ground truth' microstructural and histological data on the other hand is of outmost importance.

AGE Content of a Protein Load Is Responsible for Renal Performances: A Pilot Study.

Objective: Chronic kidney disease is associated with higher morbidity and mortality in patients with diabetes. A low-protein diet is recommended to slow diabetic nephropathy progression because each protein load leads to renal hemodynamic variations. The aim of our study was to evaluate whether the advanced glycation end products (AGE) content of a protein load is responsible for the protein-induced renal hemodynamic variations in humans.

Fluid- and Biomechanical Analysis of Ascending Thoracic Aorta Aneurysm with Concomitant Aortic Insufficiency.

We present a comprehensive and original framework for the biomechanical analysis of patients affected by ascending thoracic aorta aneurysm and aortic insufficiency. Our aim is to obtain crucial indications about the role played by deranged hemodynamics on the ATAAs risk of rupture. Computational fluid dynamics analysis was performed using patient-specific geometries and boundary conditions derived from 4D MRI.

Myocardial arterial spin labeling.

Arterial spin labeling (ASL) is a cardiovascular magnetic resonance (CMR) technique for mapping regional myocardial blood flow. It does not require any contrast agents, is compatible with stress testing, and can be performed repeatedly or even continuously. ASL-CMR has been performed with great success in small-animals, but sensitivity to date has been poor in large animals and humans and remains an active area of research.

Time course of cardiometabolic alterations in a high fat high sucrose diet mice model and improvement after GLP-1 analog treatment using multimodal cardiovascular magnetic resonance.

Background: Cardiovascular complications of obesity and diabetes are major health problems. Assessing their development, their link with ectopic fat deposition and their flexibility with therapeutic intervention is essential. The aim of this study was to longitudinally investigate cardiac alterations and ectopic fat accumulation associated with diet-induced obesity using multimodal cardiovascular magnetic resonance (CMR) in mice.

Myocardial perfusion assessment in humans using steady-pulsed arterial spin labeling.

Purpose: Although arterial spin labeling (ASL) has become a routinely performed method in the rodent heart, its application to the human heart remains challenged by low tissue blood flow and cardiac and respiratory motion. We hypothesized that an alternative steady-pulsed ASL (spASL) method would provide more efficient perfusion signal averaging by driving the tissue magnetization into a perfusion-dependent steady state.

Methods: We evaluated the feasibility of spASL in the human heart by combining pulsed labeling in the aortic root with a balanced steady state free precession sequence.

In vivo characterization of rodent cyclic myocardial perfusion variation at rest and during adenosine-induced stress using cine-ASL cardiovascular magnetic resonance.

Background: Assessment of cyclic myocardial blood flow (MBF) variations can be an interesting addition to the characterization of microvascular function and its alterations. To date, totally non-invasive in vivo methods with this capability are still lacking. As an original technique, a cine arterial spin labeling (ASL) cardiovascular magnetic resonance approach is demonstrated to be able to produce dynamic MBF maps across the cardiac cycle in rats.

Cine-ASL: a steady-pulsed arterial spin labeling method for myocardial perfusion mapping in mice. Part I. Experimental study.

Arterial spin labeling has been developed and used for the quantitative and completely noninvasive assessment of myocardial perfusion in vivo. Here we propose a novel arterial spin labeling method called cine-ASL, which is based on an electrocardiogram-gated steady-pulsed labeling approach combined with simultaneous readout over the cardiac cycle using cine-fast low-angle shot. This method led to shorter acquisition times than the previously used Look-Locker flow-sensitive alternating inversion recovery gradient-echo technique while preserving spatial resolution and robustness with respect to cardiac motion.

Cine-ASL: a steady-pulsed arterial spin labeling method for myocardial perfusion mapping in mice. Part II. Theoretical model and sensitivity optimization.

In small rodent myocardial perfusion studies, the most widely used method is based on Look-Locker measurements of the magnetization recovery after FAIR preparation, which bears limitations regarding acquisition efficiency due to the pulsed arterial spin labeling nature of the sequence. To improve efficiency, this two-article set proposes a new steady-pulsed arterial spin labeling scheme using a cine readout incorporating one tagging pulse per heart cycle. In this part, we derive a theoretical description of the magnetization time evolution in such a scheme.