3D quantitative myocardial perfusion imaging with hyperpolarized HP001(bis-1,1-(hydroxymethyl)-[1-C]cyclopropane-d8): Application of gradient echo and balanced SSFP sequences.

Purpose: This study aims to show the viability of conducting three-dimensional (3D) myocardial perfusion quantification covering the entire heart using both GRE and bSSFP sequences with hyperpolarized HP001.

Methods: A GRE sequence and a bSSFP sequence, both with a stack-of-spirals readout, were designed and applied to three pigs. The images were reconstructed using C coil sensitivity maps measured in a phantom experiment.

Hyperpolarized Water for Coronary Artery Angiography and Whole-Heart Myocardial Perfusion Quantification.

Water freely diffuses across cell membranes, making it suitable for measuring absolute tissue perfusion. In this study, we introduce an imaging method for conducting coronary artery angiography and quantifying myocardial perfusion across the entire heart using hyperpolarized water. H was hyperpolarized using dissolution dynamic nuclear polarization (dDNP) with UV-generated radicals.

Volumetric measurements of weak current-induced magnetic fields in the human brain at high resolution.

Purpose: Clinical use of transcranial electrical stimulation (TES) requires accurate knowledge of the injected current distribution in the brain. MR current density imaging (MRCDI) uses measurements of the TES-induced magnetic fields to provide this information. However, sufficient sensitivity and image quality in humans in vivo has only been documented for single-slice imaging.

A head template for computational dose modelling for transcranial focused ultrasound stimulation.

Transcranial focused Ultrasound Stimulation (TUS) at low intensities is emerging as a novel non-invasive brain stimulation method with higher spatial resolution than established transcranial stimulation methods and the ability to selectively stimulate also deep brain areas. Accurate control of the focus position and strength of the TUS acoustic waves is important to enable a beneficial use of the high spatial resolution and to ensure safety. As the human skull causes strong attenuation and distortion of the waves, simulations of the transmitted waves are needed to accurately determine the TUS dose distribution inside the cranial cavity.

Decomposition-based framework for tumor classification and prediction of treatment response from longitudinal MRI.

In the field of radiation oncology, the benefit of MRI goes beyond that of providing high soft-tissue contrast images for staging and treatment planning. With the recent clinical introduction of hybrid MRI linear accelerators it has become feasible to map physiological parameters describing diffusion, perfusion, and relaxation during the entire course of radiotherapy, for example. However, advanced data analysis tools are required for extracting qualified prognostic and predictive imaging biomarkers from longitudinal MRI data.

Optimized flip angle schemes for the split acquisition of fast spin-echo signals (SPLICE) sequence and application to diffusion-weighted imaging.

Purpose: The diffusion-weighted SPLICE (split acquisition of fast spin-echo signals) sequence employs split-echo rapid acquisition with relaxation enhancement (RARE) readout to provide images almost free of geometric distortions. However, due to the varying T -weighting during k-space traversal, SPLICE suffers from blurring. This work extends a method for controlling the spatial point spread function (PSF) while optimizing the signal-to-noise ratio (SNR) achieved by adjusting the flip angles in the refocusing pulse train of SPLICE.

Tracking of rigid head motion during MRI using an EEG system.

Purpose: To demonstrate a novel method for tracking of head movements during MRI using electroencephalography (EEG) hardware for recording signals induced by native imaging gradients.

Theory And Methods: Gradient switching during simultaneous EEG-fMRI induces distortions in EEG signals, which depend on subject head position and orientation. When EEG electrodes are interconnected with high-impedance carbon wire loops, the induced voltages are linear combinations of the temporal gradient waveform derivatives.

Data-driven separation of MRI signal components for tissue characterization.

Purpose: MRI can be utilized for quantitative characterization of tissue. To assess e.g.

On the reconstruction of magnetic resonance current density images of the human brain: Pitfalls and perspectives.

Magnetic resonance current density imaging (MRCDI) of the human brain aims to reconstruct the current density distribution caused by transcranial electric stimulation from MR-based measurements of the current-induced magnetic fields. So far, the MRCDI data acquisition achieves only a low signal-to-noise ratio, does not provide a full volume coverage and lacks data from the scalp and skull regions. In addition, it is only sensitive to the component of the current-induced magnetic field parallel to the scanner field.

Sensitivity and resolution improvement for in vivo magnetic resonance current-density imaging of the human brain.

Purpose: Magnetic resonance current-density imaging (MRCDI) combines MRI with low-intensity transcranial electrical stimulation (TES; 1-2 mA) to map current flow in the brain. However, usage of MRCDI is still hampered by low measurement sensitivity and image quality.

Methods: Recently, a multigradient-echo-based MRCDI approach has been introduced that presently has the best-documented efficiency.

Elevated body weight modulates subcortical volume change and associated clinical response following electroconvulsive therapy.

Background: Obesity is a frequent somatic comorbidity of major depression, and it has been associated with worse clinical outcomes and brain structural abnormalities. Converging evidence suggests that electroconvulsive therapy (ECT) induces both clinical improvements and increased subcortical grey matter volume in patients with depression. However, it remains unknown whether increased body weight modulates the clinical response and structural neuroplasticity that occur with ECT.

Safety evaluation of a new setup for transcranial electric stimulation during magnetic resonance imaging.

Background: Transcranial electric stimulation during MR imaging can introduce safety issues due to coupling of the RF field with the stimulation electrodes and leads.

Objective: To optimize the stimulation setup for MR current density imaging (MRCDI) and increase maximum stimulation current, a new low-conductivity (σ = 29.4 S/m) lead wire is designed and tested.

Multi-site benchmarking of clinical C RF coils at 3T.

A quality assurance protocol for RF coils is proposed, which can be used for volume (Tx/Rx) and surface (Rx) coils. Following this protocol, a benchmarking of seven coils (from three different MR sites) dedicated to C MRI at 3T is reported. Coil performance is particularly important for 3T MRI at the C frequency, since the coil-to-sample noise ratio is typically high.

Transducer modeling for accurate acoustic simulations of transcranial focused ultrasound stimulation.

Objective: Low-intensity transcranial ultrasound stimulation (TUS) is emerging as a non-invasive brain stimulation technique with superior spatial resolution and the ability to reach deep brain areas. Medical image-based computational modeling could be an important tool for individualized TUS dose control and targeting optimization, but requires further validation. This study aims to assess the impact of the transducer model on the accuracy of the simulations.

Three-dimensional accelerated acquisition for hyperpolarized C MR with blipped stack-of-spirals and conjugate-gradient SENSE.

Purpose: To test a new parallel imaging strategy for acceleration of hyperpolarized C MR acquisitions based on a 3D blipped stack-of-spirals trajectory and conjugate-gradient SENSE reconstruction with precalibrated sensitivities.

Methods: The blipped stack-of-spirals trajectory was developed for an acceleration factor of 4, based on an undersampled stack-of-spirals with gradient blips during spiral readout. The trajectory was developed with volumetric coverage of a large FOV and with high spatial resolution.

Brain Changes Induced by Electroconvulsive Therapy Are Broadly Distributed.

Background: Electroconvulsive therapy (ECT) is associated with volumetric enlargements of corticolimbic brain regions. However, the pattern of whole-brain structural alterations following ECT remains unresolved. Here, we examined the longitudinal effects of ECT on global and local variations in gray matter, white matter, and ventricle volumes in patients with major depressive disorder as well as predictors of ECT-related clinical response.

Safety of transcranial focused ultrasound stimulation: A systematic review of the state of knowledge from both human and animal studies.

Background: Low-intensity transcranial focused ultrasound stimulation (TFUS) holds great promise as a highly focal technique for transcranial stimulation even for deep brain areas. Yet, knowledge about the safety of this novel technique is still limited.

Objective: To systematically review safety related aspects of TFUS.

Inductive measurement and encoding of k-space trajectories in MR raw data.

Objectives:  The objective of this study was to concurrently acquire an inductive k-space trajectory measure and corresponding imaging data by an MR scanner.

Materials And Methods:  1D gradient measures were obtained by digital integration, regularized using measured gradient coil currents and recorded individually by the scanner concurrently with raw MR data. Gradient measures were frequency modulated into an RF signal receivable by the scanner, yielding a k-space trajectory measure from the cumulative phase of the acquired data.

Coil profile estimation strategies for parallel imaging with hyperpolarized C MRI.

Purpose: To investigate auto- and pre-calibration coil profile estimation for parallel imaging reconstruction of hyperpolarized C MRI volumetric data.

Methods: Parallel imaging reconstruction was studied with 3 different approaches for coil profile estimation: auto-calibration, phantom calibration, and theoretic calibration. Acquisition was performed with a 3D stack-of-spirals sequence with spectral-spatial excitation and Cartesian undersampling.

The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI).

Purpose: MR Current Density Imaging (MRCDI) involves weak current-injection into the head. The resulting magnetic field changes are measured by MRI. Stray fields pose major challenges since these can dominate the fields caused by tissue currents.

[Magnetic resonance imaging for the diagnosis of non-alcoholic fatty liver disease].

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver disease with an estimated overall prevalence of 25% in the global adult population. Liver biopsy is the gold standard for the diagnosis of NAFLD. However, the risk of complications and collection of only 1/50,000 of the total liver volume, limits this diagnostic method in an unselected population.

Development of a Symmetric Echo-Planar Spectroscopy Imaging Framework for Hyperpolarized C Imaging in a Clinical PET/MR Scanner.

Here, we developed a symmetric echo-planar spectroscopic imaging (EPSI) sequence for hyperpolarized C imaging on a clinical hybrid positron emission tomography/magnetic resonance imaging system. The pulse sequence uses parallel reconstruction pipelines to separately reconstruct data from odd-and-even gradient echoes to reduce artifacts from gradient imbalances. The ramp-sampled data in the spatiotemporal frequency space are regridded to compensate for the chemical-shift displacements.

Gamma-aminobutyric acid edited echo-planar spectroscopic imaging (EPSI) with MEGA-sLASER at 7T.

Purpose: For rapid spatial mapping of gamma-aminobutyric acid (GABA) at the increased sensitivity and spectral separation for ultra-high magnetic field strength (7 tesla [T]), an accelerated edited magnetic resonance spectroscopic imaging technique was developed and optimized for the human brain at 7 T.

Methods: A MEGA-sLASER sequence was used for GABA editing and volume selection to maximize editing efficiency and minimize chemical shift displacement errors. To accommodate the high bandwidth requirements at 7 T, a single-shot echo planar readout was used for rapid simultaneous encoding of the temporal dimension and 1 spatial.

Volume of the Human Hippocampus and Clinical Response Following Electroconvulsive Therapy.

Background: Hippocampal enlargements are commonly reported after electroconvulsive therapy (ECT). To clarify mechanisms, we examined if ECT-induced hippocampal volume change relates to dose (number of ECT sessions and electrode placement) and acts as a biomarker of clinical outcome.

Methods: Longitudinal neuroimaging and clinical data from 10 independent sites participating in the Global ECT-Magnetic Resonance Imaging Research Collaboration (GEMRIC) were obtained for mega-analysis.

Human in-vivo brain magnetic resonance current density imaging (MRCDI).

Magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) are two emerging modalities, which combine weak time-varying currents injected via surface electrodes with magnetic resonance imaging (MRI) to acquire information about the current flow and ohmic conductivity distribution at high spatial resolution. The injected current flow creates a magnetic field in the head, and the component of the induced magnetic field ΔB parallel to the main scanner field causes small shifts in the precession frequency of the magnetization. The measured MRI signal is modulated by these shifts, allowing to determine ΔB for the reconstruction of the current flow and ohmic conductivity.