Publications by authors named "Martijn A Cloos"

Methods of cognitive enhancement for humans are most impactful when they generalize across tasks. However, the extent to which such "transfer" is possible via interventions is widely debated. In addition, the contribution of excitatory and inhibitory processes to such transfer is unknown.

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High acceleration factors in radial magnetic resonance fingerprinting (MRF) of the prostate lead to strong streak-like artefacts from flow in the femoral blood vessels, possibly concealing important anatomical information. Region-optimised virtual (ROVir) coils is a beamforming-based framework to create virtual coils that maximise signal in a region of interest while minimising signal in a region of interference. In this study, the potential of removing femoral flow streak artefacts in prostate MRF using ROVir coils is demonstrated in silico and in vivo.

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Functional magnetic resonance imaging (fMRI) has emerged as an essential tool for exploring human brain function. Submillimeter fMRI, in particular, has emerged as a tool to study mesoscopic computations. The inherently low signal-to-noise ratio (SNR) at submillimeter resolutions warrants the use of denoising approaches tailored at reducing thermal noise - the dominant contributing noise component in high resolution fMRI.

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Purpose: The purpose of this study is to improve the image quality of diffusion-weighted images obtained with a single RF transmit channel 7 T MRI setup using time-resampled frequency-offset corrected inversion (TR-FOCI) pulses to refocus the spins in a twice-refocused spin-echo readout scheme.

Methods: We replaced the conventional Shinnar-Le Roux-pulses in the twice refocused diffusion sequence with TR-FOCI pulses. The slice profiles were evaluated in simulation and experimentally in phantoms.

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We present a custom-built MR-compatible data glove to capture hand motion during concurrent fMRI experiments at 7 Tesla. Thermal and phantom tests showed our data glove can be used safely and without degradation of image quality. Subject-specific Blood Oxygen Level Dependent (BOLD) signal models, for use in fMRI analysis, were constructed based on recorded kinematic measurements.

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Purpose: Ultra-high field (UHF) provides improved SNR which greatly benefits SNR starved imaging techniques such as perfusion imaging. However, transmit field (B ) inhomogeneities commonly observed at UHF hinders the excitation uniformity. Here we show how replacing standard excitation pulses with parallel transmit pulses can improve efficiency of velocity selective labeling.

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Background: Objective measurement of regional cortical atrophy in individual patients would be a highly desirable adjunct for diagnosis of degenerative dementias.

Objective: We hypothesized that increasing the resolution of magnetic resonance scans would improve the sensitivity of cortical atrophy detection for individual patients.

Methods: 46 participants including 8 semantic-variant primary progressive aphasia (svPPA), seven posterior cortical atrophy (PCA), and 31 cognitively unimpaired participants underwent clinical assessment and 3.

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In this work, we introduce a super-resolution method that generates a high-resolution (HR) sodium ( Na) image from simultaneously acquired low-resolution (LR) Na density-weighted MRI and HR proton density, T , and T maps from proton ( H) MR fingerprinting in the brain at 7 T. The core of our method is a partial least squares regression between the HR ( H) images and the LR ( Na) image. An iterative loop and deconvolution with the point spread function of each acquired image were included in the algorithm to generate a final HR Na image without losing features from the LR Na image.

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Article Synopsis
  • Magnetic resonance fingerprinting (MRF) is a technique that accelerates MRI data collection but typically falls short of creating contrast-weighted images needed for radiology.
  • This study aims to enhance MRF's clinical usefulness by using U-net models to synthesize high-quality contrast-weighted MR images from MRF quantitative data, employing various loss functions during training.
  • Results show that the synthetic images achieved high quality, with the best outcomes derived from a combination of loss functions, as assessed by radiologists using a 5-point Likert scale.
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A noninvasive imaging technique measures neuronal activity at a millisecond time scale.

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Background: Magnetic resonance fingerprinting (MRF) techniques have been recently described for simultaneous multiparameter cartilage mapping of the knee although investigation of their ability to detect early cartilage degeneration remains limited.

Purpose: To investigate age-dependent changes in knee cartilage T , T , and T relaxation times measured using a three-dimensional (3D) MRF sequence in healthy volunteers.

Study Type: Prospective.

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Proton MRI can provide detailed morphological images, but it reveals little information about cell homeostasis. On the other hand, sodium MRI can provide metabolic information but cannot resolve fine structures. The complementary nature of proton and sodium MRI raises the prospect of their combined use in a single experiment.

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Purpose: To develop a 3D MR technique to simultaneously acquire proton multiparametric maps (T , T , and proton density) and sodium density weighted images over the whole brain.

Methods: We implemented a 3D stack-of-stars MR pulse sequence which consists of interleaved proton ( H) and sodium ( Na) excitations, tailored slice encoding gradients that can encode the same slice for both nuclei, and simultaneous readout with different radial trajectories ( H, full-radial; Na, center-out radial). The receive chain of our 7T scanner was modified to enable simultaneous acquisition of H and Na signal.

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Quantitative MRI can detect early biochemical changes in cartilage, but its bilateral use in clinical routines is challenging. The aim of this prospective study was to demonstrate the feasibility of magnetic resonance fingerprinting for bilateral simultaneous T , T , and T mapping of the hip joint. The study population consisted of six healthy volunteers with no known trauma or pain in the hip.

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In this work, we propose a free-breathing magnetic resonance fingerprinting (MRF) method that can be used to obtain B -robust quantitative T maps of the abdomen in a clinically acceptable time. A three-dimensional MRF sequence with a radial stack-of-stars trajectory was implemented, and its k-space acquisition ordering was adjusted to improve motion-robustness in the context of MRF. The flip angle pattern was optimized using the Cramér-Rao Lower Bound, and the encoding efficiency of sequences with 300, 600, 900 and 1800 flip angles was evaluated.

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Purpose: To develop a novel MR-fingerprinting (MRF) pulse sequence that is insensitive to and B imperfections for simultaneous T , T , and T relaxation mapping.

Methods: We implemented a totally balanced spin-lock (TB-SL) module to encode T relaxation into an existing MRF framework that encoded T and T . The spin-lock module used two 180° pulses with compensatory phases to reduce T sensitivity to B and B inhomogeneities.

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Purpose: To study the effects of magnetization transfer (MT, in which a semi-solid spin pool interacts with the free pool), in the context of magnetic resonance fingerprinting (MRF).

Methods: Simulations and phantom experiments were performed to study the impact of MT on the MRF signal and its potential influence on T and T estimation. Subsequently, an MRF sequence implementing off-resonance MT pulses and a dictionary with an MT dimension, generated by incorporating a two-pool model, were used to estimate the fractional pool size in addition to the , T , and T values.

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Purpose: The goal of this work is to demonstrate a method for the simultaneous acquisition of proton multiparametric maps (T , T , and proton density) and sodium density images in 1 single scan. We hope that the development of such capabilities will help to ease the implementation of sodium MRI in clinical trials and provide more opportunities for researchers to investigate metabolism through sodium MRI.

Methods: We developed a sequence based on magnetic resonance fingerprinting (MRF), which contains interleaved proton ( H) and sodium ( Na) excitations followed by a simultaneous center-out radial readout for both nuclei.

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The dynamics of large spin-1/2 ensembles are commonly described by the Bloch equation, which is characterized by the magnetization's non-linear response to the driving magnetic field. Consequently, most magnetic field variations result in non-intuitive spin dynamics, which are sensitive to small calibration errors. Although simplistic field variations result in robust spin dynamics, they do not explore the richness of the system's phase space.

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Purpose: The optimization and analysis of spin ensemble trajectories in the hybrid state-a state in which the direction of the magnetization adiabatically follows the steady state while the magnitude remains in a transient state.

Methods: Numerical optimizations were performed to find spin ensemble trajectories that minimize the Cramér-Rao bound for -encoding, -encoding, and their weighted sum, respectively, followed by a comparison between the Cramér-Rao bounds obtained with our optimized spin-trajectories, Look-Locker sequences, and multi-spin-echo methods. Finally, we experimentally tested our optimized spin trajectories with in vivo scans of the human brain.

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Diffusion tractography is routinely used to study white matter architecture and brain connectivity in vivo. A key step for successful tractography of neuronal tracts is the correct identification of tract directions in each voxel. Here we propose a fingerprinting-based methodology to identify these fiber directions in Orientation Distribution Functions, dubbed ODF-Fingerprinting (ODF-FP).

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Owing to a technical error, this Article was originally published with an incorrect published online date of '4 May 2018'; it should have been '7 May 2018'. This has now been corrected.

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Objective: In this paper, we introduce global Maxwell tomography (GMT), a novel volumetric technique that estimates electric conductivity and permittivity by solving an inverse scattering problem based on magnetic resonance measurements.

Methods: GMT relies on a fast volume integral equation solver, MARIE, for the forward path, and a novel regularization method, match regularization, designed specifically for electrical property estimation from noisy measurements. We performed simulations with three different tissue-mimicking numerical phantoms of different complexity, using synthetic transmit sensitivity maps with realistic noise levels as the measurements.

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Densely packed resonant structures used for magnetic resonance imaging (MRI), such as nuclear magnetic resonance phased-array detectors, suffer from resonant inductive coupling, which restricts coil design to fixed geometries, imposes performance limitations, and narrows the scope of MRI experiments to motionless subjects. Here, we report the design of high-impedance detectors, and the fabrication and performance of a wearable detector array for MRI of the hand, that cloak themselves from electrodynamic interactions with neighboring elements. We experimentally verified that the detectors do not suffer from signal-to-noise degradation mechanisms typically observed with the use of traditional low-impedance elements.

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