Spinal CSF flow in response to forced thoracic and abdominal respiration.

Background: Respiration-induced pressure changes represent a powerful driving force of CSF dynamics as previously demonstrated using flow-sensitive real-time magnetic resonance imaging (MRI). The purpose of the present study was to elucidate the sensitivity of CSF flow along the spinal canal to forced thoracic versus abdominal respiration.

Methods: Eighteen subjects without known illness were studied using real-time phase-contrast flow MRI at 3 T in the aqueduct and along the spinal canal at levels C3, Th1, Th8 and L3.

Diffusion-weighted MRI of the prostate without susceptibility artifacts: Undersampled multi-shot turbo-STEAM with rotated radial trajectories.

The aim of this study was to develop and evaluate a clinically feasible approach to diffusion-weighted (DW) MRI of the prostate without susceptibility-induced artifacts. The proposed method relies on an undersampled multi-shot DW turbo-STEAM sequence with rotated radial trajectories and a multi-step inverse reconstruction with denoised multi-shot phase maps. The total acquisition time was below 6 min for a resolution of 1.

Multi-slice real-time MRI of temporomandibular joint dynamics.

Objectives: The purpose of this work was to improve the clinical versatility of high-speed real-time MRI studies of temporomandibular joint (TMJ) dynamics by simultaneous recordings of multiple MRI movies in different sections.

Methods: Real-time MRI at 3 T was realized using highly undersampled radial FLASH acquisitions and image reconstruction by regularized nonlinear inversion (NLINV). Multi-slice real-time MRI of two, three or four slices at 0.

Respiration and the watershed of spinal CSF flow in humans.

The dynamics of human CSF in brain and upper spinal canal are regulated by inspiration and connected to the venous system through associated pressure changes. Upward CSF flow into the head during inspiration counterbalances venous flow out of the brain. Here, we investigated CSF motion along the spinal canal by real-time phase-contrast flow MRI at high spatial and temporal resolution.

Diagnosis of disk displacement using real-time MRI: Clinical report of two patients.

The clinical application of real-time magnetic resonance imaging (MRI) for the diagnosis of temporomandibular joint disk displacement (DD) with and without reduction is presented. In 2 patients with presumed DD, real-time MRI at 15 frames per second was performed during the natural opening and closing of the mouth. In one patient unilateral DD with reduction and in the other patient bilateral DD without reduction were observed.

Identification of the Upward Movement of Human CSF and its Relation to the Brain Venous System.

CSF flux is involved in the pathophysiology of neurodegenerative diseases and cognitive impairment after traumatic brain injury, all hallmarked by the accumulation of cellular metabolic waste. Its effective disposal via various CSF routes has been demonstrated in animal models. In contrast, the CSF dynamics in humans are still poorly understood.

Real-time magnetic resonance imaging of deep venous flow during muscular exercise-preliminary experience.

Background: The accurate assessment of peripheral venous flow is important for the early diagnosis and treatment of disorders such as deep-vein thrombosis (DVT) which is a major cause of post-thrombotic syndrome or even death due to pulmonary embolism. The aim of this work is to quantitatively determine blood flow in deep veins during rest and muscular exercise using a novel real-time magnetic resonance imaging (MRI) method for velocity-encoded phase-contrast (PC) MRI at high spatiotemporal resolution.

Methods: Real-time PC MRI of eight healthy volunteers and one patient was performed at 3 Tesla (Prisma fit, Siemens, Erlangen, Germany) using a flexible 16-channel receive coil (Variety, NORAS, Hoechberg, Germany).

Real-time MRI of the temporomandibular joint at 15 frames per second-A feasibility study.

The purpose of this study was to develop and evaluate a novel method for real-time MRI of TMJ function at high temporal resolution and with two different contrasts. Real-time MRI was based on undersampled radial fast low angle shot (FLASH) acquisitions with iterative image reconstruction by regularized nonlinear inversion. Real-time MRI movies with T1 contrast were obtained with use of a radiofrequency-spoiled FLASH sequence, while movies with T2/T1 contrast employed a gradient-refocused FLASH version.

High-resolution myocardial T mapping using single-shot inversion recovery fast low-angle shot MRI with radial undersampling and iterative reconstruction.

Objective: To develop a novel method for rapid myocardial T mapping at high spatial resolution.

Methods: The proposed strategy represents a single-shot inversion recovery experiment triggered to early diastole during a brief breath-hold. The measurement combines an adiabatic inversion pulse with a real-time readout by highly undersampled radial FLASH, iterative image reconstruction and T fitting with automatic deletion of systolic frames.

Sensitivity of Diffusion-Weighted STEAM MRI and EPI-DWI to Infratentorial Ischemic Stroke.

Objectives: To assess the sensitivity of stimulated echo acquisition mode diffusion weighted imaging (STEAM-DWI) to ischemic stroke in comparison to echo-planar imaging diffusion weighted imaging (EPI-DWI) in the infratentorial compartment.

Methods: Fifty-seven patients presenting with clinical features of infratentorial stroke underwent STEAM-DWI, high-resolution EPI-DWI (HR-DWI, 2.5 mm slice thickness) and low-resolution EPI-DWI (LR-DWI, 5 mm slice thickness).

Inspiration is the major regulator of human CSF flow.

The mechanisms behind CSF flow in humans are still not fully known. CSF circulates from its primary production sites at the choroid plexus through the brain ventricles to reach the outer surface of the brain in the subarachnoid spaces from where it drains into venous bloodstream and cervical lymphatics. According to a recent concept of brain fluid transport, established in rodents, CSF from the brain surface also enters the brain tissue along para-arterial routes and exits through paravenous spaces again into subarachnoid compartments.

Real-time magnetic resonance imaging of cardiac function and flow-recent progress.

Cardiac structure, function and flow are most commonly studied by ultrasound, X-ray and magnetic resonance imaging (MRI) techniques. However, cardiovascular MRI is hitherto limited to electrocardiogram (ECG)-synchronized acquisitions and therefore often results in compromised quality for patients with arrhythmias or inabilities to comply with requested protocols-especially with breath-holding. Recent advances in the development of novel real-time MRI techniques now offer dynamic imaging of the heart and major vessels with high spatial and temporal resolution, so that examinations may be performed without the need for ECG synchronization and during free breathing.

Real-time flow MRI of the aorta at a resolution of 40 msec.

Purpose: To evaluate a novel real-time phase-contrast magnetic resonance imaging (MRI) technique for the assessment of through-plane flow in the ascending aorta.

Materials And Methods: Real-time MRI was based on a radial fast low-angle shot (FLASH) sequence with about 30-fold undersampling and image reconstruction by regularized nonlinear inversion. Phase-contrast maps were obtained from two (interleaved or sequential) acquisitions with and without a bipolar velocity-encoding gradient.

Real-time phase-contrast MRI of cardiovascular blood flow using undersampled radial fast low-angle shot and nonlinear inverse reconstruction.

Velocity-encoded phase-contrast MRI of cardiovascular blood flow commonly relies on electrocardiogram-synchronized cine acquisitions of multiple heartbeats to quantitatively determine the flow of an averaged cardiac cycle. Here, we present a new method for real-time phase-contrast MRI that combines flow-encoding gradients with highly undersampled radial fast low-angle shot acquisitions and phase-sensitive image reconstructions by regularized nonlinear inversion. Apart from calibration studies using steady and pulsatile flow, preliminary in vivo applications focused on through-plane flow in the ascending aorta of healthy subjects.

Spatially encoded phase-contrast MRI-3D MRI movies of 1D and 2D structures at millisecond resolution.

This work demonstrates that the principles underlying phase-contrast MRI may be used to encode spatial rather than flow information along a perpendicular dimension, if this dimension contains an MRI-visible object at only one spatial location. In particular, the situation applies to 3D mapping of curved 2D structures which requires only two projection images with different spatial phase-encoding gradients. These phase-contrast gradients define the field of view and mean spin-density positions of the object in the perpendicular dimension by respective phase differences.

Real-time MRI at a resolution of 20 ms.

The desire to visualize noninvasively physiological processes at high temporal resolution has been a driving force for the development of MRI since its inception in 1973. In this article, we describe a unique method for real-time MRI that reduces image acquisition times to only 20 ms. Although approaching the ultimate limit of MRI technology, the method yields high image quality in terms of spatial resolution, signal-to-noise ratio and the absence of artifacts.

Basal cerebral blood volume during the poststimulation undershoot in BOLD MRI of the human brain.

One of the characteristics of the blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) response to functional challenges of the brain is the poststimulation undershoot, which has been suggested to originate from a delayed recovery of either cerebral blood volume (CBV) or cerebral metabolic rate of oxygen to baseline. Using bolus-tracking MRI in humans, we recently showed that relative CBV rapidly normalizes after the end of stimulation. As this observation contradicts at least part of the blood-pool contrast agent studies performed in animals, we reinvestigated the CBV contribution by dynamic T1-weighted three-dimensional MRI (8 seconds temporal resolution) and Vasovist at 3 T (12 subjects).

Real-time cardiovascular magnetic resonance at high temporal resolution: radial FLASH with nonlinear inverse reconstruction.

Background: Functional assessments of the heart by dynamic cardiovascular magnetic resonance (CMR) commonly rely on (i) electrocardiographic (ECG) gating yielding pseudo real-time cine representations, (ii) balanced gradient-echo sequences referred to as steady-state free precession (SSFP), and (iii) breath holding or respiratory gating. Problems may therefore be due to the need for a robust ECG signal, the occurrence of arrhythmia and beat to beat variations, technical instabilities (e.g.

Efficacy of EMG-triggered electrical arm stimulation in chronic hemiparetic stroke patients.

Purpose: EMG-triggered electrostimulation (EMG-ES) may improve the motor performance of affected limbs of hemiparetic stroke patients even in the chronic stage. This study was designed to characterize cortical activation changes following intensified EMG-ES in chronic stroke patients and to identify predictors for successful rehabilitation depending on disease severity.

Methods: We studied 9 patients with severe residual hemiparesis, who underwent 8 weeks of daily task-orientated multi-channel EMG-ES of the paretic arm.

TTC post-processing is beneficial for functional MRI at low magnetic field: a comparative study at 1 T and 3 T.

This study aimed to broaden the diagnostic possibilities of low-field MRI systems (i) by examining the feasibility of functional MRI of human brain activation at 1 T, and (ii) by assessing its reliability in comparison with acquisitions at 3 T. Eight subjects were studied at 1 T and 3T using standard echo-planar-imaging sequences at 3-mm isotropic spatial resolution. Paradigms included silent word generation, sequential finger-to-thumb opposition, and passive finger movements.

Callosal dysfunction in amyotrophic lateral sclerosis correlates with diffusion tensor imaging of the central motor system.

We investigated the frequency and functional relevance of corpus callosum degeneration in amyotrophic lateral sclerosis (ALS). A total of 22 ALS patients and 29 healthy controls performed the newly developed Contralateral Co-Movement Test as indicator of callosal dysfunction. Diffusion tensor imaging was applied to determine fractional anisotropy values in the callosal area containing the crossing motor fibers and in the pyramidal tracts in 13 subjects of each group.

Black-blood imaging of the human heart using rapid stimulated echo acquisition mode (STEAM) MRI.

Purpose: To develop a rapid stimulated echo acquisition mode (STEAM) MRI technique for "black-blood" imaging of the human heart that overcomes the single-slice limitation and partially compromised blood suppression associated with double inversion-recovery techniques.

Materials And Methods: Black-blood multislice images of the heart along anatomic orientations and triggered to end diastole were obtained from healthy human subjects at 3T using rapid STEAM MRI sequences with five-eighths partial Fourier encoding and variable flip angles. Single-shot STEAM images at 2.

A novel group analysis for functional MRI of the human brain based on a two-threshold correlation (TTC) method.

This work presents a new group analysis for functional MRI of human brain activation. The two-threshold correlation (TTC) method determines two statistical thresholds by estimating the noise distribution underlying the summed histogram of correlation coefficients (CC) from all sections and subjects. The probabilistic CC thresholds (p<0.

Rhesus monkey and human share a similar topography of the corpus callosum as revealed by diffusion tensor MRI in vivo.

A recent study of the corpus callosum (CC) in humans revealed a new topographical arrangement of the cortical connectivity pattern. To explore the CC topography in nonhuman primates, we applied magnetic resonance diffusion tensor imaging and tract tracing techniques in individual rhesus monkeys in vivo. The results demonstrate that the CC topography of primates and humans is surprisingly similar.

Task- and EEG-correlated analyses of BOLD MRI responses to eyes opening and closing.

Variations of a subject's vigilance may pose a severe confound during functional brain mapping. Here, we focused on BOLD MRI responses to eyes opening and closing in complete darkness and the associated changes in the EEG's alpha frequency band (Berger's effect) as a possible approach to this problem. In awake subjects, BOLD MRI activation patterns were positively correlated to eyes opening and negatively to alpha power.