Brain activation in response to a tactile stimulation: functional magnetic resonance imaging (FMRI) versus cognitive analysis.

Objective. The aim of this study was to compare fMRI analysis of somatosensory areas activated by passive touch, to cognitive analysis of the psychological profile of human subjects. Methods.

Angular (Gothic) aortic arch leads to enhanced systolic wave reflection, central aortic stiffness, and increased left ventricular mass late after aortic coarctation repair: evaluation with magnetic resonance flow mapping.

Objective: We sought to investigate the mechanism whereby a particular deformity of the aortic arch, an angulated Gothic shape, might lead to hypertension late after anatomically successful repair of aortic coarctation.

Methods: Fifty-five normotensive patients with anatomically successful repair of aortic coarctation and either a Gothic (angulated) or a Romanesque (smooth and rounded) arch were studied with magnetic resonance angiography and flow mapping in both the ascending and descending aortas. Systolic waveforms, central aortic stiffness, and pulse velocity were measured.

Increased central aortic stiffness and left ventricular mass in normotensive young subjects after successful coarctation repair.

Background: Hypertension occurs in 20% to 40% of survivors of anatomically successful repair of aortic coarctation (CoA). The aim of the present study was to examine the role of central aortic function in this setting.

Methods: Forty normotensive asymptomatic subjects with successful CoA repair (age 12 +/- 8 years) and 20 age- and sex-matched control subjects underwent detailed magnetic resonance imaging investigation of the thoracic aorta and left ventricle.

Interobserver variability in assessing segmental function can be reduced by combining visual analysis of CMR cine sequences with corresponding parametric images of myocardial contraction.

Objective: To evaluate if color-coded parametric images could help subjective visual analysis and improve interobserver agreement in the evaluation of segmental contraction (SC) in CMR.

Background: Routine evaluation of SC in CMR remains mostly based on visual analysis of cine loops and subsequent interobserver variability remains a potential drawback.

Materials And Methods: Three short axis cine loops were obtained in 33 subjects (18 myocardial infarction, 15 control), and 528 segments were analyzed.

Velocity encoding versus acceleration encoding for pressure gradient estimation in MR haemodynamic studies.

Many methods have been proposed to extract pressure gradient maps from magnetic resonance (MR) images. They were based on the resolution of the haemodynamic model of Navier-Stokes and needed the flow acceleration to be known. Most used velocity data acquisition and computed acceleration from temporal and spatial derivatives of the velocity field.

[Aortic arch shape and flow dynamics].

Post-operative deformation of the aortic arch architecture is associated with an increased risk of hypertension following correction of coarctation. In addition to morphological analysis, MRI allows a functional analysis of the thoracic aorta. We report three examples which illustrate the direct relationship between aortic arch morphology and blood flow in the thoracic aorta.

Calculation of left ventricle relative pressure distribution in MRI using acceleration data.

Measurements of pressure variations within the cardiac chambers could provide important information for clinical assessments of cardiovascular function. In this work an MRI method for evaluating spatial distributions of intracardiac relative pressure is presented. We first calculated pressure gradients from MR maps of blood acceleration by applying the NS equation.

Local reconstruction of stenosed sections of artery using multiple MRA acquisitions.

A method for reconstructing magnetic resonance angiography (MRA) volumes from successive acquisitions is described. The method is based on double oblique acquisitions of highly anisotropic MRA volumes, each of which corresponds to reduced k-space filling. These partial k-spaces are then combined to obtain a 3D k-space adapted to the frequency spread of the angiographic image of the stenosis.

Estimation of left ventricular performance through temporal pressure variations measured by MR velocity and acceleration mappings.

Purpose: To describe a method for assessing pressure variation vs. time (dp/dt) using blood flow acceleration measured by MRI, and to demonstrate its applicability in estimating left ventricular (LV) function.

Materials And Methods: The method was tested in vitro using a pulsatile phantom, and a strong correlation was found between transducer and MRI determinations of dp/dt (r = 0.

Anatomy and physiology of subcutaneous adipose tissue by in vivo magnetic resonance imaging and spectroscopy: relationships with sex and presence of cellulite.

Background: Little is still known concerning subcutaneous adipose tissue and cellulite, and controversial questions are still under discussion.

Aims: Magnetic resonance imaging and spectroscopy were used to address two unresolved questions relating to the anatomy and physiology of subcutaneous adipose tissue.

Methods: Using high spatial resolution magnetic resonance imaging we characterized the topography of the dermo- hypodermal junction, and the three-dimensional architecture of the subcutaneous fibrous septae.

Precision of magnetic resonance velocity and acceleration measurements: theoretical issues and phantom experiments.

Magnetic resonance (MR) sequences have been developed for acquiring multiple components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precision of measurements: NS, the number of flow-encoding steps; NEX, the number of signal accumulations; and ND, the number of dimensions. Our aims were to establish a general relationship revealing the precision of these measurements as a function of NS, ND, and NEX and to validate it by experiments using phantoms.

CSF flow measurement in syringomyelia.

Background And Purpose: CSF circulation has been reported to represent a major factor in the pathophysiology of syringomyelia. Our purpose was to determine the CSF flow patterns in spinal cord cysts and in the subararachnoid space in patients with syringomyelia associated with Chiari I malformation and to evaluate the modifications of the flow resulting from surgery.

Methods: Eighteen patients with syringomyelia were examined with a 3D Fourier encoding velocity imaging technique.

Multidimensional MR mapping of multiple components of velocity and acceleration by fourier phase encoding with a small number of encoding steps.

Previous studies have shown that the multi-step approach of velocity or acceleration encoding is highly efficient in terms of the signal-to-noise ratio per unit time. This work describes a multidimensional extension of this method for simultaneously measuring multiple components of velocity and acceleration with a few encoding steps. N flow dimensions were encoded with an ND-matrix, obtained by combining the various flow-encoding gradients.

Improved estimation of velocity and flow rate using regularized three-point phase-contrast velocimetry.

We improved the three-point phase-contrast method by regularization of MR velocity data after acquisition of a low velocity-to-noise ratio (VNR) velocity image and a high VNR aliased velocity image. The phase unwrapping algorithm is based on the assumed correlation of the velocity of adjacent flow voxels on the low VNR and the unaliased high VNR images. We used Fourier encoding with eight velocity-encoding gradient steps to obtain reference velocity images of the aorta from five subjects (274 images) and compared them with the phase-contrast and three-point phase-contrast images with and without regularization.

Estimation of pressure gradients in pulsatile flow from magnetic resonance acceleration measurements.

A method for estimating pressure gradients from MR images is demonstrated. Making the usual assumption that the flowing medium is a Newtonian fluid, and with appropriate boundary conditions, the inertial forces (or acceleration components of the flow) are proportional to the pressure gradients. The technique shown here is based on an evaluation of the inertial forces from Fourier acceleration encoding.

Spatial regularization of flow patterns in magnetic resonance velocity mapping.

A technique dedicated to spatial regularization of magnetic resonance (MR) velocity data has been implemented to improve flow image quality. It is assumed that neighboring flow-velocity pixels are partially correlated, although large-velocity discontinuities remain possible. Increasing MR signal magnitude due to the in-flow effect also is used to enhance further reliability of the estimated velocity.

Pulmonary arterial resistance: noninvasive measurement with indexes of pulmonary flow estimated at velocity-encoded MR imaging--preliminary experience.

Cardiac output and pulmonary vascular resistance (PVR) were measured in 19 patients by means of catheterization of the right side of the heart. Results were compared with the cardiac output and indexes of pulmonary arterial blood flow estimated with velocity-encoded magnetic resonance (MR) imaging. Correlations were good between estimates with right-sided heart catheterization and those with velocity-encoded MR imaging.

Acceleration mapping by Fourier acceleration-encoding: in vitro study and initial results in the great thoracic vessels.

Acceleration mapping can be conducted by replacing the bipolar gradient pulse of a velocity mapping sequence by a tripolar pulse. However, since the acceleration encoding pulse is longer, the image quality is altered by the requirement of a long echo time. Since Fourier encoding velocity imaging has been shown to be robust, this velocity mapping method was transformed into an acceleration mapping method.

Functional MR imaging of the human sensorimotor cortex during haptic discrimination.

This study attempted to determine whether haptic discriminations of shape (haptic task) activate the same tissue in the central cortical region of normal human subjects as do finger movements (opposition task). Opposition and haptic tasks both activated the central sulcus, as expected from previous imaging studies. The haptic task activated about 50% of the cortical territory activated by the opposition task.

High resolution T1 weighted magnetic resonance imaging of the deep brain structures using a reduced bandwidth.

High spatial resolution T1 weighted images of the brain were acquired in 5-13 min on a whole-body magnetic resonance imager operating at 1.5 T. In order to obtain 5-8 cm field of view images, the receiver bandwidth (Bw) was lowered to 2 kHz.

[Morphological and functional study of pulmonary arteries by MRI].

This article presents an exhaustive review of MRI in the assessment of the pulmonary arteries (sequences, normal results, clinical signs of the main diseases). Its current preferential indications are: the study of the main pulmonary artery trunks (primary tumours, proximal embolism, caliber abnormalities, anatomical relations with central tumours), the assessment and post-treatment follow-up of pulmonary arterial malformations. Angio-MRI is currently being developed and, in the near future, should allow the reliable diagnosis of pulmonary embolism and will therefore be indicated alongside spiral computed tomography.

Quantification of hemodynamics in primary pulmonary hypertension with magnetic resonance imaging.

The aims of this study were first to analyze pulmonary flow differences between patients with primary pulmonary hypertension (PPH) and volunteers, and second to determine whether magnetic resonance (MR) 3D Fourier encoding velocity imaging is capable of assessing hemodynamics in PPH. Pulmonary and aortic flows were quantified with MR imaging in 13 patients with PPH confirmed by right heart catheterization (RHC) within the same week and in 10 volunteers. MR pulmonary antegrade velocities, acceleration time (defined as the time from the onset of flow to the peak velocity), and arterial distensibility (maximal surface-minimal surface/minimal surface) were significantly different in patients (p < 0.

In vivo comparison of two through-plane MR velocity mapping methods: fast Fourier encoding and phase mapping.

Magnetic resonance imaging maps of velocity were acquired with a 1.5-T system in 10 subjects in a plane perpendicular to the main pulmonary artery. Velocity images were successively acquired with a method developed from Fourier-encoding velocity imaging (FEVI) principles with eight gradient steps and one excitation, and with two-point phase-subtraction mapping.