3D TOF CE-MRA has improved spatial resolution, less saturation effects and intravoxel dephasing, and better evaluation of aneurysm lumen. With this technique, 

A technique is proposed to compensate for the slice dephasing artifact and improve the signal‐to‐noise ratio (SNR) of gradient‐echo images. This method is composed of two components: mapping of the internal gradient and design of the slice‐selective radiofrequency (RF) pulse. The RF pulse is designed with its phase response as the negative of the product of a chosen echo time and the

Home; International Admissions. Why study at Lund University rephasing gradient (red oval), leading to a small amount of intravoxel dephasing that eliminates the effects of rapidly fluctuating gradient fields. Figure 2 a) linear PE, b) We show that intravoxel gradient dephasing, which is normally associated only with signal loss, can distort phase evolution and affect a voxel’s apparent frequency. In Section III, we demonstrate these distortions experimentally, comparing gradient maps taken at different slice thicknesses and offsets, which show good agreement with the analytical expression. A technique is proposed to compensate for the slice dephasing artifact and improve the signal‐to‐noise ratio (SNR) of gradient‐echo images. This method is composed of two components: mapping of the internal gradient and design of the slice‐selective radiofrequency (RF) pulse. The RF pulse is designed with its phase response as the negative of the product of a chosen echo time and the At very low diffusion weighting the diffusion MRI signal is affected by intravoxel incoherent motion (IVIM) caused by dephasing of magnetization due to incoherent blood flow in capillaries or other sources of microcirculation.

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francois.de-guio@cemagref.fr ‘‘intravoxel dephasing,’’ but also from incomplete refocus-phase-encoding direction shift the gradient echo along corre-ing of the slice-selection gradient. Moreover, while intra-sponding directions in k space. Fourier transformation results voxel dephasing originates from an increase in broadness of Experiments were performed with a 0.2 T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing. Signal decay over echo time was assessed at different pixel sizes on real and simulated images. Each cylinder contributed to the intravoxel dephasing and associated signal loss occurring in the ROI ROI MGL decay on simulated and experimental images for the network of air-filled cylinders. These symmetrical gradient lobes have the sole purpose of enhancing dephasing of spins, thereby accelerating intravoxel incoherent motion (IVIM) signal loss. Dephasing is proportional to the square of the time (diffusion time) during which the gradients are switched on and the strength of the applied gradient field.

Intravoxel Dephasing due to Wave Gradients. This article assumes prior knowledge of Wave-CAIPI[1]. In particular, this article attempts to describe the methodology used to generate Figure 9 of [1]. For simplicity, assume a two-dimensional problem.

For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1. The varied flow velocities and directions result in more rapid dephasing and signal loss termed “intravoxel dephasing.” A commonly encountered CSF flow artifact is the signal void in the dorsal subarachnoid space on sagittal T2-weighted images of the thoracic spine ( Fig. 13 ).

Jul 8, 2016 Then full intravoxel dephasing can occur, therefore resulting in zeroing of the signal. A315651_1_En_11_Fig4_HTML.gif. Fig. 11.4. Intra-voxel 

The arterial images with suppressed background and venous signals were obtained by means of sub-traction of a dark artery measurement (Fig 1, A) and a bright artery measure-ment (Fig 1, B), both of which were in one single image. The bright artery and Displacement encoding with stimulated echoes (DENSE) with a meta-DENSE readout and RF phase cycling to suppress the STEAM anti-echo is described for reducing intravoxel dephasing signal loss.

AU - Arai, A E. PY - 2004. Y1 - 2004. meta-DENSE complex acquisition for reduced intravoxel dephasing.
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Aletras, Anthony LU and Arai, A E In Journal of Magnetic Resonance 169 (2).

Gradient-recalled echo sequences are par- ticularly prone to metallic artifact because of intravoxel dephasing [3] (Fig. the 180° refocusing pulse) and/or intravoxel dephasing (spins moving with different velocities due to turbulent or laminar flow acquire different phases) 1. short TR (~ 20-40 msec). – very short TE. • shortest TE times minimize intravoxel dephasing resulting in maximum flow effects.
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Another cause of dephasing is intravoxel dephasing. Because of laminar flow, different velocities may exist within a voxel, thus leading to phase dispersion (incoherence) and signal loss. How to decrease intravoxel dephasing and increase SNR:

Five slices  Oct 29, 2020 partly due to intravoxel dephasing and partly to a k-space center shift out of the sampled k-space FOV from local field gradients in this area. Weighting was added to account for intravoxel dephasing, and a Laplacian- based regularization was used to account for residual velocity aliasing. The jet is larger than in the cine above because the gradient echo sequence has a longer TE (6 ms vs. 2 ms), which allows for more intravoxel dephasing. In MRI  Feb 14, 2013 inhomogeneities which induce intravoxel dephasing and associated signal loss in gradient- echo (GE) images. Because of the rephasing  Gradient moment nulling is a technique used to reduce flow artifacts in our image and intravoxel dephasing. It is also a technique used in bright blood imaging.

The cause of intravoxel dephasing is not yet well understood. This phenomenon is due to the spin dephasing when the voxel size is comparable to the residual lumen at level of stenosis (7).

Several methods have been devel- Many different mechanisms have been found to influence intravoxel dephasing signal loss in stenotic jets including higher‐order motion, e.g., acceleration (11 - 14), alignment of the image plane with the jet (15, 16), voxel size and partial volume effects in voxels with large velocity distributions (10, 17 - 20) the user‐defined velocity encoding (Venc) (21), and turbulence imposing small velocity fluctuations superimposed on the principal velocity (22). Skip to main content.

‘‘intravoxel dephasing,’’ but also from incomplete refocus-phase-encoding direction shift the gradient echo along corre-ing of the slice-selection gradient.