2012-04-01

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 ). In addition to, previous studies were explained that turbulent flow in the axilla area of a small vessel may cause an intravoxel dephasing, especially at a broad bifurcation angle ( 8 , 9 ).

Magnetic Resonance in Medicine. 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-sel The most effective method for reducing intravoxel dephasing is to shorten the echo time (TE); however, the amount that TE can be shortened in conventional sequences is limited. A new sequence incorporating velocity-dependent slice excitation and ultrashort TE (UTE) centric radial readout trajectories is proposed that reduces TE from 2.85 to 0.65 ms. How to decrease intravoxel dephasing and increase SNR: Decrease the voxel size (increase spatial resolution), either by increasing the matrix (trade-off: will reduce signal-to-noise ratio ) or by reducing the FOV (trade-off: may cause wraparound). Only gold members can continue reading. ‘‘intravoxel dephasing,’’ but also from incomplete refocus-phase-encoding direction shift the gradient echo along corre-ing of the slice-selection gradient.

The new rephasing factor we introduce, which changes the intensity of a voxel in images during the registration, is used to improve the accuracy of the intensity-based nonrigid registration method and mitigate the intensity attenuation effect. meta-DENSE complex acquisition for reduced intravoxel dephasing. Research output: Contribution to journal › Article. Overview; Cite BibTeX Details. Authors: Anthony Aletras; A E Arai; External organisations: National Heart Lung and Blood Institute; Research areas and keywords 2012-04-01 2004-08-01 intravoxel dephasing effect is mainly along the slice selec-tion direction and is termed the slice dephasing artifact. Shimmingcangenerallyreducethemagneticfieldinhomo-geneity.

Decreasing the voxel size (increasing matrix/decreasing slice thickness) can reduce the intravoxel dephasing caused by magnetic susceptibility. • Increasing the

field inhomogeneities of the main magnetic field) to the examined object. See also T2*. structures with lower relative surface area (e.g. “plate-like”) should exhibit decreased dephasing within a voxel.

susceptibility, dipole effect, dipole inversion, intravoxel dephasing, nonlinear T2* magnitude image, T2* phase unwrapping, MRI transformations. INTRODUCTION. The concept of tomographic imaging refers to reproducing a digital image representation of object interior distribution (with respect to a physical property) and can be implemented by

For visualization locally induced magnetic fields are used, which disturb the homogeneity of the main magnetic field of the MR scanner. This results in signal loss in the vicinity of the device due to intravoxel dephasing, and leads to a disturbance of Measurements of Inter- and Intravoxel Dephasing of Trabecular Bone at 7T Field Strength using a Chemical Shift-Selective.

Errors arise from intravoxel dephasing and the intravoxel asymmetry. The spectral leakage due to intravoxel dephasing is roughly 6-8% from one voxel to one of its nearest neighbors. Neighbors further away are influenced less significantly. The loss of localization due to intravoxel … The resultant intravoxel dephasing is a classic T2*-shortening effect most prominent near larger veins and accentuated by use of GRE sequences with echo times (TEs) close to T2*. The effect scales linearly with field strength (Bo) and is the dominant mechanism for BOLD contrast at 1.5T. In MRI, intravoxel dephasing causes signal loss in regions of magnetic field inhomogeneity and at interfaces of tissues having different magnetic susceptibilities. In MRA, signal loss due to intravoxel dephasing also occurs when nuclei having different velocities are present in the same voxel.
Figma vs invision

intra-voxel dephasing, at least three methods have been presented previously: Method 1 (Isochromat Summation, IS) numerical methods populating the input model voxel with numerous isochromats (magnetization vectors) and thus effectively increasing the model resolution [3], 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.

Dephasing is proportional to the square of the time (diffusion time) during which the gradients are … (1999) Chen, Wyrwicz. Magnetic Resonance in Medicine.
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‘‘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

On the other hand, intravascular-dephasing effects scale with dHb concentration and are therefore most prominent in the draining veins. Both of these mechanisms of BOLD contrast are expected to contribute to the gradient-echo (GE) BOLD signal, while the static-dephasing mechanism makes effectively no contribution to the spin-echo (SE) BOLD signal, which is primarily sensitive to intravascular dephasing. Signal decay due to susceptibility-induced intravoxel dephasing on multiple air-filled cylinders: MRI simulations and experiments. De Guio F(1), Benoit-Cattin H, Davenel A. Author information: (1)Cemagref, Food Process Engineering Research Unit, 35 044, Rennes, France. francois.de-guio@cemagref.fr structures with lower relative surface area (e.g. “plate-like”) should exhibit decreased dephasing within a voxel.

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. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T1 recovering signal, yields higher quality DENSE myocardial strain maps. Phantom and human images are provided to

Författare: Anthony Aletras; A E Arai; Externa organisationer: National Heart Lung and Blood 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. Spin dephasing under nonlinear gradients: Implications for imaging and field mapping.

Removal of intravoxel dephasing artifact in gradient-echo images using a field- map based RF refocusing technique. Magnetic resonance in medicine , 42(4), 807- 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.