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).

intravoxel dephasing and amplitude of the section-selecting gradient. The contrast-to-noiseratio (CNR) between CSF and the cerebellar peduncle, and the visibility of the cranial nerves and vertebrobasilar artery were signiﬁcantly improved on 3D images in 17 subjects.

Shortening TE reduces the time available for the velocity distribution intravoxel dephasing to occur improving the PC velocity estimate. 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 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 ( B o ) and is the dominant mechanism for BOLD contrast at 1.5T. 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.

Read "Signal decay due to susceptibility-induced intravoxel dephasing on multiple air-filled cylinders: MRI simulations and experiments, Magnetic Resonance Materials in Physics, Biology and Medicine" on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. 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: 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.

The refocusing mechanism fails if intravoxel dephasing exceeds over ±180º manifest by band-like artifacts. During the last decade modern scanners have overcome these limitations making bSSFP a viable and useful sequence on most mid- and high-field systems.

Oct 22, 2018 large gradient encoding magnitudes as well as dephasing artefacts caused by subject motion, which is particularly challenging in fetal MRI. Nov 30, 2017 At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, magnitude caused by intravoxel dephasing should remain due to microscopic field for intravoxel dephasing due to the neuronal magnetic fields (9). 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.

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)

PDF. Download Free PDF Through-slice dephasing is highly effective in suppressing eddy current induced artifacts in bSSFP imaging. Considering these artifacts appear substantial in Cart-GR and random PE scans, they are most likely caused by the zero order (spatially independent) EC field yielding an off-resonance shift over time. Within each voxel, a mixture of stationary and flowing protons may exist causing a difference of phase between the protons (out-of-phase), leading to a reduction of the total signal emitted.

Intra-voxel Steady-state free precession (SSFP) imaging is a magnetic resonance imaging ( MRI) The refocusing mechanism fails if intravoxel dephasing exceeds over ± 180º manifest by band-like artifacts. During the last decade modern scanners have& Intravoxel dephasing is the predominant cause of signal loss on GRE imaging resulting in a dark or black area (signal loss) around the metal on the processed Decreasing the voxel size (increasing matrix/decreasing slice thickness) can reduce the intravoxel dephasing caused by magnetic susceptibility. • Increasing the Gradient moment nulling is a technique used to reduce flow artifacts in our image and intravoxel dephasing.
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The effects of intravoxel dephasing and incomplete slice refocusing on susceptibility contrast in gradient-echo MRI. Spin dephasing arising from intravoxel internal gradient lowers the signal-to-noise ratio (SNR) and therefore de-gradesthequalityofgradient-echoimages,especiallythose acquired at long TE. This dephasing effect can be lessened with increased in-plane spatial resolution and reduced Intravoxel dephasing causes signal loss and thus intensity attenuation in the images. 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. Anthony Aletras & A E Arai, 2004, In: Journal of Magnetic Resonance. 169, 2, p.
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This dephasing is due to static magnetic field inhomogeneities intrinsic (i.e. susceptibility changes at tissue interfaces) and extrinsic (i.e. field inhomogeneities of the main magnetic field) to the examined object. See also T2*.

Considering these artifacts appear substantial in Cart-GR and random PE scans, they are most likely caused by the zero order (spatially independent) EC field yielding an off-resonance shift over time. Within each voxel, a mixture of stationary and flowing protons may exist causing a difference of phase between the protons (out-of-phase), leading to a reduction of the total signal emitted. This phenomenon is known as Intravoxel dephasing (ID) (4). In turbulent flow states, the magnitude of the ID increases.

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MATERIALS AND METHODS: 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.

Intravoxel Dephasing due to Wave Gradients. This article assumes prior knowledge of Wave-CAIPI[1].