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

Indeed, some locations are particularly sensitive to eg coil sensitivity or intra-voxel dephasing, which can result in a reduced tSNR at specific functional brain

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. From a finite and discrete Fourier transform point of view, we discuss the sources of localization errors in Fourier chemical-shift imaging, and demonstrate them explicitly by computer simulations for simple cases. Errors arise from intravoxel dephasing and the intravoxel asymmetry.

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 ). of intravoxel dephasing among flowing spins that have large intravoxel veloc-ity variability. 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. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T1 recovering signal, yields higher quality DENSE myocardial strain maps.

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.

Decreasing the voxel size (increasing matrix/decreasing slice thickness) can reduce the intravoxel dephasing caused by magnetic susceptibility. • Increasing the 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 leave a bodily area before the magnetization is measured.signal void. (2) In MRI, any loss of signal caused by combined turbulence and intravoxel dephasing . 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).

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.

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.

– very short TE. • shortest TE times minimize intravoxel dephasing resulting in maximum flow effects. – small to medium flip angles. 9 Phase difference between flow and stationary nuclei in a voxel. Medical Dictionary for the Health Professions and Nursing © Farlex 2012. Want to thank TFD for its In MRI, particularly turbulent blood flow gives rise to intravoxel dephasing, where spins within a voxel have accrued different amounts of phase leading to reduced 3D TOF CE-MRA has improved spatial resolution, less saturation effects and intravoxel dephasing, and better evaluation of aneurysm lumen. With this technique, The most effective method for reducing intravoxel dephasing is to shorten the time the PC-UTE approach is more robust to intravoxel dephasing signal loss. Jan 30, 2016 complex T2* image via an intravoxel dephasing average.
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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. Asymmetric Spin-Echo (Chase) May 28, 2016 Another cause of dephasing is intravoxel dephasing.

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 The strong effective intravoxel dephasing caused by magnetic microparticles has made them promising candidates for MR tracking and contrast enhancement.
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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.

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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.

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

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 ).

INTRODUCTION.

However, the slice dephasing artifact in regions with strong susceptibility effect is difficult to compensate for by shimming alone.