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.
‘‘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
susceptibility changes at tissue interfaces) and extrinsic (i.e. 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. Intravoxel dephasing, leading to signal phase cancellation in the voxel, can be quantified by T2* relaxation measurements. Intervoxel dephasing can be characterized by the standard deviation of the phase image histogram. ‘‘intravoxel dephasing,’’ but also from incomplete refocus-phase-encoding direction shift the gradient echo along corre-ing of the slice-selection gradient.
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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 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. Spin dephasing under nonlinear gradients: Implications for imaging and field mapping. Magnetic Resonance in Medicine, 2012. Todd Constable. PDF. Download Free PDF 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.
from dephasing effects and confoun d the microstructural information reflected in signal amplitude and relaxation rate measures derived from GRE data. As the mechanism underlying these dropouts is well understood, correction may be possible. In fact, t hrough - plane dephasing calculation and correction ( … Intravoxel dephasing related to turbulence Accumulation of positive phase shift over the course of the scan Fat-saturation pulses as used in time-of-flight imaging Inflow of unsaturated blood into the slice after the initial 90-degree pulse Flow-related enhancement is caused by 'naive' blood entering the slice.
av P Dyverfeldt · 2010 · Citerat av 6 — Quantification of Intravoxel Velocity Standard Deviation and Turbulence Intensity by necessary to obtain a dephasing that results in a detectable signal loss.
AU - Aletras, Anthony. AU - Arai, A E. PY - 2004. Y1 - 2004. meta-DENSE complex acquisition for reduced intravoxel dephasing.
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.
Intravoxel Dephasing due to Wave Gradients.
The main effect of such macroscopic field inhomogeneities is the intravoxel dephasing that can cause significant signal losses, mainly for inhomogeneities in the slice direction (see Section 2.2.1 and Figure 2.2.3), which is a particular problem in the human spinal cord (see Section 2.2.2 and Figure 2.2.10). 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.
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In fact, t hrough - plane dephasing calculation and correction ( e.g.
At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, to signal loss or inaccurate R2* estimates. Moreover, the difference in magnetic susceptibility ([chi]) of tumors and normal tissues accelerates intravoxel dephasing of transverse magnetization in tumor and creates off-resonance effects or [T.sup.*sub.2] contrast, a combination of spin-spin relaxation ([T.sub.2]) and [B.sub.0] magnetic field inhomogeneity. On the other hand, intravascular-dephasing effects scale with dHb concentration and are therefore most prominent in the draining veins.
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These effects are negated by flow-related dephasing and are only seen well in short TE sequences. Intravoxel dephasing related to turbulence Accumulation of positive phase shift over the course of the scan Fat-saturation pulses as used in time-of-flight imaging Inflow of unsaturated blood into the
p.246-249. Mark These effects are negated by flow-related dephasing and are only seen well in short TE sequences. Intravoxel dephasing related to turbulence Accumulation of positive phase shift over the course of the scan Fat-saturation pulses as used in time-of-flight imaging Inflow of unsaturated blood into the Start Studera Välja studier Anmälan och antagning Livet som student Internationella möjligheter Examen och karriär from dephasing effects and confoun d the microstructural information reflected in signal amplitude and relaxation rate measures derived from GRE data.
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.
Frahm, J., Merboldt, K. D., & Haenicke, W. (1995). The effects of intravoxel dephasing and incomplete slice refocusing on susceptibility contrast in gradient-echo MRI. Voxel signal calculation by intravoxel dephasing integration. Exposed to an inhomogeneous fieldmap, a proton precesses with a phase angle Δϕ(x, y, z, T E) = γ · ΔB(x, y, z)·T E, where γ is the gyromagnetic ratio. It is noted that the phase angle is different from the field value by a constant factor γ ⋅ T E (Larmor law). susceptibility, dipole effect, dipole inversion, intravoxel dephasing, nonlinear T2* magnitude image, T2* phase unwrapping, MRI transformations. INTRODUCTION.
246-249. The simulation is based on physical principles and is able to produce possible artifacts in MRI images like intra-voxel dephasing, chemical shift, and cross-talk. 20 jan. 2012 — som båda minskar intravoxel dephasing med endast en liten minskning av FET känslighet. En högre bandbredd används även för att minska The simulation is based on physical principles and is able to produce possible artifacts in MRI images like intra-voxel dephasing, chemical shift, and cross-talk. 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 Moreover, the difference in magnetic susceptibility ([chi]) of tumors and normal tissues accelerates intravoxel dephasing of transverse magnetization in tumor and creates off-resonance effects or [T.sup.*sub.2] contrast, a combination of spin-spin relaxation ([T.sub.2]) and [B.sub.0] magnetic field inhomogeneity.