intravoxel dephasing effect is mainly along the slice selec-tion direction and is termed the slice dephasing artifact. Shimmingcangenerallyreducethemagneticfieldinhomo-geneity. However, the slice dephasing artifact in regions with strong susceptibility effect is difficult to compensate for by shimming alone. Several methods have been devel-
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.
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.
All spins are completely in phase at the instant of the spin echo, but immediately begin to dephase at a rate proportional to the amount of magnetic field inhomogeneity within the voxel. For voxels near metal or air/tissue boundaries, this can be considerable. 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.
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) , and turbulence imposing small velocity
Fourier transformation results voxel dephasing originates from an increase in broadness of Efficient and Accurate Bloch-based Simulation of Intra-voxel Dephasing using Multiple Isochomats and Magnetization Spatial Gradients Zhipeng Cao 1, Christopher T. Sica, Giuseppe Carluccio 2, and Christopher M. Collins 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. Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1.
(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
Todd Constable. 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. This phenomenon is known as Intravoxel dephasing (ID) (4). In turbulent flow states, the magnitude of the ID increases. Errors arise from intravoxel dephasing and the intravoxel asymmetry.
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. Absolute inter- and intravoxel dephasing was significantly enhanced at 7T and B 0 field inhomogeneities were more pronounced. From the simulations we found that a monoexponential decay function (4) is a valid assumption especially for the faster T2* decay in UHF-MRI.
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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. It is also a technique used in bright blood imaging.
‘‘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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meta-DENSE complex acquisition for reduced intravoxel dephasing. Aletras, Anthony LU and Arai, A E In Journal of Magnetic Resonance 169 (2). p.246-249. Mark
Asymmetric Spin-Echo (Chase) This leads to intravoxel dephasing, signal loss, and inaccurate ADC measurements. compensated (M =M =0) gradient waveforms to null the intravoxel phase This results in signal loss in the vicinity of the device due to intravoxel dephasing, and leads to a disturbance of the phase image. The local fields are established May 28, 2016 This was due to high velocity of CSF and subsequent turbulent flow resulting in intravoxel dephasing.