These symmetrical gradient lobes have the sole purpose of enhancing dephasing of spins, thereby accelerating intravoxel incoherent motion (IVIM) signal loss. Dephasing is proportional to the square of the time (diffusion time) during which the gradients are …

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*.

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 ). (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. 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.

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. 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.

meta-DENSE complex acquisition for reduced intravoxel dephasing. / Aletras, Anthony; Arai, A E. In: Journal of Magnetic Resonance, Vol. 169, No. 2, 2004, p. 246-249.

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.

dephasing decreases the area of the slice selection dephasing gradient (red oval), leading to a small amount of intravoxel dephasing in the slice direction. Figure 5: Signal dependencies on TSD angle for various tissues. Note extra signal loss associated with off-resonance (adipose tissue) 1999-05-01 Frahm, J., Merboldt, K. D., & Haenicke, W. (1995).

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 .

Commonly encountered artifacts on MRI due to CSF Fig. 18: Intravoxel dephasing helps in distinguishing arachnoid cysts from webs. Correction of the artifact can be achieved with the help of imaging using smaller TY - JOUR. T1 - meta-DENSE complex acquisition for reduced intravoxel dephasing. AU - Aletras, Anthony.

How to decrease intravoxel dephasing and increase SNR: Conventional phase contrast (PC) methods for imaging high-velocity jets in aortic stenosis are susceptible to intravoxel dephasing signal loss, which can result in unreliable measurements. 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. Objective Characterization of magnetic susceptibility artefacts with assessment of the gradient-echo signal decay function of echo time, pixel size, and object geometry in the case of air-filled cylinders embedded in water. Materials and methods Signal loss due to flow is induced via intravoxel dephasing which, according to Eq. 1, is dependent on velocity profile and m1. For a certain velocity profile, the flow suppression capability of FSD-preparation is determined by m1. from dephasing effects and confoun d the microstructural information reflected in signal amplitude and relaxation rate measures derived from GRE data.
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During the last decade modern scanners have overcome these limitations making bSSFP a viable and useful sequence on most mid- and high-field systems. 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. directions result in more rapid dephasing and signal loss termed “intravoxel dephasing.” A commonly encountered CSF flow artifact is the signal void in the dorsal subarachnoid space on sagittal T2-weighted images of the thoracic spine (Fig. 13).

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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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.

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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.

/ Aletras, Anthony; Arai, A E. In: Journal of Magnetic Resonance, Vol. 169, No. 2, 2004, p. 246-249. meta-DENSE complex acquisition for reduced intravoxel dephasing.

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.

How to decrease intravoxel dephasing and increase SNR: Materials and methods Experiments were performed with a 0.2T magnet on a network of small interacting air-filled cylinders along with Magnetic resonance imaging (MRI) simulations integrating intravoxel dephasing.

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. Since magnetic properties of changing blood oxygenation (Y) affect the tissue water MRI signal through intravoxel spin dephasing (Kennan et al., 1994), changes in Y can be differentially captured with the transverse relaxation rates as measured by gradient-echo R 2 * and spin-echo (R2).