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

Feb 14, 2013 inhomogeneities which induce intravoxel dephasing and associated signal loss in gradient- echo (GE) images. Because of the rephasing

Because low spatial frequencies are collected during the spin echo, while higher spatial frequencies are collected later, when the signal decays due to dephasing, this effectively reduces the contribution of high spatial frequencies to the image, reducing the effective resolution. 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 … (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.

Intravoxel dephasing

This approach allows for further improvement and precision of the calculated NMR signal and virtually avoids the problem related to an ﬁnite set of isochromats. ‘‘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 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.

susceptibility changes at tissue interfaces) and extrinsic (i.e.

Decreasing the voxel size (increasing matrix/decreasing slice thickness) can reduce the intravoxel dephasing caused by magnetic susceptibility. • Increasing the

or. Create a free account to download. PDF. PDF. susceptibility, dipole effect, dipole inversion, intravoxel dephasing, nonlinear T2* magnitude image, T2* phase unwrapping, MRI transformations. INTRODUCTION.

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 T 1 recovering signal, yields higher quality DENSE myocardial strain maps.

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. As the mechanism underlying these dropouts is well understood, correction may be possible.

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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). This artifact is due to a combination of the respiratory and cardiac- One of the shortcomings of 2D TOF MRA is vulnerability to signal-intensity drop-out (or flow-void) artifacts resulting from intravoxel dephasing related to turbulent flow associated with the stenotic segments of vasculature.

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. This phenomenon is known as Intravoxel dephasing (ID) (4).
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tively referred to as susceptibility artifact. Gradient-recalled echo sequences are par- ticularly prone to metallic artifact because of intravoxel dephasing [3] (Fig.

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 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).