What is warping in MRI?

The term WARP summarizes methods to minimize the impact of metal implants on MR image quality. This article introduces different techniques such as high bandwidth, VAT and SEMAC.

What is MRI phase shift?

Spins that are moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the velocity of the spins. This is the basis of phase-contrast angiography.

What does phase encoding direction mean?

Spatial encoding in MRI The second step of spatial localization is called phase encoding. A magnetic gradient field is applied briefly in one direction. As the change in frequency is very brief, when the gradient is switched off, it causes a change in phase that is proportional to the distance.

What does it mean when an MRI shows an artifact?

It is a feature appearing in an image that is not present in the original object. Many different artifacts can occur during MRI, some affecting the diagnostic quality, while others may be confused with pathology. Artifacts can be classified as patient-related, signal processing-dependent and hardware (machine)-related.

What is warp sequence?

The application of “WARP” (Siemens Healthcare, Erlangen, Germany) combines VAT and fast spin-echo sequences with increased bandwidth (“high bandwidth”). … The application of “WARP” (Siemens Healthcare, Erlangen, Germany) combines VAT and fast spin-echo sequences with increased bandwidth (“high bandwidth”).

What is a maverick MRI?

MAVRIC is a novel MRI technique that can be used to further reduce artifact around metallic implants. MAVRIC can be performed with conventional MRI hardware and software and generates images in clinically feasible imaging times.

What is phase gradient?

The phase encoding gradient is a gradient in the magnetic field Bo. The phase encoding gradient is used to impart a specific phase angle to a transverse magnetization vector. The specific phase angle depends on the location of the transverse magnetization vector.

What is MRI phase Matrix?

The matrix size is the number of frequency encoding steps, in one direction; and the number of phase encoding steps, in the other direction of the image plane. Assuming everything else is constant, increasing the number of frequency encodings or the number of phase steps results in improved resolution.

What is frequency direction in MRI?

The frequency-encoding direction is along the x-axis in K-space (may or may not be that axis in the image, if it is rotated); this represents the time samples of the signal. The y-axis is the phase-encoding direction: each phase-encoding step yields a separate horizontal line.

What does movement artefact mean?

Motion artifact is a patient-based artifact that occurs with voluntary or involuntary patient movement during image acquisition. Misregistration artifacts, which appear as blurring, streaking, or shading, are caused by patient movement during a CT scan.

How do you stop metal artifact on MRI?

Basic methods to reduce metallic artifacts include use of spin-echo or fast spin-echo sequences with long echo train lengths, short inversion time inversion-recovery (STIR) sequences for fat suppression, a high bandwidth, thin section selection, and an increased matrix.

What is widewrap around in image processing?

Wrap-around (also called aliasing) occurs when the size of the body part imaged exceeds the defined field-of-view (FOV) in the phase-encode direction. This causes anatomy outside the FOV to be folded in over the main part of the image.

What is a phase cancellation artifact in Mr?

The adenoma (arrow) falls in signal, a phase-cancellation artifact. Lipid droplets (arrow) in adrenal adenoma. The out-of-phase cancellation effect between fat and water give rise to a specific type of MR artifact, called the “India ink artifact” or “chemical shift artifact of the second kind.”

What is the difference between in-phase and out-of-phase GRE images?

In-phase GRE image at TE=4.4 msec shows tumor of intermediate signal intensity. Hepatic steatosis. In-phase GRE with TE=4.4 msec. Out-of-phase GRE image at TE=2.2 msec. The adenoma (arrow) falls in signal, a phase-cancellation artifact.