What is boundary artifact?
Black boundary artifact, also known as India ink artifact or type 2 chemical shift artifact, is an artificially-created black line located at fat-water interfaces such as those between muscle and fat.
What is zipper artifact?
In MR imaging, zipper artifact refers to a type of MRI artefact where one or more spurious bands of electronic noise extend perpendicular to the frequency encode direction and is present in all images of a series. There are various causes for zipper artifacts in images.
What is the chemical shift at 1.5 T?
With a 1.5 T field strength, the frequency shift is 225 Hz, corresponding to a period of 4.4 ms. Therefore, at 1.5 T, protons of fat and water will be in phase every 4.4 ms : their signals are additive.
What is chemical shift in MRI?
The chemical shift phenomenon refers to the signal intensity alterations seen in magnetic resonance (MR) imaging that result from the inherent differences in the resonant frequencies of precessing protons. Chemical shift was first recognized as a misregistration artifact of image data.
How can boundary artefacts be reduced?
The traditional solution is to smooth the image data using special window functions such as Hamming or trapezoidal windows. This is followed by zero-padding and linear convolution with the restoration filter. This method improves the results but still distorts the image, especially at the margins.
What is truncation artifact MRI?
Gibbs artifact, also known as truncation artifact or ringing artifact, is a type of MRI artifact. It refers to a series of lines in the MR image parallel to abrupt and intense changes in the object at this location, such as the CSF-spinal cord and the skull-brain interface.
What is magic angle artifact?
The magic angle artifact refers to the increased signal observed when MRI sequences with short echo time (TE) (e.g., T1 or proton density spin-echo sequences) are used to image tissues with well-ordered collagen fibers in one direction (e.g., tendon or articular hyaline cartilage).
What causes ghosting in MRI?
Ghosting is a type of structured noise appearing as repeated versions of the main object (or parts thereof) in the image. They occur because of signal instability between pulse cycle repetitions. Ghosts are usually blurred, smeared, and shifted and are most commonly seen along the phase encode direction.
What is an artifact on a brain MRI?
From Wikipedia, the free encyclopedia. An MRI artifact is a visual artifact (an anomaly seen during visual representation) in magnetic resonance imaging (MRI). It is a feature appearing in an image that is not present in the original object.
How do you fix truncation artifact on MRI?
- increasing the matrix size (i.e. sampling frequency for the frequency direction and number of phase-encoding steps for the phase direction)
- use of smoothing filters (2-D exponential filtering, Gegenbauer reconstruction etc.)
- if fat is one of the boundaries, use fat suppression.
What causes Gibbs?
The Gibbs ringing artifact arises because the Fourier series cannot represent a discontinuity with a finite number of harmonics. A sharp cut-off or truncation in the k-space is equivalent to a convolution in spatial domain with a sinc function.