Aliasing artifacts in mr imaging

Pusey, E; Yoon, Chun; Anselmo, M.; Lufkin, Robert B.

doi:10.1016/0895-6111(86)90003-0

Cited by 24 publications

(16 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The SNR of an MR image can be written as (20) SNR ϭ c ⅐ ͱT ⅐ ͑pixel size͒, [1] where c is a sequence-dependent constant, and T is the total data acquisition time. This equation is true only when the sampling density in k-space is uniform.…”

Section: Signal-to-noise Ratio Efficiencymentioning

confidence: 99%

Reduced aliasing artifacts using variable-densityk-space sampling trajectories

2000

View full text Add to dashboard Cite

A variable-density k-space sampling method is proposed to reduce aliasing artifacts in MR images. Because most of the energy of an image is concentrated around the k-space center, aliasing artifacts will contain mostly low-frequency components if the k-space is uniformly undersampled. On the other hand, because the outer k-space region contains little energy, undersampling that region will not contribute severe aliasing artifacts. Therefore, a variable-density trajectory may sufficiently sample the central k-space region to reduce low-frequency aliasing artifacts and may undersample the outer k-space region to reduce scan time and to increase resolution. In this paper, the variable-density sampling method was implemented for both spiral imaging and twodimensional Fourier transform (2DFT) imaging. Simulations, phantom images and in vivo cardiac images show that this method can significantly reduce the total energy of aliasing artifacts. In general, this method can be applied to all types of k-space sampling trajectories. Magn Reson Med 43: 452-458, 2000.

show abstract

Section: Signal-to-noise Ratio Efficiencymentioning

confidence: 99%

Reduced aliasing artifacts using variable-densityk-space sampling trajectories

2000

View full text Add to dashboard Cite

show abstract

“…1b. The appearance of these aliasing artifacts depends on the subset of lines that were sampled: sampling only one line every n leads to well‐known ghost‐like aliasing artifacts (9), while a less regular sampling strategy in k ‐space may lead to artifacts that appear less structured spatially. UNFOLD is a trick that allows aliasing artifacts (whether spatially structured or not) to be displaced in the temporal frequency domain.…”

Section: Theorymentioning

confidence: 99%

Using UNFOLD to remove artifacts in parallel imaging and in partial‐Fourier imaging

Madore

2002

Magnetic Resonance in Med

View full text Add to dashboard Cite

In dynamic MRI, it is often difficult to achieve the acquisition speed required to resolve or freeze the temporal variations of the imaged object. Several MRI methods aim at speeding up the image acquisition process. Through assumptions and/or prior knowledge, these dynamic MRI methods allow part of the needed data to be calculated instead of acquired. For example, partial-Fourier imaging assumes that phase varies smoothly within the object, and parallel imaging (e.g., simultaneous acquisition of spatial harmonics (SMASH) and sensitivity encoding (SENSE)) uses prior knowledge about receiver-coil sensitivity. While these methods accelerate acquisition, they can introduce artifacts or amplify noise in doing so. The present work aims at accelerating image acquisition significantly, while introducing almost no artifacts or noise amplification. It is shown here that new, extra information is gained if dynamic MRI methods are modified so that the sampling function changes in specific ways from time-frame to time-frame. In other words, the set of In many magnetic resonance imaging (MRI) applications, a given region of the body is imaged repeatedly to capture its time variations. For example, such dynamic applications include functional MRI (fMRI) (where brain changes are induced by a time-varying paradigm), timeresolved angiography (changes in the blood vessels are caused by the passage of a bolus of contrast agent), and cardiac imaging (where the heart changes as it beats, and also possibly as a bolus of contrast agent passes through it). The temporal resolution, i.e., the time needed to acquire a time frame, must be good enough to capture the important features of the temporal changes. In the event that the readily available temporal resolution proves insufficient, there exist many dynamic MRI methods able to improve it. Through some assumption(s) and/or the use of prior information, these methods allow a fraction of the needed data to be calculated instead of measured. This reduction in the amount of acquired data usually translates directly into a corresponding reduction in the time needed to acquire it, i.e., into an improvement in temporal resolution. Although useful, the acceleration achieved with such methods is limited by artifacts and/or noise amplification. The present proposal consists of fusing existing methods (such as partial-Fourier imaging (1-3), simultaneous acquisition of spatial harmonics (SMASH) (4), and sensitivity encoding (SENSE) (5)) with a novel temporal strategy, very significantly improving their performance. This temporal strategy is based on a method called unaliasing by Fourier-encoding the overlaps in the temporal dimension (UNFOLD) (6).Very few dynamic imaging methods (e.g., periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) (7), time-resolved imaging of contrast kinetics (TRICKS) (8), and UNFOLD (6)) exploit the temporal dimension of the acquisition process, changing the sampling function from one time frame to the next. The present work involves m...

show abstract

“…2). It can occur whenever any part of the body extends outside the FOV and a signal produced by this structure reaches the receiver coil [5]. The body part that lies outside the FOV is wrapped inside to the opposite side of the image.…”

Section: Aliasingmentioning

confidence: 99%

Artifacts in body MR imaging: their appearance and how to eliminate them

et al. 2006

View full text Add to dashboard Cite

A wide variety of artifacts can be seen in clinical MR imaging. This review describes the most important and most prevalent of them, including magnetic susceptibility artifacts and motion artifacts, aliasing, chemical-shift, zipper, zebra, central point, and truncation artifacts. Although the elimination of some artifacts may require a service engineer, the radiologist and MR technologist have the responsibility to recognize MR imaging problems. This review shows the typical MR appearance of the described artifacts, explains their physical basis, and shows the way to solve them in daily practice.

show abstract

Aliasing artifacts in mr imaging

Cited by 24 publications

References 9 publications

Reduced aliasing artifacts using variable-densityk-space sampling trajectories

Reduced aliasing artifacts using variable-densityk-space sampling trajectories

Using UNFOLD to remove artifacts in parallel imaging and in partial‐Fourier imaging

Artifacts in body MR imaging: their appearance and how to eliminate them

Contact Info

Product

Resources

About