Analysis of T2 limitations and off‐resonance effects on spatial resolution and artifacts in echo‐planar imaging

Farzaneh, Farhad; Riederer, Stephen J.; Pelc, Norbert J.

doi:10.1002/mrm.1910140112

Cited by 351 publications

(259 citation statements)

References 11 publications

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“…In addition, simulations were conducted to demonstrate the S(c)/S(0) ratio with the influence of R1 and R2 using Eq. [3]. The ratio S(c)/S(0) was denoted E(c,R1,R2, ) or E(c, ), dependent on whether calculations were based on Eq.…”

Section: Simulation Of Relaxation Rate (R1 and R2) Effect On Signal Amentioning

confidence: 99%

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Quantitative cerebral perfusion using the PRESTO acquisition scheme

Pedersen

Klarhöfer

Christensen

et al. 2004

Magnetic Resonance Imaging

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Purpose:To evaluate the feasibility of using the rapid principles of echo shifting with a train of observations (PRESTO) sequence for measurements of cerebral hemodynamic parameters based on first pass of a contrast agent. Materials and Methods:Simulations were performed to investigate potential resolution loss due to relaxation effects. Experimental evaluation was conducted in healthy monkey brains using PRESTO and echo-planar imaging (EPI).Results: For short echo trains, an insignificant contribution of the longitudinal and transversal relaxation rates to the signal amplitude in white matter and gray matter was found, whereas a contribution as large as 40% was found in large vessels. Simulations of the point spread function demonstrated that PRESTO, despite its shorter readout trains, only has a small advantage in terms of maintenance of image resolution during bolus passage compared to EPI as long as the EPI echo train can be kept similar to the T2* value at the top of the bolus. Experimental studies revealed that the PRESTO and EPI gray matter to white matter ratio were similar with respect to cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Conclusion:The study showed that PRESTO and EPI led to comparable quantitative perfusion parameters.

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Section: Simulation Of Relaxation Rate (R1 and R2) Effect On Signal Amentioning

confidence: 99%

“…The ratio S(c)/S(0) was denoted E(c,R1,R2, ) or E(c, ), dependent on whether calculations were based on Eq. [3] or Eq. [5].…”

Section: Simulation Of Relaxation Rate (R1 and R2) Effect On Signal Amentioning

confidence: 99%

Quantitative cerebral perfusion using the PRESTO acquisition scheme

Pedersen

Klarhöfer

Christensen

et al. 2004

Magnetic Resonance Imaging

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show abstract

“…A number of techniques (8)(9)(10)(11)(12)(13)(14)(15)(16)) are used to minimize distortion and ghost artifacts, which result from phase and amplitude errors between echoes. The phased array processing method for ghost cancellation adds yet another tool which may be incorporated to further mitigate EPI distortion and artifacts.…”

Section: Epi Applicationmentioning

confidence: 99%

“…To avoid ghost artifacts, images are frequently acquired using an interleaved phase encode order (9,10), although interleaved phase encode order has several drawbacks. Drawbacks of this approach are the geometric and intensity distortion caused by off-resonance phase errors due to chemical shift or susceptibility variation (8), distortion due to in-plane flow, increased echo train length which results when echo shifting is employed, and distortion due to echo delay misalignment. Using a sequential, non-interleaved phase encode order with an echo train length, ETL, will cause N g ¼ ETL-1 ghosts spaced D ¼ FOV/ETL, and therefore has not been considered viable.…”

Section: Application To Ghost Artifacts In Epimentioning

confidence: 99%

Phased array ghost elimination

Kellman

McVeigh

2006

NMR Biomed.

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Parallel imaging may be applied to cancel ghosts caused by a variety of distortion mechanisms, including distortions such as off-resonance or local flow, which are space variant. Phased array combining coefficients may be calculated that null ghost artifacts at known locations based on a constrained optimization, which optimizes SNR subject to the nulling constraint. The resultant phased array ghost elimination (PAGE) technique is similar to the method known as sensitivity encoding (SENSE) used for accelerated imaging; however, in this formulation is applied to full field-of-view (FOV) images. The phased array method for ghost elimination may result in greater flexibility in designing acquisition strategies. For example, in multi-shot EPI applications ghosts are typically mitigated by the use of an interleaved phase encode acquisition order. An alternative strategy is to use a sequential, non-interleaved phase encode order and cancel the resultant ghosts using PAGE parallel imaging. Cancellation of ghosts by means of phased array processing makes sequential, non-interleaved phase encode acquisition order practical, and permits a reduction in repetition time, TR, by eliminating the need for echo-shifting. Sequential, non-interleaved phase encode order has benefits of reduced distortion due to offresonance, in-plane flow and EPI delay misalignment. Furthermore, the use of EPI with PAGE has inherent fat-water separation and has been used to provide off-resonance correction using a technique referred to as lipid elimination with an echo-shifting N/2-ghost acquisition (LEENA), and may further generalized using the multi-point Dixon method. Other applications of PAGE include cancelling ghosts which arise due to amplitude or phase variation during the approach to steady state. Parallel imaging requires estimates of the complex coil sensitivities. In vivo estimates may be derived by temporally varying the phase encode ordering to obtain a full k-space dataset in a scheme similar to the autocalibrating TSENSE method. This scheme is a generalization of the UNFOLD method used for removing aliasing in undersampled acquisitions. The more general scheme may be used to modulate each EPI ghost image to a separate temporal frequency as described in this paper.

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“…These large-scale inhomogeneities lead to geometric distortions in the phaseencoding direction (Farzaneh et al, 1990). Researchers have sought the use of magnetic field maps to correct these geometric distortions (Jezzard and Balaban, 1995).…”

Section: Introductionmentioning

confidence: 99%

High spatial resolution increases the specificity of block-design BOLD fMRI studies of overt vowel production

Soltysik

Hyde

2008

NeuroImage

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Functional MRI (fMRI) studies of tasks involving orofacial motion, such as speech, are prone to problems related to motion-induced magnetic field variations. Orofacial motion perturbs the static magnetic field, leading to signal changes that correlate with the task and corrupt activation maps with false positives or signal loss. These motion-induced signal changes represent a contraindication for the implementation of fMRI to study the neurophysiology of orofacial motion. An fMRI experiment of a structured, non-semantic vowel production task was performed using four different voxel volumes and three different slice orientations in an attempt to find a set of acquisition parameters leading to activation maps with maximum specificity. Results indicate that the use of small voxel volumes (2×2×3 mm 3 ) yielded a significantly higher percentage of true positive activation compared to the use of larger voxel volumes. Slice orientation did not have as great an impact as spatial resolution, although coronal slices appeared superior at high spatial resolutions. Furthermore, it was found that combining the strategy of high spatial resolution with an optimum task duration and postprocessing methods for separating true and false positives greatly improved the specificity of singlesubject, block-design fMRI studies of structured, overt vowel production.

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Analysis of T2 limitations and off‐resonance effects on spatial resolution and artifacts in echo‐planar imaging

Cited by 351 publications

References 11 publications

Quantitative cerebral perfusion using the PRESTO acquisition scheme

Quantitative cerebral perfusion using the PRESTO acquisition scheme

Phased array ghost elimination

High spatial resolution increases the specificity of block-design BOLD fMRI studies of overt vowel production

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