Spatial encoding and the single-scan acquisition of high definition MR images in inhomogeneous fields

Tal, Assaf; Frydman, Lucio

doi:10.1016/j.jmr.2006.06.022

Cited by 68 publications

(104 citation statements)

References 32 publications

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“…A second consequence worth remarking on concerns the better signal-to-noise ratio that SR-processed images display when compared with their simple magnitude-calculation counterparts. While a full analysis of this improvement is still in progress, it is apparent that this also depends on the oversampling ratio as approximately ffiffiffiffiffiffiffiffiffiffiffi ffi N=M p , thus making up for the signal-to-noise ratio losses that, under equal G acq conditions, spatially encoded methods may have vis-à-vis Fourier-based counterparts (12)(13)(14).…”

Section: Discussionmentioning

confidence: 99%

“…In the present study, we relied on a straightforward ''hybrid'' 2D implementation of the single-scan acquisition (13,15,16), whereby spatial encoding and conventional k-encoding act along orthogonal y and x axes, respectively (Fig. 1e).…”

Section: Methodsmentioning

confidence: 99%

“…For an excitation time T exc and sweeping over a frequency range of cG exc L y , this power becomes solely a function of the sweep rate R ¼ cG exc L y /T exc (12). When properly tuned, such swept radiofrequency excitation imposes on the spins a quadratic phase profile given for a refocused 90 nutation by (13):…”

Section: Theorymentioning

confidence: 99%

“…Equation 4 implies that the curvature (i.e., the ''sharpness'') of the parabolic phase profile f exc (y) will define the final pixel size Dy of the image (12,13). This is in contrast to FT-based MRI methods, where the pixel size is given by acquisition criteria, rather than at the excitation stage, as in this case.…”

Section: Mm) Dmentioning

confidence: 99%

“…Central in the development of these new experiments is the spatiotemporal manipulation of the spin interactions, a concept that originated from a search for methods capable of delivering arbitrary multidimensional MR spectra in a single scan (10,11). The generality of the ensuing approach eventually led to several new routes for executing single-scan multidimensional MRI (12)(13)(14)(15)(16). Contrary to EPI, these new MRI methods were found to be local in nature in the sense that, at each instant, the spins' signal S(t) becomes proportional to the density profile rðrÞ within a limited region of the volume of interest.…”

mentioning

confidence: 99%

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Super‐resolved spatially encoded single‐scan 2D MRI

Ben‐Eliezer

Irani

Frydman

2010

Magnetic Resonance in Med

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129

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Single-scan MRI underlies a wide variety of clinical and research activities, including functional and diffusion studies. Most common among these ''ultrafast'' MRI approaches is echo-planar imaging. Notwithstanding its proven success, echo-planar imaging still faces a number of limitations, particularly as a result of susceptibility heterogeneities and of chemical shift effects that can become acute at high fields. The present study explores a new approach for acquiring multidimensional MR images in a single scan, which possesses a higher built-in immunity to this kind of heterogeneity while retaining echo-planar imaging's temporal and spatial performances. This new protocol combines a novel approach to multidimensional spectroscopy, based on the spatial encoding of the spin interactions, with image reconstruction algorithms based on super-resolution principles. Single-scan two-dimensional MRI examples of the performance improvements provided by the resulting imaging protocol are illustrated using phantom-based and in vivo experiments. Magn Reson Med 63:1594-1600, 2010. V C 2010 Wiley-Liss, Inc.Key words: single-scan imaging; super-resolution; ultrafast MRI; spatial encoded imaging; susceptibility compensation; EPI The last decades have witnessed a continuous growth in the use of single-scan MRI, both for clinical and research applications (1,2). These ''ultrafast'' protocols play an essential role in experiments demanding high temporal resolution like functional MRI (3-5); they also constitute integral components in high-dimensionality experiments such as diffusion tensor imaging (6). Foremost among the sequences enabling the acquisition of MR images in a single scan stands echo-planar imaging (EPI) (7), with its many different variants (8,9). EPI relies on a single excitation of all spins within the volume to be examined, followed by repetitive gradient oscillations that scan, in a single continuous acquisition, large regions of the image conjugate (k-space) domain. The rðrÞ spin density profile being sought is then retrieved by a numerical Fourier transform (FT) of the digitized information. Notwithstanding their real-time image-gathering capabilities, EPI-based protocols are still challenged by the relatively long data sampling times that they involve. These are ca. an order of magnitude longer than those typically involved in multiscan MRI and expose the protocol to progressive temporal artifacts arising from susceptibility variations, from unfavorable shimming conditions, or from chemical shift heterogeneities. These in turn put practical limitations to the organs and/or conditions that can be studied using ultrafast MRI protocols.By contrast to EPI's reliance on contributions arising simultaneously from the entire sample, we have recently begun exploring the consequences of relying on a progressive spatial encoding of MR images. Central in the development of these new experiments is the spatiotemporal manipulation of the spin interactions, a concept that originated from a search for methods capable of del...

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: Mm) Dmentioning

confidence: 99%

mentioning

confidence: 99%

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Super‐resolved spatially encoded single‐scan 2D MRI

Ben‐Eliezer

Irani

Frydman

2010

Magnetic Resonance in Med

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129

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Ultrafast Multidimensional NMR: Principles and Practice of Single-Scan Methods

Gal

Frydman

2008

Encyclopedia of Magnetic Resonance

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Second primary cancers after prostatic irradiation: Ensuring an appropriate analysis

Kendal¹,

Eapen²,

Nicholas³

2006

Cancer

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The use of attained age, as well as Cox modeling, seems a more appropriate strategy than the analysis presented by Moon.1 Moon's analysis did not incorporate an appropriate measure of duration of follow-up. Because malignancy risk increases with age, an older patient followed for a number of years accumulates a greater risk than a younger patient followed for the same period. Failure to account for factors like this can lead to an overstatement of the attributable risk in older subgroups, like men irradiated for prostatic cancer. Moon's finding of increased second cancer risk in men treated with transurethral resection of prostate (TURP) alone may be another example of this. 1Exclusion of cases with fewer than 5 years of follow-up is based on the assumptions that radiation-induced cancer has a long latency and that cancers arising shortly after radiotherapy are not radiationrelated.1 Indeed, we found no evidence for a latency effect.

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Spatial encoding and the single-scan acquisition of high definition MR images in inhomogeneous fields

Cited by 68 publications

References 32 publications

Super‐resolved spatially encoded single‐scan 2D MRI

Super‐resolved spatially encoded single‐scan 2D MRI

Ultrafast Multidimensional NMR: Principles and Practice of Single-Scan Methods

Second primary cancers after prostatic irradiation: Ensuring an appropriate analysis

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