Spatially encoded NMR and the acquisition of 2D magnetic resonance images within a single scan

Shrot, Yoav; Frydman, Lucio

doi:10.1016/j.jmr.2004.09.024

Cited by 107 publications

(141 citation statements)

References 26 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%

“…The effective spin-nutation angles associated with this type of excitation are determined according to the radiofrequency's power. 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.…”

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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: 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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“…First introduced for the acquisition of 2D NMR spectra in a single scan [19,20], spatiotemporal encoding (SPEN) utilizes a chirped pulse combined with a gradient for a sequential manipulation of the spins that can directly monitor their density in real space [21,22]. In an imaging context, SPEN uses such a manipulation along the low-bandwidth domain in combination with a conventional k-space readout, leading to a so-called hybrid acquisition mode [23,24]. Hybrid SPEN has a higher robustness against magnetic field inhomogeneities than EPI, reflecting the larger bandwidths it can access for the spatially sequential excitation and detection.…”

Section: Introductionmentioning

confidence: 99%

In vivo single-shot 13C spectroscopic imaging of hyperpolarized metabolites by spatiotemporal encoding

Schmidt

Laustsen

Dumez

et al. 2014

Journal of Magnetic Resonance

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Hyperpolarized metabolic imaging is a growing field that has provided a tool for analyzing metabolism, particularly in cancer. Given the short life times of the hyperpolarized signal, fast and effective spectroscopic imaging methods compatible with dynamic metabolic characterizations are necessary. Several approaches have been customized for hyperpolarized 13 C MRI, including CSI with a center-out k-space encoding, EPSI, and spectrally selective pulses in combination with spiral EPI acquisitions. Recent studies have described the potential of single-shot alternatives based on spatiotemporal encoding (SPEN) principles, to derive chemical-shift images within a sub-second period. By contrast to EPSI, SPEN does not require oscillating acquisition gradients to deliver chemical-shift information: its signal encodes both spatial as well as chemical shift information, at no extra cost in experimental complexity. SPEN MRI sequences with sliceselection and arbitrary excitation pulses can also be devised, endowing SPEN with the potential to deliver single-shot multi-slice chemical shift images, with a temporal resolution required for hyperpolarized dynamic metabolic imaging. The present work demonstrates this with initial in vivo results obtained from SPEN-based imaging of pyruvate and its metabolic products, after injection of hyperpolarized [1-13 C]pyruvate. Multi-slice chemical-shift images of healthy rats were obtained at 4.7 T in the region of the kidney, and 4D (2D spatial, 1D spectral, 1D temporal) data sets were obtained at 7 T from a murine lymphoma tumor model.

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