Echo-Planar Imaging Pulse Sequences

Wielopolski, Piotr A.; Schmitt, Franz; Stehling, Michael K.

doi:10.1007/978-3-642-80443-4_4

Cited by 14 publications

(16 citation statements)

References 64 publications

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“…This in turn has strong deleterious effects on the performance of the ultrafast experiment, since long gradient switching times lead to a concomitant increase in the associated dwell times, and thus to a decrease in the spectral window ranges that can be characterized along the direct (and to some extent also the indirect) dimension. A well‐known solution for overcoming artifacts related to long gradient switching times consists of shaping the field gradients into sinusoidal functions characterized by lower slew rates (18). A similar strategy could then be used to alleviate requirements in the single‐scan 2D NMR protocol.…”

Section: Theorymentioning

confidence: 99%

“…A feature associated with the introduction of sinusoidal gradients is that when these gradients are combined with constant data acquisition rates, they result in unequal intervals in the sampling Δ k of the indirect ν 1 ‐domain. This nonlinearity in the sampling of the k‐ axis is not as severe a hindrance in this kind of experiment as it is, for example, in echo‐planar imaging (EPI) (18), where the data must be subjected to Fourier transformation along the k‐ axis. The only Fourier transform involved in ultrafast 2D NMR occurs along the direct t 2 domain, and this can be implemented in a straightforward manner regardless of the gradient's periodic functionality, since the points' separation along this axis always remains ∼2 T a .…”

Section: Theorymentioning

confidence: 99%

See 1 more Smart Citation

Ultrafast 2D NMR spectroscopy using sinusoidal gradients: Principles and ex vivo brain investigations

Sela

Degani

Frydman

2004

Magnetic Resonance in Med

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A new methodology capable of delivering complete 2D NMR spectra within a single scan was recently introduced. The resulting potential gain in time resolution could open new opportunities for in vivo spectroscopy, provided that the technical demands of the methodology are satisfied by the corresponding hardware. Foremost among these demands are the relatively short switching times expected from the applied gradientecho trains. These rapid transitions may be particularly difficult to accomplish on imaging systems. As a step toward solving this problem, we assessed the possibility of replacing the square-wave gradient train currently used during the course of the acquisition by a shaped sinusoidal gradient. Examples of the implementation of this protocol are given, and successful ultrafast acquisitions of 2D NMR spectra with suitable spectral widths on a microimaging probe ( Key words: ultrafast 2D NMR; magnetic resonance spectroscopy; brain metabolites; 2D TOCSY spectra; sinusoidal gradients NMR spectroscopy has become an increasingly common tool in the investigation of both normal function and disease in living systems (1-3). Two-dimensional (2D) NMR, in particular, offers two distinct advantages over its simpler one-dimensional (1D) spectroscopic counterparts: enhanced resolution as resonances are spread over a plane rather than along a single frequency dimension, and spectral assignment opportunities stemming from correlations between pairs of related resonances. In recent years, several studies have utilized 2D NMR in order to investigate, within whole-body magnetic resonance imaging (MRI) settings, in vivo metabolism and function (4 -11). Most of these studies focused on brain investigations at varying degrees of localization (5-10), while others introduced 2D NMR as a promising tool for breast and prostate cancer analysis (11,12). Although 2D NMR methods are potentially useful for in vivo investigations, the routine clinical use of such techniques is hampered by the relatively lengthy nature of the procedure involved. Long acquisition times also deprive 2D NMR from much of the temporal resolution required to efficiently follow dynamic metabolite changes. 2D spectroscopy inherently takes longer to perform than 1D NMR approaches, since it necessitates the monitoring of correlations among pairs of spin evolution frequencies. To implement such correlations, 2D NMR relies on a scan-by-scan incrementation of a time variable t 1 encoding the indirect-domain interactions ⍀ 1 (13). Since each t 1 increment corresponds in essence to an independent 1D NMR experiment, long acquisition times become inherent even for systems that possess abundant signal-tonoise ratios. A number of proposals have recently been made to alleviate this extended acquisition-time problem (14), including an "ultrafast" approach capable of affording complete 2D NMR spectra within a single scan (15-17). Because it offers shorter acquisition times, this new protocol could assist investigators in developing new applications for 2D in vivo MR spectro...

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Section: Theorymentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Ultrafast 2D NMR spectroscopy using sinusoidal gradients: Principles and ex vivo brain investigations

Sela

Degani

Frydman

2004

Magnetic Resonance in Med

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show abstract

“…Gradient-recalled (GRE) echo-planar imaging (EPI), widely employed in fMRI, yields images weighted by T 2 ⁎ , the effective transverse relaxation time. T 2 ⁎ is a combination of T 2 and an inhomogeneity term T′: 1/T 2 ⁎ =1/ T 2 +1/T′≈1/T 2 +γΔB 0 , where γ is the gyromagnetic ratio of proton in conventional fMRI and ΔB 0 is the inhomogeneity of magnetic field [6].…”

Section: Introductionmentioning

confidence: 99%

Functional magnetic resonance imaging reference phantom

Renvall¹

2009

Magnetic Resonance Imaging

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“…Using a reduced interexperimental delay and low flip angle excitation, as employed in fast gradient echo imaging techniques (6), is, however, not a viable approach in this context, since CYCLCROP leads to complete saturation of the 1 H magnetization after each signal acquisition. Another approach is to multiply refocus the edited 1 H signal and thus sample multiple lines of k-space after each polarization transfer (7). The CYCLCROP echo-planar imaging (EPI) sequence described here involves taking this approach to the extreme, such that all lines of k-space are acquired after each transfer.…”

Section: Introductionmentioning

confidence: 99%