Multiple spin echoes in liquids in a high magnetic field

Bowtell, Richard; Bowley, R. M.; Glover, Paul

doi:10.1016/0022-2364(90)90297-m

Cited by 134 publications

(159 citation statements)

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“…Experimental manifestations of the DDF were first observed as multiple spin echoes in solid 3 He (13), condensed 3 He (14), and water (15), as well as additional cross peaks in 2D spectra (16,17). A theoretical description has been given in terms of a mean field treatment (13)(14)(15), and in the quantum mechanical density matrix formalism (17,18), leading to the commonly used term "intermolecular zero-quantum coherence" (iZQC) spectroscopy.…”

Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

“…A theoretical description has been given in terms of a mean field treatment (13)(14)(15), and in the quantum mechanical density matrix formalism (17,18), leading to the commonly used term "intermolecular zero-quantum coherence" (iZQC) spectroscopy.…”

Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

“…Various aspects of signal evolution in the HOMOGE-NIZED experiment were treated theoretically in previous publications (3,13,(15)(16)(17)(18)(19)(20)(21)(22). Under the assumption that the gradient imposes a 1D modulation, and that diffusion and radiation damping can be neglected, an analytical solution of Bloch's equation including the DDF can be obtained.…”

Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

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Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Balla

Melkus

Faber

2006

Magnetic Resonance in Med

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Magnetic resonance spectroscopy (MRS) techniques that use the distant dipolar field (DDF) to locally refocus inhomogeneous line-broadening promise improved spectral resolution in spatially varying fields. We investigated three possible implementations of localized DDF spectroscopy. Theoretical analysis and phantom experiments at 17.6 T showed that only localization immediately prior to acquisition provides sufficient spatial selectivity and sensitivity for in vivo applications. Spectra from an (8 mm) 3 voxel of the rat brain were acquired in 25 min, and three major metabolites were resolved. In a tumor mouse model, DDF spectra with well-resolved lines can be obtained from significantly larger voxels compared to conventional localized spectroscopy. From an inhomogeneous voxel, improved spectral resolution can be obtained with DDF techniques when a sufficient number of increments are sampled along the second spectral dimension. With fewer increments, measurement time is significantly shortened, and DDF techniques can provide higher signal-to-noise ratio ( Key words: iZQC; HOMOGENIZED; localized spectroscopy; inhomogeneous broadening; resolution enhancementIn vivo magnetic resonance spectroscopy (MRS) can be used to resolve spectral patterns to analyze the biochemical composition of tissue. High spectral resolution can be achieved when the magnetic field is extremely homogeneous over the region studied. Such field homogeneity is usually achieved with localized shimming procedures (1,2). If the region of interest (ROI) is strongly structured or includes air/tissue boundaries, homogeneous magnetic fields cannot be obtained and spectral resolution is often poor. One way to avoid inhomogeneous line-broadening caused by small-scale field variations is to use experimental techniques that exploit the effect of the distant dipolar field (DDF) originating from the sample magnetization (3-6). The homogeneity enhancement by intermolecular zeroquantum echo detection (HOMOGENIZED) experiment has been shown to produce narrow line shapes even under temporarily unstable magnetic fields (7), linear inhomogeneities across the sample volume (3-5), and field distortions in living organisms (8,9). Efficient water suppression (WS) and localization of the acquired signal are essential for in vivo applications. While different combinations of WS modules have been described and compared (5,10), the inherently low sensitivity of these methods has hampered the development of localization techniques in vivo (11).In this study we investigate three possible ways to combine localization with the HOMOGENIZED experiment, and demonstrate that high-quality spectra can be obtained in vivo. THEORY Theory of the HOMOGENIZED ExperimentThe HOMOGENIZED pulse sequence is a 2D NMR experiment derived from correlation spectroscopy (COSY) (3,12):The values in brackets indicate the flip angle of RF pulses with pulse phase given in subscript; t 1 is the incremented delay, CG is the correlation magnetic field gradient, and t 2 the acquisition period. The acquire...

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Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

Section: Theory Of the Homogenized Experimentsmentioning

confidence: 99%

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Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Balla

Melkus

Faber

2006

Magnetic Resonance in Med

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“…Alternatively, one may explain such phenomena using the classical concept of the distant dipolar field, or dipolar demagnetizing field (DDF) [15,16]. While both the classical and the quantum treatments appear equivalent, the quantum description lends itself more readily to the interpretation of experimental results using common NMR concepts such as phase cycling, and coherence selection via pulsed field gradients [13].…”

Section: Theorymentioning

confidence: 99%

Chemical exchange saturation transfer by intermolecular double-quantum coherence

Wen

Eliav

Jerschow

2008

Journal of Magnetic Resonance

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A number of contrast enhancement effects based on the use of intermolecular multiple-quantum coherences, or distant dipolar field effects are known. This phenomenon is based on the dependence on the m-th power of the initial magnetization (where m is the coherence order used). In this article we describe the contrast enhancement based on chemical exchange saturation transfer and NOE, which is achieved by the use of intermolecular double-quantum coherences (iDQC). The method was validated using clinically relevant systems based on glycosaminoglycans and a sample of cartilage tissue, showing that the CEST contrast, as well as, NOE are enhanced by iDQC.

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“…The use of intermolecular multiple-quantum coherences (iMQCs) for MRI has attracted substantial interest in recent years (1)(2)(3)(4). In such experiments, image contrast is based on dipolar couplings between nuclear spins in different molecules separated by a specific distance-the so-called 'correlation distance'-which may range from 10 m to a few millimeters (2).…”

mentioning

confidence: 99%

Functional contrast based on intermolecular double‐quantum coherences: Influence of the correlation distance

Schäfer

Möller

2007

Magnetic Resonance in Med

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The use of intermolecular multiple-quantum coherences (iMQCs) for MRI has attracted substantial interest in recent years (1-4). In such experiments, image contrast is based on dipolar couplings between nuclear spins in different molecules separated by a specific distance-the so-called 'correlation distance'-which may range from 10 m to a few millimeters (2). Dipolar couplings are not observed in conventional MRI experiments because short-range interactions average to zero in time through rapid molecular tumbling, and long-range interactions average to zero in space as long as the sample is magnetically isotropic. They reappear, however, if a magnetic field gradient is used to break this isotropy (2,5). In particular, this 'correlation gradient' of amplitude G c and duration ␦ c winds up the magnetization as a helix and modulates the sample spatially (6). It turns out that the dipolar signal predominantly comes from spins separated by one-half of the helix pitch along the gradient direction as the spherical symmetry is completely lost for this distance. A correlation distance is, hence, defined according to (3):where ␥ is the magnetogyric ratio. A unique feature of iMQC imaging is that the spatial scale of the experiment can be manipulated externally by adjusting G c and ␦ c . Intermolecular double-quantum coherences (iDQCs) are more sensitive to local magnetic susceptibility variations as compared to the conventional single-quantum coherence (SQC) signal. This has already been used to generate a strong blood oxygen level-dependent (BOLD) contrast for functional MRI (fMRI) by several research groups (7-10). In such experiments, functional contrast is thought to be sensitive to changes in local magnetic field perturbations in or around blood vessels occurring on a length scale that is defined by the correlation distance. The recorded iDQC signal is a function of the resonance frequency difference of the two interacting spins, which is sensitive to the distribution of local field gradients, whereas conventional BOLD experiments reflect the average gradient strength within an imaging voxel (7,11). Such characteristics could be especially valuable if the selection of a length scale for the detection of susceptibility changes would also imply a selection of blood vessels of a particular size. In this scenario, iDQC-based fMRI might permit focusing only on hemodynamic changes in the capillaries, which are located at a minimal spatial offset from the site of neuronal activity. However, the proposed possibility to tailor the distance scale of the BOLD sensitivity for optimum specificity remains to be shown. In nonfunctional human brain imaging studies, obvious contrast changes could not be produced by variation of the correlation distance between 88 and 530 m (12). Using numerical simulations, Marques and Bowtell (13) did not find a significant effect of the modulation length on the iDQC signal and concluded that a selection of susceptibility changes in vessels of a particular size may not be possible. A thorough experim...

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Multiple spin echoes in liquids in a high magnetic field

Cited by 134 publications

References 3 publications

Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Chemical exchange saturation transfer by intermolecular double-quantum coherence

Functional contrast based on intermolecular double‐quantum coherences: Influence of the correlation distance

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