Intramolecular zero-quantum-coherence 2D NMR spectroscopy of lipids in the human breast at 7 T

Intramolecular zero-quantum-coherence 2D NMR spectroscopy of lipids in the human breast at 7 T
Robin A. de Graaf, Dennis W. J. Klomp, Peter R. Luijten, Vincent O. Boer
Magnetic Resonance in Medicine (early view)
Keywords: human breast; unsaturated fatty acids; zero-quantum-coherences; magnetic field inhomogeneity; 7 Tesla

Purpose
Intramolecular zero-quantum-coherences (ZQCs) are intrinsically insensitive toward magnetic field inhomogeneity. This fact is used to quantify and characterize lipid signals in the human breast at 7 T despite the presence of severe magnetic field inhomogeneity caused by water–lipid susceptibility boundaries.

Methods
A novel 3D localized 2D ZQC method is presented. The combination of cardiac/respiratory triggering and post-acquisition navigator echo correction provides high-quality 2D NMR spectra in vivo.

Results
The lipid profile of the human breast could be quantified by 2D ZQC NMR in 100% of the subjects despite a wide range of magnetic field homogeneity. With conventional 1D 1H MRS, the magnetic field homogeneity was only adequate in 60% of the subjects. The results from 2D ZQC NMR and 1D NMR are in good correspondence, both in vitro and in vivo.

Conclusion
It has been demonstrated that high quality and quantitative 2D ZQC NMR spectra can be acquired from human breast tissue at 7 T. While the simplicity and sensitivity of 1D MRS are preferable when the magnetic field homogeneity is adequate, the 2D ZQC method provides a viable alternative in cases where this requirement cannot be met. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Fast high-resolution 2D correlation spectroscopy in inhomogeneous fields via Hadamard intermolecular multiple quantum coherences technique

Congbo Cai, Fenglian Gao, Shuhui Cai, Yuqing Huang and Zhong Chen
Journal of Magnetic Resonance
Article in Press, Corrected Proof

Recently, a method based on intermolecular multiple quantum coherences (iMQCs) has been proposed to obtain high-resolution 2D COSY spectra in inhomogeneous fields via 3D acquisitions. However, the very long acquisition time prevents its practical application. To overcome this shortage, the Hadamard technique was applied for the iMQC method in this paper. For the new pulse sequence, the direct frequency-domain excitation is used in the first indirect detection dimension, so the 3D acquisition was replaced by an array of 2D acquisitions. The acquisition time can be reduced to 10 min. The resulting spectra retain useful structural information including chemical shifts and multiplet patterns of J coupling even when the inhomogeneous line broadening leads to overlap of neighboring diagonal resonances in the conventional COSY spectrum. The experimental results are consistent with the theoretical predictions and computer simulations. The new sequence may provide a time-efficient way for the studies of chemical solution in inhomogeneous fields.

Nearly 106-fold enhancements in intermolecular 1H double-quantum NMR experiments by nuclear hyperpolarization

Mor Mishkovsky, Uzi Eliav, Gil Navon and Lucio Frydman
Journal of Magnetic Resonance
Volume 200, Issue 1, September 2009, Pages 142-146

Abstract

Intermolecular Multiple-Quantum Coherences (iMQCs) can yield interesting NMR information of high potential usefulness in spectroscopy and imaging – provided their associated sensitivity limitations can be overcome. A recent study demonstrated that ex situ dynamic nuclear polarization (DNP) could assist in overcoming sensitivity problems for iMQC-based experiments on 13C nuclei. In the present work we show that a similar approach is possible when targeting the protons of a hyperpolarized solvent. It was found that although the DNP procedure enhances single-quantum 1H signals by about 600, which is significantly less than in optimized low-γ liquid-state counterparts, the non-linear dependence of iMQC-derived signals on polarization can yield very large enhancements approaching 106. Cleary no practical amount of data averaging can match this kind of sensitivity gains. The fact that DNP endows iMQC-based 1H NMR spectra with a sensitivity that amply exceeds that of their thermally polarized single-quantum counterpart, is confirmed in a number of simple single-scan 2D imaging experiments.

Intermolecular single-quantum coherence sequences for high-resolution NMR spectra in inhomogeneous fields

Yuqing Huang, Shuhui Cai, Xi Chen and Zhong Chen
Journal of Magnetic Resonance
Volume 203, Issue 1, March 2010, Pages 100-107

Abstract

A new pulse sequence based on intermolecular single-quantum coherences (iSQCs) is proposed to obtain high-resolution NMR spectroscopy in inhomogeneous magnetic fields via fast 2D acquisition. Taking the intrinsic properties of iSQCs, the sequence is time-efficient with a narrow spectral width in the indirect dimension. It can recover useful information of chemical shifts, relative peak areas, J coupling constants, and multiplet patterns even when the field inhomogeneity is severe enough to erase almost all spectroscopic information. Moreover, good solvent suppression efficiency can be achieved by this sequence even with imperfect radio-frequency pulse flip angles. Spatially localized iSQC spectroscopy was performed on a sample packed with pig brain tissue and cucumber to show the feasibility of the sequence in in vivo magnetic resonance spectroscopy (MRS). This sequence may provide a promising way for the applications on in vivo and in situ high-resolution NMR spectroscopy.

Highly efficient square wave distant dipolar field and its application for in vivo MRI

Congbo Cai, Fenglian Gao , Shuhui Cai, Jianhui Zhong, Zhong Chen

Intermolecular multiple quantum coherences generated by distant dipolar field (DDF) have some attractive properties, but the intrinsic weak signal intensity prevents their widespread applications. Recently, Branca et al. (J Chem Phys 2008;129:054502) suggested that square wave DDF was more efficient than conventional sinusoidal DDF because it could simultaneously produce intermolecular multiple quantum coherences signal with various major orders. In this article, instead of a series of adiabatic inversion pulses proposed previously, a more efficient composite adiabatic inversion pulse was applied to create square wave DDF. The square wave DDF was applied to in vivo MRI for the first time, and the corresponding simulations were performed. Both experimental and simulated results show that square wave DDF with composite adiabatic inversion pulse improves over the original Z-modulation enhanced to binary for self-refocused acquisition implementation and can enhance the signal intensity to about 2-fold of that from conventional correlation spectroscopy (COSY) revamped with asymmetric Z-gradient echo detection sequence for in vivo MRI, close to the theoretical prediction. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

Fast acquisition scheme for achieving high-resolution MRS with J-scaling under inhomogeneous fields

Xi Chen, Meijin Lin, Zhong Chen, and Jianhui Zhong
Magnetic Resonance in Medicine
Volume 61 Issue 4, Pages 775 - 784
Published Online: 2 Feb 2009

Intermolecular multiple-quantum coherences (iMQCs) can refocus the phase dispersion caused by magnetic field inhomogeneities while preserving the chemical shift, so they have been applied to achieve high-resolution MR spectroscopy free of line broadening caused by susceptibility gradients. However, previous iMQC high-resolution methods all require two-dimensional spectra sampling of the full range of chemical shifts of solute evolutions in both F1 and F2 dimensions, resulting in a prolonged scanning time for data acquisition. In this work, sparse sampling in the t1 dimension and subsequent fold-over correction are used to speed up the intermolecular zero-quantum coherence spectroscopy by up to 50 times on high-field MR systems. Furthermore, three types of spectra with homo-decoupling, original J-coupling constants, and doubled J-coupling constants respectively are obtained with manipulation of the t1 period. The water suppression is also improved by the combined use of intermolecular double-quantum filter and excitation sculpting. The feasibilities of this group of new sequences are demonstrated by experiments using an agar gel phantom with an air bubble, in vitro pig brain tissues and an intact postmortem mudskipper. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

iDQC anisotropy map imaging for tumor tissue characterization in vivo

Rosa T. Branca, Yuming M. Chen, Vladimir Mouraviev, Gigi Galiana, Elizabeth R. Jenista, Challa Kumar, Carola Leuschner, Warren S. Warren

Intermolecular double quantum coherences (iDQCs), signals that result from simultaneous transitions of two or more separated spins, are known to produce images that are highly sensitive to subvoxel structure, particularly local anisotropy. Here we demonstrate how iDQCs signal can be used to efficiently detect the anisotropy created in breast tumor tissues and prostate tumor tissues by targeted (LHRH-conjugated) superparamagnetic nanoparticles (SPIONs), thereby distinguishing the necrotic area from the surrounding tumor tissue. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Hyperpolarized carbon–carbon intermolecular multiple quantum coherences

Journal of Magnetic Resonance
Article in Press, Corrected Proof

Hyperpolarized carbon–carbon intermolecular multiple quantum coherences

Elizabeth R. JenistaCorresponding Author Contact Information, a, E-mail The Corresponding Author, Rosa T. Brancaa and Warren S. Warrena
aCenter for Molecular and Biomolecular Imaging, 2220 French Family Science Center, Duke University, Durham, NC 27708, USA

Received 17 July 2008;
revised 17 September 2008.
Available online 2 October 2008.

Abstract

Intermolecular multiple quantum coherences (iMQCs) can provide unique contrast with sub-voxel resolution. However, the characteristic growth rate of iMQCs mostly limits these effects to either hydrogen or hydrogen-coupled systems for thermally polarized samples. Hyperpolarization techniques such as dynamic nuclear polarization (DNP) allow for significant increases in the carbon signal (even more signal than that from hydrogen), making carbon iMQCs achievable. We present the first intermolecular multiple quantum signal between two carbon nuclei.

Keywords: Intermolecular multiple quantum coherence; 13C hyperpolarization; Dynamic nuclear polarization; MultiCRAZED; CRAZED

Accurate Temperature Imaging Based on Intermolecular Coherences in Magnetic Resonance

Science 17 October 2008:
Vol. 322. no. 5900, pp. 421 - 424
DOI: 10.1126/science.1163242

Accurate Temperature Imaging Based on Intermolecular Coherences in Magnetic Resonance
Gigi Galiana, Rosa T. Branca, Elizabeth R. Jenista, and Warren S. Warren

Conventional magnetic resonance methods that provide interior temperature profiles, which find use in clinical applications such as hyperthermic therapy, can develop inaccuracies caused by the inherently inhomogeneous magnetic field within tissues or by probe dynamics, and work poorly in important applications such as fatty tissues. We present a magnetic resonance method that is suitable for imaging temperature in a wide range of environments. It uses the inherently sharp resonances of intermolecular zero-quantum coherences, in this case flipping up a water spin while flipping down a nearby fat spin. We show that this method can rapidly and accurately assign temperatures in vivo on an absolute scale.

Innovations Improve Accuracy Of MRI As Internal 'Thermometer'; Technique Can Enhance Cancer Therapy

ScienceDaily (Oct. 21, 2008) — Duke University chemists say they have developed a new way to measure temperature changes inside the body with unprecedented precision by correcting a subtle error in the original theory underlying Magnetic Resonance Imaging (MRI)...

BOLD imaging in the mouse brain using a turboCRAZED sequence at high magnetic fields

Johannes T. Schneider, Cornelius Faber

Functional MRI (fMRI) based on the detection of intermolecular double-quantum coherences (iDQC) has previously been shown to provide pronounced activation signal. For fMRI in small animals at very high magnetic fields, the essential fast gradient echo-based readout methods become problematic. Here, rapid intermolecular double-quantum coherence (iDQC) imaging was implemented, combining the iDQC preparation sequence with a Turbo spin echo-like readout. Four-step phase cycling and a novel intensity-ordered k-space encoding scheme with separate acquisition of odd and even echoes were essential to optimize signal to noise ratio efficiency. Compared with a single echo readout of iDQC signal, acceleration of factor 16 was achieved in phantoms using the novel method at 17.6 Tesla. In vivo, echo trains consisting of 32 echoes were possible and images of the mouse brain were obtained in 30 s. The blood oxygen level dependent (BOLD) effect in the mouse brain upon change of breathing gas was observed as average signal change of (6.3 ± 1.1)% in iDQC images. Signal changes in conventional multi spin echo images were (4.4 ± 2.3)% and (8.3 ± 3.8)% with gradient echo methods. Combination of T2*-weighting with the fast iDQC sequence may yield higher signal changes than with either method alone, and establish fast iDQC imaging a robust tool for high field fMRI in small animals. Magn Reson Med 60:850-859, 2008. © 2008 Wiley-Liss, Inc.

Enhanced nonlinear magnetic resonance signals via square wave dipolar fields

R. T. Branca,1 G. Galiana,1,2 and W. S. Warren1
1Center for Molecular and Biomolecular Imaging, Duke University, Durham, North Carolina 27708, USA
2Chemistry Department, Princeton University, Princeton, New Jersey 08544, USA
J. Chem. Phys. 129, 054502 (2008)

This report introduces a new approach that enhances nonlinear solution magnetic resonance signals from intermolecular dipolar interactions. The resulting signals can theoretically be as large as the full equilibrium magnetization. Simple, readily implemented pulse sequences using square-wave magnetization modulation simultaneously refocus all even order intermolecular multiple quantum coherences, leading to a substantial net signal enhancement, complex nonlinear dynamics, and improved structural sensitivity under realistic conditions. ©2008 American Institute of Physics

Appendices A and B with mathematical derivations as referred to in the text (10 pages)

ARTICLE INFORMATION

EPAPS Document No.: E-JCPSA6-129-617827

Journal: J. Chem. Phys. 129, 044505 (2008)

All Authors: Stefan Kirsch, William E. Hull

Title: Quantitative time- and frequency-domain analysis of the two-pulse
CRAZED NMR experiment; theoretical and experimental aspects, time-zero
data truncation artefacts, and radiation damping

Deposit Information

Description: Appendices A and B with mathematical derivations as referred
to in the text (10 pages)

Total No. of Files: 2

File Names: Readme.txt, 617827JCP appendices.pdf

File Types: .txt and .pdf

Contact:
Dr. William E. Hull (PhD)
Core Facility: Molecular Structure Analysis (W160)
German Cancer Research Center (DKFZ)
Im Neuenheimer Feld 280
Postfach 101949
D-69009 Heidelberg

Fax: +49-6221-42-4554
Tel: +49-6221-42-4515 / -4544 / -4542

Quantitative time- and frequency-domain analysis of the two-pulse COSY revamped by asymmetric Z-gradient echo detection NMR experiment: Theoretical an

Stefan Kirsch and William E. Hull
J. Chem. Phys. 129, 044505 (2008)

The two-pulse COSY revamped by asymmetric Z-gradient echo detection (CRAZED) NMR experiment has the basic form 90°−G−t_rec−−nG−t_rec-FID, with a phase-encoding gradient pulse G of length applied during the evolution time for transverse magnetization, readout pulse , rephasing gradient nG, and recovery time t_rec prior to acquisition of the free-induction decay. Based on the classical treatment of the spatially modulated dipolar demagnetizing field and without invoking intermolecular multiple-quantum coherence, a new formulation of the first-order approximation for the theoretical solution of the nonlinear Bloch equations has been developed. The nth-order CRAZED signal can be expressed as a simple product of a scaling function C_n(,) and a signal amplitude function A_n(t), where the domain t begins immediately after the pulse. Using a single-quantum coherence model, a generalized rf phase shift function has also been developed, which explains all known phase behavior, including nth-order echo selection by phase cycling. Details of the derivations are provided in two appendices as supplementary material. For n>1, A_n(t) increases from zero to a maximum value at t=t_max before decaying and can be expressed as a series of n exponential decays with antisymmetric binomial coefficients. Fourier transform gives an antisymmetric binomial series of Lorentzians, where the composite lineshape exhibits negative wings, zero integral, and a linewidth that decreases with n. Analytical functions are presented for t_max and A_n(t_max) and for estimating the maximal percent error incurred for A_n(t_max) when using the first-order model. The preacquisition delay =+t_rec results in the loss of the data points for t=0 to . Conventional Fourier transformation produces time-zero truncation artifacts (reduced negative wing amplitude, nonzero integral, and reduced effective T2 ^*" align="middle" border="0">), which can be avoided by time-domain fitting after right shifting the data by . A doped water sample (9.93 mM NiSO₄, 10 mm sample tube) was used to study the behavior of the CRAZED signal for n=1–4 with =90° at 7 T (300 MHz ¹H frequency) as a function of , with and without radiation damping. Pulse-acquire experiments were used to determine the relaxation times (T₁=61.8 ms and T2 ^*" align="middle" border="0">=29.7 ms), and the radiation damping time constant T_rd=18.5 ms. When experimental CRAZED data sets were right shifted by , excellent least-squares fits to the first-order model function were obtained for all n using a minimal set of free variables. Without radiation damping the fitted T2 ^*" align="middle" border="0">values (29.7–30.2 ms) agreed with the reference value. With radiation damping the fitted effective T2 ^*" align="middle" border="0"> values were 16.2 ms for a 90° pulse-acquire experiment and 18.8–20.2 ms for the CRAZED experiment with n=1–4 and signal amplitudes spanning a range of 10⁵. ©2008 American Institute of Physics

Diffraction-like phenomena in a periodic magnetization distribution at 1.5 T using the distant dipolar field (DDF)

Stefan Kirsch and Peter Bachert
Journal of Magnetic Resonance
Volume 185, Issue 2, April 2007, Pages 183-190

In the CRAZED experiment (COSY revamped by asymmetric Z-gradient echo detection, Warren et al.), a spatially anisotropic magnetization distribution is created by application of a magnetic field gradient (strength G, duration τ) which in turn generates a response called the distant dipolar field (DDF). The DDF is a source of intermolecular multiple-quantum coherences (iMQC) which contain information on the distance d = π/(γGτ) between pairs of dipolar-coupled spins. Diffraction-like phenomena may result for periodically structured samples. In this study, we report the observation of diffraction owing to the DDF at 1.5 T using a clinical whole-body tomograph. Based on the semi-classical treatment of the problem by Robyr and Bowtell, diffraction conditions were obtained for a CRAZED-type pulse sequence that selects iMQC of order N. The predicted distinct difference in N = 2 and N ≠ 2 coherences, i.e., a dominant continuous course as a function of τ (N = 2) and prominent diffraction peaks otherwise, could be verified in CRAZED experiments in a periodically structured sample selecting coherence orders N = 2 and N = 3. The diffractive signal component contains information on the geometric structure of the sample. Applications of this technique may permit the detection of changes in composition and geometry of periodic structures. Keywords: CRAZED; Distant dipolar field (DDF); Intermolecular multiple-quantum coherence; Diffraction

Localized intermolecular zero-quantum coherence spectroscopy in vivo

David Z. Balla , Cornelius Faber
Concepts in Magnetic Resonance Part A
Volume 32A, Issue 2 , Pages 117 - 133

Resolution enhancement in NMR spectra, acquired in spatially or temporally varying magnetic fields, can be achieved with 2D pulse sequences detecting intermolecular zero-quantum coherences (iZQC). The insensitivity towards long range field distortions renders these methods particularly appealing for in vivo NMR spectroscopy, where ample sources of field inhomogeneities are encountered. This article provides a comprehensive description of iZQC spectroscopy, following a classical treatment. A pictorial explanation is given of how iZQC signal is formed under the action of the distant dipolar field in the sample and how this local refocusing process leads to line narrowing in the indirect dimension of 2D spectra. Signal evolution and peak positions in the spectra are analyzed by solving the modified Bloch equations. Finally, it is explained how water suppression and localization can be combined with the iZQC preparation sequence, and recent in vivo applications are discussed. The given examples illustrate that iZQC spectroscopy can provide either resolution or sensitivity enhancement in vivo. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 117-133, 2008.

Intermolecular zero-quantum coherence NMR spectroscopy in the presence of local dipole fields spectroscopy in vivo

David Z. Balla and Cornelius Faber
Department of Experimental Physics 5, University of Würzburg, 97074 Würzburg, Germany
J. Chem. Phys. 128, 154522 (2008); DOI:10.1063/1.2904564

NMR experiments detecting intermolecular zero-quantum coherences (iZQCs) allow for observation of homogeneous line shapes under inhomogeneous magnetic fields. Local dipole fields impair the refocusing capacity of such experiments and render the available theoretical description of signal evolution invalid. In this article, the impact of local dipole fields on two-dimensional iZQC spectroscopy experiments was assessed by performing extensive numerical simulations, which solved the nonlinear Bloch equations for a binary solution in a magnetization array of 64³ spatial points. Local dipole fields were simulated using spherical volumes with different magnetic susceptibility values corresponding to either a glass sphere or an air inclusion with a diameter of 100 µm. The local field resulted in a broadened distribution of difference frequencies between locally interacting spins and led to the dominating effect of decreasing the amplitude of the solute peak, before line broadening was observed in the spectra. From simulations using a magnetic field strength of 17.6 T, the smallest ratio of sample to inclusion volume that still allowed for observation of the solute peak was determined to be _limit=215 and _limit=392 for glass and air inclusions, respectively. Experimental data acquired with a 100 µm diameter glass sphere embedded in agar gel yielded a value of _limit=252 and confirmed the order of magnitude obtained from the simulations. From these data, it was concluded that iZQC spectroscopy is possible as long as the relative volume occupied by air inclusions does not exceed the order of 0.1% of the sample volume. This limit, in contrast to the previous speculations, strongly excludes materials or tissues with high density of strong inhomogeneities from the investigation by iZQC spectroscopy. ©2008 American Institute of Physics

In vivo intermolecular zero-quantum coherence MR spectroscopy in the rat spinal cord at 17.6 T: a feasibility study

David Z. Balla^{1, 2} and Cornelius Faber¹

(1)	Department of Experimental Physics 5, University of Würzburg, Am Hubland, 97074 Würzburg, Germany

(2)	Present address: Max-Planck-Institute for Biological Cybernetics, 72076 Tübingen, Germany

Received: 5 April 2007 Revised: 14 August 2007 Accepted: 17 August 2007 Published online: 18 September 2007

Abstract

Objective: The feasibility of in vivo magnetic resonance spectroscopy of the healthy rat spinal cord at 17.6 T using conventional methods and intermolecular zero-quantum coherence (iZQC) spectroscopy is explored and the performance of both approaches is compared.

Methods: Localised spectra were acquired at 17.6 T from three healthy Fisher rats and phantoms with injected iron-oxide particles using the PRESS and a modified HOMOGENIZED sequence.

Results: Well-resolved in vivo spectra showing the four singlet resonances of creatine, choline, and N-acetyl aspartate were obtained with both approaches. iZQC spectra were acquired from larger voxels, but did not provide higher sensitivity or resolution in the healthy spinal cord. In the presence of paramagnetic iron-oxide particles, the quality of in vitro spectra acquired with PRESS declined and was strongly dependent on the quality of the local shim. iZQC spectra were not affected by the presence of iron-oxide particles and provided narrow lines (9 Hz) independent of the shim.

Conclusion: In vivo iZQC spectroscopy of the rat spinal cord is possible. The robustness in presence of local field distortions makes iZQC methods a promising alternative for the investigation of tissue containing labelled cells, implants, or clotted blood. New application of MRS to tissue inaccessible using conventional methods may thus become possible.

Keywords MR spectroscopy - Resolution enhancement - iMQC - DDF - SPIO

Understanding intra- and intermolecular multiple quantum coherences

This was in the weekend educational program.
Somebody registered for the weekend must login...

_____________________________________

MR Physics for Physicists
Organizer: Michael H. Buonocore, M.D., Ph.D.
Skill Level: Intermediate – Advanced
Saturday, 3 May, 08:30 – 18:15, Room 801 A/B

Spin Physics
09:30 Understanding intra- and intermolecular multiple quantum coherences
Jianhui Zhong, Ph.D.
University of Rochester, USA

Nuclear magnetic resonance (NMR), after all, is a quantum mechanical phenomenon.
Even though in the imaging community, we are mostly familiar and use in most times the
so-called vector model which describes the MR signal as from a precessing bar magnet
inside the magnetic field (not too much different from a spinning toy top in the earth’s
gravitation field), at a more fundamental level quantum mechanics should be used for
NMR. The phenomena of multiple-quantum coherence (MQC) not only provides a nice
demonstration of the true quantum mechanical nature of NMR, applications of various
MQC techniques also reveal many interesting structural and functional information in
MRS and MRI...

ISMRM 2008 DDF/iMQC

Here are the iMQC/DDF related abstracts that I found. Please email me if I missed one (especially yours!) corum@cmrr.umn.edu

Hopefully you, or a colleague has access to the login.

Curt

______________________________________

1407.
Intermolecular Zero-Quantum Coherence Imaging in Structured Samples
Bernard Siow1, Li Sun1, Andrew M. Blamire1
1Newcastle University, Newcastle upon Tyne, UK

Intermolecular multiple quantum coherence imaging sequences have recently been shown to provide a fundamentally different contrast mechanism to conventional MRI. A numerical study of intermolecular zero-quantum coherence imaging has shown sensitivity to susceptibility gradients at selected distance scales. In this study, an iZQC sequence was implemented and iZQC signal verified. The sequence was used to investigate sensitivity to susceptibility gradients at selected distance scales in structured samples. Images show contrast in areas where susceptibility gradients are present. Furthermore, contrast was modulated by the distance scale selected. Further results suggest that contrast is modulated by specific resonant frequency difference at distance scale selected.

1454.
Fast Relaxation Induced by SPIO Compromises Contrast from Intermolecular Double–quantum Coherence in CRAZED–MRI
Elvira Mehlin1, Stefan Kirsch1, Peter Bachert1
1German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany

The CRAZED sequence permits detection of signal generated by intermolecular double–quantum coherence (iDQC). When applied to 1H MRI, a novel type of contrast is obtained, in particular, a positive contrast when superparamagnetic iron oxide particles (SPIOs) are present. We demonstrate that the high T1–relaxivity of SPIOs can cause spurious signal in CRAZED MRI which cannot be attributed to iDQC.


1458.
Optimization of Parameters for the Distant Dipolar Field Signal Acquired in CRAZED-Multiecho Pulse Sequence
Chung Ki K. Wong1, Jianhui Zhong1
1University of Rochester, Rochester, New York, USA

The decrease of dipolar signal with refocusing pulses of finite duration in a CRAZED-multiecho acquisition was investigated previously. It was found that the rephasing of the dipolar signal during the refocusing pulses in the multiecho sequence depends substantially on the phase of the pulses. In this abstract, the total signal acquired from the multiecho sequence was optimized with the parameters of the sequence. The results show that the attenuation of the signal due to the finite duration of the refocusing pulses can be compensated with a longer τ2 and a proper choice of the phase of the pulses.


1562.
Time-Zero Signal Truncation in CRAZED Experiments Due to Rephasing Gradient Delays Leads to Incorrect Frequency-Domain Lineshapes
Stefan Kirsch1, William Edmund Hull1
1German Cancer Research Center (DKFZ), Heidelberg, Germany

In contrast to the decay of a conventional pulse-acquire FID, the time-domain signal from of a CRAZED-type pulse sequence for coherence order n > 1 increases from initially zero to a maximum, followed by an exponential decay. We show that the finite duration of the coherence rephasing gradient and any subsequent recovery delays lead to loss of the initial portion of the time-domain signal. This so-called “time-zero truncation artefact” results in an altered frequency-domain lineshape with incorrect integral and linewidth. Correct analysis requires time-domain fitting of right-shifted data.


1563.
In Vivo Human Whole Cerebellum MRS Under Severe Field Inhomogeneity with IDQC Method
Tianliang Gu1, 2, Zhong Chen1, Xiaoxu Liu1, Ling-chih Lin1, Jianhui Zhong1
1University of Rochester, Rochester, New York, USA

An intermolecular double quantum coherence (iDQC) 2D MRS pulse sequence was created and implemented on a 3T scanner for acquisition of human brain 1H spectra in regions susceptible to field inhomogeneity such as the cerebellum. High resolution 1D MRS could be obtained in a few minutes with iDQC over the whole cerebellum, whereas conventional single voxel 1D MRS was working successfully only when regions much smaller were covered. NAA/Cr and Cho/Cr measured with both methods in 5 healthy subjects agreed well with each other.


2361.
Enhanced BOLD Effect in the Mouse Brain with Fast CRAZED Imaging at High Magnetic Fields
Johannes Thomas Schneider, Cornelius Faber

A fast CRAZED sequence detecting the signal from intermolecular multiple-quantum coherences (iMQC) was implemented at 17.6 T to observe the BOLD effect in the mouse brain. Signal readout as echo train employing a four-step phase cycle for the refocusing pulses and an intensity-ordered k-space sampling allowed for acquisition of CRAZED images in 30 seconds. In the CRAZED images the BOLD effect was more pronounced than in RARE images but smaller than in gradient echo images. Combination of iMQC with T2*-effects may provide larger signal changes than conventional BOLD methods.


3063.
Enhanced Contrast in CEST MRI Via Intermolecular Double Quantum Coherences
Shengchun Zhang1, Huijun Sun1, Zhong Chen1, Congbo Cai1, Jianhui Zhong2
1Xiamen University, Xiamen, People's Republic of China; 2University of Rochester, Rochester, New York, USA

A CEST imaging technique based on intermolecular double quantum coherence (iDQC) is proposed. Quantitative analysis and experiments in glucose agarose-gel phantoms demonstrate that, in CEST MRI, iDQC signal is more sensitive to RF saturation than the conventional SQC signal, and thus needs RF saturation pulses of lower power to achieve similar CEST image contrast. Consequently, the method can reduce the potential RF burning in clinic applications, and is expected to facilitate the study of the CEST effect in the system with exchangeable protons of low concentrations.


3125.
High-Resolution MR Spectroscopy in Inhomogeneous and Unstable Fields Via Intermolecular Zero-Quantum Coherences
Xi Chen1, Meijin Lin1, Tao Lin1, Zhong Chen1, Jianhui Zhong2
1Xiamen University, Xiamen, People's Republic of China; 2University of Rochester, Xiamen, New York, USA

A new iZQC pulse sequence with stroboscopic acquisition is designed to achieve high-resolution magnetic resonance spectroscopy in inhomogeneous and unstable fields. Primary results suggest potential applications for suppressions of motion-caused t1 noises and inhomogeneous broadenings in in vivo studies.


3186.
High Resolution NMR Spectra in Inhomogeneous Fields Via Intermolecular Multiple Quantum Coherences Without Coherence Selection Gradients
Zhong Chen1, Congbo Cai1, Yanqin Lin1, Shuhui Cai1, Jianhui Zhong2
1Xiamen University, Xiamen, People's Republic of China; 2University of Rochester, Rochester, New York, USA

Coherence selection gradient has been thought to be essential for high resolution NMR spectra in inhomogeneous field based on intermolecular multiple quantum coherences (iMQC). However, our experimental results show that it can be omitted if correct phase cycling is applied. This means that the measured line-width of high resolution spectral peaks is not determined by the dipolar correlation distance caused by coherence selection gradient, but only affected by the effects of diffusion and T2 relaxation. This result prompts us to reconsider the iMQC high resolution mechanism.


3188.
An Effective Fast Acquisition Scheme to Achieve High-Resolution MRS with J-Coupling Scaling Via Intermolecular Multiple-Quantum Coherences
Xi Chen1, Meijin Lin1, Jincan Chen1, Tao Lin1, Zhong Chen1
1Xiamen University, Xiamen, People's Republic of China

A series of intermolecular double-quantum filtered (iDQF) sequence with efficient solvent suppression and different scaling factors of J-coupling constants, named iDQF-HOMOGENIZED II (abbreviated as iDH2), are designed to achieve fast acquisition of high-resolution spectra in inhomogeneous fields. Experiments on swine brain tissues were performed to test the feasibility of the new method. The results suggest potential applications for in vivo spectroscopy.


3189.
A Flexible IMQC Method for Accurate Determination of J-Coupling Constants in Inhomogeneous Fields
Yanqin Lin1, Shuhui Cai1, Yuqing Huang1, Zhong Chen1, Jianhui Zhong2
1Xiamen University, Xiamen, People's Republic of China; 2University of Rochester, Rochester, New York, USA

An improved pulse sequence was developed to scale apparent J coupling constants by a scaling factor ranging theoretically from zero (completely decoupled) to infinity under inhomogeneous fields via intermolecular multiple-quantum coherences. Scaling up the apparent J coupling constants allows more accurate measurement of small J coupling constants, and a completely decoupled homonuclear spectrum can be of considerable help for improving signal separation and thus peak assignment in MRS. The resulting spectrum retains conventional high-resolution NMR spectral information.


3351.
Apparent Diffusion Behaviors Modulated by Distant Dipolar Field in Solution NMR
Shuhui Cai1, Guiping Shen1, Congbo Cai1, Zhong Chen1
1Xiamen University, Xiamen, People's Republic of China

A modified CRAZED sequence was designed to observe and characterize apparent diffusion behaviors of signals from intermolecular double-quantum coherences during the mixing period. It is found that their apparent diffusion behaviors are different from conventional single-quantum coherences, and different orientation of diffusion weighting gradients relative to coherence selection gradients results in different apparent diffusion behaviors. This indicates
that the apparent diffusion behavior is influenced by the distant dipolar field.


3647.
Enhancement of MT, CEST and NOE Contrast Via Intermolecular Multiple Quantum Coherences
Wen Ling1, Uzi Eliav1, Xu Yang2, Gil Navon1, Alexej Jerschow2
1Tel Aviv University, Israel; 2New York University, New York, New York, USA

We demonstrate that using intermolecular multiple-quantum coherences can enhance contrast in MTC/CEST/NOE experiments in proportion to (Mz/Mo)p, where Mz is the the saturated level of the z-component of the magnetization, Mo its value in equilibrium and l is the coherence order used. These methods are demonstrated on a series of glycosaminoglycan (GAG) samples, and also for a piece of bovine articular cartilage.

High-resolution NMR spectra in inhomogeneous fields utilizing the CRAZED sequence without coherence selection gradients

Congbo Cai, Yanqin Lin, Shuhui Cai, Zhong Chen, , and Jianhui Zhong

Journal of Magnetic Resonance
Article in Press, Corrected Proof

Abstract: Coherence selection gradients have been considered as indispensable for high-resolution NMR spectroscopy in inhomogeneous fields utilizing the CRAZED-type sequences. However, our experimental results demonstrate that these gradients can be omitted if an appropriate phase cycling is applied. The measured linewidth of reconstructing 1D high-resolution spectral peaks does not depend on the dipolar correlation distance determined by the coherence selection gradients, but is only affected by diffusion and T2 relaxation. This finding suggests the need to reconsider the mechanism for the iMQC-based high-resolution spectroscopy.

Keywords: High-resolution spectra; Intermolecular multiple-quantum coherences; Inhomogeneous fields; Dipolar correlation distance; Coherence selection gradients

Numerical simulations of motion-insensitive diffusion imaging based on the distant dipolar field effects

Tao Lin, Huijun Sun, Zhong Chen, Rongyi You, Jianhui Zhong
Magnetic Resonance Imaging 25 (2007) 1409–1416

Abstract
Diffusion weighting in MRI is commonly achieved with the pulsed-gradient spin-echo (PGSE) method. When combined with spinwarping
image formation, this method often results in ghosts due to the sample’s macroscopic motion. It has been shown experimentally
(Kennedy and Zhong, MRM 2004;52:1–6) that these motion artifacts can be effectively eliminated by the distant dipolar field (DDF)
method, which relies on the refocusing of spatially modulated transverse magnetization by the DDF within the sample itself. In this report,
diffusion-weighted images (DWIs) using both DDF and PGSE methods in the presence of macroscopic sample motion were simulated.
Numerical simulation results quantify the dependence of signals in DWI on several key motion parameters and demonstrate that the DDF
DWIs are much less sensitive to macroscopic sample motion than the traditional PGSE DWIs. The results also show that the dipolar
correlation distance (dc) can alter contrast in DDF DWIs. The simulated results are in good agreement with the experimental results
reported previously.
D 2007 Elsevier Inc. All rights reserved.

Keywords: DDF; Motion; Diffusion; Image contrast; Computer simulation

Functional MRI at 3T using intermolecular double-quantum coherence (iDQC) with spin-echo (SE) acquisitions

Functional MRI at 3T using intermolecular double-quantum coherence (iDQC) with spin-echo (SE) acquisitions
T. Gu, S. D. Kennedy, Z. Chen, K. A. Schneider and J. Zhong
Magnetic Resonance Materials in Physics, Biology and Medicine
Published online: 5 December 2007

Abstract

Object To reinvestigate the dependence of the signal and contrast on sequence parameters and tissue relaxation times for intermolecular double-quantum coherence (iDQC) signals, and to explore the possibility to use a spin-echo (SE)-iDQC sequence for detecting activation signals at 3T.

Materials and methods Brain activations were detected in five human volunteers in a visual simulation study using a SE-iDQC sequence, in addition to a GE-iDQC and a conventional single-quantum coherence (SQC) blood-oxygenation-level-dependent (BOLD) sequence. A brain phantom was also used for some quantitative measurements.

Results By choosing an optimal echo time TE (~T2) and iDQC evolution time τ(~20 ms), robust brain activations were detected using the SE-iDQC sequence, in addition to the GE-iDQC and a conventional single-quantum coherence (SQC) BOLD sequence. A higher percentage signal change due to activation was observed for both the iDQC-based measurements in comparison to the conventional SQC acquisition.

Conclusion Even though a phenomenological analysis consistent with the experimental results was provided, a detailed model is still needed for the contrast mechanism at microscopic level to guide potential applications of brain functional imaging based on the SE-iDQC.

Keywords fMRI - Intermolecular double-quantum coherence (iDQC) - Distant dipolar field (DDF) - Spin echo (SE)

Thanks to Andreas Schaefer for sending...cac

Enhancement of magnetization transfer effects by inter-molecular multiple quantum filtered NMR

Uzi Eliav^a and Gil Navon^{, a,
a}School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel
Received 10 May 2007. Available online 28 September 2007.

Abstract

There are a number of methods that give MRI contrasts based on changes of the water M_z magnetization as a result of magnetization transfer to macromolecules. In the present work we report that a combination of these methods with inter-molecular multiple quantum coherences (iMQC) gives enhanced effects. For the magnetization transfer contrast (MTC) method an effect of (M_z/M₀) becomes (M_z/M₀)^l where l is the rank of the tensors constituting the iMQC. A similar trend was found upon combining iMQC with the Goldman–Shen experiment. It is pointed out that the method is general for all magnetization transfer methods, including the nuclear Overhauser effect.

Keywords: iMQC; Intermolecular dipolar interaction; Magnetization transfer; MTC; Goldman–Shen

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics
M. E. Hayden,1 E. Baudin,2 G. Tastevin,2 and P. J. Nacher2

1Physics Department, Simon Fraser University, 8888 University Drive, Burnaby BC, Canada V5A 1S6
2Laboratoire Kastler Brossel, Ecole Normale Supérieure; CNRS; UPMC; 24 rue Lhomond, F75005 Paris, France
Phys. Rev. Lett. 99, 137602 (2007)
(Received 23 April 2007; published 27 September 2007)

We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid ³He-⁴He mixtures through effective inversion of long-range dipolar interactions. These experiments, which involve using magic sandwich NMR pulse sequences to generate spin echoes, probe the spatiotemporal development of turbulent spin dynamics and promise to serve as a versatile tool for the study and control of dynamic magnetization instabilities. We also show that a repeated magic sandwich pulse sequence can be used to dynamically stabilize modes of nuclear precession that are otherwise intrinsically unstable. To date, we have extended the effective precession lifetimes of our magnetized samples by more than three orders of magnitude.

(Thanks to Louis Bouchard for sending...Curt)

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

Andreas Schäfer 1 2, Harald E. Möller 1 *

1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany 2University of Nottingham, School of Physics and Astronomy, Sir Peter Mansfield Magnetic Resonance Centre, University Park, Nottingham, United Kingdom

email: Harald E. Möller (moeller@cbs.mpg.de)

^*Correspondence to Harald E. Möller, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany

Keywords

BOLD contrast • correlation distance • distant dipolar field • intermolecular double-quantum coherence (iDQC)

Abstract

A functional MRI (fMRI) study with visual stimulation of healthy subjects was performed at 3T exploiting intermolecular double-quantum coherences. The correlation distance, dc, was varied between 60 and 300 m for different evolution times, . Robust activation was obtained in all experiments with average signal changes ([bar S2 ]) = 8.4 ± 0.7% and 9.4 ± 0.8% for = 15 and 20 ms, respectively) exceeding those normally associated with conventional blood oxygen level-dependent (BOLD) fMRI. Relaxation-rate changes (R2 = 0.33 ± 0.36 s-1 and R2* = 0.77 ± 0.54 s-1) were similar to those commonly obtained for the extravascular BOLD effect. The number of activated voxels increased with increasing dc until a plateau was reached at 120 m. Similar trends were observed for the activation-induced percent signal change and for the maximal Z-scores. These effects were quantitatively explained by a reduced sensitivity at short dc due to increasing signal attenuation related to diffusion and an increasing amount of signal fluctuations in the fMRI time series due to imperfect suppression of unwanted coherence pathways. Consistent indications of a preferential selection of susceptibility changes in blood vessels of a particular size were not obtained. Magn Reson Med 58:696-704, 2007. © 2007 Wiley-Liss, Inc.

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Received: 16 March 2007; Revised: 30 July 2007; Accepted: 6 August 2007

Assessing signal enhancement in distant dipolar field-based sequences

Wilson Barros Jr., Daniel F. Gochberg and John C. Gore

Abstract
The possibility of improving the signal-to-noise efficiency of NMR signal refocused by long-range dipolar interactions has been discussed recently [Branca et al., JMR 187 (2007) 38-43]. For systems where T1<< T2, by including an extra radio-frequency pulse in a standard CRAZED sequence, it is possible to increase the available signal by exploiting its sensitivity to T1 relaxation. Here, we use analytical calculations to investigate the source of this improved signal and determine the maximum enhancement provided by the method.

Apparent Longitudinal Relaxation in Solutions with Intermolecular Dipolar Interactions and Slow Chemical Exchange

Shengchun Zhang, Xiaoqin Zhu, Zhong Chen, Shuhui Cai and Jianhui Zhong

Abstract
A modified CRAZED sequence with selective inversion before excitation was designed to investigate the longitudinal relaxation under the effects of slow chemical exchange and distant dipolar interactions in highly polarized spin systems. Analytical expressions for the apparent longitudinal relaxation time of such systems were derived from a combination of the dipolar field theory and product operator formalism. The result shows that the signal intensity follows a multi-exponential function of the inversion-recovery time. Experimental results support the theoretical predictions.

Finite Element Formulation of the Bloch Equations with Dipolar Field Effects

Louis-S. Bouchard
(Submitted on 24 Jun 2007)
arXiv.org

A Galerkin finite element (FEM) formulation for the Bloch equations with dipolar field is presented which makes possible the derivation of weak solutions to the Bloch equations. The FEM formulation has the advantage that the equations of motion are local in real space, eliminating the global truncation errors associated with calculations of the dipolar field in Fourier space. The dipolar field and other geometric parameters are calculated only once, before the simulation, and used as an initial condition rather than re-calculated at every time step of some numerical integration.

Numerical simulations of contribution of chemical shift in novel magnetic resonance imaging

Huijun Sun, Tao Lin, Shuhui Cai and Zhong Chen
Lecture Notes in Computer ScienceVolume 4222/2006
Advances in Natural Computation

Abstract
Contribution of chemical shift to intermolecular multiple-quantum coherence (iMQC) imaging signals in two-component systems was simulated and discussed using an efficient numerical algorithm based on the Bloch equations with an additional nonlinear term describing distant dipolar field. Numerical simulation switches back and forth between real and Fourier spaces to handle dipolar field effects in three-dimensional sample. The iMQC signals of each component of two-component systems can be obtained respectively when the second pulse of the CRAZED pulse sequence is selective. Simulation results show that chemical shift provides an edge detection method to regions containing spins with chemical shift offset and selected by the second RF pulse, and different gray value is related to different chemical shift in detected regions. These results indicate that chemical shift may provide new imaging information helpful for iMQC magnetic resonance imaging.

Multiple quantum correlated spectroscopy revamped by asymmetric z-gradient echo detection signal intensity as a function of the read pulse flip angle

Bin Jiang, Huili Liu, China Maili Liu, Chaohui Ye, and China Xi-an Mao
J. Chem. Phys. 126, 054502 (2007)

(Received 28 August 2006; accepted 5 December 2006; published online 1 February 2007)

Heteronuclear multiple quantum (n=±0 and n=±2) correlated spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED) experiments were performed on the spins ³¹P and ¹H in a H₃PO₄ solution in order to determine the optimum flip angle for the read pulse. It has been shown that for the negative quantum signals, the maximum signals appear at =0, and for the positive quantum signals, the maximum signals appear at =. The CRAZED signals were compared to the single quantum signals in two-pulse two-gradient experiments. It is found that the CRAZED signals can also be distinguished into gradient echoes and spin echoes. The gradient-echo-type CRAZED signal requires =0 and the spin-echo-type CRAZED signal requires = for maximum echo intensities, in the same way as in single quantum experiments. ©2007 American Institute of Physics

Simultaneous acquisition and effective separation of intermolecular multiple-quantum signals of different orders

Xiaoqin Zhu, Song Chen, Zhong Chen, Shuhui Cai and Jianhui Zhong
Chemical Physics Letters
Volume 438, Issues 4-6, 20 April 2007, Pages 308-314

Abstract
A three-pulse sequence was designed to simultaneously acquire intermolecular multiple-quantum coherence (iMQC) signals of coherence order n = 2, 1, 0, −1, −2. Analytical expressions were derived from modified Bloch equations. Signal of a specific order was obtained by optimal combinations of data from different acquisition steps. This allows a time saving of 5/7 compared to the phase cycling designs targeted for individual coherence orders. The method also results in pure iMQC signal of all the above five orders which are insensitive to radio-frequency flip angle errors, in contrast to some previous methods. Theoretical predictions are supported by the experimental observations and numerically simulated results.

Magnetic resonance microscopic imaging based on high-order intermolecular multiple-quantum coherences

Jee-Hyun Cho, Sangdoo Ahn, Chulhyun Lee, Kwan Soo Hong, Kee-Choo Chung, Suk-Kyu Chang, Chaejoon Cheong and Warren S. Warren
Magnetic Resonance Imaging
Article in Press, Corrected Proof

Abstract

Most imaging studies using intermolecular multiple-quantum coherences (iMQCs) have focused on the two-spin dipolar interactions — zero and double quantum coherences. Here, we report the results of various experimental studies to assess the feasibility of magnetic resonance microscopy with high-order iMQCs in model systems at 7 and 14 T. Experimental results demonstrated that the iMQC microscopic images with high coherence orders are readily observable at high field and have unique contrast depending on the sample microstructure and coherence order.

Keywords: Intermolecular multiple-quantum coherence; iTQC; iQQC; MR microscopy

Signal enhancement in CRAZED experiments

Signal enhancement in CRAZED experiments
Rosa T. Branca, Gigi Galiana and Warren S. Warren
Journal of Magnetic Resonance
Article in Press, Corrected Proof

Many of the promising applications of the CRAZED (COSY Revamped with Asymmetric Z-gradient Echo Detection) experiments are in biomedical and clinical technologies. In tissue, however, signal from the typical CRAZED experiment is largely limited by transverse relaxation. When relaxation is included, the maximum achievable signal from a prototypical CRAZED sequence, in the linear regime, is proportional to T2/τd. This means that for samples with a short T2, as encountered in vivo, signals from intermolecular multiple-quantum coherences (iMQCs) reach very diminished signal intensities. While relaxation is generally regarded as a fundamental constraint, we show here that when T2 is short but T1 is long, as in tissue, there are simple sequence modifications that can increase signal beyond the T2 limit. To better utilize the available signal intensity from iMQCs we propose a method to substitute part of the transverse magnetization with the longitudinally modulated magnetization. In this paper we show, with both simulations and experimental results, that in the presence of strong transverse relaxation the standard CRAZED scheme is not the optimal method for observing iMQCs, and can be improved upon with simple modifications.

Keywords: CRAZED; iZQC; iDQC; Dipolar demagnetization time

Gradient-echo and CRAZED imaging for minute detection of Alzheimer plaques in an APPV717I × ADAM10-dn mouse model

Cornelius Faber, Benjamin Zahneisen, Frank Tippmann, Anja Schroeder, Falk Fahrenholz
Magnetic Resonance in Medicine
Published Online: 27 Mar 2007

Different strategies to visualize amyloid plaques with MRI at 17.6 Tesla were investigated in a novel mouse model of Alzheimer's disease (AD). Large iron-containing plaques were observed in the thalamus, but cortical plaques did not show iron deposits. Plaques in the thalamus were visualized in vivo with the use of low-resolution, 3D gradient-echo (GRE) imaging in 82 s, and with 94-m resolution in 34 min. The feasibility of obtaining bright contrast from plaques using the COSY revamped with asymmetric z-GRE detection (CRAZED) technique was investigated in experiments on fixed brains. The original CRAZED approach provided reduced signal near the plaques (similarly to GRE imaging) and additionally emphasized small structures in the brain. In CRAZED images acquired with mismatched gradients, elevated signal near the plaques was obtained, while background signal was suppressed almost to the noise level. Bright-contrast images were acquired in 2.6 min with the use of a 2D GRE sequence with slightly mismatched slice refocusing gradients. For future detection of plaques in patients, such bright-contrast visualization protocols may be of particular value when contrast agents that allow labeling of early plaques with iron oxide nanoparticles become available. Magn Reson Med 57:696-703, 2007. © 2007 Wiley-Liss, Inc.

Indirect detection of NMR via geometry-dependent dipolar fields, revisited

Journal of Magnetic Resonance
In Press, Accepted Manuscript, Available online 1 March 2007,
Wei Dong and CA. Meriles

We explore the dipolar interactions between two separate nuclear spin ensembles in a mixture containing oil and water. Here we expand initial results (C.A. Meriles and W. Dong, J. Magn. Reson. 181, 331 (2006)) to the case in which both systems have the shape of flat, stacked disks. We find that - spite of the strong inhomogeneity of thecoupling dipolar field - the signal encoded in one of the components can be made approximately proportional to the magnetization in the other. This allows us to use one of these systems as a ‘sensor’ to indirectly reconstruct the resonance spectrum or to determine the relaxation time of the ‘sample’ system. In the regime in which dipolar interactions are sufficiently strong, our method can be set to scale-up weaker signals in a non-linear fashion, which, potentially, could allow one to introduce contrast or to improve detection sensitivity of less magnetized samples.

Theoretical studies of the effect of the dipolar field in multiple spin-echo sequences with refocusing pulses of finite duration

Chung Ki Wong, Scott D. Kennedy, Edmund Kwok and Jianhui Zhong

Journal of Magnetic Resonance
Article in Press, Corrected Proof

It has been observed recently that the finite duration of refocusing rf pulses in a multiecho acquisition of the signal formed under the influence of the dipolar field leads to significant signal attenuation [S. Kennedy, Z. Chen, C.K. Wong, E.W.-C. Kwok, J. Zhong, Investigation of multiple-echo spin-echo signal acquisition under distant dipole–dipole interactions, Proc. Int. Soc. Magn. Reson. Med. 13 (2005) 2288]. Hereto, we quantify the phenomenon by evaluating analytically the influences of both the distant dipolar field (DDF) and transverse relaxation T2 on the magnetization in a multiecho pulse sequence based on correlation spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED). Analytic expressions for the magnetization were obtained, which demonstrate explicitly the origin of rephased signal in the presence of the finite π pulses in the multiecho train. The expressions also explain the effects of the DDF and T2 during the refocusing pulses on the signal strength, and show the substantial signal dependence on the phase of the rf pulses. We show that when the DDF effect during the pulse is canceled, the signal rises primarily during the free evolution time in the acquisition period. This elucidates the signal attenuation when the rf pulses cover a significant proportion of time in the sequence. In addition, we performed an optimization on the number of refocusing pulses that maximizes the total acquired signal using parameters for water, brain white matter, and muscle. We found that maximal signal-to-noise ratio is obtained when the pulse duration approximately equals the free evolution time in the samples with a wide range of T2.

Keywords: Distant dipolar field; Multiple spin-echo sequence; Finite pulse; Intermolecular double-quantum coherence

Yahoo Group ddf_imqc

Here is the link to the new yahoo discussion group.

This is to facillitate more interactive technical discussion on DDF and iMQC related magnetic resonance.

Curt

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

Magnetic Resonance in Medicine
Early View (Articles online in advance of print)
David Z. Balla, Gerd Melkus, Cornelius Faber

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 (SNR) efficiency. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc.

Sensitivity to local dipole fields in the CRAZED experiment: An approach to bright spot MRI

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Sensitivity to local dipole fields in the CRAZED experiment: An approach to bright spot MRI

Cornelius Faber, Carolin Heil, Benjamin Zahneisen, David Z. Balla and Richard Bowtell
Journal of Magnetic Resonance
Article in Press, Corrected Proof

Local dipole fields such as those created by small iron-oxide particles are used to produce regions of low intensity (dark contrast) in many molecular magnetic resonance imaging applications. We have investigated, with computer simulations and experiments at 17.6 T, how the COSY revamped with asymmetric z-gradient echo detection (CRAZED) experiment that selects intermolecular double-quantum coherences can also be used to visualize such local dipole fields. Application of the coherence-selection gradient pulses parallel to the main magnetic field produced similar, dark contrast as conventional gradient echo imaging. Application of the gradient along the magic angle leads to total loss of signal intensity in homogeneous samples. In the presence of local dipole fields, the contrast was inverted and bright signals from the dipoles were observed over a very low background. Both simulations and experiments showed that the signal strongly decreased when a phase-cycle suppressing single-quantum coherences was employed. Therefore, we conclude that most of the signal comes from directly refocused magnetization or intermolecular single-quantum coherences. Finally, we demonstrate that bright contrast from local dipole fields can also be obtained, when the pair of coherence-selection gradient pulses is deliberately mismatched. Both methods allowed visualization of local dipole fields in phantoms in experimental times of about 3 min.