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The increased signal-to-noise ratio provided by dynamic nuclear polarization presents new opportunities for the in vivo investigation of metabolism, in particular when combined with imaging. At the same time the nonrecoverable nature of the magnetization poses challenges on the data acquisition. This chapter describes the basic concepts of encoding the spatial information in magnetic resonance imaging and chemical shift imaging and then presents acquisition methods that permit the spatially and temporally resolved measurement of the metabolite signals within the limited lifetime of the hyperpolarized signal amplification.

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd.

To date, spatial encoding for MRI is based on linear X, Y and Z field gradients generated by dedicated X, Y and Z wire patterns. We recently introduced the dynamic multi-coil technique (DYNAMITE) for the generation of magnetic field shapes for biomedical MR applications from a set of individually driven localized coils. The benefits for B0 magnetic field homogenization have been shown, as well as proof of principle of radial and algebraic MRI. In this study the potential of DYNAMITE MRI is explored further and the first multi-slice MRI implementation in which all gradient fields are purely DYNAMITE based is presented. The obtained image fidelity is shown to be virtually identical to that of a conventional MRI system with dedicated X, Y and Z gradient coils. Comparable image quality is a milestone towards the establishment of fully functional DYNAMITE MRI (and shim) systems.

Purpose Intermolecular multiple quantum coherences (iMQCs) are a source of MR contrast with applications including temperature imaging, anisotropy mapping, and brown fat imaging. Because all applications are limited by signal-to-noise ratio (SNR), we developed a pulse sequence that detects intermolecular zero quantum coherences with improved SNR. Methods A previously developed pulse sequence that detects iMQCs, HOMOGENIZED with off resonance transfer (HOT), was modified with a multi-spin echo spatial encoding scheme (MSE-HOT). MSE-HOT uses a series of refocusing pulses to generate a stack of images that are averaged in postprocessing for higher SNR. MSE-HOT performance was quantified by measuring its temperature accuracy and precision during hyperthermia of ex vivo red bone marrow samples. Results MSE-HOT yielded a three-fold improvement in temperature precision relative to previous pulse sequences. Sources of improved precision were 1) echo averaging and 2) suppression of J-coupling in the methylene protons of fat. MSE-HOT measured temperature change with an accuracy of 0.6°C. Conclusion MSE-HOT improved the temperature accuracy and precision of HOT to a level that is sufficient for hyperthermia of bone marrow. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

Existing open magnetic resonance imaging (MRI) systems use biplanar gradient coils for the spatial encoding of signals. We propose using novel oval gradient coils for an open vertical-field MRI. We designed oval gradients for a 0.3 T open MRI system and showed that such a system could outperform a traditional biplanar gradient system while maintaining adequate gradient homogeneity and subject accessibility. Such oval gradient coils would exhibit high efficiency, low inductance and resistance, and high switching capability. Although the designed oval Y and Z coils showed more heat dissipation and less cooling capability than biplanar coils with the same gap, they showed an efficient heat-dissipation path to the surrounding air, which would alleviate the heat problem. The performance of the designed oval-coil system was demonstrated experimentally by imaging a human hand.

A cylindrical head gradient insert for human imaging with non-linear spatial encoding magnetic fields (SEMs) has been designed, optimized and successfully integrated with a modified 3T clinical MR system. This PatLoc (parallel acquisition technique using localized gradients) SEM coil uses SEMs that resemble second-order magnetic shim fields, but with much higher amplitude as well as the possibility for rapid switching. This work describes the optimization of a coil design and measurement methods to characterize its SEMs, induced self-eddy currents and concomitant fields. Magnetic field maps of the SEMs are measured and it is demonstrated that the induced self-eddy current magnetic fields are small and can be compensated. A method to measure concomitant fields is presented and those fields are compared to simulated data. Finally, in vivo human images acquired using the PatLoc system are presented and discussed.

Two new pulse sequences via Hadamard frequency encoding and spatial encoding are proposed to achieve high-resolution intermolecular double-quantum coherence correlation spectroscopy (iDQC-COSY) in inhomogeneous fields within a few scans. Hadamard encoding and spatial encoding are utilized to reduce acquisition time, while iDQC is used to remove the influence of inhomogeneous fields. Two Hadamard encoded schemes, namely, solute Hadamard encoding and solvent Hadamard encoding, are different in the two sequences. Detail analyses of the advantages and disadvantages of the two sequences are carried out. Acquisition times are both shortened by orders of magnitude. Experiments are performed to show their efficiencies.

Two 1-D phase-encode sequences for T 2 mapping, namely CPMG-prepared SPRITE and spin-echo SPI, are presented and compared in terms of image quality, accuracy of T 2 measurements and the measurement time. The sequences implement two different approaches to acquiring T 2 -weighted images: in the CPMG-prepared SPRITE, the T 2 -weighting of magnetization precedes the spatial encoding, while in the spin-echo SPI, the T 2 -weighting follows the spatial encoding. The sequences are intended primarily for T 2 mapping of fluids in porous solids, where using frequency encode techniques may be problematic either due to local gradient distortions or too short T 2 . Their possible applications include monitoring fluid-flow processes in rocks, cement paste hydration, curing of rubber, filtering paramagnetic impurities and other processes accomplished by changing site-specific T 2 .

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, 2010. © 2010 Wiley-Liss, Inc.

The ability to accelerate the spatial encoding process during a chemical shift imaging (CSI) scan of hyperpolarized compounds is demonstrated through parallel imaging. A hardware setup designed to simultaneously acquire 13C data from multiple receivers is presented here. A system consisting of four preamplifiers, four gain stages, a transmit coil, and a four receive channel rat coil was built for single channel excitation and simultaneous multi-channel detection of 13C signals. The hardware setup was integrated with commercial scanner electronics, allowing the system to function similar to a conventional proton multi-channel setup, except at a different frequency. The ability to perform parallel imaging is demonstrated in vivo. CSI data from the accelerated scans are reconstructed using a self-calibrated multi-spectral parallel imaging algorithm, by using lower resolution coil sensitivity maps obtained from the central region of k-space. The advantages and disadvantages of parallel imaging in the context of imaging hyperpolarized compounds are discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Pulsed Field Gradients (PFGs) have become ubiquitous tools not only for Magnetic Resonance Imaging (MRI), but also for NMR experiments designed to study translational diffusion, for spatial encoding in ultra-fast spectroscopy, for the selection of desirable coherence transfer pathways, for the suppression of solvent signals, and for the elimination of zero-quantum coherences. Some of these experiments can only be carried out if three orthogonal gradients are available, while others can also be implemented using a single gradient, albeit at some expense of performance. This paper discusses some of the advantages of triple- with respect to single-gradient probes. By way of examples we discuss (i) the measurement of small diffusion coefficients making use of the long spin-lattice relaxation times of nuclei with low gyromagnetic ratios gamma such as nitrogen-15, and (ii) the elimination of zero-quantum coherences in Exchange or Nuclear Overhauser Spectroscopy (EXSY or NOESY) experiments, as well as in methods relying on long-lived (singlet) states to study very slow exchange or diffusion processes.

The main aim of this work is to present an overview of the nuclear quadrupole resonance (NQR) spectroscopy capabilities for solid state imaging and detection of illegal substances, such as explosives and drugs. We briefly discuss the evolution of different NQR imaging techniques, in particular those involving spatial encoding which permit conservation of spectroscopic information. It has been shown that plastic explosives and other forbidden substances cannot be easily detected by means of conventional inspection techniques, such as those based on conventional X-ray technology. For this kind of applications, the experimental results show that the information inferred from NQR spectroscopy provides excellent means to perform volumetric and surface detection of dangerous explosive and drug compounds.

When magnetic resonance tomography is used in clinical practice a large number of different imaging techniques (sequences) are applied for the imaging. Despite this large number of sequences, which is often difficult to keep track of, all types of sequence work largely according to the same or very similar principles. In this continuing education course these principles are elaborated and the elements that make up a sequence are explained. These elements working together make it possible to assign the signals received from the receiver coil to their point of origin within the body. This first part of the further training is devoted largely to basic observations on spatial encoding of the signals, but also to the difference between 2D and 3D sequences. In addition, the techniques generally used in clinical practice for multislice imaging with 2D images are discussed in some detail.

La spectroscopie multidimensionnelle joue des roles essentiels dans la resonance magnetique moderne. Elle apporte une amelioration de la resolution, sans laquelle de nombreuses applications en chimie organique et inorganique resteraient impossibles ; elle est utilisee comme outil de base dans la determination et l'elucidation de structures biologiques complexes et fait partie integrante du protocole de formation de l'image en IRM. La presente revue decrit une recente approche que nous avons developpee, permettant l'acquisition de donnees RMN 2D completes en une seule acquisition continue. A condition que le signal soit suffisamment fort, le temps d'acquisition des experiences de RMN multidimensionnelle peut etre raccourci de plusieurs ordres de grandeur. Cette nouvelle methodologie est compatible avec les sequences d'impulsions multidimensionnelles (COSY, TOCSY, HSQC, IRM) et peut etre mise en oeuvre avec un equipement informatique conventionnel. Le codage spatial des interactions RMN, qui constitue le nouveau principe de ce protocole RMN utra-rapide, est discute et des exemples de ses performances sont donnes, avec une variete d'acquisitions par IRM et RMN 2D homo- et heteronucleaire. Pour citer cet article: L. Frydman, C. R. Chimie 9 (2006).

In order to decrease the total duration of 2D J-resolved 2D spectroscopic imaging, a fast spatial encoding by spiral trajectories was developed and added to a 2D J-resolved pulse sequence. Data were acquired on a rat brain in vivo at 7 T. Total acquisition time was about 42 min for a voxel size of 27 μl. A signal-to-noise ratio of 16.3 was measured on the NAA peak, enabling the reconstruction of metabolite maps for the main peaks. To cite this article: B. Hiba, A. Ziegler, C. R. Chimie 7 (2004).

In classical MRI phased-array design, optimal coil overlapping is used to minimize coupling between nearest-neighbor coils, and low input impedance preamplifiers are used to isolate the relatively weak coupling between non-nearest neighbors. However, to make the complex sensitivities of phased-array coils sufficiently distinct in parallel spatially-encoded MRI, it is desirable to have no overlapping between coils. Also, if phased arrays are used as transmit coils in MRI, one can no longer rely on the low input impedance of the preamplifiers for decoupling. Here a coupling and decoupling theory is introduced to provide a better understanding of the relations between coupled and uncoupled signals in the MRI phased array, and to offer a new method for decoupling phased-array coils without overlapping the nearest coil pairs. The new decoupling method is based on the assumption that any n-element phased array can be decoupled by a 2n-port interface system between phased array and preamplifiers. The detailed analysis and the experimental results show that a four-port interface can be used to decouple a two-element phased array. Furthermore, the four-port interfaces can serve as building blocks to construct a 2n-port decoupling interface. This new method allows one to place the coil elements anywhere that could optimize parallel spatial encoding without concern for coupling between the coils. The method can also be used for phased-array transmit coils.

13C-homodecoupling in F1: Eliminating homonuclear 13C scalar couplings is a challenging NMR problem when enriched compounds are studied by NMR. The 13C-homodecoupled heteronuclear single-quantum correlation (HSQC) experiment (BBHD-HSQC) relies on the Zangger–Sterk pulse sequence element to combine spatial encoding of the chemical shift with the refocusing of couplings. The sequence is applied to fully enriched 13C cholesterol.

For conventional multiband encoding techniques such as Hadamard encoding, scan time scales linearly with the number of slices encoded simultaneously. In this work, a new multiband encoding technique called partial discrete Fourier transform (PDFT) encoding is introduced, which overcomes this restriction. This technique incorporates the principle of partial Fourier imaging, allowing the tradeoff of SNR and imaging time without changing the number of slices. The theory behind PDFT encoding and its inherent sensitivity to phase errors are outlined. The theory was validated through simulations, showing that phase errors result in degraded slice localization. The feasibility of PDFT encoding of 12 slices was tested with experimental excitation profile measurements and heart images of a human subject using commercial MRI equipment. Imaging time was reduced to 66% with SNR reduced to 82%. Magn Reson Med 45:118-127, 2001.

Echo planar spectroscopic imaging (EPSI) allows for mapping one spatial dimension and the spectroscopic dimension in a single readout. Modern clinical magnetic resonance imaging scanners are becoming widely equipped with echo planar imaging gradient capabilities. Thus there exists an enormous potential for EPSI to facilitate clinical magnetic resonance spectroscopy. Here, a pedagogical analysis of how the spectral and spatial encoding occur within EPSI is provided along with demonstrations of the technique and a discussion of the inherent signal-to-noise limitations. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 213–237, 2001

Recently, several partially parallel acquisition (PPA) techniques have been presented which use spatial information inherent in an RF coil array to reconstruct an image from a reduced set of phase encoding steps. PPAs represent a change in paradigm for the RF coil designer since the focus for arrays to be used with PPAs is to optimize the spatial encoding that is provided by the array. One of the first practical implementations of PPA imaging was demonstrated using the SMASH technique. In this study, we present our results from the construction of the first array designed specifically for cardiac SMASH imaging. Additional design criteria are presented for SMASH arrays that are not considered in conventional array design. Using these design criteria, a four-element array was constructed and then tested in SMASH imaging experiments in the heart. This array has been used in all of our initial cardiac and head SMASH studies with good results.

Magnetorelaxometry (MRX) is a non-invasive method for the specific quantification of magnetic nanoparticles (MNP). Here, we investigate experimentally the reconstruction of the MNP concentration in an extended volume. A phantom with varying but known MNP distribution was subsequently magnetized by 48 planar coils at different locations. The MRX signal was measured using the PTB 304 SQUID-magnetometer system. The inverse problem was solved by means of a non-negative least squares (NNLS) algorithm and compared to a minimum norm estimation (TSVD-MNE). The reconstruction by NNLS shows a deviation of the total MNP amount of less than 3 % (10% by TSVD-MNE). Hence, adapted non-invasive MRX methods can reliable reconstruct the MNP content in extended volumes.

Solid state NMR imaging techniques based on magic echoes are reviewed. The theoretical background of magic echoes in general and their spatial encoding in particular is treated. The magic-echo imaging pulse sequences presently in use are described and discussed. Particular emphasis is devoted to those techniques, which allow the incorporation of spectroscopic or parameter-selective information. The applicability of these methods for the investigation of materials is demonstrated and perspectives for materials science are outlined.

A new method for fast data collecting in rotating-frame NQR imaging is reported. A single unidimensional spin-density profile is composed by this procedure, recording the evolution of the magnetization during the course of the nutation. Hence, a complete data set necessary for the reconstruction of a 1D profile is directly recorded by a single scan provided by a train of short and intense radiofrequency pulses. A reduction of one or even two orders of magnitude in the time necessary for data acquisition is achieved. One-dimensional profiles and 2D spin-density images of geometrically simple objects are compared, using data sets obtained by the present single-experiment and the previous multiexperiment methods.

During the past two decades nuclear magnetic resonance has revolutionized chemistry, biochemistry, biology and, more recently, diagnostic medicine. Nuclear magnetic resonance imaging, or mri as it is commonly called, is fundamentally different from x‐ray‐based techniques in terms of the principles of spatial encoding and mechanisms of signal and contrast generation involved. Mri has a far richer ultimate potential than any other imaging technique known today, and its technology and applications are still far from maturation, which may not occur until early in the 21st century.

Recently ultrafast techniques enable 2D NMR spectra to be obtained in a single scan. They have been successfully applied for 2D COSY, TOCSY, DOSY, HMQC, and J-resolved spectra. In this paper, two alternative ultrafast 2D COSY methods (g-COSY and gDQF-COSY) based on continuous constant-time phase-modulated spatial encoding were proposed. Theoretical expressions of the resulting signals were deduced. Experiments were performed to verify our theoretical analysis and the feasibility of the methods. Comparisons between the experimental results of our methods and those of the previous real-time phase-modulated spatial encoding method demonstrate that the signal-to-noise ratio and resolution of the 2D COSY spectra are improved, and a good 2D COSY spectrum is easier to achieve by using our methods.

Spatial encoding is a particular kind of spin manipulation that enables the acquisition of multidimensional NMR spectra within a single scan. This encoding has been shown to possess a general applicability and to enable the completion of arbitrary nD NMR acquisitions within a single transient. The present study explores its potential towards the acquisition of 2D DOSY spectra, where the indirect dimension is meant to encode molecular displacements rather than a coherent spin evolution. We find that in its simplest form this extension shows similarities with methods that have been recently discussed for the single-scan acquisition of this kind of traces; still, a number of advantageous features are also evidenced by the “ultrafast” modality hereby introduced. The principles underlying the operation of this new single-scan 2D DOSY approach are discussed, its use is illustrated with a variety of sequences and of samples, the limitations of this new experiment are noted, and potential extensions of the methodology are mentioned.

We present a spatial encoding technique for magnetic resonance force microscopy that allows for a much enhanced image acquisition rate. The technique uses multiplexing, based on spatial Hadamard encoding, to acquire several slices of the image simultaneously and at an undiminished signal-to-noise ratio. We demonstrate an improvement in imaging time by a factor of 7.6, and further advances can be expected.

NMR photography has gained significant attention as a method of storing and retrieving information using NMR spectroscopy. Among the commonly practiced methods the most important is the frequency encoding by use of a multi-frequency pulse on a liquid crystal molecule. We propose and demonstrate another robust method which relies on spatial encoding. Spatial information is mapped onto the spectrum, if excited and recorded in the presence of a gradient. The encoding is performed by applying a multi-frequency pulse in the presence of a gradient. The subsequent acquisition, under a gradient, helps storing this spatial information on a one-dimensional spectrum. Series of such spectra can also store two-dimensional patterns. This procedure is described and exemplified in this paper.

Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of 13 C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study. We report here on some initial experiments to demonstrate the feasibility of echo planar proton detected 13 C imaging using CYCLCROP based upon the PRAWN module, including the application of the technique to the measurement of transport and accumulation of 13 C-labelled sucrose in a castor bean seedling. Two methods that can be used to eliminate the effect of the J-splitting in the EP images are presented. In addition, a fast, image-based B1 field-mapping method which may be used to quantitatively map the low frequency RF field in a dual resonant ( 13 C/ 1 H) probe is presented. The technique utilises the above described imaging method, permitting fully quantitative, 64×64 axial field maps to be generated in about a minute. C � 2002 Elsevier Science (USA)

The theory and operation of a resonator which produces a uniform oscillating magnetic field gradient is described. When the resonator is operated at audio frequency, it will produce the oscillating magnetic field gradient required for use in spatial encoding in rapid acquisition magnetic resonance imaging.

Nuclear magnetic resonance (NMR) is the basic physical phenomenon in which certain nuclei absorb and emit radiofrequency (RF) radiation while in the presence of a magnetic field. The noninvasive nature of NMR techniques, including magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), has allowed explosive developments in biomedical applications since the late 1970s. MRI of protons is now a widely accepted clinical imaging technique, whereas MRS of various nuclei, including 31P, 1H, 13C, 23Na, and 19F, can provide a vast amount of metabolic and physiological information. MRI provides significant advantages over many other imaging techniques in terms of resolution, contrast, and its noninvasive nature. Although not as common in clinical medicine, MRS also provides valuable metabolic information that cannot be obtained by other techniques. This article reviews the fundamentals of spatial encoding, contrast, artifacts, and applications of MRI as well as some recent advances in the field. Some applications of biomedical MRS of various nuclei are also discussed.

The use of magnetic field gradients is important in many areas of high-resolution NMR spectroscopy. This article describes how gradients are generated, and outlines their use in high-resolution NMR. The main applications include coherence and coherence pathway selection, multiple-quantum editing and spoiling of magnetization. In addition, gradient pulses can be used to separate mixtures based on diffusion coefficients, for a variety of water suppression strategies, and for spatial encoding.

Almost 50 years ago, in 1946, the phenomenon of nuclear magnetic resonance (NMR) was discovered by F. Bloch and E.M. Purcell independently. The characteristic resonance signals of different structures were used as a physicochemical analytical tool. It took another 30 years to introduce the technique into medical imaging. P. Lauterbur was the first to apply additional linear magnetic fields to the system in order to achieve spatial encoding of the signals.

The mechanism of the fourfold signal loss during the cyclic polarization-transfer (CYCLPOT) sequence for lactate filtering is analyzed using the spin-product-operator formalism. Based on the results of the analysis, a new sequence, RECYCLPOT (refocused CYCLPOT), is proposed and experimentally tested for lactate filtering with full sensitivity and specificity. Lactate mapping is performed by spin filtering using the RECYCLPOT sequence prior to imaging by spatial encoding.

Proton nuclear magnetic resonance (NMR) signals may be obtained from the human body in such a way as to produce images of anatomical slices. The NMR signal is mapped in the selected slice by application of field gradients which provide spatial encoding. Excellent NMR images are now obtained which are useful in clinical practice. Introduction of NMR imaging into major hospitals is proceeding rapidly, with 10 commercial companies supplying the market; over 500 whole body systems have been installed worldwide. As a method of medical imaging NMR has the advantage that it uses no ionizing radiation and is therefore inherently safe; moreover, it gives sections in transverse, coronal, and sagittal planes with equal ease, and has good tissue contrast and pathological contrast arising from relaxation time differences. Contrast may be improved by use of contrast agents. Current trends suggest that before very long, whole-body NMR systems will be found in all major hospitals.