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Purpose To achieve rapid, low specific absorption rate (SAR) super-resolution imaging by exploiting the characteristic magnetization off-resonance profile in SSFP. Theory and methods In the presented technique, low flip angle unbalanced SSFP imaging is used to acquire a series of images at a low nominal resolution that are then combined in a super-resolution strategy analogous to non-linear structured illumination microscopy. This is demonstrated in principle via Bloch simulations and synthetic phantoms, and the performance is quantified in terms of point-spread function (PSF) and SNR for gray and white matter from field strengths of 0.35T to 9.4T. A k-space reconstruction approach is proposed to account for B0 effects. This was applied to reconstruct super-resolution images from a test object at 9.4T. Results Artifact-free super-resolution images were produced after incorporating sufficient preparation time for the magnetization to approach the steady state. High-resolution images of a test object were obtained at 9.4T, in the presence of considerable B0 inhomogeneity. For gray matter, the highest achievable resolution ranges from 3% of the acquired voxel dimension at 0.35T, to 9% at 9.4T. For white matter, this corresponds to 3% and 10%, respectively. Compared to an equivalent segmented gradient echo acquisition at the optimal flip angle, with a fixed TR of 8 ms, gray matter has up to 34% of the SNR at 9.4T while using a ×10 smaller flip angle. For white matter, this corresponds to 29% with a ×11 smaller flip angle. Conclusion This approach achieves high degrees of super-resolution enhancement with minimal RF power requirements.

Multi-task long-range autonomous driving in urban areas is a challenging task. Traditional methods are not applicable to situations with high-dimensional observations. Current reinforcement learning (RL) based algorithms are able to train agents to utilize high-dimensional signals for vehicle control and accomplish short-range tasks. However, current RL methods do not work well on multi-task long-range urban driving tasks. In this paper, we propose a novel Hierarchical-planning and Spatial-encoding-based Multi-task Reinforcement Learning (HSMRL) model for the autonomous driving problem in urban areas. For long-range tasks, global routes are planned in real-time based on the A* algorithm, and short-range tasks are constructed based on the global routes, through which the short-range tasks are regarded as sub-tasks of long-range tasks. Then the short-range task information is efficiently encoded using spatial encoding, and the short-range tasks are accomplished by RL algorithms. We also prove that under our settings, multiple autonomous driving tasks are capable of training a shared policy. Experiments show that our method can stably accomplish the multi-task long-range driving tasks and performs significantly better than the state-of-the-art methods.

Modern autonomous vehicles are commonly instrumented with radars for all-weather perception. Yet the radar functionality is limited to identifying the positions of reflectors in the environment. In this paper, we investigate the feasibility of smartening transportation infrastructure for the purpose of conveying richer information to automotive radars. We propose RoS, a passive PCB-fabricated smart surface which can be reconfigured to embed digital bits, and inform the radar much like visual road signs do to cameras. We design the RoS signage to act as a retrodirective reflector which can reflect signals back to the radar from wide viewing angles. We further introduce a spatial encoding scheme, which piggybacks information in the reflected analog signals based on the geometrical layout of the retroreflective elements. Our prototype fabrication and experimentation verifies the effectiveness of RoS as an RF ''barcode'' which is readable by radar in practical transportation environment.

This paper reviews two spatial encoding techniques for time-multiplexed recording front-ends. These techniques use bipolar and monopolar recordings, respectively, and are aimed to compress neural data taking advantage of the large spatial correlation of LFPs/ECoGs measured from nearby electrodes. The pros and cons of both architectures are analyzed and demonstrated with experimental results from a 32-channel time-multiplexed spatially-encoded neural front-end designed in 0.18 μm technology.

A differential laser Doppler velocimeter using 48-channel spatial encoded measurement points is proposed for dense cross-sectional velocity distribution measurements. An asymmetrical push–pull configuration and multiple photodiodes are employed to increase the number of the measurement points. The functionality of the proposed structure is experimentally demonstrated. The results indicate that a cross-sectional velocity distribution is successfully measured with the proposed structure.

Left atrial (LA) and atrial scar segmentation from late gadolinium enhanced magnetic resonance imaging (LGE MRI) is an important task in clinical practice. The automatic segmentation is however still challenging due to the poor image quality, the various LA shapes, the thin wall, and the surrounding enhanced regions. Previous methods normally solved the two tasks independently and ignored the intrinsic spatial relationship between LA and scars. In this work, we develop a new framework, namely AtrialJSQnet, where LA segmentation, scar projection onto the LA surface, and scar quantification are performed simultaneously in an end-to-end style. We propose a mechanism of shape attention (SA) via an implicit surface projection to utilize the inherent correlation between LA cavity and scars. In specific, the SA scheme is embedded into a multi-task architecture to perform joint LA segmentation and scar quantification. Besides, a spatial encoding (SE) loss is introduced to incorporate continuous spatial information of the target in order to reduce noisy patches in the predicted segmentation. We evaluated the proposed framework on 60 post-ablation LGE MRIs from the MICCAI2018 Atrial Segmentation Challenge. Moreover, we explored the domain generalization ability of the proposed AtrialJSQnet on 40 pre-ablation LGE MRIs from this challenge and 30 post-ablation multi-center LGE MRIs from another challenge (ISBI2012 Left Atrium Fibrosis and Scar Segmentation Challenge). Extensive experiments on public datasets demonstrated the effect of the proposed AtrialJSQnet, which achieved competitive performance over the state-of-the-art. The relatedness between LA segmentation and scar quantification was explicitly explored and has shown significant performance improvements for both tasks. The code has been released via https://zmiclab.github.io/projects.html.

Purpose Spatial encoding and shimming in MRI have traditionally been performed using dedicated coils that generate orthogonal spherical harmonic fields. The recently introduced multi-coil hardware has proven that MRI-relevant magnetic fields can also be created by a generic set of localized coils producing non-orthogonal fields. As a step towards establishing a purely multi-coil-based MRI field generation system, the feasibility of performing conventional Cartesian k-space encoding and echo-planar imaging (EPI), as well as concurrent encoding and shimming is demonstrated in this study. Methods We report the use of Dynamic Multi-Coil Technique (DYNAMITE) for combined Cartesian encoding and shimming, and EPI using a 48-channel multi-coil system. Experiments were performed on phantom objects and biological specimens in a 9.4 T pre-clinical scanner. Cartesian Fourier-encoded MRI and EPI were implemented whereby the magnetic fields required for encoding of the three orthogonal spatial dimensions were entirely based on linear combinations of multi-coil fields. Furthermore, DYNAMITE imaging was augmented by concurrent DYNAMITE shimming with the same hardware. Results DYNAMITE-based MR and echo-planar images were indistinguishable from those acquired with the conventional linear imaging gradients provided by the scanner. In experiments with concurrent DYNAMITE shimming and imaging, shim challenges that would result in extreme spatial distortion and signal loss were corrected very effectively with more than 92% signal recovery in case of extreme Z2 shim challenge that resulted in complete signal dephasing in most slices. Conclusions We demonstrate the first successful implementation of combined DYNAMITE imaging and shimming and show the feasibility of performing EPI with DYNAMITE hardware. Our results substantiate the potential of multi-coil hardware as a full-fledged imaging and shimming system, with additional potential benefits of reduced echo-time and risk of peripheral nerve stimulation while performing EPI.

A laser Doppler velocimeter employing 7×8-channel spatially encoded measurement points is proposed for simultaneous cross-sectional velocity distribution measurements. The measurement points arranged in two dimensions are encoded by combining wavelength-division multiplexing and multiple bias-frequency encoding. The functionality of the proposed method was experimentally demonstrated.

Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B 1 gradient result in a spatial encoding similar to that created by pulsed-field ( B 0 ) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B 1 field gradient (OFFBEAT) pulses. The advantage of B 1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B 1 field strength. B 1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B 0 pulsed-field gradients.

Basic processes underlying spatial encoding and memory have ancient evolutionary origins and are shared by many neighboring branches of the phylogenetic tree. As a result, the study of spatial cognition and its neural correlates has been a fruitful area of research that has benefited immensely from making cross-species generalizations. Converging evidence from all areas of cognitive science – from the firing of single neurons in the rodent brain, to the development of spatial abilities in chicks, fish, and children, to visual scene perception in adult humans – reveals that environmental boundaries, such as walls, ledges, cliffs, hills, and other terrain-like structures, play a fundamental role in vertebrate spatial mapping and navigation behavior. The aim of this review is to bring together three decades of research in the first comprehensive boundary-based view of spatial cognition.

To overcome the effects of static field inhomogeneities, single-scan hybrid imaging techniques that use k-space encoding in one direction and spatial encoding in the other have been shown to be superior to traditional imaging techniques based on full k-space encoding. Like traditional imaging methods, hybrid methods can be implemented in different ways that favor different sources of contrast. So far, little attention appears to have been paid to these aspects. By modifying an established hybrid imaging sequence called Rapid Acquisition by Sequential Excitation and Refocusing (RASER) so as to obtain Echo-Shifted RASER sequences, we show that by shifting spin echoes one can tune the contrast due to inhomogeneous T decay.

Purpose Multi-coil (MC) magnetic field modeling has emerged as a viable alternative to conventional field generation based on spherical harmonic shapes, and an active MC community is forming. Although all MC applications share the same modeling concept, the specific MC designs can largely differ as a result of disparities in region of interest (eg, human versus rodent), intended MR application (eg, B0 shimming versus spatial encoding), or other experimental constraints (eg, available bore space or integration with radiofrequency technology). To date, a lack of detailed information on existing MC designs complicates the assessment and precludes a meaningful comparison. Methods Here, we suggest that future publications involving the MC technique not only report the benefits for the application at hand, but also include an explicit description of the MC wire pattern used. Results This public multi-coil information (PUMCIN) policy represents a voluntary commitment to promoting free public access to the details necessary for reproducing and benefiting from MC research. Conclusions The PUMCIN policy is expected to initiate a paradigm shift with respect to the way MC innovation is reported. By setting an example, we hope to encourage the evolving MC community to maximize the benefits for science and society by embracing it. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

We describe with a theoretical and numerical analysis the use of small permanent magnets moving along prescribed helical paths for 3D spatial encoding and imaging without sample adjustment in ultra-low field magnetic resonance imaging (ULF-MRI). With our developed method the optimal magnet path and orientation for a given encoding magnet number and instrument architecture can be determined. As a proof-of-concept, we studied simple helical magnet paths and lengths for one and two encoding magnets to evaluate the imaging efficiency for a mechanically operated ULF-MRI instrument with permanent magnets. We demonstrate that a single encoding magnet moving around the sample in a single revolution suffices for the generation of a 3D image by back projection.

We propose a kernelized deep local-patch descriptor based on efficient match kernels of neural network activations. Response of each receptive field is encoded together with its spatial location using explicit feature maps. Two location parametrizations, Cartesian and polar, are used to provide robustness to a different types of canonical patch misalignment. Additionally, we analyze how the conventional architecture, i.e. a fully connected layer attached after the convolutional part, encodes responses in a spatially variant way. In contrary, explicit spatial encoding is used in our descriptor, whose potential applications are not limited to local-patches. We evaluate the descriptor on standard benchmarks. Both versions, encoding 32x32 or 64x64 patches, consistently outperform all other methods on all benchmarks. The number of parameters of the model is independent of the input patch resolution.

A differential laser Doppler velocimeter (LDV) for simultaneous two-dimensional (2-D) cross-sectional velocity distribution measurements is presented. 2-D spatial encoding of the measurement points using the combination of coherent bias-frequency encoding and wavelength-division multiplexing (WDM) is introduced into the proposed method. The function of velocity distribution measurements is demonstrated using a probe setup with eight-channel bias-frequency encoding and seven-channel WDM. The experimental results indicate that the 2-D velocity distribution measurement using the proposed method was successfully demonstrated.

Most of today’s pump–probe experiments, which rely on two-dimensional detectors, suffer from low read-out rates that prevent the implementation of fast lock-in techniques to increase the signal-to-noise ratio. The first cameras running at true kHz-frame rates are available at large-scale facilities, but require sophisticated data management strategies. Here we present a scheme for high-speed spatial encoding of modulated pump–probe signals using slow area detectors at full repetition rate of a laser system without an increase in data rate or change of the sample environment. Towards that end we block the probe light in front of the detector alternatingly with two inverted masks at the same frequency as the signal is modulated, e.g. the chopping frequency of the pump light. Modulation frequencies up to 500 Hz are demonstrated using a commercial mechanical chopper and have been applied to a time-resolved Faraday microscopy experiment probing all-optical magnetic switching of a GdFe-alloy with femtosecond temporal resolution. We believe that our concept bridges the gap between today’s slow area detectors and the upcoming generation of true kHz-frame-rate cameras.

In order to form images with the required resolution and anatomical coverage, gradient magnetic fields are used to excite magnetization in a predefined slice or slab, with subsequent spatial encoding to obtain spatial resolution in the slice or slab. It is demonstrated how the spatial encoding principle is implemented and how it can be conceptualized using the so-called k-space representation. The relations between the field of view, spatial resolution, and k-space sampling are illustrated, along with the implementation using a simple pulse sequence. Once magnetic resonance data have been collected in k-space, the process of image reconstruction will yield the final images.

Symmetric Dicke states represent a class of genuinely entangled multipartite states with superior resistance to loss and entanglement characteristics, even for low fidelity. A scalable and resource-intensive method is proposed using hybrid spatiotemporal encoding using only linear optics for generation of all symmetric Dicke states for both atomic and photonic qubits. Compared to purely spatial encoding, this method shows orders-of-magnitude improvement in success probability while also reducing the hardware complexity by a factor $N$ for $N$ qubits. This scheme will allow scalable entanglement generation of distant qubits.

Chipless radiofrequency identification (RFID) technology is very promising for sensing, identification, and tracking for future Internet of Things (IoT) systems and applications. In this paper, we propose and demonstrate a compact 18-bit, dual polarized chipless RFID tag. The proposed tag is based on L-shaped resonators designed so as to maximize the spectral and spatial encoding capacities. The proposed RFID tag operates an over 4 GHz frequency band (i.e., 6.5 GHz to 10.5 GHz). The tag is simulated, fabricated, and tested in a nonanechoic milieu. The measured data have shown good agreement with the simulation results, with respect to resonators’ frequency positions, null depth, and null bandwidth over the operating spectrum. The proposed design achieves spectral and spatial encoding capacities of 4.5 bits/GHz and 18.8 bits/cm2, respectively. This, in turn, gives an encoding density of 4.7 bits/GHz/cm2. For code identification, we exploit the frequency content of the backscattered signals and identify similarity/correlation features with reference codes.

A Si-based integrated probe is proposed for cross-sectional velocity distribution measurements. The measuring principle is based on a combination of simultaneous multipoint measurement using spatial encoding and nonmechanical scanning. The scanning function of the probe employing chirped focusing grating couplers in the transmitting optics is simulated.

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.

International audience; In longitudinal medical studies, multicomponent images of the tissues, acquired at a given stage of a disease, are used to provide information on the fate of the tissues. We propose a quantification of the predictive value of multicomponent images using information theory. To this end, we revisit the predictive information introduced for monodimensional time series and extend it to multicomponent images. The interest of this theoretical approach is illustrated on multicomponent magnetic resonance images acquired on stroke patients at acute and late stages, for which we propose an original and realistic model of noise together with a spatial encoding for the images. We address therefrom very practical questions such as the impact of noise on the predictability, the optimal choice of an observation scale and the predictability gain brought by the addition of imaging components.

The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields. The measurement results are in consistent with the measurements in homogeneous fields using the conventional method. Since spatial encoding technique is involved, the experimental time for the new method is very close to that for the conventional method. With the aid of T1 knowledge, some concealed information can be exploited by T1 weighting experiments.

Non-Cartesian parallel imaging has played an important role in reducing data acquisition time in MRI. The use of non-Cartesian trajectories can enable more efficient coverage of k-space, which can be leveraged to reduce scan times. These trajectories can be undersampled to achieve even faster scan times, but the resulting images may contain aliasing artifacts. Just as Cartesian parallel imaging can be used to reconstruct images from undersampled Cartesian data, non-Cartesian parallel imaging methods can mitigate aliasing artifacts by using additional spatial encoding information in the form of the nonhomogeneous sensitivities of multi-coil phased arrays. This review will begin with an overview of non-Cartesian k-space trajectories and their sampling properties, followed by an in-depth discussion of several selected non-Cartesian parallel imaging algorithms. Three representative non-Cartesian parallel imaging methods will be described, including Conjugate Gradient SENSE (CG SENSE), non-Cartesian generalized autocalibrating partially parallel acquisition (GRAPPA), and Iterative Self-Consistent Parallel Imaging Reconstruction (SPIRiT). After a discussion of these three techniques, several potential promising clinical applications of non-Cartesian parallel imaging will be covered.

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.

Spatial discontinuations occuring in cities introduce ambiguity in people´s mental spatial encoding and wayfinding bahavior. How do we encode and classify such misalignments? Twenty participants were asked to classify a total of 51 icons showing an upward-moving line being misaligned to the right and left as well as starting straight. The results show that subjects were very sensitive to slight discontinuations occurring to the vertical lines and that there was not exact symmetry between the left and right axis, meaning that the pieces slightly misaligned to the left were encoded differently than those misaligned to the right.

We investigated whether chimpanzees, bonobos, and orangutans encoded the location of a reward hidden underneath one of three identical cups in relation to (1) the other cups in the array-i.e., the relative position of the baited cup within the array; or (2) the landmarks surrounding the cups-e.g., the edge of the table. Apes witnessed the hiding of a food reward under one of three cups forming a straight line on a platform. After 30 s, they were allowed to search for the reward. In three different experiments, we varied the distance of the cups to the edge of the platform and the distance between the cups. Results showed that both manipulated variables affected apes' retrieval accuracy. Subjects' retrieval accuracy was higher for the outer cups compared with the Middle cup, especially if the outer cups were located next to the platform's edge. Additionally, the larger the distance between the cups, the better performance became.

We analyze the storage and retrieval of a weak light pulse, having two orthogonally (circularly) polarized components, onto an atomic ensemble of four-level atoms of the tripod type driven by a far detuned coupling field. The atoms are subject to a longitudinal magnetic field which produces a spatially varying Zeeman splitting of the lower levels along the medium and allows for a spatial encoding of the different angular frequencies of the input pulse during the storage phase. A single reversion of the external magnetic field results in a rephasing of the dipoles and leads to the release of the stored signals. The shape of the recovered pulse is a time-reversal copy of the input pulse. The application of an additional reversion of the magnetic field during the storage phase allows the release of a copy of the input pulse without time reversal. We also show that the system may operate like an all-optical multiplexer when considering two impinging optical fields which have orthogonal components. The proposal has potential applications in quantum information processing.

MRI at high magnetic field strengths promises to deliver clearer images of the body’s structure and function. However, high-field MRI currently faces several substantial engineering challenges before it can be considered robust and safe enough for routine clinical use. Challenges include increased radiofrequency (RF) energy deposition that can create unsafe patient heating, large main field inhomogeneities that prevent functional neuroimaging in the lower brain and inhomogeneous RFs transmit fields that cause spatially varying image contrast. Patient-tailored multidimensional RF excitation pulses have been proposed as a means to address many of these challenges. While these pulses show significant promise, their effectiveness has been severely limited by their long durations. Parallel excitation using multiple RF transmit coils driven simultaneously is a new technology that has been proposed to reduce multidimensional pulse durations. Parallel excitation provides an instantaneous spatial encoding mechanis...

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.

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.

Working memory (WM) is a system for the online storage of information. An emerging view is that neuronal oscillations coordinate the cellular assemblies that code the content of WM. In line with this view, previous work has demonstrated that oscillatory activity in the alpha band (8–12 Hz) plays a role in WM maintenance, but the exact contributions of this activity have remained unclear. Here, we used an inverted spatial encoding model in combination with electroencephalography (EEG) to test whether the topographic distribution of alpha-band activity tracks spatial representations held in WM. Participants in three experiments performed spatial WM tasks that required them to remember the precise angular location of a sample stimulus for 1,000-1,750 ms. Across all three experiments, we found that the topographic distribution of alpha-band activity tracked the specific location that was held in WM. Evoked (i.e., activity phase-locked to stimulus onset) and total (i.e., activity regardless of phase) power across a range of low-frequency bands transiently tracked the location of the sample stimulus following stimulus onset. However, only total power in the alpha band tracked the content of spatial WM throughout the memory delay period, which enabled reconstruction of location-selective channel tuning functions (CTFs). These findings demonstrate that alpha-band activity is directly related to the coding of spatial representations held in WM and provide a promising method for tracking the content of this online memory system.

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.

The present experiment examined how spatial judgments influenced target detection in a visual search task. Digital and analogue display formats were studied together with odd/even vs. above/below judgments. The results indicated an overall advantage for digital display formats, however, the advantage was mediated by the type of judgments that were made. Format differences were minimal when individuals were required to make judgments that involved spatial encoding. Ergonomic implications are addressed.

Three-dimensional (3D) multispectral magnetic resonance imaging (MRI) techniques can significantly reduce image artifacts commonly encountered near embedded metal hardware. These artifact reductions are enabled by applying alternative spectral and spatial encoding schemes to conventional spin-echo imaging techniques. Here, the multi-acquisition with variable resonance image combination (MAVRIC) and slice-encoding for metal artifact correction (SEMAC) multispectral imaging techniques are connected and discussed. The development of a hybrid technique that utilizes the strengths of both methods is then described. This optimized 3D multispectral imaging approach is shown to be capable of producing minimal-artifact, high-resolution images near total joint replacements in a clinical setting.

The programmable array microscope (PAM) is a powerful tool combining the capabilities of nearly all previously described optical sectioning techniques in a single microscope. Not only can the user create optical sections of threedimensional objects, but the PAM's unique adaptive optical strategy allows a user to select the best sectioning method for a particular sample or experimental need. The key to the PAM is a spatial light modulator (SLM). This device, when placed in the image plane of a microscope, can be used to create optical sectioning, generate spatial encoding masks, and/or define regions of interest.

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.

The authors investigated the type of spatial information that controls domestic dogs' (Canis familiaris) search behavior in a situation in which they have to locate a spatial position where they saw an object move and disappear. In Experiments 1 and 2, the authors manipulated all local and global sources of allocentric spatial information surrounding the hiding location. The results revealed that dogs relied on an egocentric frame of reference. Experiment 3 showed that dogs also encoded allocentric information when egocentric information was irrelevant. The authors conclude that dogs simultaneously encode both egocentric and allocentric spatial information to locate a spatial position, but they primarily base their search behavior on an egocentric frame of reference. The authors discuss under which natural conditions dogs might use these 2 sources of spatial information and detail the nature of spatial egocentric information and the circumstances underlying its use by dogs.

Previous experiments have failed to find clear motor effects in memory of movement patterns. The results did show the importance of verbal factors. This report documents that visuo-spatial encoding also improves memory of movement patterns. The results are discussed in terms of modal explanations of short-term episodic memory.

A photorefractive optical processor for accurate holographic associative memory that uses a spatial-encoding method is presented. The associative memory of both binary images and gray-scale images can be performed with this processor. The experimental results have proved that spatial-encoding can efficiently increase the addressing accuracy of real-time holographic associative memory in a simple way.

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.

The inception of spatially localized nuclear magnetic resonance (NMR) that led to medical imaging within a decade, and the ongoing refinements of the methodology during the past almost four decades, arguably represent one of the most significant advances in medical diagnostics during the second half of the twentieth century, which continues with a host of innovations. It is therefore not surprising that the two key contributors, Professors Paul Lauterbur and Sir Peter Mansfield, who conceived the basic ideas and first demonstrated the feasibility of NMR to generate spatial maps of hydrogen density, were awarded the 2003 Nobel Prize in Physiology or Medicine. The history of magnetic resonance imaging (MRI) has been reviewed previously (Wehrli, Progr NMR Spectr 1995) and notably, as part of a general review of the history of NMR, by Becker et al., in the original edition of this encyclopedia in 1996. The early phase comprising the period following the method's inception from 1972 to 1990 is therefore not covered in detail except where reference to critical precedents was deemed necessary. MRI is far richer than any other imaging technology since there are literally infinitely many ways to manipulate nuclear spins and tailor the experiment in such a manner that specific information can be extracted. While initially a structural imaging technique, it was soon recognized that the method was equally able to afford functional and physiological information, such as measurement of blood flow—both macroscopically and at the capillary level—entirely noninvasively—adding another dimension to the method. The discovery of the BOLD effect in 1990 and the subsequent demonstration that the response to neural stimulation manifests in a subtle change in local signal intensity, revolutionized neuroscience by providing unprecedented insight into the functioning of the human brain. Although the NMR signal is intrinsically weak, numerous technological advances have led to a clinical imaging modality that can detect disease with unprecedented sensitivity and acquire images at a speed approaching real time. The evolution of most technologies behaves as a sigmoid curve, with a slow beginning, followed by a phase of rapid advances, eventually decelerating during the final maturation phase. For a modality that approaches the beginning of the fifth decade since its inception, one would expect MRI to be a mature modality. However, MRI seems to defy this pattern as it continues to evolve at a vigorous pace as manifested by numerous technological advances that include ultrahigh-field imaging, parallel reception and excitation, the emergence of new detection schemes, the resurgence of radial imaging, in particular in conjunction with sparse sampling, hyperpolarization of rare spins, molecular and cellular imaging, and more, with no end in sight. These capabilities, in turn, drive the emergence of new applications, some of which are entirely unpredictable. Keywords: MRI history; MRI technology; magnetic field strength; radial imaging; spatial encoding; k-space; Fourier reconstruction; parallel imaging; compressed sensing; superconductivity

This short article is dedicated to the author's recollections of the early days of parallel MRI, which coincided with his years as a PhD student and junior faculty member. His interest in this topic was first sparked by a seminal poster presentation that Dan Sodickson gave at the 1997 ISMRM meeting. It prompted the author to devote most of his graduate research to the role of radiofrequency fields in MRI, analogies with optics, principles of spatial encoding, and image reconstruction. Working on parallel MRI was particularly exciting due to its rapid introduction into the industrial realm as well as radiology practice. Keywords: parallel MRI; array detection; image reconstruction; SMASH; SENSE

A simple nonlinear spatial encoding method is proposed for encoding fuzzy logic variables. Several optical architectures are suggested for realizing cascadable dual-rail fuzzy logic modules which can be used as basic building blocks for constructing an optical fuzzy computing system. The programmability, the infinite cascadability, and the ability to integrate the modules are carefully considered in the optical implementations. Furthermore, if the nonlinear spatial encoding method is used, then optical spatially continuous binary logic techniques and optical image processing techniques, both of which have been extensively studied previously, can be directly applied to the implementation of optical fuzzy logic.

Purpose: (1) To extend the single-voxel based 2D MRS version of L-COSY to multi-voxel based analogue on a 3T MRI/MRS scanner using the echo-planar imaging (EPI) based spatial encoding for determining metabolic distributions over many voxels; (2) To implement a Matlab-based post-processing algorithm in order to process the 2D COSY data recorded in breast cancer; (3) To record DWI and to calculate ADC maps in breast cancer patients and healthy controls, and iv) To correlate the changes in metabolite and lipid levels with ADC changes in breast cancer patients and healthy women. Scope: Improving the specificity of malignant and benign tumors will be a major outcome. Improved imaging techniques will enable unambiguous measurement of metabolites and the lipids in situ, which could potentially complement the existing diagnostic modalities commonly used in breast carcinoma. Major Findings: Part of the 1st half of the year was spent on securing the HSRRB and UCLA IRB approvals of the protocol. The MR protocol including DWI-MRI and 4D EP-COSI was successfully implemented on a 3T MRI scanner. Report of the Progress: First few months (July 2010-November 2010) were spent on the preparation and resubmission of the IRB protocol to HSRRB and UCLA IRB offices. The proposed protocol including multi-slice DWI-MRI and 4D EP-COSI has been tested in 5 healthy women. The ADC maps using DWI and lipid/water images using EP-COSI have been derived.