Pulse Sequence Design Research Articles

Modified look-locker inversion recovery T1 mapping indices: assessment of accuracy and reproducibility between MRI scanners

Background Cardiac magnetic resonance (CMR) T1 mapping indices, including T1 time, partition coefficient (l), and extracellular volume fraction (ECV) measurements, are a group of emerging noninvasive, quantitative imaging biomarkers that can be used to assess diffuse myocardial fibrosis. Similar to other quantitative MRI measurements, T1 mapping results can be influenced by multiple scanner dependent factors, such as field strength, gradient systems, coil configuration, pulse sequence design, and artifacts related to field inhomogeneity and eddy currents. The purpose of this ex-vivo phantom, multicenter study was to investigate how scanner and field strength variation affected the accuracy and precision of T1 mapping indices. Methods MR studies were performed on two 1.5T (1 Philips, 1 Siemens) and three 3T (2 Philips, 1 Siemens) scanners. Two sets of four phantoms were made to mimic the T1/T2 of pre- and post-contrast myocardium and blood at 1.5T and 3T. T1 mapping using modified look locker with inversion recovery (MOLLI) was performed with simulated heart rate of 40-100bpm using a standard 17 heart beat and a shorter 11 heart beat MOLLI protocol. Inversion recovery spin echo (IR-SE) sequence with TR = 10 sec was acquired during the same session to estimate the reference T1. The phantoms were taken out the magnet after IR-SE and all MOLLI protocols were re-scanned after 10 min to evaluate inter-scan reproducibility. The partition coefficient (l) was estimated by ΔR1myocardium/ΔR1blood. General linear model was used to compare the accuracy and reproducibility of T1 and l across field strength, scanners and protocols. Results The IR-SE T1 values were significantly different across scanners within the same field strength. The average partition coefficient estimated from IR-SE was 43.7% (1.5T) and 46.0% (3T), similar to normal in-vivo values. Accuracy was defined as the percent error between MOLLI and IR-SE, and scan/re-scan reproducibility was reported as the relative percent mean difference between the two back to back MOLLI scans. T1 and l accuracy both varied significantly between different scanners (p<0.0001 for both T1 and l) and across heart rates (p<0.0001 for T1 and p=0.001 for l). However, neither varied across the standard 17HB and 11HB protocols (p=0.177 for T1 and p=0.574 for lamda). Additionally, field strength significantly affected T1 accuracy but not l accuracy (p<0.0001 for T1 vs. p=0.109 for l). In addition to less variability in accuracy, l also had lower percent error overall between scan repetitions, or higher scan/re-scan reproducibility, than T1 measurements (4.59% vs. 5.54%).

Optimization of nuclear magnetic resonance refocusing pulses to enhance signal intensity in gradient B0 field

It is an efficient protocol to use the refocusing flip angle pulse optimization technique to solve special engineering technical problems in nuclear magnetic resonance (NMR) measurements. By reducing RF pulse duration, the low refocusing flip angle pulses can consume lower power, satisfy specific absorption rate of samples, and improve signal-to-noise ratio as well. To further analyze the function mechanism of pulse angles, the dependence of signal intensity on RF pulse is studied in homogenous magnetic field and constant gradient magnetic field respectively. Afterwards, echo amplitudes with various tip angles and flip angles ranging from 0° to 180° are compared with conventional sequence of 90° pulse followed by 180° pulses theoretically and experimentally. For the constant gradient field, the refocusing pulse of flip angle can be as low as 140°, defined as the optimum herein, to obtain the strongest signal intensity, enhanced by 13% compared with that of 180°. Moreover, T1 distributions measured by the conventional and optimal sequences for distilled water at room temperature are compared, and good conformances of T1 between the two pulse sequences are obtained, which demonstrates the optimal refocusing pulse can be directly applied to T1 measurement. The results provide constructive suggestion for designing pulse sequences for signal intensity enhancement in NMR logging while drilling and NMR online quick analysis.

Spatiotemporal evolution of cavitation dynamics exhibited by flowing microbubbles during ultrasound exposure

Ultrasound and microbubble-based therapies utilize cavitation to generate bioeffects, yet cavitation dynamics during individual pulses and across consecutive pulses remain poorly understood under physiologically relevant flow conditions. SonoVue(®) microbubbles were made to flow (fluid velocity: 10-40 mm/s) through a vessel in a tissue-mimicking material and were exposed to ultrasound [frequency: 0.5 MHz, peak-rarefactional pressure (PRP): 150-1200 kPa, pulse length: 1-100,000 cycles, pulse repetition frequency (PRF): 1-50 Hz, number of pulses: 10-250]. Radiated emissions were captured on a linear array, and passive acoustic mapping was used to spatiotemporally resolve cavitation events. At low PRPs, stable cavitation was maintained throughout several pulses, thus generating a steady rise in energy with low upstream spatial bias within the focal volume. At high PRPs, inertial cavitation was concentrated in the first 6.3 ± 1.3 ms of a pulse, followed by an energy reduction and high upstream bias. Multiple pulses at PRFs below a flow-dependent critical rate (PRF(crit)) produced predictable and consistent cavitation dynamics. Above the PRF(crit), energy generated was unpredictable and spatially biased. In conclusion, key parameters in microbubble-seeded flow conditions were matched with specific types, magnitudes, distributions, and durations of cavitation; this may help in understanding empirically observed in vivo phenomena and guide future pulse sequence designs.

MRI of the pancreas: Problem solving tool

Advances in MR hardware and pulse sequence design over the years have improved the quality and robustness of MR imaging of the pancreas. Today, MRI is an indispensible tool for studying the pancreas and can provide useful information not attainable with other noninvasive or minimally invasive imaging techniques. In the present review, specific cases are reviewed where the strengths of MRI demonstrate the utility of this imaging modality as a problem solving tool.

Imaging of the Spine at 3 Tesla

Magnetic resonance (MR) imaging at 3 T has proved superior to 1.5 T in the brain for detecting numerous pathologic entities including hemosiderin, tiny metastases, subtle demyelinating plaques, active demyelinating plaques, and some epileptogenic foci, as well as small aneurysms with MR angiography. 3 T is superior to most advanced imaging techniques including diffusion, diffusion tensor imaging, perfusion, spectroscopy and functional MR imaging. The increased signal/noise ratio at 3 T permits higher spatial resolution. Initially spine imaging at 3 T proved more difficult with less successful results. During the past 7 years, technological advances in magnet and surface coil design as well as improved radio frequency transmitters and pulse sequence design in combination with the large body of knowledge accrued by radiologists and physicists during a nine year experience with clinical imaging of the spine with the doubled B0, has resulted in 3 T MRI of the spine achieving a reputation similar to that for brain imaging.

Towards fast and accurate temperature mapping with proton resonance frequency-based MR thermometry.

The capability to image temperature is a very attractive feature of MRI and has been actively exploited for guiding minimally-invasive thermal therapies. Among many MR-based temperature-sensitive approaches, proton resonance frequency (PRF) thermometry provides the advantage of excellent linearity of signal with temperature over a large temperature range. Furthermore, the PRF shift has been shown to be fairly independent of tissue type and thermal history. For these reasons, PRF method has evolved into the most widely used MR-based thermometry method. In the present paper, the basic principles of PRF-based temperature mapping will be reviewed, along with associated pulse sequence designs. Technical advancements aimed at increasing the imaging speed and/or temperature accuracy of PRF-based thermometry sequences, such as image acceleration, fat suppression, reduced field-of-view imaging, as well as motion tracking and correction, will be discussed. The development of accurate MR thermometry methods applicable to moving organs with non-negligible fat content represents a very challenging goal, but recent developments suggest that this goal may be achieved. If so, MR-guided thermal therapies may be expected to play an increasingly-important therapeutic and palliative role, as a minimally-invasive alternative to surgery.

Mapping the Organization of Axis of Motion Selective Features in Human Area MT Using High-Field fMRI

Functional magnetic resonance imaging (fMRI) at high magnetic fields has made it possible to investigate the columnar organization of the human brain in vivo with high degrees of accuracy and sensitivity. Until now, these results have been limited to the organization principles of early visual cortex (V1). While the middle temporal area (MT) has been the first identified extra-striate visual area shown to exhibit a columnar organization in monkeys, evidence of MT's columnar response properties and topographic layout in humans has remained elusive. Research using various approaches suggests similar response properties as in monkeys but failed to provide direct evidence for direction or axis of motion selectivity in human area MT. By combining state of the art pulse sequence design, high spatial resolution in all three dimensions (0.8 mm isotropic), optimized coil design, ultrahigh field magnets (7 Tesla) and novel high resolution cortical grid sampling analysis tools, we provide the first direct evidence for large-scale axis of motion selective feature organization in human area MT closely matching predictions from topographic columnar-level simulations.

A tribute to Lewis E Kay on his 50th birthday

It is a great pleasure for us to introduce this special issue of the Journal of Biomolecular NMR on the occasion of Prof. Lewis E. Kay’s 50th birthday. We are grateful to the Editors of the Journal of Biomolecular NMR for accepting our proposal. In particular, we thank Prof. Martin Billeter for editing this issue, and Dr. Ad Bax for advice and support. We believe that Lewis merits this special issue of Journal of Biomolecular NMR for his innovative contributions to biomolecular NMR spectroscopy, as well as for his role as inspirer for a large group of young research professionals. The following short list of examples serves to illustrate how the work of Lewis Kay has helped to advance our field: Lewis has consistently been a pioneer in the development of novel methods essential to increasing the size of proteins that may be studied by NMR. In the days when assigning chemical shifts of a protein with 150 amino acids was a major endeavour, the Kay lab––in collaboration with Prof. Cheryl Arrowsmith––combined advances in gradientenhanced spectroscopy, protein deuteration and pulse sequence design to establish the resonance assignments for a 37 kDa complex. As these techniques became more broadly used, his lab forged ahead with clever biochemical tricks for incorporating protonated methyl groups in otherwise deuterated proteins, and developed methyl TROSY experiments that permit well-resolved spectra to be obtained for high molecular weight complexes, extending to 1 MDa. Lewis has been a leader in using NMR to measure fast timescale macromolecular dynamics, starting with his contributions to inverse-detected N relaxation experiments. His deuterium spin relaxation methodologies have had a huge impact on our ability to characterize side chain dynamics in proteins. In addition, the Kay lab has extensively developed and applied new methodologies for studying low-populated states of proteins and their roles in biology. Building on transverse relaxation dispersion experiments, the Kay lab has introduced approaches to elucidate the threeK. H. Gardner (&) Department of Biochemistry, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8816, USA e-mail: Kevin.Gardner@UTSouthwestern.edu

Fetal Magnetic Resonance Imaging at 3.0 T

Magnetic resonance imaging (MRI) has been used to image the in utero fetus for the past 3 decades. Although not as commonplace as other patient-oriented MRI, it is a growing field and demonstrating a role in the clinical care of the fetus. Indeed, the body of literature involving fetal MRI exceeds 3000 published articles. Indeed, there is interest in accessing even the healthy fetus with MRI to further understand the development of humans during the fetal stage. On the horizon is fetal imaging using 3.0-T clinical systems. Although a clear path is not necessarily determined, experiments, theoretical calculations, advances in pulse sequence design, new hardware, and experience from imaging at 1.5 T help define the path.

Three-dimensional MREIT simulator of static bioelectromagnetism and MRI

Magnetic resonance electrical impedance tomography (MREIT) aims to produce high-resolution cross-sectional images of a conductivity distribution inside the human body. We perform conductivity image reconstructions based on a relation between the conductivity distribution and induced magnetic flux density distributions subject to externally injected currents. This induced magnetic flux density is measured in MREIT using an MRI scanner. To facilitate MREIT research, we need a numerical simulator including static bioelectromagnetism and MRI data collection process. In this paper, we describe the development of a three-dimensional MREIT simulator (MREITSim). We describe various features of MREITSim including geometry modeling, meshing, finite element modeling and numerical computations of magnetic flux density and k-space MR data. We demonstrate the underlying bioelectromagnetic phenomena and MR data collection process using phantom models of without and with anomaly. We illustrate effects of noise in MR data and echo time on magnetic flux density computations. We demonstrate numerical computations of current density and magnetic flux density distributions for current injections orthogonal to z-direction, the direction of the main magnetic field of an MRI scanner. The k-space MREIT data generation procedure is illustrated using a phantom model with an insulating anomaly. The simulator functions as a virtual MREIT scanner and provides quantitative numerical results of intended experimental studies. We suggest the simulator as a basic research tool for future MREIT studies of its theory, algorithm, experimental techniques and pulse sequence design.

Multipathway sequences for MR thermometry

MR-based thermometry is a valuable adjunct to thermal ablation therapies as it helps to determine when lethal doses are reached at the target and whether surrounding tissues are safe from damage. When the targeted lesion is mobile, MR data can further be used for motion-tracking purposes. The present work introduces pulse sequence modifications that enable significant improvements in terms of both temperature-to-noise-ratio properties and target-tracking abilities. Instead of sampling a single magnetization pathway as in typical MR thermometry sequences, the pulse-sequence design introduced here involves sampling at least one additional pathway. Image reconstruction changes associated with the proposed sampling scheme are also described. The method was implemented on two commonly used MR thermometry sequences: the gradient-echo and the interleaved echo-planar imaging sequences. Data from the extra pathway enabled temperature-to-noise-ratio improvements by up to 35%, without increasing scan time. Potentially of greater significance is that the sampled pathways featured very different contrast for blood vessels, facilitating their detection and use as internal landmarks for tracking purposes. Through improved temperature-to-noise-ratio and lesion-tracking abilities, the proposed pulse-sequence design may facilitate the use of MR-monitored thermal ablations as an effective treatment option even in mobile organs such as the liver and kidneys.

6. Diffusion tensor MRI study of the spinal cord in patients with multiple sclerosis

Introduction Anatomical MR contrasts (such as T1 and T2) fail to identify occult lesions and diffuse demyelination which are known to occur in multiple sclerosis (MS). Diffusion tensor imaging (DTI) can potentially discern axonal loss in white-matter tissue and serve as a marker for loss of tissue integrity (demyelination, axonal degeneration) [1,2]. Poor image quality and the limited resolution in spinal cord DWI has so far impeded focal evaluation of spinal cord tissue i.e. the differentiation between grey and white matter. Furthermore, adequate image quality was achievable only at the cervical level of the spinal cord. Recent improvements in MR pulse sequence design have overcome these problems, thereby providing a new instrument for the assessment of multiple sclerosis. We tested the newly available technique in a comprehensive clinical MS study and measured diffusivity values of the spinal cord at three levels. Methods Imaging was performed on a 3 T Philips Achieva (Philips Healthcare, Best, the Netherlands) using a dedicated spine coil. DTI data of 18 volunteers and 41 patients with relapsing remitting MS (RRMS), secondary progressive MS (SPMS) or primary progressive MS (PPMS) (Table 1) were acquired at cervical (~C5) and thoracic level (~T5) as well as at the lumbar enlargement of the spinal cord. In each region 6 transverse slices were acquired using an outer volume suppressed reduced field of view single-shot EPI sequence [3,4] (NEX = 6/12 for b = 0/b = 750 s/mm2, acquisition matrix = 176x44, FOV = 120x30 mm, z=5mm, TR = 4000 ms, TE = 49 ms, 60% partial-Fourier acquisition). After subsequent image co-registration fractional anisotropy (FA) and apparent diffusion coefficient (ADC) maps were calculated. Diffusivity values were evaluated in the posterior white matter (PWM) (Fig. A). Only normal appearing spinal cord tissue, i.e. spinal cord tissue without T2-hyperintense lesions, was evaluated. ROI sizes were kept constant for all evaluated subjects.

Comprehensive 4D velocity mapping of the heart and great vessels by cardiovascular magnetic resonance.

BackgroundPhase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated.MethodsCurrently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification.ApplicationsMultidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thrombo-embolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters.ConclusionsMultidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.

Flow measurement in MRI using arterial spin labeling with cumulative readout pulses—Theory and validation

This article systematically examines arterial spin labeling (ASL) as a flow quantification technique through theoretical simulation, in vitro, and in vivo experiment. The authors present a novel imaging pulse sequence design consisting of a single ASL magnetization preparation followed by Look-Locker-like image readouts. Bloch-equation-based modeling has been developed and validated using a hemodialyzer as a tissue-mimicking flow phantom. After the single in-plane slice-selective double inversion magnetization preparation, multiple TFL readouts are acquired with linear k-space ordering, causing a signal variation that depends on through-slice flow velocity. Computer simulations were performed to assess the behavior of the flow-dependent ASL signal as a function of varying imaging parameters. The signal was optimized by choosing imaging parameters that maximize the simulated flow-sensitive signal. Furthermore, a hemodialyzer which mimics blood flow in human tissues was tested with a wide range of flow rates. An exponential curve fitting of the flow-sensitive dynamics to the model derived from Bloch equations provides a method to estimate through-slice velocity for varying flow rates on the hemodialyzer and in vivo human brain. The flow dependency of the ASL signal and the sensitivity of the ASL signal to imaging parameters were demonstrated. Experimental results from a hemodialyzer when fitted with a Bloch-equation-based model provide flow measurements that are consistent with ground truth velocities. Human brain velocity mapping was obtained as well. The results provide evidence that the proposed pulse sequence design is an effective technique to measure total fluid flow through image voxels. The unique combination of the two main features, multiple-image readout after a single ASL preparation and linear acquisition ordering in the phase encoding direction in TFL imaging, make this technique an appealing flow imaging method to quantify through-plane flow in a time-efficient manner.

Longitudinal and multi‐echo transverse relaxation times of normal breast tissue at 3 Tesla

To measure longitudinal (T(1)) and multi-echo transverse (T(2)) relaxation times of healthy breast tissue at 3 Tesla (T). High-resolution relaxation time measurements were made in six healthy female subjects. Inversion recovery images were acquired at 10 inversion times between 100 ms and 4000 ms, and multiple spin echo images were acquired at 16 echo times between 10 ms and 160 ms. Longitudinal relaxation times T(1) were measured as 423 ± 12 ms for adipose tissue and 1680 ± 180 ms for fibroglandular tissue. Multi-echo transverse relaxation times T(2) were measured as 154 ± 9 ms for adipose tissue and 71 ± 6 ms for fibroglandular tissue. Histograms of the voxel-wise relaxation times and quantitative relaxation time maps are also presented. T(1) and multi-echo T(2) relaxation times in normal human breast tissue are reported. These values are useful for pulse sequence design and optimization for 3T breast MRI. Compared with the literature, T(1) values are significantly longer at 3T, suggesting that longer repetition time and inversion time values should be used for similar image contrast.

Flow compensation for the fast spin echo triple-echo Dixon sequence

The fast spin echo (FSE) triple-echo Dixon (FTED) sequence uses bipolar triple-echo readout during each echo-spacing period of FSE to collect all the images necessary for Dixon water and fat separation in a single scan. In comparison to other FSE implementations of the Dixon technique, the triple echo readout used in FTED incurs minimal deadtime in the pulse sequence design and thus greatly enhances the overall scan efficiency. A potential drawback of FTED is that the time dependence of the gradient moment along the frequency encode direction becomes more complicated than in FSE and flow compensation based on the gradient moment (GM) nulling is difficult to achieve. In this work, the first order GM along the frequency encode direction of FTED was examined and two different methods to minimize the GM were proposed. The first method nulls the GM at all the locations of the refocusing radiofrequency pulses so that the Carr-Purcell Meiboom-Gill condition is always maintained. The second method minimizes the GM of the spin echo component of the FSE signal at the echo locations. The efficacy of both methods in reducing the first order GM and flow-related artefacts was demonstrated both in phantom and in images in vivo.

MRI artifacts and correction strategies

Artifacts appear in MRI for a variety of reasons. Potential sources of artifacts include nonideal hardware characteristics, intrinsic tissue properties and biological behavior, assumptions underlying the data acquisition and image reconstruction process, and poor choice of scanning parameters. Careful study design and scanning protocols can prevent certain artifacts from occurring, but some are unavoidable. Numerous correction methods have been developed to mitigate the corruptive effects of artifacts and improve image diagnostic quality. These methods include special pulse sequence designs, improved scanning procedures and equipment, and advanced postprocessing algorithms. Recognizing artifacts and understanding their underlying causes are important when interpreting images and choosing a correction approach.

TH‐C‐204C‐02: Advanced MR Spectroscopy Methods for Studying Metabolism and Radiation Treatment Response in Brain Tumors

Magnetic resonance spectroscopy imaging (MRSI) provides completely non‐invasively detailed metabolic information which correlates with physiological or pathological conditions. Hence it is becoming a valuable tool in image guided radio(proton)therapy where it can probe dose conformity (radiation delivered over the tumor volume and surrounding tissues) and could provide in‐vivo new insights about the biology of tumor response to radiation.Traditionally in‐vivo MRSI faces several challenges that may limit its potential such as: 1) inaccuracy in signal localization (chemical shift displacement error and voxel bleeding); 2) low spatial resolution; and 3) long acquisition times for 3D volumetric scans. However recent advances in hardware and pulse sequence design can mitigate many of these problems. Use of adiabatic pulses can provide precise and uniform signal excitation and together with fast acquisition schemes of the k‐space such as spiral trajectories allows fast acquisition of high resolution 3D MRSI scans. In addition real‐time motion correction and shimming strategies can improve the reliability of MRSI scans. Moreover MRSI scans that have multiple frequency dimensions (such as 2D chemical shift correlation spectra) can now be performed in‐vivo to unambiguously identify overlapped metabolite signals.This lecture will begin with an overview of the basic principles of in‐vivo MRS which will be followed by details of advanced MRSI methods such as adiabatic excitation fast spiral acquisition of 3D MRSI data and 2D chemical shift correlation spectra. Examples of in‐vivo MRSI data obtained on brain tumor patients treated with conventional radiotherapy and proton beam therapy will be shown in the end.Learning Objectives:1. Basic principles of MRSI.2. Understand the critical artifacts that might confound MRS and the importance of improved methods for reliable MRSI.3. Clinical applications of MRSI to monitor radiation therapy for brain tumors.

A System for NMR Stark Spectroscopy of Quadrupolar Nuclei

Electrostatic influences on NMR parameters are well accepted. Experimental and computational routes have been long pursued to understand and utilize such Stark effects. However, existing approaches are largely indirect informants on electric fields, and/or are complicated by multiple causal factors in spectroscopic change. We present a system to directly measure quadrupolar Stark effects from an applied electric (E) field. Our apparatus and applications are relevant in two contexts. Each uses a radiofrequency (rf) E field at twice the nuclear Larmor frequency (2omega(0)). The mechanism is a distortion of the E-field gradient tensor that is linear in the amplitude (E(0)) of the rf E field. The first uses 2omega(0) excitation of double-quantum transitions for times similar to T(1) (the longitudinal spin relaxation time). This perturbs the steady state distribution of spin population. Nonlinear analysis versus E(0) can be used to determine the Stark response rate. The second context uses POWER (perturbations observed with enhanced resolution) NMR. Here, coherent, short-time (<<T(2), the transverse relaxation rate) excitation at 2omega(0) is synchronized with an NMR multiple-pulse line-narrowing sequence. Linear analysis of the Stark response is then possible: a quadrupolar multiplet with splitting proportional to E(0). The POWER sequence converts the 2omega(0) interaction from off-diagonal/nonsecular to the familiar diagonal form (I(z)(2)) of static quadrupole interactions. Meanwhile, background contributions to line width are averaged to zero, providing orders-of-magnitude resolution enhancement for correspondingly high sensitivity to the Stark effect. Using GaAs as a test case with well-defined Stark response, we provide the first demonstration of the 2omega(0) effect at high-field (14.1 T) and room temperature. This, along with the simplicity of our apparatus and spectral approach, may facilitate extensions to a wider array of material and molecular systems. The POWER context, which has not previously been tested, is detailed here with new design insights. Several key aspects are demonstrated here, while complete implementation is to be presented at a later time. At present, we (1) account for finite pulse times in pulse sequence design, (2) demonstrate two-channel phase coherence for magnetic (omega(0)) and electric (2omega(0)) excitation, and (3) provide line narrowing by a factor of 10(3). In addition, we find that certain anomalous contributions to the line shape, observed in previous low-field (250 mT) applications, are absent here.

MRI Pulse Sequence Design With First-Order Gradient Moment Nulling in Arbitrary Directions by Solving a Polynomial Program

We suggest a polynomial program for the calculation of optimized gradient waveforms for magnetic resonance tomography pulse sequences. Such non-linear mathematical programs can describe gradient system capabilities, meet k-space trajectory specifications, and capture sequence timing conditions. Moreover they allow the incorporation of gradient moment nulling constraints in one or several arbitrary spatial directions, which can reduce flow motion artifacts in the images. We report first experiences in solving such automatic pulse sequence design programs with the interior point solver Ipopt.