Multiple Pulse Sequences Research Articles

Quantification and compensation of the influence of pulse transients on symmetry-based recoupling sequences

Deviations of amplitude and phase of radio-frequency pulses from the desired values, can have a severe impact on the performance of multiple-pulse sequences in NMR spectroscopy. A particular problem are pulse transients that appear every time there is a discontinuity in amplitude or phase. Based on a Floquet description using pulses with arbitrarily shaped amplitudes and phases we present a systematic study of the influence of pulse transients on symmetry-based pulse sequences in solid-state NMR under magic-angle spinning. This treatment explains the dependence of the experimentally observed transfer efficiency on the details of experimental setups. In addition, three approaches are compared which have the aim to re-establish highly efficient recoupling. We demonstrate that the application of transient-compensated pulses as basic elements of symmetry-based sequences leads to a significantly improved robustness of the experiments with respect to variations in the experimental setup.

Off-resonance effects in 14N NQR signals from the pulsed spin-locking (PSL) and three-pulse echo sequence; a study for monoclinic TNT

In NQR detection applications signal averaging by the summation of rapidly regenerated signals from multiple pulse sequences of the pulsed spin-locking (PSL) type is often used to improve sensitivity. It is important to characterise and if possible minimise PSL sequence off-resonance effects since they can make it difficult to optimise detection performance. We illustrate this with measurements of the variation of the decay time T2e and the amplitude of PSL signal trains with pulse spacing and excitation offset frequency for the 870kHz ν+14N NQR line of monoclinic TNT under carefully stabilised temperature conditions. We have also carried out a similar study of signals from monoclinic TNT and 1H-1,2,3-triazole generated by a three-pulse echo sequence and the results are shown to agree well with a theoretical treatment appropriate to polycrystalline NQR samples such as TNT for which spin I=1, asymmetry parameter η≠0 and T1≫T2. Based on this theory we derive simple models for calculating TNT PSL signal trains and hence the pulse spacing and off-resonance dependence of signal amplitude and T2e which we compare to our experimental data. We discuss the influence of PSL echo summation on off-resonance effects in detected signal intensity and show how a phase-alternated multiple pulse sequence can be used in combination with the PSL sequence to eliminate variation in detection performance due to off-resonance effects.

14N NQR, relaxation and molecular dynamics of the explosive TNT

Multiple pulse sequences are widely used for signal enhancement in NQR detection applications. Since the various 14N NQR relaxation times, signal decay times and frequency of each NQR line have a major influence on detection sequence performance, it is important to characterise these parameters and their temperature variation, as fully as possible. In this paper we discuss such measurements for a number of the ν+ and ν− NQR lines of monoclinic and orthorhombic TNT and relate the temperature variation results to molecular dynamics. The temperature variation of the 14N spin-lattice relaxation times T1 is interpreted as due to hindered rotation of the NO2 group about the C–NO2 bond with an activation energy of 89kJmol−1 for the ortho and para groups of monoclinic TNT and 70kJmol−1 for the para group of orthorhombic TNT.

Multiple acquisition of magic angle spinning solid-state NMR experiments using one receiver: Application to microcrystalline and membrane protein preparations

Solid-state NMR spectroscopy of proteins is a notoriously low-throughput technique. Relatively low-sensitivity and poor resolution of protein samples require long acquisition times for multidimensional NMR experiments. To speed up data acquisition, we developed a family of experiments called Polarization Optimized Experiments (POE), in which we utilized the orphan spin operators that are discarded in classical multidimensional NMR experiments, recovering them to allow simultaneous acquisition of multiple 2D and 3D experiments, all while using conventional probes with spectrometers equipped with one receiver. POE allow the concatenation of multiple 2D or 3D pulse sequences into a single experiment, thus potentially combining all of the aforementioned advances, boosting the capability of ssNMR spectrometers at least two-fold without the addition of any hardware. In this perspective, we describe the first generation of POE, such as dual acquisition MAS (or DUMAS) methods, and then illustrate the evolution of these experiments into MEIOSIS, a method that enables the simultaneous acquisition of multiple 2D and 3D spectra. Using these new pulse schemes for the solid-state NMR investigation of biopolymers makes it possible to obtain sequential resonance assignments, as well as distance restraints, in about half the experimental time. While designed for acquisition of heteronuclei, these new experiments can be easily implemented for proton detection and coupled with other recent advancements, such as dynamic nuclear polarization (DNP), to improve signal to noise. Finally, we illustrate the application of these methods to microcrystalline protein preparations as well as single and multi-span membrane proteins reconstituted in lipid membranes.

Investigation into the structural composition of hydroalcoholic solutions as basis for the development of multiple suppression pulse sequences for NMR measurement of alcoholic beverages.

An eight-fold suppression pulse sequence was recently developed to improve sensitivity in (1) H NMR measurements of alcoholic beverages [Magn. Res. Chem. 2011 (49): 734-739]. To ensure that only one combined hydroxyl peak from water and ethanol appears in the spectrum, adjustment to a certain range of ethanol concentrations was required. To explain this observation, the structure of water-ethanol solutions was studied. Hydroalcoholic solutions showed extreme behavior at 25% vol, 46% vol, and 83% vol ethanol according to (1) H NMR experiments. Near-infrared spectroscopy confirmed the occurrence of four significant compounds ('individual' ethanol and water structures as well as two water-ethanol complexes of defined composition - 1 : 1 and 1 : 3). The successful multiple suppression can be achieved for every kind of alcoholic beverage with different alcoholic strengths, when the final ethanol concentration is adjusted to a range between 25% vol and 46% vol (e.g. using dilution or pure ethanol addition). In this optimum region, an individual ethanol peak was not detected, because the 'individual' water structure and the 1 : 1 ethanol-water complex predominate. The nature of molecular association in ethanol-water solutions is essential to elucidate NMR method development for measurement of alcoholic beverages. The presented approach can be used to optimize other NMR suppression protocols for binary water-organic solvent mixtures, where hydrogen bonding plays a dominant role.

Time-optimal universal control of two-level systems under strong driving

We report on a theoretical and experimental study of time-optimal construction of arbitrary single-qubit rotations under a single strong driving field of finite amplitude. Using radiation-dressed states of nitrogen vacancy centers in diamond we realize a strongly driven two-level system, with driving frequencies four times larger than its precession frequency. We implement time-optimal universal rotations on this system, characterize their performance using quantum process tomography, and demonstrate a dual-axis multiple-pulse control sequence where the qubit is rotated on time scales faster than its precession period. Our results pave the way for applying fast qubit control and high-density pulse schemes in the fields of quantum information processing and quantum metrology.

SU-E-J-257: Image Artifacts Caused by Implanted Calypso Beacons in MRI Studies

Purpose: The presence of Calypso Beacon-transponders in patients can cause artifacts during MRI imaging studies. This could be a problem for post-treatment follow up of cancer patients using MRI studies to evaluate metastasis and for functional imaging studies.This work assesses (1) the volume immediately surrounding the transponders that will not be visualized by the MRI due to the beacons, and (2) the dependence of the non-visualized volume on beacon orientation, and scanning techniques. Methods: Two phantoms were used in this study (1) water filled box, (2) and a 2300 cc block of pork meat. Calypso beacons were implanted in the phantoms both in parallel and perpendicular orientations with respect to the MR scanner magnetic field. MR image series of the phantom were obtained with on a 1.0T high field open MR-SIM with multiple pulse sequences, for example, T1-weighted fast field echo and T2-weighted turbo spin echo. Results: On average, a no-signal region with 2 cm radius and 3 cm length was measured. Image artifacts are more significant when beacons are placed parallel to scanner magnetic field; the no-signal area around the beacon was about 0.5 cm larger in orthogonal orientation. The no-signal region surrounding the beacons slightly varies in dimensionmore » for the different pulse sequences. Conclusion: The use of Calypso beacons can prohibit the use of MRI studies in post-treatment assessments, especially in the immediate region surrounding the implanted beacon. A characterization of the MR scanner by identifying the no-signal regions due to implanted beacons is essential. This may render the use of Calypso beacons useful for some cases and give the treating physician a chance to identify those patients prior to beacon implantation.« less

Optimal filtering in multipulse sequences for nuclear quadrupole resonance detection

The application of the multipulse sequences in nuclear quadrupole resonance (NQR) detection of explosive and narcotic substances has been studied. Various approaches to increase the signal to noise ratio (SNR) of signal detection are considered. We discussed two modifications of the phase-alternated multiple-pulse sequence (PAMS): the 180° pulse sequence with a preparatory pulse and the 90° pulse sequence. The advantages of optimal filtering to detect NQR in the case of the coherent steady-state precession have been analyzed. It has been shown that this technique is effective in filtering high-frequency and low-frequency noise and increasing the reliability of NQR detection. Our analysis also shows the PAMS with 180° pulses is more effective than PSL sequence from point of view of the application of optimal filtering procedure to the steady-state NQR signal.

Performance of RINEPT is amplified by dipolar couplings under ultrafast MAS conditions

The refocused insensitive nuclei enhanced by polarization transfer (RINEPT) technique is commonly used for heteronuclear polarization transfer in solution and solid-state NMR spectroscopy. Suppression of dipolar couplings, either by fast molecular motions in solution or by a combination of MAS and multiple pulse sequences in solids, enables the polarization transfer via scalar couplings. However, the presence of unsuppressed dipolar couplings could alter the functioning of RINEPT, particularly under fast/ultrafast MAS conditions. In this study, we demonstrate, through experiments on rigid solids complemented by numerical simulations, that the polarization transfer efficiency of RINEPT is dependent on the MAS frequency. In addition, we show that heteronuclear dipolar coupling is the dominant factor in the polarization transfer, which is strengthened by the presence of 1H–1H dipolar couplings. In fact, the simultaneous presence of homonuclear and heteronuclear dipolar couplings is the premise for the polarization transfer by RINEPT, whereas the scalar coupling plays an insignificant role under ultrafast MAS conditions on rigid solids. Our results additionally reveal that the polarization transfer efficiency decreases with the increasing duration of RF pulses used in the RINEPT sequence.

Method for feature extraction of radar full pulses based on EMD and chaos detection

A novel method for extracting frequency slippage signal from radar full pulse sequence is presented. For the radar full pulse sequence received by radar interception receiver, radio frequency (RF) and time of arrival (TOA) of all pulses constitute a two-dimensional information sequence. In a complex and intensive electromagnetic environment, the TOA of pulses is distributed unevenly, randomly, and in a nonstationary manner, preventing existing methods from directly analyzing such time series and effectively extracting certain signal features. This work applies Gaussian noise insertion and structure function to the TOA-RF information sequence respectively such that the equalization of time intervals and correlation processing are accomplished. The components with different frequencies in structure function series are separated using empirical mode decomposition. Additionally, a chaos detection model based on the Duffing equation is introduced to determine the useful component and extract the changing features of RF. Experimental results indicate that the proposed methodology can successfully extract the slippage signal effectively in the case that multiple radar pulse sequences overlap.

Strong pulsed excitations using circularly polarized fields for ultra-low field NMR

A pulse, which is produced by a single coil and thereby has a linear polarization, cannot coherently drive nuclear spins if the pulse is stronger than the static field B0. The inaccuracy of the pulse, which arises from the failure of the rotating wave approximation, has been an obstacle in adopting multiple pulse techniques in ultra-low field NMR where B0 is less than a few μT. Here, we show that such a limitation can be overcome by applying pulses of circular polarization using two orthogonal coils. The sinusoidal nutation of the nuclear spins was experimentally obtained, which indicates that coherent and precise controls of the nuclear spins can be achieved with circularly polarized pulses. Additional demonstration of the Carl–Purcell–Meiboom–Gill sequence verifies the feasibility of adopting multiple pulse sequences to ultra-low field NMR studies.

Boosting the electron spin coherence in binuclear Mn complexes by multiple microwave pulses

We investigate a possibility to enhance the coherence time of electron spins in magnetic molecular complexes by application of the Carr-Purcell-Meiboom-Gill (CPMG) multiple microwave pulse sequence. Our theoretical analysis shows that the CPMG sequence can efficiently suppress the spin decoherence channel arising due to spectral diffusion induced by a random modulation of the hyperfine interaction which is an important source of the spin dephasing in molecular magnets. We confirm this by employing the CPMG protocol in pulse electron spin resonance experiments on model binuclear 1,2-diphosphacyclopentadienyl manganese complexes. We show that, compared to the standardly used two-pulse primary spin-echo technique, the CPMG experiment can boost the phase memory time up to one order of magnitude, bringing it to above 10 $\ensuremath{\mu}$s at low temperatures. This finding may be important for the implementation of quantum computation protocols on molecular magnets. We discuss a possible interesting analogy with the Zeno's paradox in quantum theory (the Zeno quantum effect), which could be implicit in the CPMG experiment.

MRI of the Elbow: Techniques and Spectrum of Disease

Magnetic resonance imaging (MRI) of the elbow allows for high-resolution evaluation of osseous and soft-tissue structures, including ligaments, tendons, nerves, and muscles. Multiple imaging techniques and pulse sequences exist. The purpose of this article is to update orthopaedic surgeons on current MRI techniques and illustrate the spectrum of elbow pathology detectable by MRI. We searched MEDLINE with use of the keywords "MRI" and "elbow" for studies less than five years old evaluating MRI techniques. These papers, our experience, and textbooks reviewing elbow MRI provided the information for this article. We discuss the essentials and applications of the following techniques: (1) conventional, non-gadolinium-enhanced MRI; (2) gadolinium-enhanced MRI; and (3) magnetic resonance arthrography. The classic MRI appearances of occult fractures, loose bodies, ulnar collateral ligament injuries, lateral collateral ligament complex injuries, biceps tendon injuries, triceps tendon injuries, lateral epicondylitis, medial epicondylitis, septic arthritis, osteomyelitis, osteochondritis dissecans, compression neuropathies, synovial disorders, and various soft-tissue masses are reviewed. MRI is a valuable, noninvasive method of elbow evaluation. This article updates orthopaedic surgeons on the various available MRI techniques and facilitates recognition of the MRI appearances of the most commonly seen pathologic elbow conditions.

The Interference Suppression in Pulse Sequence Signal Measurement for Calibration in Outdoor Field

In a kind of large test system, the whole equipment is constituted of many multiple subsystems. These subsystems become one by the interconnection. During the measuring and calibrating procedure for the test system at the outdoor training venue, there are several multiple pulse sequence signals amplitude and cycle period need to measured, because of the complexity of the system composing structure and the ever-changing for practical training environment, the signal being measured is often subject to strong noise interference. In order to ensure the accuracy and reliability of the measuring results, thus we can provide effective and reliable data reference for the effectiveness of the equipment systems, we must do in-depth analysis for actual interference, and to take effective method to suppress the interference.

TH-C-WAB-01: BEST IN PHYSICS (JOINT IMAGING-THERAPY)-Semi-Automated Probabilistic Segmentation of Head and Neck Anatomy Through Structure Specific Feature Selection From Multi-Sequence MRI

Purpose: To develop semi‐automatic methods for robust segmentation of head and neck anatomy through structure‐specific image features selection from multiple MRI sequences. Methods: We developed a semi‐automatic approach for probabilistic segmentation of head and neck anatomy that combines several candidate segmentations using random forests and structure‐specific image features selection from multiple MRI sequences. Starting from user‐drawn line segments on a single axial image, in each tree, structure segmentations are generated from composite feature images computed at the tree split nodes. Composite features are computed through random combinations of the MRI sequences and image features, including texture and Laplacian of Gaussian gradients. We used seven different MRI pulse sequences obtained from a Phillips scanner, including Dixon water only T1, Dixon fat only T1, Dixon in‐phase, Dixon opposed‐phase, T1‐weighted, T2‐weighted and diffusion weighted whole body imaging with background body signal suppression (DWIBS). The highest quality anatomical structure segmentation in a tree is extracted from all available split node segmentations with segmentation quality measured using within‐segment statistics including kurtosis, edge quality, and inter‐segment dissimilarity. The joint segmentation with probabilistic score is obtained by combining all the generated tree segmentations. Results: We used our approach to segment anatomical structures in head and neck images using the seven MRI sequences listed above. The algorithm returned the segmentations, their probabilistic scores, and the highest quality feature images for each structure. We evaluated our approach by computing DICE overlap scores with manually segmented ground truths and obtained an overall segmentation accuracy of 80% for the various radiotherapeutically‐relevant anatomic structures. Conclusion: We developed a semi‐automatic, random forest‐based probabilistic segmentation of head and neck anatomy by combining multiple MRI pulse sequences. Our approach achieves accurate segmentation for various radiotherapeutically‐relevant anatomic structures. Additionally, it extracts the highest quality composite feature images for obtaining optimal segmentation for the same structures. Phillips

Magnetic Resonance Imaging of the Hand and Wrist: Techniques and Spectrum of Disease

Magnetic resonance imaging (MRI) is an excellent imaging modality for the evaluation of pathologic processes of the hand and wrist. MRI of the hand and wrist provides high-resolution imaging of osseous structures and soft-tissue structures (including ligaments, tendons, nerves, and muscles) through the use of multiple imaging techniques and pulse sequences. This article updates orthopaedic surgeons on current MRI techniques and illustrates the spectrum of hand and wrist disease detectable by MRI. We searched PubMed with use of the keywords “MRI” plus “hand” or “wrist” for studies less than five years old evaluating MRI techniques. On the basis of a review of the recently published literature and the authors’ experience, we define and describe the applications of the following: (1) conventional, non-gadolinium-enhanced MRI, (2) gadolinium-enhanced MRI, and (3) MR arthrography. We also describe the classic MRI appearance of lesions commonly evaluated by MRI, including occult fracture, triangular fibrocartilage complex injury, interosseous ligament injury, extrinsic carpal ligament injury, thumb ulnar collateral ligament injury, traumatic tendon injury, finger pulley injury, ulnar impaction syndrome, tendinopathy, Kienbock disease, posttraumatic scaphoid osteonecrosis, infection, inflammatory arthropathy, compression neuropathy, and various soft-tissue masses. The incorporation of dedicated surface coils and higher-strength magnets has improved the quality of magnetic resonance imaging (MRI) scanners substantially over the last decade. By manipulating the scanning parameters when performing an MRI examination, contrast differences between tissues can be emphasized on the basis of inherent tissue properties known as T1 and T2. T1-weighted images are generally regarded as best for illustrating anatomic detail. T2-weighted sequences highlight alterations in water content, which are characteristic of most pathologic conditions. Short tau inversion recovery (STIR) and fat-suppressed T2-weighted images accentuate fluid and edema and are the most sensitive for detecting pathologic changes in both bone and soft tissue. The intravenous administration of a gadolinium-based contrast agent …

MRI of persistent cloaca: Can it substitute conventional imaging?

PurposeTo define the role of MRI in the preoperative assessment of patients with persistent cloaca and whether it can substitute other imaging modalities. MethodsWe prospectively examined eleven patients with persistent cloaca between July 2007 and March 2012. Non contrast MRI examinations were performed on 1.5T magnet using head coil. Multiple pulse sequences (T1WI, T2WI, fat suppression) were obtained in axial, sagittal and coronal planes of the pelvis, abdomen, and spine. The scans were reviewed for the following: the level and type of rectal termination, the developmental state of striated muscle complex (SMC), associated genitourinary and spinal anomalies. MRI findings were compared to conventional fluoroscopic imaging, operative and endoscopic findings. We applied novel MRI parameters (urethral length, relative hiatal distance and vaginal volume). The relation between different parameters was tested statistically using Pearson correlation test. ResultsMRI could accurately demonstrate the level of bowel termination in patients with persistent cloaca, in addition to its high sensitivity for detection of mullerian anomalies which were present in 73% of patients. Furthermore, MRI could disclose associating renal and spinal anomalies, and assess the developmental state of SMC.The shorter the urethra (higher urogenital confluence), the narrower the pelvic hiatus, and the more was the obstruction (vaginal distension). ConclusionMRI is a valuable tool in exploring the different internal anatomical features of the cloacal anomaly; and when combined with endoscopy, MRI can make other preoperative conventional imaging unnecessary.

Evaluation of Renal Artery in Hypertensive Patients by Unenhanced MR Angiography Using Spatial Labeling With Multiple Inversion Pulses Sequence and by CT Angiography

The purposes of this study were to determine the performance of a new unenhanced MR angiography (MRA) sequence, spatial labeling with multiple inversion pulses (SLEEK), with regard to its ability to present the renal arteries and to reveal renal artery disease in patients with secondary hypertension. Unenhanced MRA using SLEEK was performed on a 1.5-T MRI system for assessing renal arteries in 50 patients with hypertension. Then all patients underwent CT angiography (CTA) within 1-7 days. The ability to present the renal arteries and to reveal renal artery disease with SLEEK was evaluated by two experienced radiologists and was compared with CTA results using a joint reading performed in consensus. Forty-six patients with hypertension successfully underwent SLEEK MRA. A total of 119 renal arteries were assessed, including 86 normal arteries, 26 with stenoses, and seven with fibromuscular dysplasia on CTA. There was excellent correlation between SLEEK and CTA in presenting the degree of renal artery stenosis (r(s) = 0.851; p < 0.05). SLEEK was superior to CTA in revealing the third- and fourth-order segmental branches in the renal parenchyma (p < 0.05). SLEEK has the advantage of avoiding interference from vertebra, atherosclerotic plaques, and early venous system enhancement. Unenhanced MRA using SLEEK is a reliable diagnostic method for evaluating renal artery disease and revealing segmental branches in the renal parenchyma. It is relatively inexpensive and is not associated with renal complications. It can be used as an alternative to CTA for screening for renal artery disease, especially in patients with hypertension and renal insufficiency.

Lactate detection in inducible and orthotopic Her2/neu mammary gland tumours in mouse models

This study compared the steady state concentration of lactate in an inducible Her2/nue transgenic breast cancer mouse model and in tumours from the same Her2/neu model grown orthotopically. In vivo lactate was detected by MRS using the Hadamard encoded selective multiple quantum coherence pulse sequence (HadSelMQC) recently developed by our laboratory. A lower lactate signal was observed in the inducible tumours compared to orthotopic tumours in vivo, while ex vivo analysis of perchloric acid extracts revealed similar amounts of this metabolite in both models. Histological staining of mammary tumour specimens showed a much higher level of fat tissue in inducible tumours compared to the orthotopic model. Phantom studies with [3-(13) C] lactate indicated that a lipid environment could significantly reduce the T2 of lactate and impede its detection. The transgenic inducible model for breast cancer not only better recapitulated the biological aspects of the human disease but also provided additional characteristics related to in vivo detection of lactate that are not available in orthotopic or xenograft models. This study suggests that the level of lactate measured by the HadSelMQC pulse sequence may be underestimated in human patients in the presence of high lipid levels that are typically encountered in the breast.

The Design and Implementation of Multiple Square Wave Pulse Sequence Recorder

For the need to test square wave pulse sequence, designed and implemented a recorder. Recorder using FPGA for judging square wave pulse’s edge and precise timing functions, using C8051F MCU to storage the results of time-series data and printing functions, FPGA and MCU using a custom protocol for data exchange and command transfer. After experimental verification, the recorder have 1ms accuracy to record 28 roads square wave pulse signal timing, and fixed-format print the results.