Three-dimensional Pulse Sequence Research Articles

Accelerated Reliability Growth Test for Magnetic Resonance Imaging System Using Time-of-Flight Three-Dimensional Pulse Sequence.

A magnetic resonance imaging (MRI) system is a complex, high cost, and long-life product. It is a widely known fact that performing a system reliability test of a MRI system during the development phase is a challenging task. The major challenges include sample size, high test cost, and long test duration. This paper introduces a novel approach to perform a MRI system reliability test in a reasonably acceptable time with one sample size. Our approach is based on an accelerated reliability growth test, which consists of test cycle made of a very high-energy time-of-flight three-dimensional (TOF3D) pulse sequence representing an actual hospital usage scenario. First, we construct a nominal day usage scenario based on actual data collected from an MRI system used inside the hospital. Then, we calculate the life-time stress based on a usage scenario. Finally, we develop an accelerated reliability growth test cycle based on a TOF3D pulse sequence that exerts highest vibration energy on the gradient coil and MRI system. We use a vibration energy model to map the life-time stress and reduce the test duration from 537 to 55 days. We use a Crow AMSAA plot to demonstrate that system design reaches its useful life after crossing the infant mortality phase.

Recommendations of the Russian League Against Epilepsy (RLAE) on the use of magnetic resonance imaging in the diagnosis of epilepsy

Introduction. The MRI method has revolutionized the diagnosis of epilepsy. However, the widespread adoption of MRI in clinical practice is slowed by an insufficient number of high-field MRI scanners, a shortage of trained specialists, and the lack of standard examination protocols. The aim of this article is to present the Recommendations of the Russian League Against Epilepsy (RLAE) on the use of magnetic resonance imaging in the diagnosis of epilepsy.Materials and methods. As a structural element of the International League Against Epilepsy (ILAE), the RLAE considers it important to adapt the Protocol developed by ILAE for specialists in Russia and EAEU countries. The working group analyzed and generalized the clinical practice existing in the Russian Federation, the Republic of Kazakhstan, the Republic of Belarus and the Republic of Uzbekistan. These recommendations are intended for doctors in specialized centers of epilepsy surgery, and for doctors in general medical centers. The recommendations are applicable primarily to adult patients, but the general principles are relevant to children as well.Results. In all patients with convulsive seizures shortly after the first seizure, or patients diagnosed with epilepsy who have an unexplained increase in the frequency of seizures, rapid decrease in cognitive functions or the appearance / worsening of neuropsychiatric symptoms, the RLAE recommends using a unified MR protocol for the neuroimaging of structural sequences in epilepsy with three-dimensional pulse sequences T1 and T2 FLAIR with isotropic voxel 1 × 1 × 1 mm3 and two-dimensional T2- weighted pulse sequences with a pixel size of 1 × 1 mm2 or less. The MRI examination should be combined with EEG or EEG-video monitoring. Using this protocol allows one to set a unified standard for examining patients with epilepsy in order to detect (with high sensitivity) brain lesions playing a key role in the occurrence of seizures. Here, all 13 recommendations are presented.Conclusion. Implementation of these recommendations in clinical practice will improve the access to high-tech medical care and optimize health care costs.

Measurement of protein backbone 13CO and 15N relaxation dispersion at high resolution

Peak overlap in crowded regions of two-dimensional spectra prevents characterization of dynamics for many sites of interest in globular and intrinsically disordered proteins. We present new three-dimensional pulse sequences for measurement of Carr-Purcell-Meiboom-Gill relaxation dispersions at backbone nitrogen and carbonyl positions. To alleviate increase in the measurement time associated with the additional spectral dimension, we use non-uniform sampling in combination with two distinct methods of spectrum reconstruction: compressed sensing and co-processing with multi-dimensional decomposition. The new methodology was validated using disordered protein CD79A from B-cell receptor and an SH3 domain from Abp1p in exchange between its free form and bound to a peptide from the protein Ark1p. We show that, while providing much better resolution, the 3D NUS experiments give the similar accuracy and precision of the dynamic parameters to ones obtained using traditional 2D experiments. Furthermore, we show that jackknife resampling of the spectra yields robust estimates of peak intensities errors, eliminating the need for recording duplicate data points.

Chemical shift separation with controlled aliasing for hyperpolarized (13) C metabolic imaging.

A chemical shift separation technique for hyperpolarized (13) C metabolic imaging with high spatial and temporal resolution was developed. Specifically, a fast three-dimensional pulse sequence and a reconstruction method were implemented to acquire signals from multiple (13) C species simultaneously with subsequent separation into individual images. A stack of flyback echo-planar imaging readouts and a set of multiband excitation radiofrequency pulses were designed to spatially modulate aliasing patterns of the acquired metabolite images, which translated the chemical shift separation problem into parallel imaging reconstruction problem. An eight-channel coil array was used for data acquisition and a parallel imaging method based on nonlinear inversion was developed to separate the aliased images. Simultaneous acquisitions of pyruvate and lactate in a phantom study and in vivo rat experiments were performed. The results demonstrated successful separation of the metabolite distributions into individual images having high spatial resolution. This method demonstrated the ability to provide accelerated metabolite imaging in hyperpolarized (13) C MR using multichannel coils, tailored readout, and specialized RF pulses.

Commentary on an article by Richard B. Frobell, PhD

The anterior cruciate ligament (ACL) is an important stabilizer of the knee joint. At the time of ACL disruption, the “bone bruise” sustained during pivot shift and tibial translation has been recognized as a transchondral fracture of varying severity. Little is known, however, about the risk factors of osteoarthritis following initial ACL injury, or the effect on cartilage morphology following the initial transchondral fracture. Because of its direct multiplanar capabilities and superior soft-tissue contrast, as well as the availability of reproducible, standardized, and surgically validated cartilage pulse sequences, magnetic resonance imaging (MRI) is an extremely well-suited tool to provide objective longitudinal evaluation of cartilage changes following ACL disruption. In a young cohort of patients (mean age, twenty-six years) who sustained an ACL tear, the investigators performed a longitudinal, comprehensive, prospective MRI analysis, using standardized three-dimensional pulse sequences to evaluate morphologic changes and cartilage thickness as well as the extent of subchondral bone marrow edema pattern and joint fluid volume. The patients were captured from a prior randomized controlled trial comparing delayed versus acute ACL reconstruction with a clinical rehabilitation regimen alone. The investigation disclosed significant cartilage thickening in the central portion of the medial femoral condyle, associated with an older age at the time of the ACL tear, …

19F-MRT of pulmonary ventilation in the breath-hold technic using SF6 gas

Development of a method to analyze lung ventilation by 19F-magnetic resonance imaging (MRI) of inspired SF6 gas during breath hold. Measurements were performed with a Siemens Magnetom Vision 1.5 T scanner using the conventional gradient overdrive. Coronal images of the lung were acquired using ultrafast gradient-echo pulse sequences with TR/TE/alpha = 1.4 ms/0.48 ms/40 degrees without slice selection. With NEX = 200 averages and MA = 32 x 64 raw data matrix, the acquisition time was 9 s/image. Higher spatial resolution of 4.7 x 6.3 x 15 mm3 was obtained with a three-dimensional pulse sequence (TR/TE/alpha = 1.6 ms/0.48 ms/65 degrees, NEX = 20) running for 49 s. Measurements wer performed in three anesthetized and ventilated pigs (18 kg). A nearly linear relation between SF6 concentration and 19F signal intensity was observed. The signal-to-noise ratio in images obtained without slice selection was 30.9, with slice selection it was 14.9. No differences between SF6 distribution to both lungs were observed in the animals. Breath-hold MRI of SF6 gas distribution in the lung was demonstrated for the first time. The low spin-density was compensated for by highly repetitive signal averaging. Breath-hold 19F-MR imaging of ventilated airspaces to assess SF6 distribution in the human lung appears to be an interesting new method, which can be implemented with little technical efforts, and does not rely on radioactive isotopes.

Pulmonary perfusion: respiratory-triggered three-dimensional MR imaging with arterial spin tagging--preliminary results in healthy volunteers.

The authors used a spin-tagging method of magnetic resonance perfusion imaging to measure pulmonary perfusion in eight healthy volunteers with use of a respiratory-triggered three-dimensional pulse sequence. The average signal intensity (SI) decrease upon arterial labeling was 24%. The perfusion SI increased by 21% after exercise (P = .02). Focal blood flow abnormalities were observed in a patient with chronic obstructive pulmonary disease.

Three-Dimensional 13C Shift/1H–15N Coupling/15N Shift Solid-State NMR Correlation Spectroscopy

Triple-resonance experiments capable of correlating directly bonded and proximate carbon and nitrogen backbone sites of uniformly 13C- and 15N-labeled peptides in stationary oriented samples are described. The pulse sequences integrate cross-polarization from 1H to 13C and from 13C to 15N with flip-flop (phase and frequency switched) Lee–Goldburg irradiation for both 13C homonuclear decoupling and 1H–15N spin exchange at the magic angle. Because heteronuclear decoupling is applied throughout, the three-dimensional pulse sequence yields 13C shift/1H–15N coupling/15N shift correlation spectra with single-line resonances in all three frequency dimensions. Not only do the three-dimensional spectra correlate 13C and 15N resonances, they are well resolved due to the three independent frequency dimensions, and they can provide up to four orientationally dependent frequencies as input for structure determination. These experiments have the potential to make sequential backbone resonance assignments in uniformly 13C- and 15N-labeled proteins.

Alternative E.COSY techniques for the measurement of 3J(C (i) (') (-1),C (i) (beta) ) and (3) J(H (i) (N) ,C (i) (beta) ) coupling constants in proteins.

Experiments are proposed for the measurement of the vicinal coupling constants between beta-carbons and either amide protons of the same or carbonyl carbons of the preceding amino acid residue in 13C/15N-labeled proteins. Both couplings depend on the backbone torsional angle phi. The three-dimensional pulse sequences give rise to E.COSY-like multiplet patterns in which heteronuclear one-bond couplings separate the doublet components corresponding to the two spin states of the respective passive nuclei. Thus, in contrast to previously published pulse schemes which employed the homonuclear 1J(Calpha,Cbeta) interaction, difficulties due to overlap of spectral regions of active and passive spins are avoided. A major drawback of the novel sequences is their limited sensitivity. Nevertheless, application to Desulfovibrio vulgaris flavodoxin yielded coupling constants for more than 85% of all non-glycine and non-proline residues.

A New Three-Dimensional Pulse Sequence for Correlating Intraresidue NH, N, and CO Chemical Shifts in13C,15N-Labeled Proteins

veloped in recent years to obtain the complete assignment which allows optimum refocusing of the Ca, Cb coupling of N, C-labeled proteins (1) . An experiment that often and also allows the buildup of the Ca, N coupling. At the proves useful is one that correlates backbone NH and N same time, the inclusion of a constant-time [2T(CO)] multiresonances with the intraresidue carbonyl resonance CO (2) . ple-quantum period (Ca, CO) of 10–12 ms allows the moniIn the original experiment, named HN(CA)CO, the pulse toring of the directly attached carbonyl frequencies ( t1) . scheme illustrated in Fig. 1a is used. Finally, the coherence is transferred to the N resonances for Before discussing the improved performances of the new constant-time [2T(N)] monitoring ( t2) and then to the amide pulse sequence, we shall briefly outline the rationale of the protons for detection ( t3) . The delay s of 1.78 ms, followed original experiment. NH proton magnetization is transferred by the proton inversion pulse, allows the refocusing of Ha, to N via an INEPT scheme (3) . After a short delay for Ca couplings at the beginning of the sequence. The eliminarefocussing the NH, N coupling, a constant-time monitoring tion of this coupling term is necessary, since the coherence is of N resonance frequencies follows ( t1) . During this period, finally transferred to a different nucleus (namely, the amide the coupling N–Ca builds up, thereby allowing the coherproton) for detection. For all residues except glycines, the ence transfer to Ca nuclei. After an additional constant delay transfer factor to the final observable term is sin (2pJHa,Cas) , for the evolution of the Ca, CO coupling, the magnetization which is equal to one for JHa,Ca A 140 Hz. For glycine is finally transferred to the carbonyl nuclei for monitoring residues, the coupling of Ca coherences cannot be efficiently ( t2) . Then, by reversing the pathway just described, the magrefocused with respect to both a protons at the same time, netization is brought back to the protons whence it originally and the transfer factor is sin(2pJHa,Cas)cos(2pJHa,Cas) , started for detection ( t3) . In this pulse sequence, two relawhich is equal to zero. Therefore, as a direct consequence of tively long delays (each about 25 ms) are needed in order the coherence-transfer pathway of this experiment, glycine to transfer the magnetization from N nuclei to Ca nuclei signals are expected to be filtered out or at least severely and vice versa (JN–Ca A 11 Hz). During these delays, the diminished, depending on the actual value of the coupling magnetization resides on the N nuclei. Moreover, two addiconstant JHa,Ca involved (4) . The delay r of 2.7 ms allows tional delays (each about 7 ms) are used for the coherence the build up of the N, NH couplings prior to the final magneto be transferred to the carbonyl nuclei from the Ca nuclei tization transfer to amide protons for detection. and vice versa (JCa–CO A 55 Hz). During these periods, the We named our pulse sequence (HACA)CO,NH where magnetization resides on the Ca nuclei. In the center of the the nuclei whose frequencies are monitored are outside pulse sequence, the incremented t2 period is used to monitor brackets. The new pulse scheme (Fig. 1b) provides better the carbonyl frequencies. sensitivity, thanks to several factors. First, the total duration In Fig. 1b, we illustrate an alternative pulse scheme, which of the pulse sequence is about 30 ms shorter than the original allows better sensitivity to be obtained. The magnetization one. However, the advantage, in terms of diminished relaxsources are the Ha nuclei, whose coherence is transferred ation loss, is partially reduced by the increased residence to the directly attached Ca nuclei via an INEPT scheme. A time of the magnetization on the usually fast relaxing Ca