Use Of Pulse Sequences Research Articles

A fast and simple method for calibrating the flip angle in hyperpolarized 13C MRS experiments

ABSTRACTHyperpolarized 13C Magnetic resonance represents a promising modality for in vivo studies of intermediary metabolism of bio‐molecules and new biomarkers. Although it represents a powerful tool for metabolites spatial localization and for the assessment of their kinetics in vivo, a number of technological problems still limits this technology and needs innovative solutions. In particular, the optimization of the signal‐to‐noise ratio during the acquisitions requires the use of pulse sequences with accurate flip angle calibration, which is performed by adjusting the transmit power in the prescan step. This is even more critical in the case of hyperpolarized studies, because the fast decay of the hyperpolarized signal requires precise determination of the flip angle for the acquisition. This work describes a fast and efficient procedure for transmit power calibration of magnetic resonance acquisitions employing selective pulses, starting from the calibration of acquisitions performed with non‐selective (hard) pulses. The proposed procedure employs a simple theoretical analysis of radiofrequency pulses by assuming a linear response and can be performed directly during in vivo studies. Experimental MR data validate the theoretical calculation by providing good agreement. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 78–84, 2015

Trace Level Detection of Compounds Related to the Chemical Weapons Convention by 1H-Detected 13C NMR Spectroscopy Executed with a Sensitivity-Enhanced, Cryogenic Probehead

Two-dimensional 1H-13C HSQC (heteronuclear single quantum correlation) and fast-HMQC (heteronuclear multiple quantum correlation) pulse sequences were implemented using a sensitivity-enhanced, cryogenic probehead for detecting compounds relevant to the Chemical Weapons Convention present in complex mixtures. The resulting methods demonstrated exceptional sensitivity for detecting the analytes at trace level concentrations. 1H-13C correlations of target analytes at < or = 25 microg/mL were easily detected in a sample where the 1H solvent signal was approximately 58,000-fold more intense than the analyte 1H signals. The problem of overlapping signals typically observed in conventional 1H spectroscopy was essentially eliminated, while 1H and 13C chemical shift information could be derived quickly and simultaneously from the resulting spectra. The fast-HMQC pulse sequences generated magnitude mode spectra suitable for detailed analysis in approximately 4.5 h and can be used in experiments to efficiently screen a large number of samples. The HSQC pulse sequences, on the other hand, required roughly twice the data acquisition time to produce suitable spectra. These spectra, however, were phase-sensitive, contained considerably more resolution in both dimensions, and proved to be superior for detecting analyte 1H-13C correlations. Furthermore, a HSQC spectrum collected with a multiplicity-edited pulse sequence provided additional structural information valuable for identifying target analytes. The HSQC pulse sequences are ideal for collecting high-quality data sets with overnight acquisitions and logically follow the use of fast-HMQC pulse sequences to rapidly screen samples for potential target analytes. Use of the pulse sequences considerably improves the performance of NMR spectroscopy as a complimentary technique for the screening, identification, and validation of chemical warfare agents and other small-molecule analytes present in complex mixtures and environmental samples.

GROWTH CARTILAGE: Normal Appearance, Variants and Abnormalities

The cartilaginous structures in the growing ends of the bone have a complex anatomy. MR imaging allows exquisite depiction of these structures. The normal anatomy and biochemical features of the zones of cartilage are reviewed. Based on an analysis of signal characteristics, it is possible to optimize the use of pulse sequences to study the normal structures and abnormalities of growing bone.

Multiphoton ionization under sequential excitation by coherent pulses

The use of pulse sequences offers a solution to the conflicting requirements of spectral selectivity and high peak intensities needed to study multiphoton processes. In addition, it is shown that random---rather than regular---pulse sequences can provide unique information on the influence of coherence on a resonant multiphoton process, because the coherence can be adjusted independently of the resonance condition.