PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9543420

Gradient characterization using a Fourier-transform technique.

M T Alley·G H Glover·N J Pelc
View original source ↗Export metadata ↓

Abstract

This paper describes a technique for characterizing the gradient subsystem of a magnetic resonance (MR) system. The technique uses a Fourier-transform analysis to directly measure the k-space trajectory produced by an arbitrary gradient waveform. In addition, the method can be easily extended to multiple dimensions and can be adapted to measuring residual gradient effects such as eddy currents. Several examples of gradient waveform and eddy-current measurements are presented. Also, it is demonstrated how the eddy-current measurements can be parameterized with an impulse-response formalism for later use in system tuning. When compared to a peak-fitting analysis, this technique provides a more direct extraction of the k-space measurements, which reduces the possibility of analysis error. This approach also has several advantages as compared to the conventional eddy-current measurement technique, including the ability to measure very short time constant effects.

Explore related subjects

Fourier AnalysisImage Processing, Computer-AssistedMagnetic Resonance ImagingMagneticsModels, StructuralPredictive Value of TestsComparative StudyJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

M T Alley, G H Glover, N J Pelc. 1998. Gradient characterization using a Fourier-transform technique.. https://doi.org/10.1002/mrm.1910390411

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1998

"Hidden" sequence periodicities and protein architecture.

I demonstrate the existence in protein domain sequences of sets of statistically significant periodic signals, characteristic of the architectures of those domains. It is shown that, although the frequencies of the signals characteristic of a particular architecture have definite wave numbers, they can occur in any physical property. The characteristic signals define sequence units, which may correspond to specific structural features. Study of signals in different architectures suggests that symmetric structures are characterized by sets of sequence signals, which are members of harmonic series and which therefore impose commensurate periodicities on the structure. Asymmetric structures are characterized by mutually incommensurate sets of sequence signals. It is pointed out that, although these periodic sequence units can be very short, their existence is a property of the entire sequence.

Fourier Analysis↗
PubMed1998

Formalistic description of multislice calculation method.

This paper presents a formalistic description of the multislice method. The effects of the number of beams, the number of Fourier components for the projected potential used for the phase grating, the number of the iterations and the slice thickness on multislice calculations are discussed qualitatively. The phenomenon of "leaking" of the wave function to higher order reflections in reciprocal space in a multislice calculation is also discussed. The relationship between the number of Fourier components of the projected potential and the number of beams used for the wave function in reciprocal space is discussed. Additionally, the difference between the eigenvalue method and the multislice method is introduced. The difference between the use of the Fourier transformation vs. the convolution in reciprocal space on multislice calculations is also discussed. Multislice computer simulations were carried out using the commercial program Cerius2 for rutile TiO2. Calculated results are compared with the results of other programs reported in the literature. The effect of slice thickness of the multislice calculation is also shown.

Fourier Analysis↗
PubMed1998

An 1H-13C-13C-edited 1H NMR experiment for making resonance assignments in the active site of heme proteins.

In paramagnetic heme proteins, it is often problematic to make proton resonance assignments for heme substituents that do not have large isotropic shifts and consequently lie under the large envelope of polypeptide resonances. Furthermore, assignments that would normally be performed with the aid of HMBC experiments in diamagnetic molecules can prove difficult in the active site of paramagnetic heme proteins if T2(-1) > 2JCH. To circumvent this problem, a new method is presented to selectively detect 1H in 1Hn-13C-13C fragments biosynthetically introduced into the active site of heme proteins. The pulse sequence combines well-known building blocks such as INEPT to transfer 1H spin magnetization to bonded 13C nuclei, followed by INADEQUATE to generate 13C-13C double-quantum coherence that is selected with pulsed field gradients, and finally reverse-INEPT to transfer magnetization back to 1H nuclei for subsequent observation. The new 1Hn-13C-13C edited experiment takes advantage of the relatively large values of 1JCH and 1JCC, avoiding the long interpulse delays in HMBC that compromise the detectability of rapidly relaxing nuclei. The potential applicability of the pulse sequence is demonstrated by its contribution to the unambiguous assignment of the carbonyl carbons in the heme propionates of ferricytochrome b5.

Fourier Analysis↗