PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 3431395

A simple field map for shimming.

I S Mackenzie·E M Robinson·A N Wells·B Wood
View original source ↗Export metadata ↓

Abstract

A field-mapping procedure based on volume-selective spectroscopy is described. For proton NMR the method may be used to optimize magnet shimming, on the sample under investigation, prior to spectroscopy or imaging experiments. Examples of field maps obtained on our 4.7-T system, using phantoms and biological samples of up to 6 cm in diameter, are presented.

Explore related subjects

Magnetic Resonance ImagingMathematicsJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

I S Mackenzie, E M Robinson, A N Wells, B Wood. 1987. A simple field map for shimming.. https://doi.org/10.1002/mrm.1910050307

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

KEEP EXPLORING

Related citations

PubMed2026

Ultra-high-field 7T MRI reveals neural abnormalities of attention networks in relation to cognitive impairment in hypertension.

Hypertension is a significant risk factor for cognitive impairment (CI), yet the corresponding neural network abnormalities remain underexplored. In this study, we examined the associations among global and domain-specific cognitive dysfunction, neuroimaging measures, and blood pressure in a subgroup of hypertensive patients with CI (N = 41) from a randomized controlled trial who underwent ultra-high-field 7 T MRI. Structural atrophy related to CI was localized to regions overlapping the attention networks. Both whole-brain and within-network dysfunction of the attention networks were associated with worse global cognitive performance. Notably, hyperconnectivity within key attention network hubs, including the right anterior insula and posterior intraparietal sulcus, was associated with declined processing speed in hypertensive patients, mediating the association between pulse pressure and processing speed. These findings provide new insights into the neural pathophysiology of hypertension-related CI and suggest potential network-based targets for intervention.

Magnetic Resonance Imaging↗
PubMed2006

Structure-specific magnetic field inhomogeneities and its effect on the correlation time.

We describe the relationship between the correlation time and microscopic spatial inhomogeneities in the static magnetic field. The theory takes into account diffusion of nuclear spins in the inhomogeneous field created by magnetized objects. A simple general expression for the correlation time is obtained. It is shown that the correlation time is dependent on a characteristic length, the diffusion coefficient of surrounding medium, the permeability of the surface and the volume fraction of the magnetized objects. For specific geometries (spheres and cylinders), exact analytical expressions for the correlation time are given. The theory can be applied to contrast agents (magnetically labeled cells), capillary network, BOLD effect and so forth.

Magnetic Resonance Imaging↗
PubMed2006

[Experimental study of coil selection considered from subject size].

We examined the index of coil selection in consideration of subject size to measure signal-to-noise ratio (SNR) and uniformity in a phantom experiment. The QD-Head, 8-channel-Head, and 8-channel-Head-Neck coil were used for head examination, QD-Body, 4-channel-TORSO, and 8-channel-Body coil were used for body examination. In the examination of the head, measurements were performed at various positions in a coil. The SNR measured by the QD-Head coil showed the highest values for 9 cm or 12 cm diameters of the phantom, and 10 cm to 15 cm distance from the coil entrance. The QD-Head coil also showed adequate uniformity at most sizes of phantoms. In the body examination, both multi-channel coils showed an SNR higher than the QD-Body coil for all sizes, but they were inferior to the QD-Body coil in uniformity. The 4-channel-TORSO coil showed an SNR higher than the 8-channel-Body coil when a phantom with a diameter of 21 cm or less was used. Since sensitivity distributions differ according to various cases, the 8-channel coil does not necessarily always show a high SNR. It is necessary to perform coil selection according to the subject's size and purpose.

Magnetic Resonance Imaging↗