<i>In vivo</i> rapid magnetic field measurement and shimming using single scan differential phase mapping

Kanayama, Shoichi; Kuhara, Shigehide; Satoh, K.

doi:10.1002/mrm.1910360421

Cited by 45 publications

(33 citation statements)

References 18 publications

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“…The theoretical error in the field determination (Eq. [7] in Ref. 1) is rewritten here with the factors dependent on T* 2 and as ppm Ϫ2 ͑n ,T* 2 ͒ ϭ ͓n ͔ 2 1 ϩ e 2n րT2* [2] Calculating from Eq.…”

Section: Resultsmentioning

confidence: 99%

Field mapping without reference scan using asymmetric echo-planar techniques

2000

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in B 0 mapping and shimming were achieved by measuring the static field information in multiple subsequent echoes generated by an asymmetric echo-planar readout gradient train. With careful compensation, eddy current effects were shown to affect the adjustment of the shim coils minimally. In addition to reducing the time required for field mapping by two-fold, the sensitivity was simultaneously optimized irrespective of the prevalent T* 2 present, thereby minimizing the error of the static field measurement to below 0.1 Hz. With adiabatic low flip-angle excitation, the time required for field mapping was below 1 second. Magn Reson Med 43:319 -323, 2000.

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Section: Resultsmentioning

confidence: 99%

Field mapping without reference scan using asymmetric echo-planar techniques

2000

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“…At 1.5 T, it may be sufficient to use the linear shim coils for many applications; however, since susceptibility JOURNAL OF MAGNETIC RESONANCE 135, 260 -264 (1998) effects increase linearly with static field, higher-order terms become increasingly important. Shimming of in vivo human tissue requires extremely efficient methods that minimize the time needed for this critical adjustment (2,5,6,8,12,23). One of these techniques, fast, automatic, shimming technique by mapping along projections, FASTMAP, has proven to be useful for human applications at high fields.…”

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confidence: 99%

Resolution Improvements inin Vivo1H NMR Spectra with Increased Magnetic Field Strength

Gruetter¹,

Weisdorf²,

Rajanayagan³

et al. 1998

Journal of Magnetic Resonance

177

131

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The measurement of cerebral metabolites using highly homologous localization techniques and similar shimming methods was performed in the human brain at 1.5 and 4 T as well as in the dog and rat brain at 9.4 T. In rat brain, improved resolution was achieved by shimming all first- and second-order shim coils using a fully adiabatic FASTMAP sequence. The spectra showed a clear improvement in spectral resolution for all metabolite resonances with increased field strength. Changes in cerebral glutamine content were clearly observed at 4 T compared to 1.5 T in patients with hepatic encephalopathy. At 9.4 T, glutamine H4 at 2.46 ppm was fully resolved from glutamate H4 at 2.37 ppm, as was the potential resonance from gamma-amino-butyric acid at 2.30 ppm and N-acetyl-aspartyl-glutamate at 2.05 ppm. Singlet linewidths were found to be as low as 6 Hz (0.015 ppm) at 9.4 T, indicating a substantial decrease in ppm linewidth with field strength. Furthermore, the methylene peak of creatine was partially resolved from phosphocreatine, indicating a close to 1:1 relationship in gray matter. We conclude that increasing the magnetic field strength increases spectral resolution also for 1H NMR, which can lead to more than linear sensitivity gains.

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“…( 4,5)]. The use of a Carr-Purcell echo rather than a gradient echo removes the need to change the shim power supplies.…”

Section: Figmentioning

confidence: 98%

“…It is a tedious and at times maps obtained from time-shifted spin echoes (4). Similar principles have recently been applied with impressive suca frustrating task, and few instrument operators would hesitate to delegate it to an automatic system were such a system cess in ''gradient shimming'' methods for high-resolution NMR.…”

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confidence: 98%