Title:
NMRイメージング操作中に誘導される渦電流の測定および補償のための装置及びシステム
Document Type and Number:
Japanese Patent JP4201993
Kind Code:
B2
Abstract:
A method and apparatus is disclosed for measuring and compensating the effects of eddy currents induced during NMR imaging operations. A cubic or cylindrical sample is placed in the imaging volume of a MRI system at a position centrally located with respect to the main magnetic field and oriented with its longitudinal axis parallel to a desired measuring direction. A magnetic field gradient pulse is applied for inducing eddy currents as well as for generating a slice-selective spin-echo signal. The spin-echo signal is acquired immediately after the termination of each eddy-current inducing gradient pulse. Two slices are selected along the desired measurement direction at symmetrical equal distance from the center of the main magnetic field. Two spin-echo signals are acquired for each slice with the polarity of the eddy-current inducing gradient pulse reversed between the two echo signals. Quantitative values for eddy-current induced field gradients and B0 oscillations are determined based on the precessing frequencies of the acquired NMR signals. NMR imaging is improved by compensating for eddy currents effects by applying the quantified values of the field gradients and B0 oscillations to set an appropriate pre-emphasis network. Gradient pulses in MRI/MRS pulse sequences may also be selectively pre-distorted or modified to compensate for resulting gradient-switching induced eddy currents. Other aspects of the disclosed method include measuring the time course of gradient switching, altering the pulse sequences to measure eddy currents having long time constants, repeatedly measuring the eddy currents to assist in pre-emphasis adjustments, and measuring EC-induced field gradients and B0 oscillation in the presence of moderately large background field inhomogeneities.
Inventors:
Wei Guo Tsang
Application Number:
JP2001049792A
Publication Date:
December 24, 2008
Filing Date:
February 26, 2001
Export Citation:
Assignee:
TOSHIBA AMERICA MRI, INC.
International Classes:
A61B5/055; G01R33/387; G01R33/565
Domestic Patent References:
| JP2224735A | ||||
| JP10075940A | ||||
| JP2000262485A |
Foreign References:
| US6448773 |
Attorney, Agent or Firm:
Takehiko Suzue
Sadao Muramatsu
Ryo Hashimoto
Toshio Shirane
Sadao Muramatsu
Ryo Hashimoto
Toshio Shirane