DocumentCode :
1396730
Title :
Measurement of AC magnetic field distribution using magnetic resonance imaging
Author :
Ider, Y. Ziya ; Muftuler, L. Tugan
Author_Institution :
Dept. of Electr. & Electron. Eng., Middle East Tech. Univ., Ankara, Turkey
Volume :
16
Issue :
5
fYear :
1997
Firstpage :
617
Lastpage :
622
Abstract :
Electric currents are applied to body in numerous applications in medicine such as electrical impedance tomography, cardiac defibrillation, electrocautery, and physiotherapy. If the magnetic field within a region is measured, the currents generating these fields can be calculated using the curl operator. In this study, magnetic fields generated within a phantom by currents passing through an external wire is measured using a magnetic resonance imaging (MRI) system. A pulse sequence that is originally designed for mapping static magnetic field inhomogeneity is adapted. AC current in the form of a burst sine wave is applied synchronously with the pulse sequence. The frequency of the applied current is in the audio range with an amplitude of 175-mA rms. It is shown that each voxel value of sequential images obtained by the proposed pulse sequence is modulated similar to a single-tone broadband frequency modulated (FM) waveform with the AC magnetic field strength determining the modulation index. An algorithm is developed to calculate the AC magnetic field intensity at each voxel using the frequency spectrum of the voxel signal. Experimental results show that the proposed algorithm can be used to calculate AC magnetic field distribution within a conducting sample that is placed in an MRI system.
Keywords :
bioelectric phenomena; biomedical NMR; biomedical measurement; magnetic field measurement; 175 mA; AC magnetic field distribution measurement; applied electric currents; burst sine wave; cardiac defibrillation; conducting sample; curl operator; current density imaging; electrical impedance tomography; electrocautery; external wire; magnetic resonance imaging; phantom; physiotherapy; pulse sequence; sequential images; single-tone broadband frequency modulated waveform; voxel signal frequency spectrum; Biomedical imaging; Current measurement; Frequency modulation; Impedance; Magnetic field measurement; Magnetic fields; Magnetic modulators; Magnetic resonance imaging; Pulse modulation; Tomography; Algorithms; Computer Simulation; Electric Countershock; Electric Impedance; Electric Stimulation Therapy; Electricity; Electrocoagulation; Electromagnetic Fields; Feasibility Studies; Fourier Analysis; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Models, Biological; Phantoms, Imaging; Physical Therapy Modalities; Sound; Time Factors; Tomography;
fLanguage :
English
Journal_Title :
Medical Imaging, IEEE Transactions on
Publisher :
ieee
ISSN :
0278-0062
Type :
jour
DOI :
10.1109/42.640752
Filename :
640752
Link To Document :
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