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Measurement of AC magnetic field distribution using magnetic resonance imaging. IEEE Trans Med Imaging 1997 Oct;16(5):617-22 PMID: 9368117


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.

Author List

Ider YZ, Muftuler LT


Lutfi Tugan Muftuler PhD Associate Professor in the Neurosurgery department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Computer Simulation
Electric Countershock
Electric Impedance
Electric Stimulation Therapy
Electromagnetic Fields
Feasibility Studies
Fourier Analysis
Image Processing, Computer-Assisted
Magnetic Resonance Imaging
Models, Biological
Phantoms, Imaging
Physical Therapy Modalities
Time Factors

View this publication's entry at the Pubmed website PMID: 9368117
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