Measuring AC magnetic field distribution using MRI

Electric currents Pre applied to body in numerous applications in medicine, such as Electrical Impedance Tomography (EIT), cardiac defibrillators, electrocautery and some treatment methods in physiotherapy. IT 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 by AC currents injected into a phantom is measured using MRI. A pulse sequence that is originally designed for mapping static magnetic field Is used. AC currents In the form of burst sine wave is applied sychronous with the pulse sequence, Results show that this method can be used in applications where the frequency of the currents is in the audio range and the amplitude is a few milliamperes or larger depending on SNR

Measurement of AC magnetic field distribution using magnetic resonance imaging

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