RF coil system design for MRI applications inhomogeneous main magnetic field

Yılmaz, Ayhan Ozan
In this study, RF coil geometries are designed for MRI applications using inhomogeneous main magnetic fields. The current density distributions that can produce the desired RF magnetic field characteristics are obtained on predefined cubic, cylindrical and planar surfaces and Tikhonov, CGLS, TSVD and Rutisbauer regularization methods are applied to match the desired and generated magnetic fields. The conductor paths, which can produce the current density distribution calculated for each surface selection and regularization technique, are determined using stream functions. The magnetic fields generated by the current distributions are calculated and the error percentages between the desired and generated magnetic fields are found. Optimum conductor paths that are going to be produced on cubic, cylindrical and planar surfaces and the required regularization method are determined on the basis of error percentages and realizability of the conductor paths. The optimum conductor path calculated for the planar coil is realized and in the measurement done by LakeShore 3-Channel Gaussmeter, an average error percentage of 11 is obtained between the theoretical and measured magnetic field. The inductance values of the realized RF coil are measured; the tuning and matching capacitance values are calculated and the frequency characteristics of the system is tested using Electronic Workbench 5.1. The quality factor value of the tested system is found to be 162.5, which corresponds to a bandwidth of 39,2 KHz at 6,387 MHz (operating frequency of METU MRI system). The techniques suggested in this study can be used in order to design and realize RF coils on prede¯ned arbitrary surfaces for inhomogeneous main magnetic fields. In addition, a hand held MRI device can be manufactured which uses a low cost permanent magnet to provide a magnetic field and generates the required RF field with the designed RF coil using the techniques suggested in this study.


Optimum current injection strategy for magnetic resonance electrical impedance tomography
Altunel, Haluk; Eyüboğlu, Behçet Murat; Department of Electrical and Electronics Engineering (2008)
In this thesis, optimum current injection strategy for Magnetic Resonance Electrical Impedance Tomography (MREIT) is studied. Distinguishability measure based on magnetic flux density is defined for MREIT. Limit of distinguishability is analytically derived for an infinitely long cylinder with concentric and eccentric inhomogeneities. When distinguishability limits of MREIT and Electrical Impedance Tomography (EIT) are compared, it is found that MREIT is capable of detecting smaller perturbations than EIT. ...
Light flicker evaluation of electric arc furnaces based on novel signal processing algorithms
Köse, Neslihan; Leblebicioğlu, Mehmet Kemal; Department of Electrical and Electronics Engineering (2009)
In this research work, two new flickermeters are proposed to estimate the light flicker caused by electric arc furnaces (EAFs) where the system frequency deviates significantly. In these methods, analytical expressions of the instantaneous light flicker sensation are obtained beginning from a voltage waveform and these expressions are used to obtain a flicker estimation method based on the IEC (International Electrotechnical Commission) flickermeter. First method is a spectral decomposition based approach u...
Magnetic resonance current density imaging using one component of magnetic flux density
Ersöz, Ali; Eyüboğlu, Behçet Murat; Department of Electrical and Electronics Engineering (2010)
Magnetic Resonance Electrical Impedance Tomography (MREIT) algorithms using current density distribution have been proposed in the literature. The current density distribution can be determined by using Magnetic Resonance Current Density Imaging (MRCDI) technique. In MRCDI technique, all three components of magnetic flux density should be measured. Hence, object should be rotated inside the magnet which is not trivial even for small size objects and remains as a strong limitation to clinical applicability o...
RF Coil Design for MRI Applications in Inhomogeneous Main Magnetic Fields
Yılmaz, Ayşen; Eyueboglu, B. M. (2006-09-01)
Conventional Magnetic Resonance Imaging (MRI) techniques require homogeneous main magnetic fields. However, MRI applications that are executed in inhomogenous main magnetic fields have been developed in recent years. In this study, RF coil geometries are designed for MRI applications in inhomogeneous magnetic fields. Method of moments is used to obtain the current density distribution on a predefined surface that can produce a desired magnetic field, which is perpendicular to the given inhomogenous main mag...
Removal of baseline wandering from the electrocardiogram
Tanrıverdi, Volkan; Serinağaoğlu Doğrusöz, Yeşim; Department of Electrical and Electronics Engineering (2006)
ECG measures electrical potentials on the body surface via contact electrodes. Conditions such as movement of the patient, breathing, and interaction between the electrodes and skin cause baseline wandering of the ECG signal. Baseline wandering noise can mask some important features of the ECG signal; hence it is desirable to remove this noise for proper analysis of the ECG signal. This study includes an implementation and evaluation of methods to remove this noise, such as finite impulse response filters, ...
Citation Formats
A. O. Yılmaz, “RF coil system design for MRI applications inhomogeneous main magnetic field,” M.S. - Master of Science, Middle East Technical University, 2007.