Optimal specialty RF coils have always been desirable for their high signal to noise ratio (SNR) in today's magnetic resonance imaging (MRI) applications, such as breast imaging. A technique based on the least square field error minimization for designing a hemispherical RF coil that yields an optimal field homogeneity is presented. Based on this minimization approach, the continuous current density on a spherical surface is expanded in the Associated Legendre polynomial series, the resulting field within the hemispherical volume is also expressed in term of the current expansion coefficients, and an error function E is defined as the mean squared field difference over a volume of interests. Then, the continuous current density distribution for the hemispherical coil is obtained by minimizing E with respect to all the independent current expansion coefficients. The self inductance of the coil can be estimated analytically for a given current discretization. Applying the stream function technique, the discrete current pattern can be generated to closely represent the field produced by the continuous current distribution. In order to validate the theory, the magnetic field has been re-evaluated employing the Biot-Savart law to the discrete current loops. Using this approach, a hemispherical RF coil has been successfully designed for imaging a hemispherical volume. A prototype of the coil has been built and tested for imaging at 4.0 Tesla. The analytical and experimental results are in an excellent agreement. Initial results indicate the potential use of such a coil for in vivo NMR breast imaging applications.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of SPIE - The International Society for Optical Engineering|
|State||Published - 2001|
|Event||Medical Imaging 2001: Physics of Medical Imaging - San Diego, CA, United States|
Duration: Feb 18 2001 → Feb 20 2001