Inverse design of an organ-oriented RF coil for open, vertical-field, MR-guided, focused ultrasound surgery.

The advantages of open, vertical-field, magnetic resonance-guided, focused ultrasound surgery (MRgFUS) are attractive. The inverse technique using the bi-boundary conditions is proposed to design a uterine-oriented intraoperative RF coil with an ultrasound aperture for the MRgFUS system. In the current proposed scheme, the desired magnetic field of the RF coil was set to completely overlap the target organ. The current density distribution on the RF coil surface, accounting for the expected magnetic field, was solved using the inverse technique. The stream function was available through the 'discretization' of the current density distribution on the RF coil surface. The coil windings were obtained from the contour plot of the stream function. As a modification of previous designs, the bi-boundary conditions are proposed in the inverse technique for the existence of the ultrasound aperture. Based on the obtained coil windings, a prototype coil was constructed. MR imaging of the phantom and the human body was performed to show the efficacy of the prototype coil. The results of temperature measurement using the prototype coil in a 0.4-T MR system were satisfactory. The performance of the prototype coil improved compared with the previously reported design.