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The presented work details the basic feasibility of using radiofrequency (RF) fields generated by ultrahigh field (UHF) magnetic resonance (MR) (B0≥7.0T) systems for therapeutic applications such as RF hyperthermia and targeted drug delivery. Theoretical considerations and numerical electromagnetic field (EMF) simulations conducted in this work demonstrate the increased selectivity and efficiency for thermal dose applications at higher RF frequencies (f >300 MHz). En route to an integrated MR system that supports RF hyperthermia application and imaging simultaneously, RF coil arrays were designed, constructed and evaluated. This novel RF technology was first applied in cardiac and brain MR imaging (MRI) at 7.0 T to examine and demonstrate the basic feasibility of this approach for in vivo imaging. The lessons learned from these pilot studies were employed to develop the physical, conceptual and technical underpinnings of a truly hybrid 8-channel transmit/receive (TX/RX) applicator operating at the 7.0 T proton MR frequency of 298 MHz. The proposed hybrid is a class of its own since it is the world's first. Experimental verification conducted in this work demonstrated that the hybrid applicator supports targeted RF heating, MR imaging and MR thermometry (MRTh). The applicator supports a single feeding RF power amplifier regime but can be also operated via multi-channel RF transmission hardware integrated into the MR scanner. The approach offers extra degrees of freedom (RF phase, RF amplitude) that afford deliberate changes in the location and thermal dose of targeted RF induced heating. While this approach makes additional RF hardware components (RF power amplifiers, RF electronics, filters, RF heating antennas) or software to drive these components obsolete, it allows for high spatial and temporal MR temperature mapping due to intrinsic signal-to-noise ratio (SNR) gain of UHF MR together with the enhanced parallel imaging performance inherent to the multi-channel receive architecture used. Temperature simulations in human voxel models revealed that the proposed hybrid setup is capable to deposit a controlled and localized RF induced thermal dose in the center of the human brain. After demonstrating basic feasibility, theoretical considerations and proof-of-principle experiments were conducted for RF frequencies of up to 1.44 GHz to explore electrodynamic constraints for MRI and targeted RF heating applications for a frequency range larger than 298 MHz. For this frequency regime a significant reduction in the effective area of energy absorption was observed when using dedicated RF antenna arrays proposed and developed in this work. Based upon this initial experience it is safe to conclude that the presented concepts generate sufficient signal strength for the circular polarized spin excitation fields (B1+) with acceptable specific absorption rate (SAR) on the surface, to render in vivo MRI at B0= 33.8 T or in vivo electron paramagnetic resonance (EPR) at L-Band feasible.