In magnetic resonance imaging, the patient is placed in a main magnetic field, also called B0 magnetic field. High power radiofrequency signals are transmitted into the patient to excite dipoles in the subject to resonate and to manipulate selected dipoles. Low power signals from the resonating dipoles are received and processed. In magnetic resonance imaging, magnetic field gradients are applied across the imaged region to encode spatial position in the resonance, e.g. by phase or frequency encoding.
In many applications, it is advantageous to place the radiofrequency transmit coils and/or the radiofrequency receive coils as close to the region of the subject to be imaged as possible. To this end, a variety of local coils have been developed, such as head coils, spine coils, surface coils, and a variety of other coils which are positioned on or close to a surface of the patient adjacent the region to be imaged. The receive coils are connected by cables with the remainder of the system in order to receive power for preamplifiers, and other electronic components that process received signals, as well as for carrying control signals for controlling the coil, and for carrying the received magnetic resonance signals. The cables carry RF pulses from RF transmitters to the transmit portion of the coil. The cables leading to and from the transmit and receive coils have numerous drawbacks such as subject discomfort, inconvenience during setup, and reducing patient throughput. Moreover, the RF fields could induce currents in these cables which could burn or injure the subject, damage electronic components on the transmit or receive coils, reduce image quality, and the like.
In an effort to reduce this cabling, there have been numerous proposals for wireless receive coils. Receive coils have very modest power requirements for preamplifiers, analog to digital converters, and other relatively low power consuming electronics. Typically, a few watts of power are sufficient for powering wireless receive coils. Whole body RF transmit coils built into the bore are often used to excite and manipulate resonance while the resonance signals are received by a wireless receive coil. Local transmit coils which transmit RF pulses on the order of a couple of kilowatts per pulse are generally considered too power consumptive to be made wireless.
It is an object of the present application to provide a wireless transmit, or transmit and receive RF coil for magnetic resonance studies.