A Four-Element 'Clover' Transceiver Array For 3 Tesla Cardiac MRISource: EM Software & Systems (USA) Inc.
By Shumin Wang and Hai Lu
The design of radio frequency (RF) coils is of paramount importance to the quality and safety of Magnetic Resonance Imaging (MRI). Being the signal generator and detector of MRI, RF coils are required to generate a uniform excitation in the target during transmission and high signal-to-noise ratio (SNR) during reception. In the meantime, RF coils must not cause subject overheating in in-vivo human studies. This requires that RF energy deposited inside the human body and coupled to receivers should be minimized.
With the advent of clinical high-field MRI systems, that is B0 = 3 Tesla or higher, the much improved SNR enables the development of fast and effective diagnostic and therapeutic techniques. However, electromagnetic wave effects appear as an issue that challenges the conventional MR imaging methodology. Because the size of human torso is approximately several wavelengths at the MR resonant frequency, that is 123 MHz at 3 Tesla, standing waves appear and sufficient RF excitation is no longer guaranteed in the target region. The volume-coil-induced eddy currents that circulate in the human body also make the use of a body transmit coil less appealing, for safety reasons, when a specific organ, such as the heart, is imaged. Last but not least, the RF energy coupled to receiver cables and detuned circuits is a persistent concern of subject burning.
Reprinted with permission of Microwave Journal from the December 2012 issue.