Development and testing of a switchable fractionated dipole antenna for ultrahigh field MRI
Ultrahigh field imaging has provided us with brain images of unprecedented resolution and information. To extend these great advantages towards the body, RF related challenges have to be overcome. Therefore, technologies have been developed in the past decade to account for these challenges including multi-transmit (using mulitple independent waveforms to drive the elements of a coil array) and surface arrays (using transmit-receive elements directly on the patient, rather than a body coil surrounding the patient at some distance). Surface arrays have been presented in many kinds, consisting of loop coils, microstrip elements or, more recently, antennas. Our institute launched the very first introduction of dipole antennas in MRI in 2010. By now, we have developed a more advanced design that is called 'The fractionated dipole antenna'. It is a dipole antenna where the legs are divided into segments. These segments are interconnected by lumped elements (capacitors or inductors). In this way, the currents and voltages on the antenna can be manipulated and, subsequently, the performance of the antenna can be improved. With this design, body imaging at 7 Tesla is taking off and image quality has improved considerably in comparison to previous designs. However, images obtained at 3 Tesla are still superior. Therefore, the antenna array needs further improvement. The antenna design currently in use is a design optimized for imaging with low tissue heating (low SAR). This requires the use of inductors between the dipole segments. An alternative design using capacitors between the segments results in higher SAR levels but a larger receive sensitivity thus better image quality. In fact, during the transmit phase of the MRI sequence, low SAR levels are optimal but during the subsequent receive phase of the sequence, high sensitivity is preferred. The best of both worlds would be created if a switchable design is created where between the dipole segments circuits are located that can switch between transmit and receive operation of the antenna. Such switching networks can be realized by PIN-diodes.
Project outside the universityUniversity Medical Center Utrecht (UMCU)
AssignmentThe objective is to design, build and test a switchable fractionated dipole antenna and/or to characterize its performance in an array setup by simulation.
RequirementsThe actual M.Sc. assignment will take place in consultation with the M.Sc. candidate. A solid background in antenna theory, basic electromagnetics, and signal processing is preferred.
dr.ir. Rob Remis
Circuits and Systems Group
Department of Microelectronics
Last modified: 2014-09-26