A growing number of studies show that the quality and safety of Magnetic Resonance Imaging (MRI) can be significantly improved with careful selection and arrangement of materials having a high electric permittivity, or High Permittivity Materials (HPMs) in the space around the radiofrequency (RF) coil and the human subject. With strategic use, these materials act to convert otherwise useless electric field energy in the space surrounding the RF coil and patient into useful magnetic field energy through the effects of displacement currents. These displacement currents are more distributed sources of magnetic fields than are the conductive currents in the discrete wires alone, and can be closer to the subject than the discrete wires improving the sensitivity without compromising safety. The net result is higher SNR (by about 40% in many experiments and simulations) in reception and significantly less RF energy absorbed by the subject in transmission. Given the SNR-limited nature of MRI, the multiple significant costs of going to ever-higher field strengths (including finding superconductive alternatives to NbTi), and the fact that HPMs can be used in all existing scanners for an immediate boost in SNR, pursuing this work is critical to the advancement of MRI on existing and future systems. We propose to develop thin, solid HPMs that will fit within the space that is currently occupied by the plastic coil formers in state-of-the-art clinical coils and integrate them into new coil designs. Thus, the final result will be no larger than existing clinical coils and the conducting coils will be no further from the subject. Preliminary simulation and experiments demonstrate the feasibility of this approach. Numerical simulations considering both SNR and patient heating (SAR) will guide the design of the materials both in terms of desired properties and shape. Otherwise equivalent RF head coils with and without the incorporation of HPMs will be constructed for use on 7T research and 3T clinical systems. The performance of coils with and without HPMs will be compared in a number of clinically relevant protocols at both field strengths. Performance will also be compared to existing state-of-the-art clinical coils. We expect significant gains in SNR and reduction in SAR at both field strengths. Successful completion of this research will overcome numerous obstacles to practical, routine use of HPMs and make significant (~40%) gains in SNR possible on both future and existing MRI systems.
With this project we will make significant improvements to Magnetic Resonance Imaging (MRI) technology. We will develop, implement, and demonstrate novel advances to improve the quality, speed, and safety of MRI for research and medical applications. These developments are centered around strategic use of materials with high electric permittivity, which can improve the efficiency of the radiofrequency fields used in MRI by converting much of the wasted electric energy through space into useful magnetic energy needed for MRI.
|Vaidya, Manushka V; Deniz, Cem M; Collins, Christopher M et al. (2018) Manipulating transmit and receive sensitivities of radiofrequency surface coils using shielded and unshielded high-permittivity materials. MAGMA 31:355-366|
|Haemer, Gillian G; Vaidya, Manushka; Collins, Christopher M et al. (2018) Approaching ultimate intrinsic specific absorption rate in radiofrequency shimming using high-permittivity materials at 7 Tesla. Magn Reson Med 80:391-399|
|Vaidya, Manushka V; Sodickson, Daniel K; Collins, Christopher M et al. (2018) Disentangling the effects of high permittivity materials on signal optimization and sample noise reduction via ideal current patterns. Magn Reson Med :|
|Vaidya, Manushka V; Lazar, Mariana; Deniz, Cem M et al. (2018) Improved detection of fMRI activation in the cerebellum at 7T with dielectric pads extending the imaging region of a commercial head coil. J Magn Reson Imaging 48:431-440|
|Yu, Zidan; Xin, Xuegang; Collins, Christopher M (2017) Potential for high-permittivity materials to reduce local SAR at a pacemaker lead tip during MRI of the head with a body transmit coil at 3?T. Magn Reson Med 78:383-386|