Travelling wave magnetic resonance imaging at 3 T

Abstract

Waveguides have been successfully used to generate magnetic resonance images at 7 T with whole-body systems. The bore limits the magnetic resonance signal transmitted because its specific cut-off frequency is greater than the majority of resonant frequencies. This restriction can be overcome by using a parallel-plate waveguide whose cut-off frequency is zero for the transversal electric modes and it can propagate any frequency. To investigate the potential benefits of traveling-wave excitation for whole-body imaging at 3 T, we compare numerical simulations at 1.5 T, 3 T, 7 T, and 9 T via the propagation of the principal mode of a parallel-plate waveguide filled with a cylindrical phantom and two surface coils. B1 mapping was computed and used to investigate the feasibility of the traveling-wave approach at 3T. The point spread function method was used to measure the imager performance for the traveling-wave magnetic resonance imaging experiment. Human leg images were acquired to experimentally validate this approach. The principal mode shows very little variations in the field magnitude along the propagation direction at 3 T when compared to other higher resonant frequencies. The B1 mapping showed that it is possible to conduct experiments using the traveling-wave approach at 128 MHz. The point spread function results showed a good performance of the scanner for these type of experiments. Leg images were obtained with the whole-body birdcage coil and the waveguide with two circular coils for comparison purposes. The simulated and in vivo results correspond very well for both magnetic field and specific absorption rate. A pretty similar performance was observed for the traveling-wave approach and the conventional one. We have demonstrated the feasibility of traveling-wave magnetic for whole-body resonance imaging at 3T, using a parallel-plate waveguide with standard pulse sequences and only one coil array. This extends the use of the waveguide approach to a wider range of resonant frequencies.

Subject‐loaded quadrifilar helical‐antenna RF coil with high B1+ field uniformity and large FOV for 3‐T MRI

“…In addition, the traveling‐wave concept has been mostly invoked and tested in 60‐cm MRI bores at 7 T . On the other hand, there exist several traveling‐wave‐inspired designs at 3 T employing a parallel‐plate waveguide, dielectric inserts, and a cylindrical metallic waveguide as an RF shield, respectively, to facilitate RF field coupling to the subject.…”

Electromagnetic interaction simulation of parallel-plate waveguide and Maxwell gradient coils in low field magnetic resonance imaging systems

“…This may be present in the images as hyper intensities that should be digitally corrected in order to improve the image quality. Another way to overcome this possible artifact, is mounting the waveguide plates on a cylindrical former as previously reported by our group [4]. No important distortion of the magnetic field along the region of interest for the parallel-plate waveguide can be appreciated.…”

“…Recently, the parallel-plate waveguide (PPWG) has being employed because all frequencies can propagate and its cut-off frequency is zero for the lowest-order transverse electric mode (M 0 ). We have experimentally demonstrated that the PPWG can produce MR images with remote sensing at 3 Tesla with a clinical system and standard pulse sequences [4]. The electromagnetic interaction between the waveguide and the RF subsystem of a MRI scanner may be a cause of concern in terms of the SAR and image distortion.…”

Comparing Saddle, Slotted-tube and Parallel-plate Coils for Magnetic Resonance Imaging

“…Waveguides have been successfully used to generate magnetic resonance images at 7 T for whole-body systems [18]. From these results, it has been established that waveguides are only suitable for 7 T systems with wide bores of at least 60 cm.…”