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Simulated phase of driving voltage for travelling wave MRI with a parallel-plate waveguide at 7 T F. 1Mexico
Puropose Travelling wave Magnetic Resonance Imaging (twMRI) offers to overcome the inhomogeneities due to the standing wave patterns [1-2], and the multiple coil arrays [3]. The spin excitation has been commonly done with RF coils, dipole and patch antennas, etc. The resonant device should be able to generate an adequate magnetic field to transmit the signal to a distant object using a waveguide. We simulated the principal mode magnetic field (TM0) as a function of the driving voltage phase.
1 Vazquez ,
S.
1 Solis
, R.
1 Martin
and A.
2 Rodriguez .
City, MX,Faculty of Sciences, UNAM,Physics Department,Mexico City, MX, 2Universidad Autonoma Metropolitana Iztapalapa,Electrical Engineering Department
The driving voltage phase varied from 00 to 3600, to investigate the optimal phase value. All simulations were performed along the z-direction at 300MHz with electrical constants: a) destilledwater phantom: μ=0.999991, ε=78.4, σ=5.55e6S/m, ρ= 998Kg/m3 and, thermal conductivity= 0.6W/K/m, b) copper plates: μ=1, σ=5.8e-7S/m, ρ=8930Kg/m3, thermal conductivity= 401W/K/m.
Figure 1. Simulation setup.
B1 shows a sinusoidal pattern, reaching its maximums at π/2 and 3π/2, representing the optimal values to transmit the RF signal to a distant phantom with a PPWG. z-direction profiles inside and outside the PPWG were taken for comparison purposes and shown in Fig. 3. For the green profile, the peak at 50cm represents the coil B1, and the peak around 2m is the B1 inside the spherical phantom. The red profile shows very interesting results because peaks appear. These numerical results demonstrate that it is possible to transmit the RF signal with a specific driving voltage phase using a PPWG and a circular coil located outside the magnet to a phantom 1.5m away.
Methods To investigate how the TM0 magnetic field propagates inside a parallel-plate waveguide for twMRI, numerical simulations were run using CST (CST Microwave Studio, Darmstadt, Germany). Fig. 1 shows the setup. Waveguide copper plates were 2m long and 16cm wide and separated 16cm. A 7cm-radius phantom was 1.5m away from the 7cmradius coil (linearly driven).
Figure 3. B1 simulations of 00 phase (top). Uniformity plots were taken along the green (inside) and red (outside) lines (bottom).
References
Results & Conclusion B1 simulations as a function of the driving voltage phase for a PPWG were computed for different phases along the z-direction and shown in Fig. 2.a). These results were then used to compute phantom B1 for the different phase values and shown in Fig. 2.b).
Figure 2. B1 simulations varying the driving voltage phase (a) and showing sinusoidal pattern (b).
1. Brunner, et. al. Nature. 457(2009)994. 2. Geschewski, et. al. Proc. ISMRM. 18 (2010)1478. 3. Vazquez, et. al. J. App. Phys. 114(2013)064906. 4. Fu et. al. J. Magn. Reson. 177(2005)1.
Acknowledgments CONACYT-Mexico number 112092. Contact: [email protected].
Puropose Travelling wave Magnetic Resonance Imaging (twMRI) offers to overcome the inhomogeneities due to the standing wave patterns [1-2], and the multiple coil arrays [3]. The spin excitation has been commonly done with RF coils, dipole and patch antennas, etc. The resonant device should be able to generate an adequate magnetic field to transmit the signal to a distant object using a waveguide. We simulated the principal mode magnetic field (TM0) as a function of the driving voltage phase.
1 Vazquez ,
S.
1 Solis
, R.
1 Martin
and A.
2 Rodriguez .
City, MX,Faculty of Sciences, UNAM,Physics Department,Mexico City, MX, 2Universidad Autonoma Metropolitana Iztapalapa,Electrical Engineering Department
The driving voltage phase varied from 00 to 3600, to investigate the optimal phase value. All simulations were performed along the z-direction at 300MHz with electrical constants: a) destilledwater phantom: μ=0.999991, ε=78.4, σ=5.55e6S/m, ρ= 998Kg/m3 and, thermal conductivity= 0.6W/K/m, b) copper plates: μ=1, σ=5.8e-7S/m, ρ=8930Kg/m3, thermal conductivity= 401W/K/m.
Figure 1. Simulation setup.
B1 shows a sinusoidal pattern, reaching its maximums at π/2 and 3π/2, representing the optimal values to transmit the RF signal to a distant phantom with a PPWG. z-direction profiles inside and outside the PPWG were taken for comparison purposes and shown in Fig. 3. For the green profile, the peak at 50cm represents the coil B1, and the peak around 2m is the B1 inside the spherical phantom. The red profile shows very interesting results because peaks appear. These numerical results demonstrate that it is possible to transmit the RF signal with a specific driving voltage phase using a PPWG and a circular coil located outside the magnet to a phantom 1.5m away.
Methods To investigate how the TM0 magnetic field propagates inside a parallel-plate waveguide for twMRI, numerical simulations were run using CST (CST Microwave Studio, Darmstadt, Germany). Fig. 1 shows the setup. Waveguide copper plates were 2m long and 16cm wide and separated 16cm. A 7cm-radius phantom was 1.5m away from the 7cmradius coil (linearly driven).
Figure 3. B1 simulations of 00 phase (top). Uniformity plots were taken along the green (inside) and red (outside) lines (bottom).
References
Results & Conclusion B1 simulations as a function of the driving voltage phase for a PPWG were computed for different phases along the z-direction and shown in Fig. 2.a). These results were then used to compute phantom B1 for the different phase values and shown in Fig. 2.b).
Figure 2. B1 simulations varying the driving voltage phase (a) and showing sinusoidal pattern (b).
1. Brunner, et. al. Nature. 457(2009)994. 2. Geschewski, et. al. Proc. ISMRM. 18 (2010)1478. 3. Vazquez, et. al. J. App. Phys. 114(2013)064906. 4. Fu et. al. J. Magn. Reson. 177(2005)1.
Acknowledgments CONACYT-Mexico number 112092. Contact: [email protected].
