Investigations on accelerated imaging at 9.4T with electronically modulated time-varying receive sensitivities
Felix Glang1, Kai Buckenmaier1, Jonas Bause1, Alexander Loktyushin1, Nikolai Avdievich1, and Klaus Scheffler1,2
1High-field Magnetic Resonance Center, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Department of Biomedical Magnetic Resonance, Eberhard Karls University Tübingen, Tübingen, Germany
Time-varying receive sensitivities can be achieved by introducing variable capacitance diodes to the receive loops, which allow to dynamically tune B1-. This offers an additional degree of freedom for MR image encoding, with the potential for improved parallel imaging performance.
Figure 1. Schematic of the proposed receive loop geometry and circuitry. (a) Simulation setup for one of the four modulatable receive loops placed circumferentially around a cylindrical phantom. (b) Circuit diagram of the receive loop with tuning and matching capacitors as well as six adjustable varactor diodes (each in a range between 2 and 20pF) placed on the long sides of the loop, which are used to modulate receive sensitivity profiles B1-.
Figure 4. Sensitivity modulation during readout (RO) of k-space lines. k-space configuration weightings for (a) linear ramp, (b) 8 and (c) 64 sinusoidal oscillations between C1 and C2 along each RO line. The latter is equivalent to switching between C1 and C2 for each ADC sample. (d), (e), (f) G-factors for the respective sensitivity switching patterns. (g) Maximum g-factor for sinusoidal sensitivity switching versus number of oscillations, compared to static sensitivity sets of C1, C2 and combined C1 & C2.