An Inexpensive, Scalable Vector Modulator and Application to 2D RF Pulses

It has previously been reported the use of vector modulators for B1 shimming . In that application, all vector modulators were fed with the same RF pulse, and vector modulators were used to vary the overall phases and amplitudes of the RF pulses for each channel. Other groups have also reported the use of vector modulators for MRI parallel transmission . Besides the reported application in “static modulation”, the vector modulator system is also fully capable of high speed modulation for more complex transmit pulses. 2D pulses have interesting applications such as curved slice selective excitation [3] and spin labeling . By providing the vector modulators with a hard pulse from a Varian Inova system, and generating complex analog modulation control signals from an eight channel D/A card, we were able to output four totally independent RF waveforms. Results shows that the system generates 2D pulses or phase modulated slice selective pulses that perform comparably to the modulator in the host Inova console.