title: Minimum envelope roughness pulse design for reduced amplifier distortion in parallel excitation.
abstract: Parallel excitation uses multiple transmit channels and coils, each driven by independent waveforms, to afford the pulse designer an additional spatial encoding mechanism that complements gradient encoding. In contrast to parallel reception, parallel excitation requires individual power amplifiers for each transmit channel, which can be cost prohibitive. Several groups have explored the use of low-cost power amplifiers for parallel excitation; however, such amplifiers commonly exhibit nonlinear memory effects that distort radio frequency pulses. This is especially true for pulses with rapidly varying envelopes, which are common in parallel excitation. To overcome this problem, we introduce a technique for parallel excitation pulse design that yields pulses with smoother envelopes. We demonstrate experimentally that pulses designed with the new technique suffer less amplifier distortion than unregularized pulses and pulses designed with conventional regularization.
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, California, USA. wgrissom@gmail.com
authors.forename: William A
authors.initials: WA
authors.lastname: Grissom
authors.forename: Adam B
authors.initials: AB
authors.lastname: Kerr
authors.forename: Pascal
authors.initials: P
authors.lastname: Stang
authors.forename: Greig C
authors.initials: GC
authors.lastname: Scott
authors.forename: John M
authors.initials: JM
authors.lastname: Pauly
mesh_terms: D000669:Amplifiers, Electronic; D016477:Artifacts; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D010363:Pattern Recognition, Automated / Q000379:methods*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*