title: Constrained optimization of gradient waveforms for generalized diffusion encoding.
abstract: Diffusion MRI is a useful probe of tissue microstructure. The conventional diffusion encoding sequence, the single pulsed field gradient, has recently been challenged as more general gradient waveforms have been introduced. Out of these, we focus on q-space trajectory imaging, which generalizes the scalar b-value to a tensor valued entity. To take full advantage of its capabilities, it is imperative to respect the constraints imposed by the hardware, while at the same time maximizing the diffusion encoding strength. We provide a tool that achieves this by solving a constrained optimization problem that accommodates constraints on maximum gradient amplitude, slew rate, coil heating and positioning of radio frequency pulses. The method's efficacy and flexibility is demonstrated both experimentally and by comparison with previous work on optimization of isotropic diffusion sequences.
authors.affiliation: Elekta Instrument AB, Kungstensgatan 18, Box 7593, SE-103 93 Stockholm, Sweden; Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Center for Medical Image Science and Visualization (CMIV), Linköping University, Sweden. Electronic address: jens.sjolund@liu.se.
authors.forename: Jens
authors.initials: J
authors.lastname: Sjölund
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Filip
authors.initials: F
authors.lastname: Szczepankiewicz
authors.affiliation: Lund University Bioimaging Center, Lund University, Lund, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: Department of Chemistry, Lund University, Lund, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Topgaard
authors.affiliation: Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Carl-Fredrik
authors.initials: CF
authors.lastname: Westin
authors.affiliation: Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Center for Medical Image Science and Visualization (CMIV), Linköping University, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Knutsson
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology; D003337:Corpus Callosum / Q000033:anatomy & histology; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D016011:Normal Distribution; D011846:Radio Waves; D059629:Signal-To-Noise Ratio
keywords: Diffusion MR; Generalized gradient waveforms; Hardware constraints; Optimization; Q-space trajectory imaging