title: Correcting surface coil excitation inhomogeneities in single-shot SPEN MRI.
abstract: Given their high sensitivity and ability to limit the field of view (FOV), surface coils are often used in magnetic resonance spectroscopy (MRS) and imaging (MRI). A major downside of surface coils is their inherent radiofrequency (RF) B1 heterogeneity across the FOV, decreasing with increasing distance from the coil and giving rise to image distortions due to non-uniform spatial responses. A robust way to compensate for B1 inhomogeneities is to employ adiabatic inversion pulses, yet these are not well adapted to all imaging sequences - including to single-shot approaches like echo planar imaging (EPI). Hybrid spatiotemporal encoding (SPEN) sequences relying on frequency-swept pulses provide another ultrafast MRI alternative, that could help solve this problem thanks to their built-in heterogeneous spatial manipulations. This study explores how this intrinsic SPEN-based spatial discrimination, could be used to compensate for the B1 inhomogeneities inherent to surface coils. Experiments carried out in both phantoms and in vivo rat brains demonstrate that, by suitably modulating the amplitude of a SPEN chirp pulse that progressively excites the spins in a direction normal to the coil, it is possible to compensate for the RF transmit inhomogeneities and thus improve sensitivity and image fidelity.
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Rita
authors.initials: R
authors.lastname: Schmidt
authors.affiliation: Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Mor
authors.initials: M
authors.lastname: Mishkovsky
authors.affiliation: School of health, University of Applied Sciences and Arts Western Switzerland, Geneva, Switzerland.
authors.forename: Jean-Noel
authors.initials: JN
authors.lastname: Hyacinthe
authors.affiliation: Center of Biomedical Imaging (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Kunz
authors.affiliation: Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.|Center of Biomedical Imaging (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
authors.affiliation: Institute of the Physics of Biological Systems, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Comment
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Lucio
authors.initials: L
authors.lastname: Frydman
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000033:anatomy & histology; D017352:Echo-Planar Imaging / Q000295:instrumentation; D004574:Electromagnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011846:Radio Waves; D051381:Rats
keywords: B(1) corrections; Spatiotemporal encoding; Surface coil MRI; Swept pulses; Ultrafast MRI