title: Simultaneous B1 + homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil.
abstract: In high-field MRI severe problems with respect to B(1) (+) uniformity and specific absorption rate (SAR) deposition pose a great challenge to whole-body imaging. In this study the potential of a phased array transmit coil is investigated to simultaneously reduce B(1) (+) nonuniformity and SAR deposition. This was tested by performing electromagnetic simulations of a phased array TEM coil operating at 128 MHz loaded with two different homogeneous elliptical phantoms and four dielectric patient models. It was shown that the wave interference of a circularly polarized RF field with an ellipse and a pelvis produces largely identical B(1) (+) and electric field patterns. Especially for obese patients, this results in large B(1) (+) nonuniformity and global areas with elevated SAR deposition. It is demonstrated that a phased array transmit coil can reduce these phenomena. The technique was especially successful in suppressing SAR hotspots with a decrease up to 50%. The application of optimized settings for an ellipse to the patient models leads to comparable results as obtained with the patient-specific optimizations. This suggests that generic phase/amplitude port settings are possible, requiring no preinformation about patient-specific RF fields. Such a scheme would, due to its simultaneous B(1) (+) homogenization and extra SAR margin, have many benefits for whole-body imaging at 3 T.
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Cornelis A T
authors.initials: CA
authors.lastname: Van den Berg
authors.forename: Bob
authors.initials: B
authors.lastname: van den Bergen
authors.forename: Jeroen B
authors.initials: JB
authors.lastname: Van de Kamer
authors.forename: Bas W
authors.initials: BW
authors.lastname: Raaymakers
authors.forename: Hugo
authors.initials: H
authors.lastname: Kroeze
authors.forename: Lambertus W
authors.initials: LW
authors.lastname: Bartels
authors.forename: Jan J W
authors.initials: JJ
authors.lastname: Lagendijk
mesh_terms: D000042:Absorption; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D019047:Phantoms, Imaging; D011846:Radio Waves; D051598:Whole Body Imaging / Q000379:methods*