title: Virtual population-based assessment of the impact of 3 Tesla radiofrequency shimming and thermoregulation on safety and B1 + uniformity.
abstract: To assess the effect of radiofrequency (RF) shimming of a 3 Tesla (T) two-port body coil on B1 + uniformity, the local specific absorption rate (SAR), and the local temperature increase as a function of the thermoregulatory response.
  
  
  
  RF shimming alters induced current distribution, which may result in large changes in the level and location of absorbed RF energy. We investigated this effect with six anatomical human models from the Virtual Population in 10 imaging landmarks and four RF coils. Three thermoregulation models were applied to estimate potential local temperature increases, including a newly proposed model for impaired thermoregulation.
  
  
  
  Two-port RF shimming, compared to circular polarization mode, can increase the B1 + uniformity on average by +32%. Worst-case SAR excitations increase the local RF power deposition on average by +39%. In the first level controlled operating mode, induced peak temperatures reach 42.5°C and 45.6°C in patients with normal and impaired thermoregulation, respectively.
  
  
  
  Image quality with 3T body coils can be significantly increased by RF shimming. Exposure in realistic scan scenarios within guideline limits can be considered safe for a broad patient population with normal thermoregulation. Patients with impaired thermoregulation should not be scanned outside of the normal operating mode. Magn Reson Med 76:986-997, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: IT'IS Foundation, Zurich, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Murbach
authors.affiliation: IT'IS Foundation, Zurich, Switzerland.
authors.forename: Esra
authors.initials: E
authors.lastname: Neufeld
authors.affiliation: IT'IS Foundation, Zurich, Switzerland.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Cabot
authors.affiliation: IT'IS Foundation, Zurich, Switzerland.|Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.
authors.forename: Earl
authors.initials: E
authors.lastname: Zastrow
authors.affiliation: Department of Electronic and Communication Technology, Universidad Autónoma de Madrid (UAM), Escuela Politécnica Superior, Madrid, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Córcoles
authors.affiliation: US Food and Drug Administration (FDA), Center for Devices and Radiological Health (CDRH), Silver Spring, Maryland, USA.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kainz
authors.affiliation: IT'IS Foundation, Zurich, Switzerland.|Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.
authors.forename: Niels
authors.initials: N
authors.lastname: Kuster
mesh_terms: D065638:Absorption, Radiation / Q000502:physiology*; D049628:Body Size / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology / Q000528:radiation effects; D001833:Body Temperature Regulation / Q000502:physiology*; D003198:Computer Simulation; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D000069079:Radiation Exposure / Q000032:analysis* / Q000517:prevention & control; D011846:Radio Waves
keywords: MRI safety; RF shimming performance; SAR; human thermoregulation; impaired thermoregulation; virtual population