title: RF system calibration for global Q matrix determination.
abstract: The use of multiple transmission channels (known as Parallel Transmission, or PTx) provides increased control of the MRI signal formation process. This extra flexibility comes at a cost of uncertainty of the power deposited in the patient under examination: the electric fields produced by each transmitter can interfere in such a way to lead to excessively high heating. Although it is not possible to determine local heating, the global Q matrix (which allows the whole-body Specific Absorption Rate (SAR) to be known for any PTx pulse) can be measured in-situ by monitoring the power incident upon and reflected by each transmit element during transmission. Recent observations have shown that measured global Q matrices can be corrupted by losses between the coil array and location of power measurement. In this work we demonstrate that these losses can be accounted for, allowing accurate global Q matrix measurement independent of the location of the power measurement devices.
authors.affiliation: King's College London, Division of Imaging Sciences and Biomedical Engineering, The Rayne Institute, 3rd Floor, Lambeth Wing, St Thomas' Hospital, London, UK, SE1 7EH. Electronic address: francesco.padormo@kcl.ac.uk.
authors.forename: Francesco
authors.initials: F
authors.lastname: Padormo
authors.affiliation: King's College London, Division of Imaging Sciences and Biomedical Engineering, The Rayne Institute, 3rd Floor, Lambeth Wing, St Thomas' Hospital, London, UK, SE1 7EH.
authors.forename: Arian
authors.initials: A
authors.lastname: Beqiri
authors.affiliation: King's College London, Division of Imaging Sciences and Biomedical Engineering, The Rayne Institute, 3rd Floor, Lambeth Wing, St Thomas' Hospital, London, UK, SE1 7EH.
authors.forename: Shaihan J
authors.initials: SJ
authors.lastname: Malik
authors.affiliation: King's College London, Division of Imaging Sciences and Biomedical Engineering, The Rayne Institute, 3rd Floor, Lambeth Wing, St Thomas' Hospital, London, UK, SE1 7EH; King's College London, Centre for the Developing Brain, Division of Imaging Sciences and Biomedical Engineering, The Rayne Institute, 3rd Floor, Lambeth Wing, St Thomas' Hospital, London, SE1 7EH, UK.
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Hajnal
mesh_terms: D002138:Calibration; D006358:Hot Temperature; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods
keywords: MRI Calibration; Parallel transmission; Q Matrix; SAR