PURPOSE: To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. MATERIALS AND METHODS: We present both numerical calculations and experimental images at 3 T of a 35-cm-diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. RESULTS: With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. CONCLUSION: Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. (c) 2005 Wiley-Liss, Inc.
PURPOSE: To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. MATERIALS AND METHODS: We present both numerical calculations and experimental images at 3 T of a 35-cm-diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. RESULTS: With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. CONCLUSION: Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. (c) 2005 Wiley-Liss, Inc.
Authors: Richard G Boyes; Jeff L Gunter; Chris Frost; Andrew L Janke; Thomas Yeatman; Derek L G Hill; Matt A Bernstein; Paul M Thompson; Michael W Weiner; Norbert Schuff; Gene E Alexander; Ronald J Killiany; Charles DeCarli; Clifford R Jack; Nick C Fox Journal: Neuroimage Date: 2007-10-30 Impact factor: 6.556
Authors: Zhenghui Zhang; Chun-Yu Yip; William Grissom; Douglas C Noll; Fernando E Boada; V Andrew Stenger Journal: Magn Reson Med Date: 2007-05 Impact factor: 4.668
Authors: Nikolai I Avdievich; Ken Bradshaw; Jing-Huei Lee; Andrey M Kuznetsov; Hoby P Hetherington Journal: J Magn Reson Date: 2007-05-16 Impact factor: 2.229
Authors: Gregory J Metzger; Carl Snyder; Can Akgun; Tommy Vaughan; Kamil Ugurbil; Pierre-Francois Van de Moortele Journal: Magn Reson Med Date: 2008-02 Impact factor: 4.668
Authors: Stefan Maderwald; Susanne C Ladd; Elke R Gizewski; Oliver Kraff; Jens M Theysohn; Karsten Wicklow; Christoph Moenninghoff; Isabel Wanke; Mark E Ladd; Harald H Quick Journal: MAGMA Date: 2008-01-04 Impact factor: 2.310