Emerging RF Methods
Wednesday 22 April 2009
Room 316A 16:00-18:00

Moderators:

 Arne Reykowski and Andrew G. Webb
 
16:00 498. Whole-Body Traveling-Wave Imaging at 7 Tesla: Simulations and Early In-Vivo Experience
    Bei Zhang1, Graham Wiggins1, Qi Duan1, Riccardo Lattanzi1, Daniel K. Sodickson1
1Radiology, Center for Biomedical Imaging, NYU School of Medicine, New York, NY, USA
    Using full-wave electrodynamic simulations with a human body model as well as in-vivo human imaging, we explore basic principles of signal distribution and energy deposition for whole-body traveling wave MR driven by a patch antenna at 7T. Both simulations and experimental results demonstrate preferential excitation and energy deposition proximal to the patch antenna, with increasing attenuation at increasing distance. This phenomenon can be explained using simple models of dielectric-filled waveguides. Reflections from dielectric boundaries can result in local field focusing. Incomplete containment of fields from the patch antenna within the scanner bore reduces transmit and receive efficiency.
     
16:12 499. Travelling-Wave MRI: Initial Results of In-Vivo Head Imaging at 7T
    David Otto Brunner1, Jan Paska2, Juerg Froehlich2, Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 2Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, Zurich, Switzerland
    Travelling wave MRI has been tested for safety aspects for its application to human head imaging by means of full wave simulations including anatomical tissue models. It could be shown, that such a setup can be safely used within the same power limitations as volume head coils. Based on that, initial experiments revealing the RF coverage achieved by travelling wave MRI have been performed. The scans showed, that covering the head including the shoulders is feasible. In order to cope with present non-uniformities, an initial approach to match dielectric interfaces reducing reflections has been evaluated.
     
16:24 500. Effective Delivery of the Traveling Wave to Distant Locations in the Body at 7T
    Anna Andreychenko1, Dennis W.J. Klomp1, Bob van den Bergen1, Bart L. van de Bank1, Hugo Kroeze1, Jan J.W. Lagendijk1, Peter Luijten1, Cornelis A.T. van den Berg1
1Dept. of Radiotherapy and Radiology, University Medical Center Utrecht, Utrecht, Netherlands
    A strong attenuation of the traveling wave occurs during the passage through the body. In this study we propose a new concept to deliver a maximum B1+ to distant locations in the body using the waveguide with a coaxial conductive inset. A 2 to 6 times higher SNR ratios in 7T MR images of the male pelvis comparing to the standard traveling wave excitation were achieved with this concept. On top of that, the use of the coaxial conductive inset results in significantly lower SAR levels in the body.
     
16:36 501. An Optically Detunable Coil for Improved Self Gating in Small Animals
    Matthias Korn1, Reiner Umathum1, Jessica Schulz1,2, Axel Joachim Krafft1, Wolfhard Semmler1, Michael Bock1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2Siemens Healthcare, Erlangen, Germany
    Physiological motion correction using MR-signals (self gating) has become a widely used method. However in small animal MRI the acquisition of motion dependent signals can be challenging. In this work a hardware-device, consisting of an inductively coupled coil that can be dynamically detuned by an optical trigger signal, is presented. Only during acquisition of the gating signal the coil is tuned and therefore enhances the gating signal while the over all image remains homogeneous. Experiments on mice are shown where the self gating signal was amplified by a factor of 1.7 to 2.8.
     
16:48 502. Calcium Titanate Based Ceramic Resonators for High Field Magnetic Resonance
    Kristina Haines1, Thomas Neuberger2, Michael Lanagan3, Elena Semouchkina3, Andrew Webb4
1Electrical Engineering, Penn State University, USA; 2Huck Institute, Penn State University, USA; 3Materials Research Laboratory, Penn State University; 4Radiology, Leiden University Medical Center, Leiden, Netherlands
    A high sensitivity resonator was constructed from CaTiO3, relative permittivity 156, Q value of 2081, for magnetic resonance experiments at 600 MHz. This design is simple to construct, avoids wavelength effects, is highly mechanically stable and is low loss. The sample is placed in a volume of strong, homogeneous B field and very low E field. High resolution images of zebrafish have been acquired using this probe.
     
17:00 503. Beyond Copper: MR Imaging with Carbon Nanotube Receiver Coils
    Raju Viswanathan1, Bradley Goldstein1, Kevan Anderson2, Michael Bronskill2, Ray Baughman3, Mei Zhang4, Shaoli Fang3, Anvar Zakhidov3, Ali Aliev3
1Tursiop Technologies, LLC, Cleveland, OH, USA; 2University of Toronto, Toronto, Ontario, Canada; 3University of Texas at Dallas, Richardson, TX, USA; 4Florida State University, Tallahassee, FL, USA
    Fabrication advances in nanotechnology have recently enabled construction of nanostructured materials with macroscopic dimensions and interesting electrical properties. A macroscopic sheet composed of carbon nanotubes was used to construct an MR receiver coil. The electrically conducting nanomaterial is made by a solid-state process akin to textile drawing. It displays negligible electrical skin effects over the range of frequencies relevant to MR imaging. The receiver coil was used to image a mouse head at 3T at 0.25 mm in-plane resolution and resulted in excellent image quality. The material offers the possibility of significant enhancements in SNR in clinical MR imaging applications.
     
17:12 504. Operational Inkjet-Printed Metal-On-Kapton MRI Receiver Coil
    Dario Mager1, Ute Loeffelman1, Andreas Peter1, Laura Del Tin1, Elmar Fischer2, Patrick James Smith1, Juergen Hennig2, Jan Gerrit Korvink1
1Dept. of Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany; 2Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany
    We present for the first time the results of a self-resonant MR receiver coil, manufactured on a flexible Kapton foil, with the metal lines pattern by inkjet printing. An MRI image sequence was taken using a Bruker BioSpec scanner at 9.4 T. The results of the measurement were comparable to a standard receiver coil. Inkjet printing can therefore be considered as a feasible approach in the rapid and low cost production of receiver coils. Inkjet printing is not limited to planar substrates, since it can be easily adapted to produce non-planar structures.
     
17:24 505. A Mechanically Rotating RF Transceive System and Method  for Applications in Magnetic Resonance
    Adnan Trakic1, Bing Keong Li1, Ewald Weber1, Feng Liu1, Stephen Wilson1, Stuart Crozier1
1The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
    This study introduces a new MRI approach using a rapidly rotating RF (RRF) transceive coil. RF coil rotation offers an additional degree of freedom for MR imaging in that it emulates a large conventional RF coil array. To test its feasibility, a small RRF transceive coil system was constructed and operated at about 1200 revolutions per minute in a 2 Tesla field. The MR images obtained were uniform and of good quality. The RRF approach may obviate the need for multiple channels and tedious RF coil decoupling.
     
17:36 506. Real-Time Full-Wave Simulations of RF Coils by Fast Integral Equation Methods
    Shumin Wang1, Jacco de Zwart1, Jeff Duyn1
1NIH, Bethesda, MD, USA
    A fast integral equation method is proposed for real-time patient-dependent simulations of high-field RF coils. This topology-based multi-level Crout method starts by partitioning a model into sub-domains and organizing them in a multi-level fashion. Based on the rank-deficient nature of the interactions between distant sub-domains, the Crout algorithm was applied to compress the corresponding matrix blocks. Numerical results were used to verify this method and to demonstrate its efficiency in real-time coil simulations. A promising application is per-patient specific absorption ratio (SAR) estimation.
     
17:48 507. Improving SNR by Generalizing Noise Matching for Array Coils
    Christian Findeklee1
1Philips Research Europe, Hamburg, Germany
    The theory of noise matching is well known for single elements or well decoupled coils. However, in practical applications, residual mutual coupling leads to noise coupling, which decreases the final SNR. As shown in this paper, this can be avoided by generalizing the scalar noise matching for array coils. Simulations and Experiments have been performed to prove the new concept.