Room 151 AG

10:00 - 12:00

Moderators:

David O. Brunner, Cornelis A. T. van den Berg

Sukhoon Oh¹, Elena Semouchkina², Thomas Neuberger³, Michael T. Lanagan⁴, Bei Zhang¹, Cem Murat Deniz⁵, and Christopher Michael Collins^1
1Center for Biomedical Imaging, School of Medicine, New York University, New York, New York, United States, ²Department of Electrical and Computer Engineering, Michigan Technological University, Houghton, MI, United States, ³Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, United States, ⁴Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, United States, ⁵New York University, New York, New York, United States

Traveling-wave excitation in ultra-high field MRI has been introduced in an effort to increase field of view and to enhance RF transmit field homogeneity. Here we present initial results at 300 MHz using a recently-developed patch antenna for excitation. The antenna is 80% smaller in size than conventional patch antenna and has an asymmetric design to produce a circularly-polarized field with only a single feed.

Anna Andreychenko¹, Hugo Kroeze¹, Wouter Koning¹, Alexander J.E. Raaijmakers¹, Froukje E. Euwe², Jan J.W. Lagendijk¹, Peter R. Luijten¹, Dennis W.J. Klomp¹, and Cornelis A.T. van den Berg^1
1Imaging Division, UMC Utrecht, Utrecht, Utrecht, Netherlands, ²Medical Technology, UMC Utrecht, Utrecht, Utrecht, Netherlands

A multi-mode coaxial waveguide was proposed as an alternative to volume body coil at 7T. However, use of the initial design in clinical practice was not feasible. Here, the design was adapted to use together with the patient table in the bore of a clinical MR scanner. With the first in-vivo MR experiments a sufficient RF shimming performance and B1+ efficiency of the modified design was demonstrated. The modified multi-mode coaxial waveguide is significantly easier to handle and, thus, can be effectively applied in clinical practice as a high field “body coil” at 7T.

Jan Paška¹, David Otto Brunner², Juerg Froehlich¹, and Klaas P. Pruessmann^2
1Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, Zurich, Switzerland, ²Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Travelling wave with multiple channels (TWM) is a new RF system. First experimental results in phantoms exist. For in-vivo imaging a careful safety assessment is necessary. EM-simulations of the TWM are difficult due to the large setup. In a previous work, the EM-domain was divided into subdomains and combined in a post-processing step, the FDTD method was used for EM-simulations, which has difficulties in modeling evanescent modes and the waveguide discontinuity. In this work this approach was extended. FEM was used for the simulation of all subdomains. The improved method yields more precise EM-simulations and a less conservative power limit.

Daniel James Lee¹ and Paul M. Glover^1
1SPMMRC, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

The travelling wave approach to MRI uses an antenna to propagate a TW through the bore of a 7T+ scanner. A novel design where the antenna is incorporated into a dielectric waveguide which then matches the incident wave into the head is presented. Such a set up has been constructed and tested in vivo.

Yigitcan Eryaman^1,2, Bastien Guérin³, Robert Kosior^1,2, Elfar Adalsteinsson^4,5, and Lawrence L. Wald^2,5
1Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, United States, ²Martinos Center for Biomedical Imaging, Dept. of Radiology, MGH, Charlestown, MA, United States, ³Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ⁴Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ⁵Harvard-MIT Health Sciences and Technology, Cambridge, MA, United States

We compared the trade-off between local SAR and excitation fidelity for three 7T head transmit array configurations to determine if the approximate orthogonality between the loop coil and dipole element field patterns could be exploited for pTx. Using simulated E and B fields for 8 and 16 element loop arrays and an 8 loop + 8 dipole array, we calculated SAR constrained pTx and RF shimming pulses. Our results show that an array composed of both loop and dipole elements outperforms an array that is composed of loops only in SAR and excitation fidelity.

Celal Özerdem¹, Lukas Winter¹, Katharina Fuchs¹, and Thoralf Niendorf^1,2
1Berlin Ultrahigh Field Faciliy (BUFF), Max Delbrück Center for Molecular Medicine (MDC), Berlin-Buch, Germany, ²Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty, Berlin, Germany

This work demonstrates use of meander formed RX dipoles to improve the receive capability of an array consisting of TX/RX bow tie dipole antennas.For this purpose numerical field simulations and phantom experiments are performed to characterize the transmit behavior of the array and to measure the SNR of the proposed array.

Andreas Graessl¹, Lukas Winter¹, Celal Özerdem¹, Fabian Hezel¹, Katharina Fuchs¹, Harald Pfeiffer², Werner Hoffmann², and Thoralf Niendorf^1,3
1Berlin Ultrahigh Field Facility, Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany, ²Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ³Experimental and Clinical Research Center (ECRC), Charité Campus Buch, Humboldt-University, Berlin, Germany

A two-dimensional 16-channel transceiver array based on dipole elements is designed and applied to Cardiac MR (CMR) at 7.0 Tesla. Dipole Antennas are a promising approach to provide a homogeneous B1+ field distribution and good transmit efficiency in the short wavelength regime of Ultrahigh field MRI. RF efficiency optimization is applied and assessed for slice-by-slice shimming based on simulation data. The transition to in-vivo studies succeeded and revealed excellent B1+-homogeneity and a high myocardium/blood contrast over the whole cardiac region with a single RF shim setting and without subject-specific B1+-shimming or element retuning.

Sebastian Rupprecht¹, Christopher T. Sica¹, Raffi Sahul², Seongtae Kwon², Michael T. Lanagan³, and Qing X. Yang^1,4
1Department of Radiology, The Pennsylvania State University College of Medicine, Hershey, PA, United States, ²TRS Technologies Inc., State College, PA, United States, ³Department of Engineering Science and Mechanics, The Pennsylvania State University, State College, PA, United States, ⁴Department of Neurosurgery, The Pennsylvania State University College of Medicine, Hershey, PA, United States

Utilization of monolithic materials with ultra high dielectric constant (_r = 800 -1200) to generate a drastically focused and enhanced transmission field in the sample of interest (up to 500% increased) and reception field (up to 4 fold increased) with standard hardware at 3T. Currently this translates to at least 40 % higher signal to noise ratio with strong potential higher values. Additionally the transmission power was reduced to 1/3 (_r =800) and respectively 1/27 (_r =1200) of the initial power with no uHDC material.

Simone Angela Winkler¹ and Brian K. Rutt^1
1Department of Radiology, Stanford University, Stanford, CA, United States

3T MRI is increasingly used because of its intrinsic SNR benefits compared to 1.5T MRI. Increased B1+ inhomogeneities in 3T MRI can lead to left-right B1+-asymmetry in the breast. This abstract presents simulations of several different methods for compensating left-right B1+-asymmetries in the breast region by means of 1) 2-channel RF shimming (I/Q-phase/amplitude adjustments); 2) dielectric-absorptive shimming; or 3) a combination. Both approaches are adaptable to a wide range of MR systems to yield a simple, practical, and inexpensive procedure without SAR penalty for uniform contrast and quantitative parameter estimates, and ultimately, more accurate detection and monitoring of breast cancer.

Sebastian A. Aussenhofer¹, Maarten J. Versluis¹, and Andrew Webb^1
1Department of Radiology Leiden University Medical Center, CJ Gorter Center for High Field MRI, Leiden, South Holland, Netherlands

Most high field imaging coils are based on lumped elements and copper strips or transmission line elements. Recently an alternative design was presented using dipole antennas mounted on high permittivity non-resonant ceramic blocks in order to force the penetrating wave into the far field region. In this current work a new concept is presented which uses unilaterally shielded high permittivity ceramic discs which, when coupled to the body, are designed to resonate in the TE01 mode.