ELECTRONIC POSTER - ismrm

even with RF coil setups that are optimized for sensitivity only. Here, a proof of principle is given at 7T using a quadrature antenna for
acquisition of the reference images, together with an array of dedicated surface coils for carotid artery imaging.
14:30 3790. A Novel Matching Strategy to Increase Power Efficiency of the Travelling Wave
MR Imaging
Anna Andreychenko 1 , Hugo Kroeze 2 , Dennis W. Klomp 2 , Jan J. Lagendijk 1 , Peter
Luijten 2 , Cornelius A.T. van den Berg 1
1 Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands; 2 Radiology, University Medical
Center Utrecht, Utrecht, Netherlands
Travelling wave MR imaging exploits the RF shield of the scanner as a waveguide. When a patient is placed in the bore a strong
impedance mismatch occurs between the hollow (where antenna is located) and loaded parts of the bore. It causes wave reflection and
inefficient power is transferred to the target region. To avoid this impedance mismatch we propose to insert a quarter-wavelength
coaxial waveguide between the antenna and load which gradually transforms impedance of the antenna to the load impedance. The
effectiveness of this inset has been demonstrated both in the simulations and in-vivo experiments.
15:00 3791. Shortened Quarter Lambda Antenna for Traveling Wave Excitation in High Field
MRI
Hugo Kroeze 1,2 , Anna Andreychenko 3 , Cornelis A.T. van den Berg 3 , Dennis W.J. Klomp 1 ,
Peter R. Luijten 1
1 Radiology, UMC Utrecht, Utrecht, Netherlands; 2 Medical Technology, UMC Utrecht, Utrecht, Netherlands;
3 Radiotherapy, UMC Utrecht, Utrecht, Netherlands
A patch antenna can be used for travelling wave excitation in high field MRI. Due to its size, this antenna has to be placed at the far
end of the bore, reducing it efficiency when imaging in the abdominal area. A Shortened Quarter Lambda antenna is proposed to
overcome this problem. By placing the SQL antenna between the lags of the patient, an 8 fold improved efficiency can be
demonstrated in the abdomen, compared to a patch antenna. Images of the prostate and the head of a healthy volunteer are presented.
15:30 3792. Waveguide Magnetic Resonance Imaging at 3 Tesla
F Vazquez 1 , R Martin 1 , O Marrufo 1 , Alfredo O. Rodriguez 1
1 Departament of Electrical Engineering, Universidad Autonoma Metropolitana Iztapalapa, Mexico, DF, Mexico
Waveguides have been successfully used to generate magnetic resonance images at 7 Tesla for whole-body systems. From these
results, it has been established that waveguides are only suitable for 7T systems with wide bores of al least 60 cm. This is mainly due
to the cut-off frequency of the cylindrical waveguides used. To overcome this limitation a parallel-plate waveguide was employed
since its cut-off frequency depends on the separation of the plates. A parallel-plate waveguide was built and used to acquire images of
a healthy volunteer’s leg at 3 Tesla on a clinical MR imager.
Tuesday 13:30-15:30 Computer 43
13:30 3793. A Traveling-Wave Setup for Parallel RF Transmission
Jan Paska 1 , David Otto Brunner 2 , Klaas P. Pruessmann 2 , Ingmar Graesslin 3 , Juerg
Froehlich 1 , Ruediger Vahldieck 1
1 Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, Zurich, Switzerland; 2 Institute
for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 3 Philips Research Europe,
Hamburg, Germany
The traveling wave concept for ultra high field MRI offers a large FOV and patient space. Only the two TE11 modes can propagate in
an empty bore at 7T. To extend the traveling wave concept for parallel transmission also the higher order modes are needed,
increasing the degrees of freedom.
This is done by lowering the cut-off frequencies of the higher order modes with dielectric inserts. Selective coupling into the
orthogonal waveguide modes is desirable. This is however a demanding task in a multimodal waveguide, as known from optics.
14:00 3794. Parallel Traveling-Wave MRI: Antenna Array Approach to Traveling-Wave MRI
for Parallel Transmission and Acquisition
Yong Pang 1 , Chunsheng Wang 2 , Daniel Vigneron 2,3 , Xiaoliang Zhang 2,3
1 Radiology and Biomedical imaging, University of California San Francisco, San Francisco, CA , United States;
2 Radiology and Biomedical imaging, University of California San Francisco, San Francisco, CA, United States;
3 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, United States
Traveling-wave MRI utilizes the far field of a single piece patch antenna to generate homogeneous RF field covering large size
imaging samples. In this work, we demonstrate a method to applying the “traveling wave” technology to parallel excitation and
reception by using a multi-element patch antenna array. Each array element is a CP patch antenna which generates quadrature RF
fields. FDTD simulation results demonstrate the excellent decoupling among elements, great g-factors at various reduction factors for
1D SENSE, demonstrating the feasibility of parallel imaging using traveling-wave.