Receive Arrays & LNAs
Thursday 6 May 2010
Room A6 16:00-18:00 Moderators: James A. Bankson and Mary P. McDougall

16:00 641. 

An 8-Channel TX, 16-Channel RX Flexible Body Coil at 7 Tesla Using Both Branches of Centrally Fed Strip Lines as Individual Receive Elements
Stephan Orzada1,2, Stefan Maderwald1,2, Mark Oehmigen1, Mark E. Ladd1,2, Klaus Solbach3, Andreas K. Bitz1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, NRW, Germany; 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany; 3High Frequency Engineering, University Duisburg-Essen, Duisburg, NRW, Germany

To further increase the capabilities of centrally fed strip line elements, they can be split up into two branches for reception, thereby doubling the number of elements. In this work a flexible body coil with 8 transmit and 16 receive channels built from centrally fed strip line elements with meanders is presented for imaging at 7 Tesla. The new array shows enhanced parallel imaging performance, while good decoupling and transmit penetration are maintained.

16:12 642. 

A 7-Tesla High Density Transmit with 28-Channel Receive-Only Array Knee Coil
Matthew Finnerty1, Xiaoyu Yang1, Tsinghua Zheng1, Jeremiah Heilman1, Nicholas Castrilla1, Joseph Herczak1, Hiroyuki Fujita1,2, Tamer S. Ibrahim3,4, Fernando Boada3,4, Tiejun Zhao5, Franz Schmitt6, Bernd Stoeckel5, Andreas Potthast6, Karsten Wicklow6, Siegfried Trattnig7, Charles Mamisch7, Michael Recht8, Daniel Sodickson8, Graham Wiggins8, Yudong Zhu8
Quality Electrodynamics, LLC., Mayfield Village, OH, United States; 2Departments of Physics and Radiology, Case Western Reserve University, Cleveland, OH, United States; 3Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; 4Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States; 5Siemens Medical Solutions USA, Inc., Malvern, PA, United States; 6Siemens Healthcare, Erlangen, Germany; 7Department of Radiology, Medical University of Vienna, Vienna, Austria; 8Department of Radiology, NYU Langone Medical Center, New York, United States

As more advanced 7T MRI technology continues to emerge, the development of a wider anatomical range of RF coils has become a greater priority.  In an effort to take advantage of the greater spatial resolution and higher SNR at 7T, a 12-rung birdcage transmitter and 28-channel receive-only array coil has been developed.  To overcome the challenges associated with the shorter wavelength within the human body at 7T, several novel design strategies have been utilized.

16:24 643. 

Age-Optimized 32-Channel Brain Arrays for 3T Pediatric Imaging
Boris Keil1, Azma Mareyam1, Kyoko Fujimoto1, James N. Blau1, Veneta Tountcheva1, Christina Triantafyllou1,2, Lawrence L. Wald1,3
A.A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH, Harvard Medical School, Charlestown, MA, United States; 2A.A. Martinos Imaging Center, Mc Govern Institute for Brain Research, MIT, Cambridge, MA, United States; 3Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

Compromising the size and shape of pediatric brain arrays so that “one size fits all” or using adult brain or knee arrays causes a significant degradation of SNR and parallel imaging performance compared to a coil of the appropriate size and shape for a given aged child. Unfortunately, rapid head growth in the first years of life requires either a flexible array approach or multiple sizes which span the size range with reasonable discrete increments. In this work, we developed and tested four incremental sized 32-channel receive only head coils for pediatric patients spanning an age range of 6 months to 7 years old. The constructed coils show significant SNR gains for both accelerated and unaccelerated imaging in pediatric brain imaging.

16:36 644.  

16-Channel Custom-Fitted Bilateral Breast Coil for Parallel Imaging in Two Directions
Anderson N. Nnewihe1,2, Thomas Grafendorfer3, Bruce L. Daniel1, Paul Calderon3, Marcus T. Alley1, Fraser Robb3, Brian A. Hargreaves1
Radiology, Stanford University, Stanford, CA, United States; 2Bioengineering, Stanford University, Stanford, CA, United States; 3GE Healthcare

High spatial and temporal resolution imaging could be used to better classify breast lesions with the potential to improve breast cancer diagnosis.  In this work we compare a novel 16-channel bilateral breast coil to a standard commercially-available 8-channel coil, in terms of SNR and parallel imaging capability in two directions.  Overall we have demonstrated that a closely-fitted surface array can substantially improve both SNR and parallel imaging capability compared with standard 8-channel bilateral breast coils.

16:48 645.

Modular Multi-Channel Parallel-Imaging Microfluidics Platform with Exchangeable Capillary Diameters
Dario Mager1, Andreas Peter1, Elmar Fischer2, Patrick James Smith1, Jürgen Hennig2, Jan Gerrit Korvink1,3
Dept. of Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany; 2Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; 3Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany

Solenoidal receiver coils have been directly patterned onto glass capillaries using inkjet printing; in an extension of work that has successfully been used to produce planar receiver coils. Each patterned capillary is housed in a PCB/PMMA holder, which acts as a parallel imaging system for microfluidic analysis.

17:00 646

Travelling Wave Parallel Imaging
David Otto Brunner1, Jan Paska2, Ingmar Graesslin3, Jürg Froehlich2, Klaas Paul Pruessmann1

1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 2Electromagnetic Fields and Microwave Laboratory, ETH Zurich, Zurich, Switzerland; 3Philips Research Europe, Hamburg, Germany

Since the sample becomes considerably larger than the wavelength in human ultra high field MRI, the electrodynamic degrees of freedom within the loaded bore increases. Using a mode selectively fed waveguide section coupling into the loaded bore it is demonstrated that parallel imaging techniques in transmission and reception such as RF shimming and SENSE can be applied in a travelling wave approach in the absence of a RF array coil close by the object. A direct dependence between the parallel imaging performance of this 8 channel system and the number of modes in the waveguide could be shown.

17:12 647

A Modular Automatic Matching Network System
Matteo Pavan1, Klaas Paul Pruessmann

1ETH Zurich, Zurich, Switzerland

In MR measurement, coils are detecting proton signal; they are usually connected through a matching network to very low noise amplifier. The Noise Figure of the amplifier depends on the impedance that its input port sees. To optimize SNR, is important to match this impedance to the one that is reducing at the minimum the noise figure. A new approach for automatic impedance measurement is here presented. This new approach is easy and modular in such a way that it can be scaled to any number of reception channels.

17:24 648

Accurate Noise Level and Noise Covariance Matrix Assessment in Phased Array Coil Without a Noise Scan
Yu Ding1, Yiu-Cho Chung2, Orlando P. Simonetti1
1The Ohio State University, Columbus, OH, United States; 2Siemens Medical Solutions, Columbus, OH, United States

In this study, we propose an novel method to assess noise level and noise covariance matrix in the k-space data when both signal and noise are present. Experimental results show that the noise level as well as the noise covariance matrix can be accurately derived from multi-frame k-space data without deploying a separate noise scan.

17:36 649.

A Magnetic-Field-Tolerant Low-Noise SiGe Pre-Amplifier and T/R Switch
David Ian Hoult1, Glen Kolansky1
1Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba, Canada

The noise figure and gain of GaAs field effect transistors degrade in magnetic fields. A SiGe bipolar transistor is advocated as a replacement giving at 123 MHz a noise figure of 0.6 dB with ~ 20 dB current blocking. Our SiGe pre-amplifier has a noise figure < 1dB from 90 to 200 MHz, a gain of 30 dB, a bandwidth of 73 to 163 MHz and a group delay of 5.4 ns. The accompanying 300 W quarter-wave PIN diode transmit/receive switch has 0.1 dB noise figure, an insertion loss of 1 dB and isolation of ~ 65 dB.

17:48 650

Frequency Selective Negative Feedback to Avoid Preamplifier Oscillation in Multi-Channel Arrays
Thomas Grafendorfer1,2, Greig Scott2, Paul Calderon3, Fraser Robb4, Shreyas Vasanawala5

1RX & ATD Coils, GE Healthcare, Stanford, CA, United States; 2Electrical Engineering, Stanford University, Stanford, CA, United States; 3MR Hardware Engineering, GE Healthcare, Fremont, CA, United States; 4Advanced Technology, GEHC Coils, Aurora, OH, United States; 5Radiology, Stanford University, Stanford, CA, United States

Placing the preamplifiers close to the coil elements in multi-channel arrays increases preamplifier-decoupling performance, which leads to better SNR and better acceleration performance. Unfortunately it also opens a new feedback path that can easily lead to oscillation. We developed a new strategy by applying frequency selective negative feedback that suppresses the gain at the so-called match split peaks outside the frequency band relevant for MRI. This greatly reduces the possibility for oscillation, and the gain within the signal band stays more or less unaffected.



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