Receive Array Technology
Monday 20 April 2009
Room 312 16:30-18:30


James A. Bankson and Graham Wiggins

16:30  100. Cutting the Cord - Wireless Coils for MRI
    Oliver Heid1, Markus Vester2, Peter Cork3, Peter Hulbert3, David William Huish3
H Technology and Concepts, Siemens, 91052 Erlangen, Germany; 2H IM MR PLM SC, Siemens, 91052 Erlangen, Germany; 3Technology and Innovation, Roke Manor Research, Romsey, Hampshire, UK
    MRI scanner workflow improvement will result from replacing the existing cable connection from patient coils to image processing system with a cordless link. A multiple input multiple output microwave link system is proposed. Parametric upconverters in the patient coils will convert Larmor signals from the coils to microwave frequency. A transceiver array integrated into the bore will provide the local oscillator and receive functions. Parametric amplifiers implement upconversion with gain in simple and cheap circuits. Since only patient coils in the field of view are active the system is ideally suited to whole body scan.


16:42 101. A Generalized Analog Mode-Mixing Matrix for Channel Compression in Receive Arrays
    Jonathan Rizzo Polimeni1, Vijayanand Alagappan1, Thomas Witzel2, Azma Mareyam1, Lawrence Leroy Wald1,2
A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; 2Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
    Highly parallel arrays of small receiver coils enable dramatic gains in both SNR and accelerated imaging performance, but at a considerable cost in system complexity. Here we present a general analog mode-mixing matrix that can compress a large array coil into a small subset of channels, while retaining most of the SNR of the array. The matrix is calculated via SVD of the whitened signal correlation matrix, and implemented with phase shifters and programmable attenuators. By combining data from a 32-element array into 8 modes the mode-mixing matrix was able to retain 70% of the full-array image SNR.
16:54 102. element Design for Increased Sensitivity in 64-Channel Wide-Field-Of-View Microscopy
    Chieh-Wei Chang1, Steve M. Wright2, Mary Preston McDougall1,2
1Biomedical Engineering, Texas A&M University, College Station, TX, USA; 2Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
    Single Echo Acquisition (SEA) has decreased imaging time dramatically through the implementation of 64 channel array elements to provide spatial localization in the phase encode direction. Previous versions of the array coil employed a planar pair design. This coil design does not afford the SNR values and imaging depth needed to pursue high-resolution applications such as wide-field-of-view microscopy. In this work, a raised-leg coil design was implemented as a variation of the planar pair coil, and improvements in SNR and imaging depth were attained. Future coil modifications will seek to maintain imaging speed while moving into high-resolution applications.
17:06 103. Resonance Shift Decoupling: A Potential Alternative to Low Input Impedance Preamplifiers
    Marc Stephen Ramirez1, James Andrew Bankson1
The Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA
    Current minimization schemes are critical to reduce inductive coupling between non-adjacent elements in MRI phased arrays. Traditionally, low input impedance preamplifiers have been used to accomplish this. In this work, we test an alternate method involving a transistor amplifier that is built into the coil to minimize loop current and maximize gain, while simultaneously achieving low-noise operation. Design methodologies involving low-noise, high-gain transistor impedance matching and a shift in the resonance frequency due to the parasitic capacitance of the transistor are described. Initial results indicate the potential to provide effective element decoupling for MRI phased arrays.
17:18  104. Studies on MR Reception Efficiency and SNR of Non-Resonance RF Method (NORM)
    Xiaoliang Zhang1,2, Chunsheng Wang1, Daniel Vigneron1,2, Sarah Nelson1,2
Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA; 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco/Berkeley, CA, USA
    Non-resonance method (NORM) for MR signal excitation and reception has been advocated due to its unmatched advantages in multinuclear and parallel imaging applications. In this work, the reception efficiency and SNR of the NORM technology were validated. No statistical difference in reception efficiency was observed between NORM and the conventional resonance technology. The advantages of NORM technology is not a trade-off of MR sensitivity.
17:30 105.

The Shielding of RF MRI Coils Using Double-Sided EMI Shield

    Ibrahim Abu El-Khair1, Jan G. Korvink1, Juergen Hennig2, Gerhard Moenich3
Dept. of Microsystems Engineering–IMTEK, University of Freiburg, Freiburg, Germany; 2Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; 3Dept. of Radio Frequency Technology, Technical University of Berlin, Berlin, Germany
    Radiation losses associated with RF coils increase up to the fourth power of frequency; it becomes significant at high fields above 2 Teslas. Furthermore, loading an RF MRI Coil with a sample leads to a shift in the resonant frequency, f0 away from the one specified. This also leads to a very poor reception at f0. A double-sided EMI (ElecroMagnetic Interference) shield using the CTLM (Coaxial Transmission Line Modeling) technique of shielding restores f0, and eliminates the radiation loss. The mutual capacitive coupling among the neighboring coils within an array, and associated electronics, is also eliminated.
17:42 106.

A 30 Channel Receive-Only 7T Array for Ex Vivo Brain Hemisphere Imaging

    Azma Mareyam1, Jonathan Rizzo Polimeni1, Vijayanand Alagappan1, Bruce Fischl1,2, Lawrence L. Wald1,3
A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology,MGH, Charlestown, MA, USA; 2CSAIL, MIT, Cambridge, MA, USA; 3Harvard-MIT Division of Health Sciences and Technology , Harvard-MIT , Cambridge, MA, USA
    High-field MRI of ex vivo samples provides 3D image encoding at resolutions capable of resolving laminar and myeloarchitectonic features, thus providing a potential replacement for the technically challenging task of whole-brain histological sectioning. Here we present a 30-channel receive-only coil array for high-resolution whole-cerebral-hemisphere imaging. With this array, whole-hemisphere acquisitions of 150 µm voxel size in which laminar details are clearly detectable are possible within six hours. Considerations for satisfying the many constraints imposed by ex vivo imaging on surface coil are discussed, and imaging performance is compared with other available 3T and 7T arrays.
17:54 107. Multi-Purpose Flexible Transceiver Array at 7T
    Bing Wu1, Chunsheng Wang1, Roland Krug1, Douglas Kelley2, Yong Pang1, Duan Xu1, Sharmila Majumder1,3, Sarah Nelson1,3, Daniel Vigneron1,3, Xiaoliang Zhang1,3
Radiology&Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA; 2GE Healthcare, San Francisco, CA, USA; 3UCSF/UC Berkeley Joint Group Program in Bioengineering, San Francisco & Berkeley, CA, USA

A multi-purpose flexible transceiver array was designed for ultra-high field MRI using a mixing technique of primary and 2nd harmonic microstrips. Besides the coil geometry, the number of coil elements in the proposed design is also selectable for different applications. The feasibility of this multi-purpose flexible array has been demonstrated by 7T MR imaging for human wrist, knee, head and liver.

18:06 108. A 32-Channel Receive Array Coil for Pediatric Brain Imaging at 3T
    Vijayanand Alagappan1,2, Graham Charles Wiggins3, Jonathan Rizzo Polimeni3, Lawrence Leroy Wald3,4
Department  of Radiology, A.A Martinos Center for Biomedical Imaging, Charlestown, MA, USA; 2Department of Biomedical engineering, Tufts University, Medford, MA, USA; 3Department of Radiology, A.A Martinos Center for Biomedical Imaging, Charlestown, MA, USA; 4Health Science and Technology, MIT, Cambridge, MA, USA

We describe a 32 channel receive-only 3T phased array head coil for the pediatric population. The 32-channel coil was built on a close fitting fiberglass helmet with soccer-ball element geometry. SNR gains of 4 and 2 times in the cortex and 1.2 and 2 times in the center of the head were observed when compared to a commercial 32-channel adult head coil and a 12-channel adult head coil. The Maximum G factors were also reduced significantly with the 32-channel coil optimized for the pediatric head imaging.



18:18 109. Hole-Slotted Phased Array at 7 Tesla
    Marcos A. Lopez1,2, Philipp Ehses1, Felix Breuer2, Daniel Gareis1, Peter Michael Jakob1,2
Experimental Physics 5, University of Wuerzburg, Wuerzburg, Bavaria, Germany; 2Research Center Magnetic Resonance Bavaria, Wuerzburg, Bavaria, Germany

The hole-slot magnetron is used as a HF oscillator in radar applications. A surface coil based on the hole-slot magnetron’s geometry was introduced showing deeper RF penetration than a conventional coil at 1.5 and 4 Tesla. Four different conventional coil geometries were compared with a hole-slotted coil at 7 Tesla. Furthermore a hole-slotted array was built and evaluated. The hole-slotted loop improves RF penetration depth compared to the different loops showing a improved SNR in the second half of the phantom. The images acquired with the hole-slotted array show high SNR as well as good homogeneity and RF penetration depth.