128 Channel Receive-Only Radio-Frequency Coil Design for High Resolution Brain Imaging

Poster No:

2137 

Submission Type:

Abstract Submission 

Authors:

William Mathieu1, Guangxing Li1, Charbel Matta2, Reza Farivar2

Institutions:

1Research Institute of the McGill University Health Centre, Montréal, Québec, 2McGill University, Montréal, Québec

First Author:

William Mathieu, MEng  
Research Institute of the McGill University Health Centre
Montréal, Québec

Co-Author(s):

Guangxing Li, Ph.D.  
Research Institute of the McGill University Health Centre
Montréal, Québec
Charbel Matta, BEng.  
McGill University
Montréal, Québec
Reza Farivar, PhD  
McGill University
Montréal, Québec

Introduction:

MRI plays an important role on the research of neuroscience and clinic evaluation of brain diseases. The quality of MRI critically depends on the radio-frequency (RF) receiver coils. The standard receive-only RF coil of today is typically a phased-array of circular loop shaped elements mounted onto a rigid plastic shell. This one-size-fits-all philosophy that has always existed in RF coil designs, severely limits their signal-to-noise (SNR) capabilities. We know that large phased arrays provide exceptional SNR performance, however unless a coil perfectly fits the user, air gaps between the patient and the coil array can cause significant signal loss. Our design aims to bring in advantages of large phased arrays while also minimizing signal loss caused by air gaps and gaps between coil loop elements. As such, we have adopted a novel flexible plate approach where small groupings of coil elements, forming traditional phased arrays, are placed on flexible, movable rubberized paddles enveloping the entire head. The boundaries of paddles are chosen based on the approximate outline of cranial bones. The gaps between paddles are bridged with flexible loop elements able to bend upwards, away from the subject, allowing the coil to fit a variety of head shapes and sizes.

Methods:

The initial shape of the coil was based on the average head dimensions. Given the dimension limits, a 3D model was created to map different regions of the head to certain groups of phased arrays. Paddles were cut based on the approximate locations of the cranial sutures, leaving gaps between one another to allow for shape/size adjustability. Placement and packing of loops was checked by wrapping arrays of hexagons over the paddles using the soccer ball pattern (see figure included in this section). A loop diameter of 36mm was chosen based on this analysis as well as previous work in which loop diameter was optimized given signal depth and SNR (Gruber et al., 2018). To tackle the SNR drops across the gaps between paddles, also known as sutures, the coils were extended onto a flexible semi-rigid film capable of bending in the orthogonal direction away from the subject.This allowed a dynamic variation of the loop surface area in the suture region depending on the size setting of the head coil.
Supporting Image: Untitledpicture.png
   ·Analysis of placement and packing of loop elements using hexagons in a "soccer ball pattern".
 

Results:

The figure included in this section shows the mechanical design featuring the flexible paddles capable of accommodating an array of at least 128 36-mm diameter elements. Each paddle is independently adjustable by the operator using posts held by adjustable collars. The subject and operator are electrically isolated from all electronics by neoprene gaskets (not shown here), hence the unusual looking post support structures. Posts can move each paddle away or towards the subject, they also allow the operator to pitch and rotate the paddles as needed. Suture coils allow signal to be received from brain areas under the gaps between paddles.
Supporting Image: 128coilmechanical.png
   ·Mechanical Drawing showing the flexible, movable paddles in blue and the support structure of the paddles.
 

Conclusions:

By using flexible paddles, suture coils across the gaps between paddles, and optimizing the shape of each paddle to better fit the subject and maximize the number of coils able to fit on each pad, our 128-channel coil could be easily adjusted to optimally fit the multiple head sizes with minimal SNR drops. The high density of elements, their size, and their proximity to cortical areas, makes this coil well suited for investigations into brain connectivity and function.

Novel Imaging Acquisition Methods:

BOLD fMRI 2
Imaging Methods Other 1

Keywords:

Acquisition
Cortex
Design and Analysis
Development
FUNCTIONAL MRI
Other - RF Coils

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Other

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Healthy subjects

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Not applicable

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Computational modeling

For human MRI, what field strength scanner do you use?

If Other, please list  -   Not used

Which processing packages did you use for your study?

Other, Please list  -   NA

Provide references using author date format

Gruber B, Froeling M, Leiner T, Klomp DWJ. RF coils: A practical guide for nonphysicists [published online ahead of print, 2018 Jun 13]. J Magn Reson Imaging. 2018;48(3):590–604. doi:10.1002/jmri.26187