A SADDLE QUADRATURE RF COIL for IN VIVO RODENT

IMAGING at 21.1 T

Jose A. Muniz1 ,2, Jens T. Rosenberg1 ,2 & S.C. Grant1 ,2

1 The Nat iona l H igh Magnet i c F ie ld Labora to ry2 Chemica l & B iomed ica l Eng ineer ing , F lo r ida S ta te Un ivers i ty

Introduction

Simulated B1 field distribution

Haase et al., 2000

Quadrature RF Designs

Circularly polarized field

More effi cient use of transmitted power Reduction in the Specific Absorption

Rate (SAR) for in vivo applications

Multiple Coils Sensitivity enhancement Reduction of sampled noise SNR enhancement =

UWB 21.1-T magnet (900 MHz 1H)

Vertical system

64 mm gradient clearance

Bruker Avance III Console

Animal care and monitoring Can accommodate large

rodents (> 350 g)

In Vivo Animal Imaging at NHMFL

Coil assembly mounted on animal

cradleQian et al., 2012

Readily fi ts current animal probe Two RF Channels External tuning (x4 variable

capacitors)

Localized field of view Rodent head/body imaging

Rat brain Mouse body

Center of brain located 10-15 mm away

Deliver Sensitivity for MR microscopy MR spectroscopy (selective

excitation) Fast imaging techniques

Quadrature Surface Coil

Quad Surface Coil pictured next to 21.1 T

magnet

Copper-clad laminates adhered to 35.7mm fiberglass epoxy former 32 x 30 mm ~100° azimuthal coverage

Two channel saddle design Transceive coil configuration

Common center conductor

Single decoupling capacitor Johanson Giga-Trim (0.6 – 4.5 pF)

Tuning & matching Voltronics (1-8 pF)

Coil Design

0.9 pF0.9 pF

Quad coil schematic

Quadrature excitation achieved via 90° hybrid coupler

Coil Design

Transmission/Reception Schematic

S21 = -24 dB @ 896 MHz

Loaded Q (-3 dB bandwidth)

Channel 1 Q = 130

Channel 2 Q = 132

Coil Performance

S-Parameter Reflection Curve

Coil Performance

Water Phantom Absolute signal intensity profile

 Comparison to same size linear

surface coil

In Vivo SNR Comparison

Linear Birdcage Quad Surface

Image SNR = 14.6(n = 6)

Image SNR = 27.6(n = 6)

In Vivo Homogeneity

Linear Birdcage Quad Surface

In Vivo Homogeneity

Linear Birdcage

Quad Surface

Absolute signal intensity profile (left to right)

In Vivo Homogeneity

Linear Birdcage

Quad Surface

Absolute signal intensity profile (bottom to top)

Ultrafast In Vivo Diff usion Imaging Echo-Planar Imaging

segmented 4-shot EPI-DWI Super-Resolved Ultrafast Single-Shot Spatiotemporally

Encoded Imaging single-shot SPEN DWI

Applications (EPI & SPEN)

Frequency sweep insensitive to B1 inhomogeneities

Quadrature Surface coil provides the necessary sensitivity

In Vivo MCAO Stroke Rat DWI @ 21.1 TAcquisition times for either 4 or 6 b values

SE-DWI (>1.5 h), 2-Shot EPI-DWI (2.4 m), 1-Shot SPEN-DWI & EPI (1.2 m)

Applications (EPI & SPEN)

In Vivo MCAO stroked rat magnitude DWI and ADC maps

Longitudinal Relaxation Enhancement (LRE) Spectrally Selective Excitation

SNR Enhancement

Applications (LRE 1H MRS)

Selective excitation pulse based on Shinnar-Le Roux (SLR) algorithm

In Vivo Stroke Rat Model: Middle cerebral artery occlusion (MCAO) Male Sprague Dawley rats ~250 g 5 mm3 voxel

Applications (LRE 1H MRS)

Applications (LRE 1H MRS)

In Vivo Rat Model: 5 mm3 voxel

Applications (DW Metabolic 1H MRS)

Control

Stroke

900 MHz Quadrature Surface Coil

Localized Field of View

Enhanced Sensitivity

Provides suffi cient sensitivity for Ultrafast imaging techniques

fMRI, water-based diffusion imaging at high field, super-resolution Spectrally selective MRS

Upfield and Downfield Spectra Compartmental Diffusion Weighted Metabolic Spectroscopy

Probing compartments in normal & pathological tissue

Conclusions

Prof. Samuel C. GrantDr. Jens T. Rosenberg

Funding provided by: User Collaborative Grant Program (NHMFL)

Acknowledgements

Posters # 46, 47