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A SADDLE QUADRATURE RF COIL for IN VIVO RODENT IMAGING at 21.1 T

A SADDLE QUADRATURE RF COIL for IN VIVO RODENT IMAGING at 21.1 T. Jose A. Muniz 1,2 , Jens T. Rosenberg 1,2 & S.C. Grant 1,2 1 The National High Magnetic Field Laboratory 2 Chemical & Biomedical Engineering , Florida State University. I ntroduction. Quadrature RF Designs

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A SADDLE QUADRATURE RF COIL for IN VIVO RODENT IMAGING at 21.1 T

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  1. 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 1The National High Magnetic Field Laboratory 2Chemical & Biomedical Engineering, Florida State University

  2. Introduction • Quadrature RF Designs • Circularly polarized field • More efficient 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 = Simulated B1 field distribution Haase et al., 2000

  3. In Vivo Animal Imaging at NHMFL • UWB 21.1-T magnet (900 MHz 1H) • Vertical system • 64 mm gradient clearance • BrukerAvance III Console • Animal care and monitoring • Can accommodate large rodents (> 350 g) Coil assembly mounted on animal cradle Qian et al., 2012

  4. Quadrature Surface Coil • Readily fits 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 Quad Surface Coil pictured next to 21.1 T magnet

  5. Coil Design • 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) 0.9 pF 0.9 pF Quad coil schematic

  6. Coil Design • Quadrature excitation achieved via 90° hybrid coupler Transmission/Reception Schematic

  7. Coil Performance • S21 = -24 dB @ 896 MHz • Loaded Q (-3 dB bandwidth) • Channel 1 Q = 130 • Channel 2 Q = 132 S-Parameter Reflection Curve

  8. Coil Performance Absolute signal intensity profile Water Phantom Comparison to same size linear surface coil

  9. In Vivo SNR Comparison Linear Birdcage Quad Surface Image SNR = 14.6 (n = 6) Image SNR = 27.6 (n = 6)

  10. In Vivo Homogeneity Linear Birdcage Quad Surface

  11. In Vivo Homogeneity Linear Birdcage Absolute signal intensity profile (left to right) Quad Surface

  12. In Vivo Homogeneity Linear Birdcage Absolute signal intensity profile (bottom to top) Quad Surface

  13. Applications (EPI & SPEN) • Ultrafast In Vivo Diffusion Imaging • Echo-Planar Imaging • segmented 4-shot EPI-DWI • Super-Resolved Ultrafast Single-Shot Spatiotemporally Encoded Imaging • single-shot SPEN DWI • Frequency sweep insensitive to B1 inhomogeneities • Quadrature Surface coil provides the necessary sensitivity

  14. Applications (EPI & SPEN) • In Vivo MCAO Stroke Rat DWI @ 21.1 T • Acquisition 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) In Vivo MCAO stroked rat magnitude DWI and ADC maps

  15. Applications (LRE 1H MRS) • Longitudinal Relaxation Enhancement (LRE) • Spectrally Selective Excitation • SNR Enhancement Selective excitation pulse based on Shinnar-Le Roux (SLR) algorithm

  16. Applications (LRE 1H MRS) • In Vivo Stroke Rat Model: Middle cerebral artery occlusion (MCAO) • Male Sprague Dawley rats ~250 g • 5 mm3 voxel

  17. Applications (LRE 1H MRS)

  18. Applications (DW Metabolic 1H MRS) • In Vivo Rat Model: 5 mm3 voxel Control Stroke

  19. Conclusions • 900 MHz Quadrature Surface Coil • Localized Field of View • Enhanced Sensitivity • Provides sufficient 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

  20. Acknowledgements • Prof. Samuel C. Grant • Dr. Jens T. Rosenberg • Funding provided by: • User Collaborative Grant Program (NHMFL) Posters # 46, 47

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