An LCD Monitor for Visual Stimulation fMRI at 7 Tesla J. Groebner, M An LCD Monitor for Visual Stimulation fMRI at 7 Tesla J. Groebner, M. Berger, R. Umathum, M. Bock, W. Semmler, and J. Rauschenberg Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany No: 3463

TFT-LC-Display at 7 Tesla Jens Groebner Slide 3 No: 3463 Table of Contents Introduction Materials and Methods Hardware Phantom measurements Volunteer measurements Results and Discussion fMRI experiment Pros / Cons TFT-LC-Display at 7 Tesla

Goggles showing a test image at 3 different field strengths Jens Groebner Slide 4 No: 3463 Introduction Presentation methods for visual stimuli in fMRI: dedicated projection systems MR compatible goggles [1, 2] Problem: Difficult to apply at MR systems with B0 > 3 T due to longer magnet and display sensitivity Solution: Fully compatible TFT-LCD for fMRI that can operate within B0 of up to 7 T ~0T 2T 7T Goggles showing a test image at 3 different field strengths [1] S. Ohlendorf et. al. PLoS ONE 3(12): e4043. doi:10.1371/journal.pone.0004043 [2] M.B. Hoffmann et. al., Clinical Neurophysiology 120 (2009) 108–116

Materials and Methods: Hardware Jens Groebner Slide 5 No: 3463 Materials and Methods: Hardware 17” TFT-LCD: Samsung SyncMaster 770TFT Removed: all ferromagnetic components Cold cathode fluorescence lamp electronic components (control board, LCD-board) Segmented LCD back plate (aluminum) reduces eddy-currents

Materials and Methods: Hardware Jens Groebner Slide 6 No: 3463 Materials and Methods: Hardware 1. Modified 17” TFT-LCD: 1. LED backlight 10 clusters of 10 LEDs [3] powered by current sources, integrated in LCD-casing 2. RF-shield metallic coated glass plate (screening attenuation ~54dB at 300MHz) covering front adhesive copper-film shielding at back and sides Removable shield for signal cable connectors 2. [3] DDW-PJG-WX1-1, max2240mcd, Dominant Semiconductors, Melaka, Malaysia

Materials and Methods: Hardware Jens Groebner Slide 7 No: 3463 Materials and Methods: Hardware Signal cable RF-shield connected to the waveguide (outside) with connecting ring Shielded by tube made of copper mesh 100Ω twisted pair cable Length: 15m

Materials and Methods: Hardware Jens Groebner Slide 8 No: 3463 Materials and Methods: Hardware Control unit Placed outside RF-cabin Connected to PC via a standard VGA cable or DB13W3 Provides functions e.g.: Contrast settings Image Position Color temperature Brightness is controlled by an extra voltage source (40V/300mA) Supply voltage (Backlight) Signal cable VGA cable Control buttons

Materials and Methods: Phantom Jens Groebner Slide 9 No: 3463 Materials and Methods: Phantom Phantom measurements to evaluate RF noise during fMRI Performed on Magnetom 7T (Siemens, Erlangen, Germany) 24-channel Rx/Tx-coil (Nova Medical, Inc., Wilmington, USA) EPI sequence: Measurement 1: without LCD Measurement 2: Switched-on LCD, 20 cm away from the magnet bore TR/TE = 2530 ms / 27 ms α = 90° SL = 3 mm Matrix = 64x64 FOV = 210 mm BW = 1630 Hz/px

Results: Phantom measurements Jens Groebner Slide 10 No: 3463 Results: Phantom measurements Measurement 1: without LCD, SNR: 37.2 Measurement 2: Switched-on LCD SNR: 34.3

Materials and Methods: Volunteer fMRI Jens Groebner Slide 11 No: 3463 Materials and Methods: Volunteer fMRI Visual stimulus: flickering checkerboard (1 Hz rate) fMRI-BOLD experiment (same EPI parameters as phantom measurement) 6 stimulation blocks (30 s each) separated by 30 s resting blocks (white image) Activation map calculation: SPM 8 (Wellcome Department of Imaging Neuroscience, University College London, London, England).

Results: Visual Stimuli Experiment Jens Groebner Slide 12 No: 3463 Results: Visual Stimuli Experiment LCD checkerboard LCD white [a.u.] Fitted response for visual stimuli for pixel at center of the activated region from left picture. Activation maps for visual stimuli experiment (checkerboard)

Discussion Pros: MR-compatible monitor for 7T Jens Groebner Slide 13 No: 3463 Discussion Pros: MR-compatible monitor for 7T No distinct RF-induced artifacts No video image distortion due to static magnetic fields, gradients, RF.. Higher spatial resolution (1280×1024) than common projectors (1024×768) Can be placed very close to volunteer Clearly visible activation maps in fMRI experiment Can additionally be used as a In-Room monitor for MR-guided interventions Cons: Slightly reduced SNR in EPI when switched on up to 20% reduced SNR in anatomical sequences  Solution: switch off during anatomical imaging (improvement of RF-shield in progress)