1. 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

2. 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

3. 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: /journal.pone [2] M.B. Hoffmann et. al., Clinical Neurophysiology 120 (2009) 108–116

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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).

11. 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)

12. 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)