Ying-Hua Chu1, Yi-Cheng Hsu1, Pu-Yeh Wu1, Kevin W.-K. Tsai2, Wen-Jui Kuo2, and Fa-Hsuan Lin1
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, 2Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan
Synopsis
We developed a MRI-compatible wireless multi-purpose game
controller. With the presence of the game controller, EPI shows minimal
distortion and time-domain SNR degradation. Subjects’ responses were
successfully recorded from a two-person hyper-scanning experiment.TARGET AUDIENCE
Researchers interested in using MR-compatible
game controller to design functional magnetic resonance imaging (fMRI) studies.
PURPOSE
One major field in social neuroscience is to study human
interactions and their neural correlate. Compared to electroencephalography
(EEG), functional magnetic resonance imaging (fMRI) using BOLD signal has
advantages of high spatial resolution and homogeneous sensitivity across the
whole brain. However, the strong magnetic field in fMRI experiments poses a
technical challenge in using commercial computer peripheral devices to record
subjects’ responses. This challenge has been partially addressed by using devices
with fiber optical interface, such as joysticks and response buttons.
Alternatively, keyboard1 and joystick2 after
replacing ferromagnetic components, filtering noise, or using electromagnetic
shielding, have been proposed. However, these wired devices may increase the
risk of RF burning and decrease the signal-to-noise ratio (SNR) because of the common-mode
current along the connecting wire3.
Here, we developed a multi-purpose joystick
controller with Bluetooth communication. This wireless device was first tested
on a 3T MRI scanner to ensure that it causes minimal image distortion and
time-domain SNR degradation. We then used these joysticks in a preliminary hyper-scanning4 experiment to record
two subjects’ brain responses during a chess game.
METHODS
Our Bluetooth multi-purpose game controller was modified from
a commercial wired game controller (USB interface) with a D pad, 4 buttons, and
4 triggers. All electronic components on the circuit board were removed. A Bluetooth
module (Bluefruit EZ-Key, Adafruit Industries, New York, New York) was used to
receive key strokes and to transmit the signal to a dongle placed outside the
MRI bore but inside the MRI shielding room. The Bluetooth dongle was connected
to a computer to present fMRI stimuli and to record subject’s responses
(Psychtoolbox, 3). The power of the wireless game controller was provided a
lithium polymer battery (3.7 V; 280 mAh) mounted inside.
Imaging experiments were
done on a 3T MRI scanner (Skyra, Siemens, Erlangen, Germany) on a saline
phantom using a 32-channel head array and EPI (TR = 2 s; TE = 30 ms; Flip Angle
=90°; 3.50 mm isotropic). The game controller was parametrically placed with
distances to the periphery of the phantom at 0 cm (next to the phantom), 20 cm,
40 cm, and 60 cm. Images without the game controller were also acquired to
check if the game controller caused image distortions. Maps of time-domain SNR
were calculated by taking the ratio between the mean and the standard deviation
of the time series of each image voxel in EPI over 5 minutes. Two game
controllers were used by two subjects at two separate 3T MRI scanners (Tim Trio
and Skyra, Siemens) to engage a chess game (Reversi). Four runs of EPI data
were collected. The interaction between brains were quantified by calculating
the inter-subject correlation coefficients transformed to the Z-scores.
RESULTS
Figure 1 shows the exterior view of our wireless game
controller and its circuit. Figure 2 shows the tSNR maps. No visible distortion was observed in instantaneous phantom images with and without the game controller. We found that the tSNR was moderately reduced
when the game controller was right next to the phantom. However, in cases where
the distance between the game controller and the phantom is larger than 20 cm,
there is no discernable tSNR difference. Figure 3 shows the inter-subject
correlations of the hyper-scanning. Enabled by our game controller, two
subjects successfully played the game in two MRI’s for about 12 minutes in 4
runs (min: 614 s; max: 940 s). Stronger inter-subject correlations were found
at bi-hemispheric occiptotemporal lobe junctions and percuneus (Figure 3).
DISCUSSION
We developed a low-cost wireless game controller for
fMRI experiments. Results show that the game controller caused minimal
distortion and tSNR degradation. This is likely to be explained by the fact
that the operating frequency (2.4 GHz) of our Bluetooth module was far away
from the Larmor frequency of MRI. Preliminary results from a two-person
hyperscanning experiment successfully recorded subjects’ responses and
interesting inter-subject correlated brain activity. The wireless design
ensures no risk to the subject caused by the common-mode current in wired
devices. The Bluetooth interface allows our game controller to be easily used
in different software packages to process behavior responses and to coordinate
stimuli presentation on computers with most operating systems.
Acknowledgements
This study was supported by Ministry of Science and Technology, Taiwan (MOST 104-2314-B-002-238, MOST 103-2628-B-002-002-MY3), National Health Research Institute, Taiwan (NHRI-EX104-10247EI), and Ministry of Economic Affairs, Taiwan (100-EC-17-A-19-S1-175).
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