Table of Contents
Advertisement
fMRI User Guide
11
4 Peripherals
A targeted search for brain activity requires precisely defined stimulation. Various stimuli are presented in fMRI
such as visual, auditory, etc. and subject responses to these stimuli are registered, along with/without the
subject's physiological information during the fMRI scan.
Following are some of the typical peripheral devices that are used for fMRI studies, and can be interfaced with the
Siemens scanners:
1. Response pad
2. Visual stimulus (LCD screen, projector)
3. Auditory stimulus (headphones and microphone)
4. Eye tracker
5. Physiological monitoring (galvanic skin resistance (GSR), heart rate, respiration, pulse)
An illustration of a typical setup is shown in Figure 4.
4.1 Response Pad
This is a response pad that is used to register subject responses to stimuli. It acts as a keyboard input if interfacing
with a stimulus computer. The signal from the response pad to the stimulus computer is typically carried over an
optical cable, which prevents any introduction of external noise into the scanner room. A standard waveguide can
be used to pass this cable from the scanner room to the control room.
4.2 Visual stimulus
Visual stimulus is generally presented by means of a projector or an LCD screen. If any of the electrical equipment
is inside the scanner room, or electrical cables are running from the outside to the scanner room, care must be
taken to shield the equipment and prevent contamination of the images by RF noise. Appropriate RF filters (typical
attenuation > 60dB) must be used in the filter panel to pass electrical cables between the control and scanner
rooms.
A number of commercial and free softwares are available to generate presentation scripts. These scripts are
synchronized with the scanner activity by means of the TRIGGER_OUT (optical converted to TTL) pulse generated
by the EPI sequence.
4.2.1 Projector
Projectors can be used in several ways. The simplest is to project through the scanner control window to a screen
at the foot of the table with the lights lowered, and the subject looking at the screen with the head coil mirror. A
more permanent setup is to project from outside the scanner room through a large waveguide to a screen placed
at the head end of the magnet. Mirrors are required unless the waveguide enters the room from the head end of
the magnet. A variety of projectors can be used, but they must be sufficiently bright and should allow additional
lenses to be attached in order to minify the projection so that it is not too large when it reaches the screen. If the
application demands, high-end projectors with superior contrast and resolution may be required. Depending on
the type of projector and the scanner room layout, the projector can potentially be put inside a Faraday cage (an
electrically conducting enclosure) and placed inside the scanner room, but care must be taken that this does not
introduce significant RF noise.
Advertisement
Table of Contents
