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Additional fMRI equipment

The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast. The contrast means the difference between two particular tasks, where one of them most often is the resting state fMRI, or task-less fMRI.

A task could involve sensory or motor mechanisms or both. Thus, in addition to the fMRI scanner, supplementary equipment is necessary to implement.
Added equipment should be MR-compatible, which means:

1) The equipment should NOT influence the MR-scanner function.
2) The MR-scanner should NOT influence the added equipment.
3) The combined MR-scanner and the added equipment should NOT threat or injure the human / animal in the scanner.

The complementary device primarily stimulates sensory organs or measure the motor response from muscles (which also could be monitored by the subject/patient). Further, an experimenter in the scanner room sometimes use equipment with preprogrammed commands to control the experiment (i.e. sensory stimulation). Finally, various mechanical supports are necessary.

 

Sensory stimulation

Visual stimulation

Visual stimulation most often use a display screen located at the head side of the scanner (GE 3T viewing angles: horizontal 23 deg., vertical 13 deg.). Another alternative is a back projection from a MR-compatible video projector on an opaque screen located at the foot side of the scanner. The display is viewed thru a mirror located above the head coil and (rotated 45 deg. from a vertical line). For 3-D viewing, 5 mirrors are attached to the head-coil. They horizontally offset the view to match the two separated displays of the screen independent of pupil distance. The two optical paths are separated by a "midline curtain". In case no head-coil is used, a mirror attached to glasses could be used. Natural visual observation of ongoing motor activity (i.e. from hand/fingers) could be observed by the subject/patient "thru a dual mirror", which doesn't vertically swap the view. However, as the subject/patient is looking upwards while the view is horizontal, a sensory-motor-transformation is necessary in the brain. To avoid this drawback, the head-coil could be tilted to allow direct viewing without mirrors.

 

Auditory stimulation

Normally stereo sound is transmitted to the ears thru plastic tubes ending in earmuffs. A set of tube connections allow one channel to reach both earmuffs of the subject / patient. Then, the other channel could reach earmuffs of the experimenter for preprogrammed verbal commands.

 

Tactile stimulation

Six mechanical stimulators could stimulate the fingers (digit 2-5, right thumb, left thumb).  Each stimulator has two coils which acts in the static magnetic field, but are differential connected to avoid influence from the gradient fields. The frequency response is DC-90 Hz at small amplitudes and amplitude of 3 mm peak-to-peak at low frequencies. Emotional touch could be performed by the experimenter applying mirror movements; one hand on the subject and one hand on a "dummy-arm". The perpendicular and lateral forces as well as the touching speed are measured on the dummy arm and displayed to the experimenter for visual feedback. An optical sensor attached to a finger could sample the pulse rate. Nociceptive stimulation could be applied having a drum with 8 rows of 5 pins (tip diameter 0,1mm) each loading the skin with 60-120mN by gravitational force on the object (5-10 pins simultaneously contact the skin). Timing is fulfilled using the "mirror movement" device.

 

Proprioceptive stimulation

A handheld rod producing flexion-extension movement of one wrist. Two coils which acts in the static magnetic field, but are differential connected to avoid influence from the gradient fields. The equipment is combined with the device for "pronation-supination measurements of a wrist".

 

Motor output

Verbal output thru an optic differential microphone. The noise from the gradient coils reach both sides of the microphone and is thus cancelled out. The subject / patient only reach on side and could be heard clearly despite the background noise (Optoacoustics FOMRI III+). Body movements (3D) using 3 infrared video-cameras (Qualisys) and reflex-markers. Two optical keyboard for the two hands with 4 keys each.

Handheld optical “pistol” switches (one for each hand). Uni- or Bi-manual handling of an object with optical transducers for pushing/pulling forces and rotation torques. Equipped with a mechanical clamp (experimenter controlled) for uni-manual handling. Equipped with optical position transducer during bimanual handling. Six- axis optical force/torque transducers (Fx, Fy, Fz, Tx, Ty, Tz). Could be used for general cursor control on the display screen or/and control of other functions. Pronation-supination measurements of a wrist. The device is combined with the "Wrist-flexion motor" Optical accelerometer (DC-300 Hz) for studying tremor. Active handling of an object between the two hands or between one hand and the experimenters hand to produce muscle output.

 

Mechanical support

Various mechanical supports are necessary

1) Permit additional equipment.

2) Stabilize arms and hands.

3) Stabilize the head (using bite bars).

4) Mechanical insulate arms/hands from the torso.

5) Stabilize foot for key pressing (with big toe). 

6) Remount the head coil.

7) Allow experimenter to reach necessary positions and

8) Control natural vision with a shutter.

 

Zero tesla scanners

Zero tesla scanners could be used for evaluating an experimental setup for a certain subject / patient. One scanner is located at Integrative Medical Biology (IMB), section Physiology. This has the same dimension as the GE 3T scanner. Prerecorded gradient coil sound could be given thru headphones. Another is located at department of Psychology, but with different dimensions.