Development of a three-axis acceleration signal measurement system for fMRI motor studies

The purpose of this study was to develop a three-axis acceleration signal measurement system that could measure acceleration signals without deteriorating the functional magnetic resonance imaging (fMRI) data and not affect the main magnetic field, the gradient magnetic field, which varies rapidly with time, or the radio frequency (RF) pulse during fMRI acquisition. A three-axis accelerometer was used to measure acceleration signals, and Velcro was used to attach the accelerometer module to a finger or wrist. To minimize the mutual interference effect between the fMRI system and the acceleration signal measurement system, an amplifier circuit was constructed of analog devices, and the amplifier was located in the shielded case, which was made of copper and aluminum. The acceleration signal was modulated to an optic signal using pulse width modulation (PWM), and the modulated optic signal was transmitted outside the fMRI room using a light emitting diode (LED) and optic cable. We were able to verify that fMRI data and the tri-directional acceleration signal were measured simultaneously and stably. Various movement variables such as position, velocity, and jerk could be obtained numerically. Therefore, this system could be used for studying of the relationship between various movement variables and brain motor function, especially for the study of the rehabilitation field.