Exploring Electrical Capacitance Volume Tomography for Human Brain Visual Activity Detection

    Mahdi Mahendra, BS Thesis, Dept. of Physics, Bandung Institute of Technology, December 2013

    Purpose
    Electrical capacitance volume tomography (ECVT) is a method of imaging based on material permittivity distribution. The permittivity distribution is reconstructed from capacitance data measured by an array of sensor surrounding the material. Recent study pointed out a possibility of using ECVT as a modality to monitor human brain activity. This study aim to investigate the differences of ECVT images resulted from measurements of human brain in three different visual conditions.

    Methods
    Experiment was conducted on 9 human subjects, 3 of whom are females. Each subject underwent 3 conditions with different visual stimuli. Subject is placed in a dark room with both eyes closed in the first condition. During second condition, subject is asked to see a beam of light projected into a wall. Subject is also asked to minimize blinking when capacitance data is being measured. In the third condition, subject was presented with a series of line drawings depicting familiar objects. Subject was asked to recognize the drawing at an instant. During one condition, 50 capacitance data was measured using helm-shaped sensor. Capacitance data was then reconstructed using iterative linear back-projection (ILBP) algorithm using Landweber iteration to obtain voxels of permittivity distribution inside the sensor. The reconstruction was optimized by varying number of iteration and  value from Landweber iteration. The resulted permittivity distribution (image) was then compared one another using statistical method, the Kolmogorov-Smirnov (K-S) test. P-value in a volume of interest (VOI) sized 7x6x3 voxels were then observed. VOI location was chosen based on approximation of primary visual cortex (V1) area in the brain.

    Results
    Reconstructed image showed permittivity changes at all conditions. The changes are not limited to occipital area. These changes are potentially a result of brain activity, which are not limited to visual activity but other as well.

    Conclusion
    P-value analysis showed that comparison between open eye and closed eye conditions has more significant difference compared to a comparison between two open eye conditions in 5 of 9 subjects. Experiment on more subject is encouraged to validate the finding.