Mohamed K. Metwally

A novel P300-based BCI system for words typing

The conventional P300 BCI system for character spelling is typically composed of a paradigm that displays flashing characters and a classifier which identifies target characters. Typically a user has to type each character of a word at a time: this spelling process is slow and it can take several minutes to type an entire word. In this work, we propose a new word typing scheme by integrating a word suggestion mechanism via a dictionary search into the conventional P300-based speller. Our new P300-based word typing system consists of an initial character spelling paradigm, a smart dictionary unit to give suggestions of possible words, and the final word selection paradigm to select a word out of the suggestions. Our proposed methodology reduces typing time significantly and makes word typing more convenient. We have tested our system with four subjects and our results demonstrate an average words typing time of 1.66 minute, whereas the conventional took 2.9 minute for the same words.

Influence of the anisotropic mechanical properties of the skull in low-intensity focused ultrasound towards neuromodulation of the brain

Lately, neuromodulation of the brain is considered one of the promising applications of ultrasound technology in which low-intensity focused ultrasound (LIFU) is used noninvasively to excite or inhibit neuronal activity. In LIFU, one of critical barriers in the propagation of ultrasound wave is the skull, which is known to be highly anisotropic mechanically: this affects the ultrasound focusing, thereby neuromodulation effects. This study aims to investigate the influence of the anisotropic properties of the skull on the LIFU via finite element head models incorporating the anisotropic properties of the skull. We have examined the pressure and stress distributions within the head in LIFU. Our results show that though most of the pressure that reaches to the brain is due to the longitudinal wave propagation through the skull, the normal stress in the transverse direction of the wave propagation has the main role to control the pressure profile inside the brain more than the shear stress. The results also show that the anisotropic properties of skull contribute in broadening the focal zone in comparison to that of the isotropic skull.

Investigation of the electric field components of tDCS via anisotropically conductive gyri-specific finite element head models

Transcranial Direct Current Stimulation (tDCS) is considered as one of the promising techniques for noninvasive brain stimulation and brain disease therapy. In this study, we have investigated the effect of skull and white matter (WM) anisotropy on the induced electric field (EF) by tDCS in two different montages; one using a pair of clinically used rectangular pad electrodes and the other 4(cathodes)+1(anode) ring electrodes. Using a gyri-specific finite element (FE) head model, we simulated tDCS and investigated the radial and tangential components of the induced EF in terms of their distribution over the cortical surface besides the distribution of the transverse and longitudinal components within WM. The results show that the tangential component of the EF on the cortical surface seems to be the main cause of the cortical stimulation of tDCS. Also WM anisotropy seems to increase the dispersion of the transverse component of the EF that affects the dispersion of the EF magnitude within the WM region.

Influence of Skull Anisotropic Mechanical Properties in Low-Intensity Focused Ultrasound

Low-intensity focused ultrasound (LIFU) is a new noninvasive brain stimulation technique where ultrasound is applied with low frequency and intensity to focus at a target region within the brain in order to exhibit or inhibit neuronal activity. In applying LIFU to the human brain, the skull is the main barrier due to its well-known high anisotropic mechanical properties which will affect the ultrasound focusing thereby affecting the neuromodulation or brain stimulation. This study aims at investigating the influence of the anisotropic mechanical properties of the skull on ultrasound propagation and focusing in LIFU. In this study, we used 2D finite element (FE) head models incorporating the isotropic and anisotropic properties of the skull. Three kinds of stresses were examined and shown within the skull: namely the normal stress in the direction of wave propagation (x-stress), normal stress in the transverse direction to the wave propagation (y-stress), and shear stress. Our analysis show that although most of the pressure that reaches to the brain is due to the longitudinal wave propagation through the skull, the stress in the transverse direction to the wave propagation direction (y-stress) has the main influence on the pressure profile inside the brain. The results also show that the anisotropic properties of the skull broaden the focal size about 19% and 13% in the longitudinal and transverse directions, respectively more than the case of considering the isotropic properties in the realistic 2D FE head model. The results indicate the importance of considering the anisotropic properties of the skull in practicing LIFU to achieve accurate targeting within the brain.

Influence of the anisotropic mechanical properties of the breast cancer on photoacoustic imaging

Photoacoustic imaging (PAI) is a non-invasive imaging modality that combines the absorption contrast of light with ultrasound resolution. Laser is used to deposit optical energy (i.e., optical fluence) into a target. As a result, the target temperature changes and causes thermal expansion to the target that leads to generating a PA signal. One of the important parameters that control the PA is the elasticity of the target. In general, most the PA studies and image reconstruction algorithms for PAI assumes isotropic elasticity within the target. However, it is known that certain soft tissues, like muscles and glands, are anisotropic with respect to elastic deformation. Also, observations indicate that breast tumors tend to be anisotropic. This could affect the reconstruction of PA images. In this study, we have investigated the influence of the anisotropic elasticity on PA back-propagation imaging using finite element method. The Fluence distribution was estimated by solving light propagation within a tissue model using Monte Carlo method. The results show that the object may appear in the reconstructed image about 10% larger or 12% smaller than the expected size based on the distribution of the youngs modulus within the object if its anisotropic elasticity was not considered in the reconstruction algorithm.