Research program
TEBAM: study, development and physiological-clinical validation of a multi-modal methodology for the 3D "True Electrical Brain Activity Mapping" in normal and pathological subjects
University Co-ordinator
Università degli Studi di TRIESTE -
SCIENZE CLINICHE, MORFOLOGICHE E TECNOLOGICHE - TRIESTE(TS)
Research Unit Leader
Roberto POZZI MUCELLI
Description
Scientific studies performed by the international scientific community based upon DT-MRI technique for improving clinical diagnosis using MRI imaging cover only partially the requests from research and clinical environment. In particular, while functional mapping of cerebral neo-cortex is at advanced steps by means of well consolidated methods (BOLD techniques), the anatomic and functional reconstruction of the underlying fibers is still in an initial phase. The use of DT-MRI technique can result to be extremely precious for this purpose, and we intend to carry out this study by coupling it with indirect electric brain activity mapping methods. The results of this research study will allow the validation of this new technique. The adjustment of this technique will be performed upon the basis of a model of visuo-motor integration with experiments on normal and pathologic subjects, informed and consenting, certainly rightly. The stimulation protocol is described hereafter.The subject is set within the magnet of the MRI machine, in supine position. In front of him a back-illuminated panel is set on which many diverse images ore projected. The subject's task is to jerk up the right hand only when the image presented on the panel is corresponding to determinate characteristics. This simple stimulation allows to the resonance machine to reveal the activation of the visual cortex and of the primary and supplementary motor areas. During the tests the subjects will undertake the recording of electrical brain activity by means of computer electroencephalography with 32 recording channels and sampling frequency of 1 KH. The objective is of co-recording the electroencephalographic brain signal with the signal obtained by means of DT-MRI.The indirect methods of the above cited electrical brain activity mapping foresee a correlation analysis of the electroencephalographic recording which will allow to point out the relationship between the fibers' geometry evidence by DT-MRI acquisition with the recorded electrical signal. Furthermore, these mapping methods are based upon an approach of anatomo-functional integration. This approach requires the co-elaboration of anatomical information (bioimages) and scalp-recorded functional data (multi-channel electroencephalographic measures) for the reconstruction and visualization of the "in vivo" brain activity within the specific anatomical structure of the patient with the best spatial and temporal resolution.Knowledge of the electrical conductivity properties of the tissues is a key point to find the relationship between electromagnetic fields generated by a tissue, e.g., the measure of electroencephalographic potentials, and the neural sources the activation of which generates the measured electroencephalographic signals. Source reconstruction accuracy heavily depends on the accuracy of the conductivity values assigned to the tissues. The attempt of characterizing the active brain zones starting form the associated electroencephalographic potential measurements could find great improvements from the availability of measuring tissue electrical conductivity non-invasively, instead of basing upon mean values taken from the literature, as it is done at present in the scientific community and it is implemented in commercially available products for the analysis of the sources of brain activity.In this project we aim to develop, in collaboration with the research unit of bioengineering of Trieste an original method which will allow obtaining the individual conductivity values evaluated from DT-MRI measurements, by quantitative deduction of tissues' electrical conductivity tensor starting form water self-diffusion tensor. The hypothesis of relationship between electrical conductivity and water self-diffusion in the tissues is based upon the observation that, even if there is no fundamental relationship between the two transport modalities in a free solution, in a structured medium as a tissue the relationship between the two processes is given by the fact that both comply the bounding condition imposed by the tissue geometry itself.The possibility of a relationship between electric conductivity and diffusion tensor can be seen observing that the two tensors exhibit a comparable anisotropy in brain's white matter.The existing relationship between a generic transport tensor, e.g., the diffusion or conductivity tensor and underlying medium microstructure can be obtained by means of a perturbative expansion of microstructure statistical correlations. Such expansion of the statistical correlation, also called contrast moment expansion, gives a method for finding the relationship many different transport tensors by means of the statistics of the microstructure constituting the medium. To obtain the relationship between conductivity and diffusion tensor in the brain tissues, we may therefore estimate the statistical moments of the microstructure starting from the observation of the diffusion tensor and therefore obtaining the conductivity tensor starting form the computed moments.By this way we will be able to obtain, in collaboration with the bioengineering research unit of Trieste, a mapping of tissue conductivity that will be used by this latter research unit in the phase of brain activity mapping together with the electroencephalographic recordings obtained by means of the above described stimulation protocol.The same stimulation protocol will be presented again to the subject for the acquisition of the relative BOLD signal (fMRI), to localize the brain areas functionally interested in task execution, instead of the fibers transmitting the signal.The subject will also undertake a structural sagittal acquisition T1-weighted which will be used for the tri-dimensional reconstruction of the head and of the brain and the exact localization of the active brain areas by means of the tool CURRY (Neuroscan), the results of which will be used in the phase of cross-control with the results of brain activity mapping obtained in collaboration with the bioengineering research unit of Trieste.
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