In Phase I we propose to test the feasibility of developing a high-resolution scanning magnetometry for neuroscience based on a simple, but novel concept of primary source mirror (PRISM). The PRISM can be made with different designs, but in this project it will be an air-filled glass pipette with a small glass plate at the end with a tilt of 45o toward bottom. We claim that this mirror can be used to visualize the current distribution regardless of source orientations in an in vitro neuronal tissue with a spatial resolution as high as 10 5m when we complete the Phase II of this project. It has been well known that the magnetic field outside a conducting medium such as a bath filled with saline or the human head is solely due to currents tangential to the conducting boundary. In the case of human head, magnetoencephalography (MEG) measures only the currents tangential, but not radial, to the brain-air boundary. In the case of a neuronal tissue in a bath, the magnetic field is solely due to currents tangential, but not perpendicular, to bath surface. This fundamental limitation has restricted the use of biomagnetometry. In Phase I we will use the PRISM in a physical phantom to test whether the PRISM will make the vertically oriented currents in a bath """"""""visible"""""""". When this mirror is submerged in a bath of physiological saline just above a neural tissue, it will produce the so- called secondary source oriented perpendicular to its surface when a population of neurons produces vertical or horizontal intracellular currents below the mirror. According to our simulation study, the horizontal component of the secondary source on the PRISM will make the vertical current """"""""visible"""""""" to a magnetometer above the bath. We will compare the results with a realistic simulation study using a boundary element method to fully represent the experimental condition. We will further evaluate two important properties of this technique that may enable us to develop a high resolution scanning magnetometry in Phase II. We will test our claim that: (1) the spatial resolution primarily depends on the distance between the mirror and active neurons below, instead of the distance between the magnetic field sensing coils above the bath and the volume of active neurons, and (2) the spatial resolution is independent of the dection coil size (within reasonable limits). These results will enable us to develop a novel high-resolution scanning magnetometry in Phase II.
This simple, but novel invention will expand applications of magnetometry since it will enable us to obtain images of current distribution in biological tissues, containing currents in any directions with an unprecedent-ed level of spatial resolution. The scanning magnetometry should become an important new tool in bio-medical research in the area of direct high resolution imaging of electrical currents such as neural currents in biological tissues in vitro. This technique can be in principle applied to human MEG studies as well.
