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The purpose of this study is to test the feasibility of using acoustoelectric brain imaging (ABI) to map physiological activity in the rat hippocampus using depth and surface recording electrodes on a new mobile system. A new method in imaging brain activity using the acoustoelectric (AE) allows for the combination of high temporal and spatial resolution imaging beyond existing techniques. AE imaging takes advantage of mechanoelectrical properties of ultrasound (US) pressure waves which modulate the tissue's electrical resistivity. Using surface and depth electrodes we record these modulated signals to electrically map local brain activity. In recent experiments we have been able to image evoked responses in the hippocampus of an anesthetized rat showing high temporal correlations between low frequency recordings and ABI. Further optimization of ABI can allow for better detection of evoked potentials in the brain to allow for faster real-time scanning possibilities with capabilities of miniaturizing a system for hand held imaging.

In vivo brain activity imaging is a key to understanding the mechanisms of complex neural behavior. Functional MRI records brain-wide mechanisms, but at the cost of subject sedation which excludes behavioral experiments. Functional Ultrasound (fUS) Imaging, based on Doppler Imaging, is a powerful new tool for imaging brain activation with high spatiotemporal sampling (80μm, 1ms). It has been successively applied in anesthesized and awake rodents and in humans in preoperative settings. However, the brain mechanisms and functional connectivity are inherently three-dimensional, it is thus crucial to work toward imaging of the full brain in 3D. In this study, we present the first full 3D fUS Imaging of a mouse using a matrix array.

Neurophotonics involves optical techniques for brain imaging - in health and disease. This review will present two technologies, laser speckle imaging and photoacoustic imaging. Laser speckle contrast can be correlated with blood flow and therefore can be used for imaging brain blood flow and microcirculation in applications such as stroke. Further, speckle imaging can be combined with electrophysiological monitoring. Photoacoustic imaging is a more recent technique suitable for imaging deeper into brain tissue, and for studying cortical structures and function in applications such as angiogenesis accompanying tumors. Further improvements in contrast and specificity may come from using nanoparticles. These technologies are advancing rapidty towards clinical applications.

Intrinsic Optical Signal (IOS) imaging is a widely accepted technique for imaging brain activity. We propose an integrated device consisting of interleaved arrays of gallium arsenide (GaAs) based semiconductor light sources and detectors operating at telecommunications wavelengths in the near-infrared. Such a device will allow for long-term, minimally invasive monitoring of neural activity in freely behaving subjects, and will enable the use of structured illumination patterns to improve system performance. In this work we describe the proposed system and show that near- infrared IOS imaging at wavelengths compatible with semiconductor devices can produce physiologically significant images in mice, even through skull.

Gamma cameras based on multi-wire proportional chambers offer much potential as imaging tools in nuclear medicine. Advantages of these detectors over traditional crystal detectors include superior spatial resolution, higher count rate capabilities, portability and low cost. We have developed a gamma camera based on a multi-wire proportional chamber equipped with a high rate, digital electronic read-out system for imaging applications in nuclear medicine. The complete, highly transportable system has been demonstrated to operate reliably and with predictable accuracy in a hospital environment. The camera demonstrates an intrinsic spatial resolution of 1.27 mm and a maximum count rate capability of 1 million cps. Thallium-201 is a radioisotope with a strong affinity for viable tumor tissue owing to its potassium like characteristics. There is substantial uptake in primary and metastatic cerebral tumors with little uptake in the normal brain. It is ideally suited for imaging with a multi-wire proportional chamber due to its relatively low energy photon emission. The gamma camera has been used to image Thallium-201 labeled brain tumors in patients undergoing treatment in order to detect recurrent or residual tumor. The results and images obtained demonstrate the great potential of the gamma camera in the field of neuro-oncology. We present some design features of the camera and results obtained from measurements carried out to assess its performance characteristics. Clinical images obtained using the camera will also be presented.

The authors developed a novel microscope system to image changes in light scatter that occur within a hippocampal slice. The system is based on Mie scatter theory predictions for light scatter as well as empirical observations. The authors evaluated the imaging system with two types of samples, a thin layer of microspheres, radius 450 nm, suspended in water and a brain tissue slice. The variation of the dilution of the microspheres revealed two regimes in which the system responds differently. The authors believe the transition from one regime to the other occurs when single scatter begins to dominate. The authors also tested the system on 350 micron thick hippocampal slices. They detected increases in light scatter of up to 50% in 100 /spl mu/M NMDA treated slices. Thus, optical scatter imaging captures changes in brain tissue morphology that occur with brain injury.

We have developed a new algorithm to estimate the surface Laplacian of the scalp potential on a realistic geometry scalp surface. The performance of the algorithm was evaluated by computer simulations. The algorithm was applied to study the scalp Laplacian maps of visual evoked potentials induced by pattern onset stimuli in a human subject. The present results indicate the excellent performance of the newly developed algorithm and its potential for application in imaging brain electrical activity.