Biophysics of Imaging (Physics 4347)
 
Tuesday / Thursday, 2:00-3:15
Beginning: Jan., 13, 2007

Vassiliy Tsytsarev

One of the main goals for neuroscience is to understand the localization of various functions in the brain. Through this, we expect to learn how the central nervous system realizes perception and analysis of information. Different brain imaging methods is a powerful approach to address this problem.

Neuroimaging falls into two broad categories: structural imaging and functional imaging. Structural imaging deals with the structure of the brain and the diagnosis of intracranial disease (such as tumor), and injury. Functional imaging is used to visualize metabolic changes. It enables, for example, the processing of information by centers in the brain to be visualized directly.

There are numerous types of brain imaging technique but we would like to concentrate on the Functional Magnetic Resonance Imaging (fMRI), Positron Emission Tomography (PET) and Optical Imaging of the Brain Surface – Intrinsic Optical Imaging Signal (IOS) and Voltage –Sensitive Dye (VSD).

fMRI is the use of nuclear magnetic resonance to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. Is well known that changes in blood flow and blood oxygenation in the brain (collectively known as hemodynamics) are closely linked to neural activity. Haemoglobin is diamagnetic when oxygenated but paramagnetic when deoxygenated. The magnetic resonance (MR) signal of blood is therefore slightly different depending on the level of oxygenation; these differential signals can be detected and visualized.

Figure 1. Human Somatosensory Cortex visualized by fMRI

Figure 2. Structures of the rat’s brain vizualized by PET.

PET is an imaging technique which produces a three dimensional image or map of functional processes in the brain. As the short-lived isotope decays (110 minute half-life), it emits a positron. After traveling up to a few millimeters the positron encounters and annihilates with an electron, producing a pair of annihilation photons moving in nearly opposite directions. These are detected when they reach a scintillator material in the scanning device, creating a burst of light which is detected by photomultiplier tubes. The technique depends on simultaneous or coincident detection of the pair of photons: photons which do not arrive in pairs are ignored.

Figure 3. The functional maps od the Cat Auditory Cortex, obtained in response to in response to sound frequencies of 5, 10, 15, and 20 kHz.

At present, the easiest and most effective strategy of imaging functional architecture is based on the slow intrinsic changes in the optical properties of active brain tissue, permitting visualization of active cortical regions at a spatial resolution greater than 50 μm. The sources for these activity-dependent intrinsic signals include either changes in physical properties of the tissue itself which affect light scattering and/or changes in the absorption, luorescence or other optical properties of intrinsic molecules having significant absorption or

fluorescence. Both of these methods, Intrinsic- (IOS) and VSD- brain imaging is a primary experimental technique in our lab, and both of them will be expounded within the current course. At the presented course will be observed foregoing brain imaging methods, and also brain multiphoton imaging, human transcranial optical imaging, their using at the neuroscience experiment and analysis of experimental data.

Main recommended literature:

Frostig R. In Vivo Optical Imaging of Brain Function. ISBN: 0849323894

Van Bruggen N., Roberts T . Biomedical Imaging in Experimental Neuroscience ISBN: 084930122X

Grinvald A.., Shoham D., Shmuel A.., Glaser D., Vanzetta I., Shtoyerman E., Slovin H., Sterkin A., Wijnbergen C., Hildesheim R. and Arieli A.. In Vivo Optical Imaging of cortical architecture and dynamics. Technical Report GC-AG/99-6 (In: Modern Techniques in Neuroscience Research. U. Windhorst and H. Johansson (Editors) Springer Verlag)

Webb A. Introduction to Biomedical Imaging. ISBN 0-471-23766-3