Pixel densities, image analysis

As computers are used to organize and manipulate the three-dimensional data, it is possible to look at the activity of many different brain regions, from many different angles, simultaneously. The computer, under instruction from the investigator, decides from what angle to take the image and at what depth to focus its density analysis. It then produces a myriad of pixels, or points that measure density, plots them in two dimensions as a slice , and colour codes the density patterns to make them easy to read qualitatively. 

Whereas FCS measures fluorescence fluctuations over time, a related technique, ICS, measures fluorescence fluctuations over space, in particular from images collected using a laser-scanning microscope (56). ICS analysis of pixels within a single image provides information about protein clustering and density. A variation of ICS known as image cross-correlation spectroscopy evaluates the interactions of molecules labeled with different fluorescent probes. ICS can also be performed on stacks of... 

The decay-time constant Tae,short of the fast component is mainly from the motions of the phenylene protons, whereas Tae.iong for the slow component depends on the motions of the methyl protons. The parameters of such a biexponential analysis for each pixel lead to four images, one for the spin density, which is given by the sum A -I- B of the amplitudes of both exponentials, one for each of the relaxation rates of the exponentials, 2e short 2e,iong respectively, and one for the difference A — B of the amplitudes of both exponentials. The spatial distributions of the first three of these parameters are shown in Fig. 10.3.8(b)-(d). The contour-level image (b) of the spin density provides information only about the different thickness of the sample. Here the shear band is hidden. But it becomes visible if the relaxation rates are evaluated. In agreement with the photograph (cf. Fig. 10.3.5(b)) the shear band runs from the upper left to... 

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